western hemlock looper and forest disturbance in the ich...

Western Hemlock Looper and Forest Disturbance

in the ICH wk3 of the Robson Valley

Stage 2: The Effects of Western Hemlock Looper -

Report and Silviculture Recommendations

Aled Hoggett

Faculty of Forestry

University of British Columbia

March 15, 2000

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Table of Contents

SUMMARY ......................................................................................................................... 4

INTRODUCTION ............................................................................................................... 6

METHODS.......................................................................................................................... 8

FIELD METHODS .................................................................................................................. 8

ANALYSIS ........................................................................................................................... 11

CURRENT ECOSYSTEM CONDITIONS ........................................................................ 12

SITE.................................................................................................................................... 12

CURRENT STAND CONDITION............................................................................................. 13

DIAMETER ...........................................................................................................................13

VOLUME AND BASAL AREA ..................................................................................................17

HEIGHT................................................................................................................................18

DECAY.................................................................................................................................20

CROWN CONDITION..............................................................................................................22

OTHER TREE CHARACTERISTICS............................................................................................24

DEAD MATERIAL..................................................................................................................28

TREE REGENERATION ........................................................................................................ 31

OTHER ECOSYSTEM COMPONENTS .................................................................................... 33

UNDERSTOREY VEGETATION ................................................................................................33

FOREST FLOOR AND CHARCOAL............................................................................................36

ANALYSIS OF WITHIN PLOT SPATIAL PATTERN .................................................... 40

DESCRIPTIVE...................................................................................................................... 40

CORRELATION ANALYSIS ................................................................................................... 41

POINT-PATTERN ANALYSIS ................................................................................................ 42

SILVICULTURE RECOMMENDATIONS ...................................................................... 45

THE BASIS FOR SILVICULTURE........................................................................................... 45

WHAT IS ECOSYSTEM MANAGEMENT?............................................................................... 46

THE IMPLICATIONS OF ECOSYSTEM MANAGEMENT FOR SILVICULTURE ............................ 46

ASSUMPTIONS OF THE RECOMMENDATIONS ....................................................................... 47

A FRAMEWORK FOR RECOMMENDATIONS ......................................................................... 49

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DISTURBANCE SCALE ...........................................................................................................49

DISTURBANCE INTENSITY .....................................................................................................51

SILVICULTURE OPTIONS .................................................................................................... 51

SCENARIO 1: NO ACTION ......................................................................................................55

SCENARIO 2 – INFLUENCE COMPOSITION ONLY......................................................................58

SCENARIO 3 – INFLUENCE COMPOSITION AND STRUCTURE .....................................................60

INCREMENTAL SILVICULTURE............................................................................................ 66

MONITORING THE IMPLEMENTATION OF SILVICULTURE.................................................... 66

RESEARCH RECOMMENDATIONS .............................................................................. 67

CONCLUSION.................................................................................................................. 68

ACKNOWLEDGEMENTS ............................................................................................... 69

APPENDIX 1 – VARIABLES MEASURED IN EACH PLOT .......................................... 70

APPENDIX 2 – SYSTEM FOR CLASSIFYING EVIDENCE OF DAMAGING AGENTS 72

APPENDIX 3 – SUMMARY OF SYSTEM FOR CLASSIFYING WILDLIFE TREETYPES ............................................................................................................................... 73

APPENDIX 4 – COARSE WOODY DEBRIS CLASSIFICATION SYSTEM ................... 74

APPENDIX 5 - CLASSIFICATION FOR SNAGS ............................................................ 75

APPENDIX 5 – CORRELATION BETWEEN VARIABLES AT THE PLOT LEVEL..... 76

VARIABLES CONSIDERED IN THE SIMPLE CORRELATION ANALYSIS ................................... 78

APPENDIX 6 – EXAMPLES OF RESULTS OF THE THREE DIFFERENT TYPES OFSPATIAL ANALYSIS ....................................................................................................... 79

DESCRIPTIVE ANALYSIS ..................................................................................................... 79

CORRELATION ANALYSIS ................................................................................................... 83

INTENSITY ANALYSIS ......................................................................................................... 85

K-FUNCTION ANALYSIS ..................................................................................................... 87

REFERENCES.................................................................................................................. 91

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Summary

Western hemlock looper (Lambdina fiscellaria ssp lugubrosa) has caused extensive

forest disturbance within forests in the Robson Valley (Rocky Mountain Trench) in

central eastern British Columbia. In the early 1990s it caused defoliation over 39 000

hectares of forest that were largely dominated by western hemlock (Tsuga heterophylla)

and western redcedar (Thuja plicata). The effects of western hemlock looper on a range

of ecosystem features have not been well documented.

This report describes the current condition of thirteen separate stands of trees that were

located within the area damaged by western hemlock looper in the 1990s outbreak. These

stands were located in areas where mortality of canopy trees due to defoliation was more

than forty percent.

The effects were variable across the stands. The major effect was the death of a high

proportion of trees from the range of tree species and sizes present. Both surviving and

dead trees displayed high levels of stem decay and a high incidence of damage from other

disturbance agents. The crown dimensions and conditions of surviving trees suggested

that they had largely recovered from the effects of the outbreak. Tree mortality had

created a high density of snags across the range of diameter classes. It was apparent that

these would be augmenting the already large pool of coarse woody debris for some time

to come. Tree regeneration consisted mostly of western hemlock with a moderate

component of western redcedar. Regeneration tended to be associated with stands where

mortality had been lower. The majority of trees in the sapling phase were already

showing evidence of decay. Stands generally contained two understorey layers. The

development of the upper understorey layer was most pronounced in areas of higher

mortality. A high proportion of the upper understorey cover consisted of species that

were generally associated with disturbance.

A search for spatial pattern revealed that a range of tree variables were distributed

randomly at scales of less than 50 m, and that sapling regeneration generally occurred in

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clumps of less than 6 m diameter. A range of variables showed associations at a plot scale

(1480 m2) but no association at a smaller scales (100 m2). Boundaries in the state of

variables were frequently present within plots indicating that some degree of patterning

may exist at larger scales than those examined in this study.

The information on ecosystem composition and structure was coupled with conventional

silviculture knowledge to recommend silviculture strategies consistent with ecosystem

management. The primary goal was to provide a range of silviculture actions that would

create effects that mimic those of western hemlock looper. Four scenarios were proposed.

They were defined by the degree to which they maintained the frequency distribution of

disturbance patch sizes, and the compositional and structural characteristics created by

looper disturbance.

It was apparent that there were still critical gaps in knowledge concerning the ecology

and effects of western hemlock looper in the Robson Valley. Research that examined the

periodicity, pattern at large scales and cause of western hemlock looper events was

recommended.

Introduction

6

Introduction

An outbreak of western hemlock looper (Lambdina fiscellaria ssp lugubrosa)(WHL)

between 1990 to 1994 caused defoliation over 39 000 ha of forest within the Robson

Valley (Taylor unpublished) (see Photograph 1). The majority of defoliation occurred in

1991 and 1992 (Taylor unpublished). This outbreak followed a defoliation event in 1954

and 1955 in which over 45 000 ha of forest in the Robson Valley was defoliated (Parfett

et al. 1995).

The effects of WHL on forest ecosystems are not well understood. Studies have mainly

concentrated on the biology and control of WHL. The same can be said for the closely

related eastern hemlock looper (Lambdina fiscellaria ssp fiscellaria). Only one study of

the ecological impacts of WHL was found during an extensive literature search.

(Kinghorn 1954) examined tree and stand characteristics of areas defoliated during a

WHL outbreak in the 1940’s in the Coastal Western Hemlock Zone on Vancouver Island.

Kinghorn’s study occurred shortly after the cessation of the outbreak, concentrated on the

tree component of the ecosystem and presented only a snapshot of the effects of WHL.

A study was initiated in 1999 to address the issue of WHL in the Robson Valley.

Specifically (Hoggett unpublished-a) the study set out to:

1. Provide an indication of the relative importance of WHL as a natural disturbance

agent within a specified landscape unit.

2. Examine the effects of WHL on the structure and composition of stands within

Interior Cedar Hemlock (ICH) (Anon. 1996) forests.

3. Compare these effects with those of other disturbance agents (including harvesting).

Introduction

7

Photograph 1: Defoliation caused during the 1990s outbreak of western hemlock

looper (Goat River)

Photograph 2: An example of conditions within a stand defoliated by western

hemlock looper. Of particular note was the relatively high tree species diversity,

degree of tree mortality and development of the understorey

Introduction

8

4. Relate the landscape and stand level findings to the strategic provision of production

or environmental values1.

These aims were to be met using a three-stage project (termed the ‘project’ from here)

(Hoggett unpublished-b). This report covers the second of the aims. It was intended to

meet the requirements of a contract signed in 1999 between Zeidler Forest Industries Ltd.

and the University of British Columbia (ICH Investigation – The historical importance of

western hemlock looper in the ICH ecosystems of the Robson Valley).

The data for this report was collected as during Stage 2 of the project. It represents only

part of the information collected during field sampling. Further information concerning

the disturbance history of the ICH will continue to be made available as data analysis

continues.

Methods

Field Methods

Thirteen stands of ICH forest were sampled between June and October of 1999. The

approximate locations of the sampled stands have been indicated on Map 1. All stands

areas were located in a wet cool variant of the ICH (ICHwk3) (Anon. 1996) in the Rocky

Mountain Trench (Robson Valley). The stands were also located within the Crescent Spur

and Northern Trench Landscape units and within the B.C. Ministry of Forest Robson

Valley District. They were predominantly age class 9 (250 years or older). Two plots fell

in stands classified as age class 8 (140-250 years old). All stands demonstrated moderate

to severe tree mortality (more than 40% of canopy trees died) because of defoliation

during the WHL outbreak of the early 1990s (1990s outbreak).

1 Termed commodity (production) and amenity (environmental) throughout this report.

Introduction

9

Map 1: Approximate location of sampled stands

Map reproduced from – Sheet 93H McBride 1:250 000 scale topographical map. Department of Energy, Mines andResources Canada (1990).

N

10 kmApproximate Plot Locations

Introduction

10

The sampling population included all polygons identified as disturbed by WHL during

Stage 1 of the project (see Hoggett (unpublished-c)). Plot centre points were located

randomly within this population. Some latitude was used in locating final plot centres2.

This ensured that the plot occurred sufficiently far from boundaries of damage, and on

sites of mesic moisture regime and of moderate fertility (soil moisture regime 2-4, soil

nutrient regime B-D (Anon. 1996)). A 1480 m2 plot was placed perpendicular to aspect. It

consisted of a 10 x 100 m ‘extensive’ plot, overlaying a 22 x 40 m ‘intensive’ plot

(Diagram 1).

Diagram 1: Plot layout showing the arrangement of extensive and intensive plots

and the various subplots used for sub-sampling

A range of individual tree variables was measured for all trees (a tree was classified as

any individual of a tree species that was greater than 10 cm diameter at breast height over

bark (dbhob)). Additional tree variables were sampled for pre-specified subsets of trees.

A range of other variables were measured or estimated in a series of subplots that were

located within these two larger plots. Finally, four 20 m transects were used to assess

2 A systematic search procedure starting at the original plot centre was used. A maximum search radius of 200 m fromthe original plot centre limited the distance that the plot centre could be moved.

10 Metres

Intensive Plot

Extensive Plot

Subplots

Coarse woody debristransect

Introduction

11

characteristics of coarse woody debris. A comprehensive list of variables collected during

field sampling has been included in Appendix 1. These variables were selected following

examination of literature relating to disturbance and disturbance history assessment

(Hoggett unpublished-a).

Plot and sub-plot sizes were arbitrary but were thought likely to be of sufficient size and

appropriate shape to pick up important variation in the spatial distribution of ecosystem

elements. Total sample size was restricted by budget.

Analysis

Data were entered into spreadsheets and checked for field or data entry errors. A number

of derived variables were calculated in addition to the original variables collected in the

field. Non-spatial analysis was mostly conducted using SAS. Analysis of spatial

disposition and correlation was conducted using both SAS and S-PLUS.

Current Ecosystem Condition

12

Current Ecosystem Conditions

The results presented below concentrate on the data that was considered most useful for

describing current ecosystem conditions. They are applicable to all areas identified in

Stage 1 of the project as damaged during the 1990s outbreak.

Site

Physical site characteristics for all plots have been listed in Table 1.

Plots occurred on a range of aspects, in lower to mid topo-sequence positions, and in

areas of shallow slope. Underlying soils were moderate to deep, and generally had some

degree of clay accumulation in the B-horizon (Luvisolic). Coarse fragment contents were

generally low, and gleying was generally absent.

Table 1: Physical site characteristics for all plots in the study

Plot Elevation(m)

Slope(degrees)

Aspect SlopePosition

Total SoilDepth (cm)

Soil Type3 CoarseFragment

Content (%)

IN01 880 2 208 lower 75 O.GL 0

IN02 880 4 3 lower 60+ BR.GL 5

IN03 840 4 3 toe 80+ O.HFP 0

IN04 880 24 358 lower 90+ E.DYB 20

IN05 900 10 18 toe 70 E.DYB 5

IN06 1050 32 353 mid 60+ O.SB 50

IN07 950 12 70 mid 55 PZ.GL 5

IN08 850 5 128 mid 70+ BR.GL 0

IN09 950 8 318 mid 60+ BR.GL 10

IN10 850 4 3 lower 60+ D.GL 0

IO01 850 2 185 mid 90 GLBR.BL 0

IO02 880 5 280 mid 60 O.HFP 10

IO04 790 8 308 mid 60+ PZ.GL 5

3 Using classification presented in Soil Classification Working Group (1998)


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Classification of site series using the Biogeoclimatic Ecosystem Classification (Pojar et

al. 1987) placed all plots either in the CwHw – Oak Fern site series (01) of the CWHw –

Devils Club – Lady fern site series (05) (Anon. 1996). A photograph of conditions that

were relatively typical within a defoliated stand has been included as Photograph 2.

Current Stand Condition

Diameter

The average diameter distribution for all stems greater than 10 cm dbhob has been

included as Graph 1. Diameter classes have been separated into the number of live and

dead individuals for each species.

The shape of Graph 1 (decreasing number of stems per hectare with increasing diameter

class) suggests stands of uneven age structure. Stands were generally dominated by

western hemlock (Tsuga heterophylla) and western redcedar (Thuja plicata). The

proportion of western redcedar increased as diameter increased. Subalpine fir (Abies

lasiocarpa) and spruce (Picea glauca x engelmanni) were the only other species of

numerical importance. They were generally confined to diameter classes of less than 50

cm. The high mortality illustrated in Graph 1 was expected. The level of basal area

mortality was the major criterion in delineating the sample population.

Estimates of mean mortality rates and standard errors (SE) for each species within each

diameter class have been depicted in Graph 2 (for those classes where more than two

observations were available). These rates were calculated using live trees, and trees that

had died recently (decay class 3). Old dead trees were excluded (decay classes 4 to 9).

The assumption was that all recent mortality was either directly or indirectly attributable

to defoliation during the 1990s WHL outbreak. Systematic examination of all trees in the

interior plot did not reveal any evidence to the contrary.


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Species codes used throughout report: Tp – Thuja plicata; Th-Tsuga heterophylla; Al – Abies

lasiocarpa; Px – Picea glauca x engelmannii; Bp Betula papyrifera; Pm – Pseudosuga menziesii var

glauca

Graph 1: Average Diameter Distribution


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Graph 2: Estimated mortality by species

Mean mortality of more than 60% of the estimated number of stems that were living prior

to the outbreak was observed for all species for almost all diameter classes (Photograph

3). Estimates of standard errors indicated a reasonable degree of variability between

observations from different plots. Differences in mortality between diameter classes

within species, and between species were not significant (α=0.05).


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Photograph 3: Variable mortality from defoliation associated with the 1990s

outbreak.

Photograph 4: Logs harvested from areas defoliated during the 1990s outbreak. The

camera case has been included for scale.


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Volume and Basal Area

The distribution of volume by species within each diameter class has been presented in

Graph 3. Volume considers not only the number of individuals, but also the size of

individuals. It is closely related to basal area and both were better representations of site

occupancy4 than number of individuals alone.

The volume distribution indicated that looper affected stands were dominated by western

redcedar and hemlock.

Examination of basal area figures revealed that live western redcedar occupied 21.6

m2ha-1 and western hemlock 10.1 m2ha-1. The three other coniferous species contributed

only approximately 1 m2ha-1 to live basal area respectively. The majority of basal area

was found in stems of between 35 and 80 cm dbhob. Approximately two-thirds (55.0

m2ha-1, SE=5.7) of the total basal area (86.4 m2ha-1, SE=4.0) was dead.

The 1990s WHL event caused a shift in basal area dominance. Prior to the event, both

western redcedar and western hemlock had basal areas of approximately 40 m2ha-1.

Following the event, the basal area of western redcedar was half of its pre-outbreak level,

but nearly twice that of western hemlock. This shift in dominance was not apparent from

examining the simple diameter distribution. It suggested a reduction in the importance of

western hemlock in the overstorey due to the outbreak.

4 Better indices of site occupancy exist. Volume and basal area account not only for current site occupancy (live basalarea), but includes an element of historical site occupancy (accumulated dead basal area). Other indices of siteoccupancy include sapwood basal area or leaf area index. These are, however, considerably more difficult to accuratelyestimate.


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Graph 3: Volume in diameter classes by species and status

Height

Average frequency of live and dead individuals of different species are represented in

Graph 4 for each height class.


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Graph 4: Density distribution by height class

Two major height groupings were apparent from Graph 4. The classes between 6 and 12

m height and between 18 and 26 m height account for the majority of stems. This

suggested that trees generally occur in two major layers. The upper layer represented the

canopy. The live component of this upper layer was generally dominated by western

redcedar. The live component of the lower layer was dominated by western hemlock.

Live western hemlock was generally absent in height classes of over 30 m. Live

subalpine-fir and spruce were confined to the canopy layer.

The mean densities for classes of trees less than 14 m and over 30 m was more variable

(higher coefficients of variation). This suggested that most plots had relatively stable


20

densities of trees in the 14 to 30 m height range, but that the density of trees outside this

range was much more variable between plots.

Decay

The estimated mean and standard errors for percent of decayed basal area have been

presented for each species in Graph 5. The same estimates are presented for each

diameter class for both western redcedar and western hemlock in Graphs 6 and 7. In this

study, decay was recognized as the presence of evidence of decay fungi within the stem

(decayed wood or wood discoloured by decay fungi). Estimates of decay were made by

coring a sub-sample of trees from the range of canopy classes within each plot. Decay

estimates were made at 0.3 m for all sub-sampled trees of greater than 10 cm dbhob

(diameter at 1.3 m over bark), and at 0.0 m for sub-sampled trees of less than 10 cm

dbhob. Photograph 4 depicted the degree of decay often found in ICH stands.

Graph 5: Percent basal area decayed


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Graph 6: Percent basal area decayed by diameter class for western redcedar

Graph 7: Percent basal area decayed by diameter class for western hemlock


22

These graphs suggested that the proportion of decay was greater in dead than live stems,

and that the proportion of decay increased from subalpine fir to western hemlock to

western redcedar. The proportion of decay also increased with increasing diameter class

for both western redcedar and western hemlock. A mean of greater than 50% decay was

observed for almost all diameter classes of western redcedar. Mean observed decay was

between 40 and 50% for most western hemlock diameter classes. Decay extended even

into the smallest diameter classes, with an observed mean of approximately 30% for

western redcedar saplings.

Crown Condition

The mean crown cover5 of live and dead trees and proportion of gap have been presented

in Graph 8. Live crown ratio estimates by diameter class for trees surviving the 1990s

outbreak have been included in Graph 9.

Graph 8: Percent cover by cover type class


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Graph 9: Mean live crown ratio by diameter class

Graph 8 illustrated that only an estimated average of 40% of canopy area was occupied

by living trees at the time of sampling. This left approximately 60% of the canopy area in

gap, up from an estimate of just over 13% prior to the WHL outbreak. The majority of

the area available for light foraging by canopy trees was no longer occupied by living

crown.

The majority of trees that survived the WHL event had deep crowns (Graph 9). Mean live

crown ratios were generally greater than 50% in all diameter classes and stable between

plots (low standard errors for all diameter classes). This coupled with incidental field

5 Crown cover was defined as the projected outline of the outer extremities of either foliage (for live trees) or branchstructure (for dead trees).


24

observations and supplemental data, indicated that most of the surviving trees had largely

recovered from any defoliation had occurred. Crown volume was, therefore, unlikely to

have significantly constrained the ability of surviving trees to respond to the new growth

conditions created by the WHL event.

A relatively systematic fluctuation in live crown ratios with increasing diameter was

evident in Graph 9. This suggested some degree of competitive stratification within

height classes. Expression of relative dominance within any height strata would tend to

allow trees to increase diameter and maintain greater live crown ratios over less dominant

trees within the same height strata.

Other Tree Characteristics

Evidence of Damaging Agents

Each tree within the intensive plot was assessed for evidence of a range of other

damaging agents. The classification system used for recording this evidence has been

provided in Appendix 2.

It is important to note that observation of other tree characteristics was conducted from

ground level. This method was robust for features that were close to, or readily

observable from ground level. The ability to detect smaller or more obscure features was

reduced as height above ground level increased, and as branches and live crown obscured

the upper stem. Observations were also made based on external features. Soil or bark

excavations were only conducted if some external feature of the tree suggested the

presence of a hidden damaging agent. The following information was, therefore, likely to

be a conservative estimate of the occurrence of the other tree characteristics.

It is also important to note that some degree of interpretation was necessary in classifying

some features. For example, it was often difficult to determine the cause of a scar that had

healed. If the cause was not obvious, the feature was classified as of unknown origin.


25

Finally, it was considered impractical to attempt to assess the total number of some

features (e.g. small scars made by some insect feeding birds). The number of individuals

of a feature on a single tree was counted if there were less than 10. Trees with more than

10 of an individual feature were considered as a separate class.

The mean and standard error for the density of the most common forms of evidence of

damaging agents has been presented in Graph 10.

Graph 10: Density of the most common damaging agents (Size: 1= <10 cm longest

dimension; 2= 10 to 99 cm; 3= 99 to 9999 cm)

Conks and cankers were the most frequently observed evidence of damaging agents.

These were generally confined to western hemlock and were endemic for this species

(though they did occasionally occur on subablpine fir and spruce where these species

were present). The most common species was brown stringy trunk rot (Echinodontium


26

tinctorium). The only other regularly observed decay fungi was brown crumbly rot

(Fomitopsis pinicola). Mechanical scars were also relatively common and generally of

greater than 10 cm in their longest dimension (see Photograph 5). The relatively high

density of deep mechanical scars for size class three resulted from classifying cracks

caused by mechanical stress as mechanical scars.

Wildlife Trees

The estimated mean density and standard error for types of wildlife trees has been

included as Graph 11.

Graph 11: Mean density of wildlife tree types


27

Photograph 5: Surface scarring on western redcedar caused by mechanical

abrasion. Scars were one of the more common effects of damage observed.

Photograph 6: Advance regeneration showing typical form and species composition


28

The classification used for wildlife trees (WLT) followed that provided by Keisker

(1999). A brief summary of the WLT classification has been included in Appendix 3.

Searches for features corresponding with Keisker (1999) first two coarse woody debris

classes were also made on all standing trees (small and large low spaces, WLT 11-12).

The caveats mentioned for the interpretation of evidence of damaging agents apply to the

WLT observations. Assessment of WLTs was conducted in a similar manner to that for

damaging agents.

The highest estimated WLT densities occurred for trees that displayed hard outer wood

with decay softened inner wood (WLT-1). Western hemlock constituted the majority of

trees in this class. The density presented in Graph 11 was likely to have been a substantial

underestimate for this WLT type. Coring revealed that the majority of western redcedar

trees would also have fallen into this class, had evidence of decay been readily

observable from exterior features.

The data also revealed relatively high densities of low large spaces (WLT 11). Moderate

densities were observed for; trees with outer and inner wood softened by decay (WLT 2);

cracks, loose bark, or deeply furrowed bark (WLT 6); large branches, multiple leaders, or

large diameter broken tops (WLT 8)6; and small concealed spaces at or below ground

level (WLT 12).

Dead Material

Coarse Woody Debris

Coarse woody debris (CWD) was defined as any dead stem that formed an angle of less

than forty-five degrees with the ground and was greater than 10 cm average diameter at

the point where it intersected with the sampling transect line. CWD was classified using a

6 Trees were only included as WLT 8 if they were judged to meet the functional requirements of this class as nest orroost sites for large bodied species.


29

decay class system based on that of Triska and Cromack (1980). A class was added to the

classification to allow differentiation between heavily decayed CWD found on the forest

floor (Class V), and heavily decayed CWD that was largely submerged within the forest

floor (Class VI). The classification system has been presented in Appendix 4.

The data from CWD sampling has been included in Graphs 12 and 13.

Large volumes of CWD were present. The majority of CWD was difficult to attribute to

particular species, because of its relatively advanced stage of decay. It was, however,

apparent from Graph 12 that all major species have contributed to the CWD pool. The

majority of coarse woody debris was in decay classes (DC) three and above. This

suggested that input of CWD from trees that died during the 1990s outbreak had been

relatively low at the time of sampling.

Snags

Graph 14 presents the mean densities of snags by diameter and decay classes. Snags were

classified using the classes provided by Caza (1993). The summary of the classification

has been provided in Appendix 5.

Snags in DC3 dominated across all diameter classes. There were generally 10 or more

DC3 snags per hectare for every DC4 snag in each diameter class. DC4 was the only

other class of snags that was consistently represented across diameter classes. Densities

of DC5 and DC6 snags were low, and DC7 and DC8 snags were rare. The average

density of dead trees of greater than 10cm dbhob was 521 ha-1 (SE = 45.7). Twenty

percent of these dead stems were greater than 50cm dbhob.


30

Graph 12: Volume of CWD by species

Graph 13: Volume of CWD by decay class


31

Graph 14: Densities of snags by diameter and decay class

Tree Regeneration

Densities of regeneration (saplings and seedlings) have been presented in Graphs 15 and

16.

Both graphs show that regeneration was dominated by western hemlock (see Photograph

6). There was also a substantial component of western redcedar and a minor component

of subalpine fir. Spruce regeneration was virtually absent, and birch regeneration was

infrequent. Seedlings were the majority of regeneration (less than 1 cm diameter over

bark at ground level).


32

Graph 15: Densities of regeneration by class

Graph 16: Densities of regeneration by plot


33

The high standard errors associated with estimates in Graph 15 suggested that

regeneration was very variable between plots. This observation was supported by the data

in Graph 16. Some plots provided estimates of regeneration of close to 12 000 stems per

hectare, while some provided estimates of less than 1000 stems per hectare. There was a

moderate positive correlation between plot estimates for mean live canopy cover and total

density of regeneration (0.53). This suggests that higher levels of regeneration tend to be

associated with higher levels of live canopy.

Saplings showed high incidence of decay. An average of 71.8 percent of sub-sampled

saplings (SE=7.9) contained some evidence of decay. This decay generally constituted a

significant proportion of individual sapling basal area (see Graphs 6 and 7).

Other Ecosystem Components

Understorey Vegetation

The understorey vegetation (non-tree species) was generally two layered. The lower layer

(layer 1) had an average maximum height of 46 cm (SE=3). The upper layer (layer 2) had

an average maximum height of 213 cm (SE=11). Average covers for the thirty-five most

common understorey species are presented by layer in Graphs 17 and 18.

Average total covers for layers 1 and 2 were 52.4 percent (SE=3.9) and 39.6 percent

(SE=7.6) respectively. Layer 2 was generally of lower total and cover estimates for layer

2 were generally more variable between plots than those for layer 1. There was little

correlation between layer 1 cover and live canopy cover, or between covers in layers 1

and 2. Layer 2 demonstrated a moderate negative correlation with live canopy cover at

the plot level (increasing layer 2 cover as live canopy cover decreased) (See Photograph

7).


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Graph 17: Cover of common understorey species in layer 1

Graph 18: Cover of common understorey species in layer 2


35

Photograph 7: Dense development of an upper understorey layer consisting of

species normally associated with disturbance (photograph taken after leaf fall)


36

The lower layer of the understorey was generally dominated by oak fern (Gymnocarpium

dryopteris). Other important species in this layer included bunchberry (Cornus

canadensis), common horsetail (Equisetum arvense), five-leaved bramble (Rubus

pedatus), and one-leaved foamflower (Tiarella unifoliata). Layer 2 was generally

dominated by devils club (Oplopanax horridus) and red elderberry (Sambucus

racemosa). Other important species included lady fern (Athyrium filix-femina), fireweed

(Epilobium angustifolium), red raspberry (Rubus idaeus) and oval-leaved blueberry

(Vaccinium ovalifolium). Average moss cover was approximately 35% (SE=6.5).

The observations from the lower understorey layer were generally consistent with the

expected species composition in climax communities (Anon. 1996). The same could not

be said for three of the most important species from the upper layer. Red elderberry,

fireweed and red raspberry were all species that would be expected to be more common

on disturbed sites (Haeussler et al. 1990). These species were competing successfully in

many stands despite there being no soil or forest floor disturbance during or since the

outbreak.

Forest Floor and Charcoal

Forest floor depth averaged 8.0 cm (SE=0.6) across all plots. Evidence of past fires in the

form of forest floor charcoal was generally weak. Graph 19 illustrates the average

proportion of subplots that contained charcoal. It was divided into charcoal index classes.

The charcoal index considered both the amount and the continuity of charcoal within the

forest floor. In general, the greater the index, the greater the amount of charcoal.

The majority of subplots within each plot had no readily observable charcoal within the

forest floor. Only a small proportion of subplots had high levels of charcoal. Despite the

low proportion of subplots with charcoal, some amount of charcoal was found in 11 of

the 13 plots. This indicated that fires had occurred in the past in most, if not all, of the

plots.


37

Graph 19: Mean proportion of subplots containing charcoal

Correlation between Ecosystem Elements at the Plot Level

Simple correlations were calculated using observed values for pairs of variables from

each plot. The variables that were used have been listed in Appendix 6. The pairs of

variables that had moderate to high correlation (absolute correlation of 0.6 or greater) and

were not considered trivial have also been listed in Appendix 6. The correlation analysis

has been discussed briefly below.

• There was a strong negative correlation between western redcedar and western

hemlock for both total and live basal area. This suggested that the relationship

between the two species is substitutive (when one species increases the other

decreases).


38

• There was also a strong positive correlation between total and live basal area of

western redcedar and total basal area for all species. Total basal area of western

hemlock was negatively correlated with total basal area for all species. Stands with

higher total basal area had higher proportions of western redcedar at the expense of

western hemlock.

• Total live basal area, survival and mean live cover all had strong positive correlation

with the basal area of live western redcedar. This suggested that survival in stands

was closely linked with the presence and survival of western redcedar.

• The mean dbh and height of live canopy trees was positively correlated with the basal

area of western redcedar. Stands with greater proportions of western redcedar tended

to have surviving canopies that consisted of taller and larger trees.

• Plots with live trees with higher heights to base of live crown, and with smaller live

crown ratios suffered more basal area mortality. This suggested a relationship

between tree characteristics and the stand’s response to the WHL outbreak.

• Stands with greater proportions of western redcedar tended to have greater covers of

the lower understorey layer (layer 1), and reduced covers of moss.

• Regeneration density was positively correlated with the total basal area of live

western hemlock. Both of these variables were also positively correlated with moss

cover.

• There was increased development of a second understorey layer as tree mortality

associated with WHL increased. The development of a second understorey layer was

also coupled with a decrease in moss cover and regeneration density, and with an

increase in the average height to live crown in canopy level trees.

• The density of Type 1 wildlife trees (WT1) was found to decrease as the proportion

of total basal area affected by decay increased.


39

This result was clearly spurious, as the definition of WT1 includes all trees with internal

decay. The correlation between WT1 and other ecosystem features clearly demonstrated

the limitations of external examination for assessing internal tree features. The

explanation lies in the ability to detect WT1 from external examination. WT1 were

positively correlated with western hemlock basal area and negatively correlated with

western redcedar basal area. This was because evidence of internal decay was visible in

the form of conks and cankers on western hemlock, but was not visible on western

redcedar. Graphs 5 and 6 demonstrated that mean decay levels were higher in western

redcedar than hemlock. This was confirmed by correlation, which found that total decay

levels were positively correlated with total basal area of western redcedar and were

negatively correlated with total basal area of western hemlock. In other words, as the

proportion of western redcedar in the stand increased so did the proportion of decay.

Spatial Pattern

40

Analysis of Within Plot Spatial Pattern

The method of data collection used for this project enabled the analysis of the spatial

pattern of ecosystem elements within each plot. The purpose of this analysis was to

describe spatial disposition at a range of resolutions. This approach acknowledges that

the information provided when using a single scale of observation (such as a single plot

size) provides just one perspective. It may miss important relationships at different scales.

The use of a variety of scales may provide a more complete picture of ecosystem

interactions, and assist in more accurately describing and predicting ecosystem condition.

Spatial data can be collected in a number of ways (Cressie 1993). A range of techniques

was available for assessing spatial pattern for each type of spatial data (Cressie 1993).

During this study, point-pattern data was collected for all trees and for a subset of

saplings. Geostatistical and lattice data were collected for a range of other variables.

Forest floor depths and overstorey crown cover estimates are examples of geostatistic

data, while understorey cover and seedling density estimates are examples of lattice data.

Spatial data was examined using four approaches. These were: (1) purely descriptive; (2)

an examination of average correlation: and analysis of point-pattern data using both (3)

intensity and (4) K-functions. Examples of the outcomes of the analyses have been

presented in Appendix 7. Each is discussed briefly below.

Descriptive

Descriptive examination of lattice and geostatistical data involved the plotting of values

for each variable of interest against distance from the southernmost endpoint of the plot

centerline (x=0, y=0 coordinate). Descriptive analysis of the point-pattern data involved

the mapping of tree locations with symbols that reflected diameter, height and tree status

(live or dead).

The graphs were useful for visualizing the change in variable values over space, but did

not reveal any consistent pattern in the data. They demonstrated that the state of a number

Spatial Pattern

41

of variables changed dramatically within individual plots. They also revealed that values

for any given variable were often quite different between plots. This suggested that the

distribution of variable states was patchy following the outbreak, and patch boundaries in

many variables could be identified when examining data from a 100 x 10 m plot.

Correlation Analysis

A simple correlation analysis was undertaken using the geostatistical and lattice data.

This approach was used as sequences of lattice and geostatistical data were too short to

effectively undertake more conventional analysis techniques. The correlation analysis

calculated the correlation between pairs of variables for all subplots within a plot. For

example, the correlation between overstorey canopy cover and moss cover was calculated

for each plot using pairs of measurements from each subplot. An average and its

associated standard error were then estimated for the population from the 13 plot-level

correlations.

Consistent correlation between variables in space represented one form of spatial

patterning. Some degree of spatial patterning had already been identified between plots

(see Correlation between Ecosystem Elements at the Plot Level). This implied a spatial

scale of 1480 m2 or greater. It was considered possible that some degree of spatial

association between variables existed at smaller scales than this.

Twenty variables were selected for the correlation analysis. This analysis was conducted

using a regular lattice of 10 by 10 m, centered on the plot centerline, and running from

one end of the plot to the other. Both 5 and 10 m intervals were used. Correlation at

larger scales than this was not tested. Correlation between overstorey and other features

at smaller scales than these were thought unlikely because of the scale of individual

canopy trees.

While the correlation between a number of variable pairs were significantly different

from 0 (α=0.05), only two were both non-trivial and had an absolute correlation of

greater than 0.25 (α=0.05). These were:

Spatial Pattern

42

• a weak negative correlation between the basal area of sub-canopy trees and the

proportion of overstorey in canopy gap

• a moderate positive correlation between the height of layer A trees (emergent,

dominant, and codominant) and the total live basal area.

In other words, sub-canopy level trees tended to be more prevalent under canopy (either

live or dead), and higher levels of live basal area were associated with stands with taller

canopy heights.

The general conclusion from this analysis was that relationships between canopy and sub-

canopy features were operating at scales of greater that 10 m.

Point-Pattern Analysis

Point-pattern analysis was conducted for tree and sapling data. The tree data from the

extensive plot was used (100 x10 m) and sapling data from the contiguous subplots

within the intensive plot (25 x 5 m). Both intensity and K-function analysis were

attempted. Both types of analysis are capable of detecting departures from complete

spatial randomness (CSR). In essence, they were capable of showing where point-

patterns are more aggregated or regular than would be expected if the underlying process

of point distribution was purely random. Examples of both types of analyses are

presented in Appendix 7. The results of the K-function analysis were more revealing than

the intensity analysis. The K-function analysis has been discussed below.

Both tree and sapling data were analyzed on a plot by plot basis. Initially tree data in each

plot was treated as a whole, and then classes of trees within each plot were examined

separately. Sapling data was treated as a whole because of the relatively low number of

saplings. The maximum scale at which pattern could be detected was equal to half the

maximum dimension of the plot (in this case diagonal of the rectangular plots). This

limited pattern analysis to approximately 50 m scale for trees and 13 m scale for saplings.

The results of the K-function analysis for both tree and sapling data have been presented

in Table 2.

Spatial Pattern

43

Table 2: Results of K-function analysis – the numbers in the table represent the

number of plots displaying the spatial arrangement

No Pattern Aggregated Regular Both

Trees Western redcedar 10 0 2 0

Western hemlock 10 2 0 1

Ht=4 to 17.9 m 8 2 2 1

Ht=18-36 m 11 1 1 0

Tree layer 1 9 1 3 0



Live trees 9 1 1 0

Dead trees 9 1 3 0

All trees 10 1 2 0

Saplings All 0 8 0 4

The K-function analysis revealed that there was no consistent pattern in tree distribution

at scales of less than 50 m for any of the classes of trees examined. Trees were, overall

randomly distributed at this scale. This meant that, at scales of less than 50 m, species

were not clumped, height strata were relatively continuous, and individuals that died from

WHL defoliation were randomly distributed.

This finding does not preclude the existence of pattern at large scales than 50 m. Indeed,

the differences between the values for variables between plots, suggested that boundaries

between states of single variables exist within the area disturbed by WHL. Distinct

changes in the state of single variables within plots were revealed by the descriptive

spatial analysis (see Graphs 1-3 in Appendix 7). This suggested that boundaries occurred

over relatively short distances. The frequency of observed boundaries further suggested

that scales of the order of around 100 m may be a useful starting point for searching for

larger scale pattern in overstorey variables.

Saplings demonstrated a strong tendency to aggregate at scales of generally less than 6 m.

They also demonstrated an occasional tendency to regular distribution at scales of

Spatial Pattern

44

between 8 and 12 m. In other words, there were more saplings closer together at all

distances less than 6 m than were expected under a random distribution. There were also

less saplings closer together than 8 to 12 m than were expected with a random pattern.

The data for seedling distributions were not amenable to K-function analysis. An

examination of stocking across subplots did, however, tend to suggest that seedlings also

had a patchy distribution. Only an average of 25 percent (SE=4.9) of the seedling

subplots contained seedlings. This confirmed general field observations of clumping of

both classes of regeneration.

The general conclusions of the spatial analysis were that:

• The distribution of a range of classes of trees was essentially random at scale of less

than 50 linear m.

• Regeneration was clumped. Saplings were aggregated in groups of less than 6 m

dimension.

• Large changes in the state of variables were frequently observed at a 1000 m2 scale.

This suggested a logical point for continuing any analysis of spatial pattern.

• Any association between overstorey variables and other variables occurred at a scale

of greater than 100 m2.

• Associations between overstorey variables and other variables were observed at the

1480 m2 scale.

Recommendations

45

Silviculture Recommendations

The Basis for Silviculture

Informed and appropriate silviculture works on the interface between science and social

values. It requires:

• A good knowledge of the current state of the ecosystem in which it is to occur.

• An understanding of the likely responses of ecosystem elements to a broad range of

possible silvicultural actions.

• A clear understanding of the values which the forest owner demands from the area

that is to be managed.

With this information it is possible to design silviculture which sustains ecosystems while

meeting the objectives of the forest owner as efficiently as possible.

This report has provided a description of the current state of ecosystems that have been

affected by WHL. The likely responses of ecosystem elements to a broad range of

silvicultural actions are relatively well known in general terms for major ecosystem

elements. Knowledge concerning likely responses in specific circumstances, and linked

to the Robson Valley has been increasing (Coxson 1996, Jull et al. 1999, Stevenson et al.

1995).

The most problematic of these requirements has generally been to understand the values

that the forest owner demands. This has certainly been the case where forest ownership

was largely public, as in British Columbia. For the purposes of this report, information

concerning a specific goal was requested in the contract specification. Advice was sought

on silviculture practices that would assist in meeting the goals of ecosystem management.

This request reflected the recent broad emphasis on the adoption of the principles of

ecosystem management in provincial and federal policy and regulation.

Recommendations

46

What is Ecosystem Management?

Ecosystem management has been hailed as the emerging management paradigm in

natural forested areas in North America (and some other regions of the developed and

developing world). It is defined, in cumbersome language, by Christensen et al. (1996)

as:

“… management driven by explicit goals, executed by policies, protocols, and

practices, and made adaptable by monitoring and research based on our best

understanding of the ecological interactions and processes necessary to sustain

ecosystem composition , structure and function” .

It attempts to meet a number of societal, cultural, institutional and scientific challenges to

enable the management of natural ecosystems that is both ecologically and socially

sustainable (Gerlach and Bengston 1994). Ecosystem management focus primarily on

sustainability of ecosystem structures and processes necessary to deliver commodities or

amenities, rather than on the commodities or amenities that ecosystems are capable of

providing (Christensen et al. 1996).

Ecosystem management has been widely adopted in the United States (Gerlach and

Bengston 1994, Thomas 1994). In Canada, the central tenets of ecosystem management

have, either explicitly or implicitly, been incorporated into a number of national policy

documents including Sustainable Forestry - a Canadian Commitment developed by the

Canadian Council for Forest Ministers (Galindo-Leal and Bunnell 1995). In British

Columbia the precepts of ecosystem management have been incorporated into the Forest

Practices Code, the Commission on Resources and Environment, the Protected Areas

Strategy, and the Biodiversity Guidelines (Galindo-Leal and Bunnell 1995).

The Implications of Ecosystem Management for Silviculture

A foundation of ecosystem management was the concept of intergenerational equity

(Christensen et al. 1996). As national and global societies, intergenerational equity

required that future generations inherit forest resources of the same size and that present

Recommendations

47

the same or a greater range of opportunities as those that this generation inherited

(Christensen et al. 1996).

With complete knowledge and certainty, intergenerational equity would be a predictably

achievable target. Unfortunately, uncertainty, surprise and limits to knowledge are

acknowledged features of natural systems (Kay 1995, Christensen et al. 1996). For

instance, though it is generally acknowledged that there are limits to the stress that

natural ecosystems can withstand and remain viable (Christensen et al. 1996), these limits

are usually not known. Intuitively, in the face of uncertainty and incomplete knowledge

manage must either capitulate, or adopt strategies that are most likely to perpetuate the

features of existing forests that society views as significant in terms of intergenerational

equity.

Ecosystem management has pursued the latter course by adopting, as a central strategy,

management that conserves or restores natural ecosystem disturbance patterns

(Christensen et al. 1996, Galindo-Leal and Bunnell 1995, Kaufmann et al. 1994).

Kimmins (1993) provided an explanation for the basis for this strategy. He noted that in

the absence of full ecological knowledge and experience, forest managers “… must use

available scientific knowledge and theory, and empirical evidence from nature’s own

experiments with ecosystems” as a guide for forest management. The implication of this

approach was that the appropriate elements of ecosystem form and function are most

likely to be sustained within a range of disturbance that approximates the natural range

(Galindo-Leal and Bunnell 1995, Kimmins 1993). As Parminter (1998) said “…the

greater the similarities between the effects of a natural disturbance and the effects of

management activities, the greater the probability that natural ecological processes will

continue with minimal adverse impact”. It is this risk management strategy that provides

the justification for linking silvicultural action with precedents found in nature.

Assumptions of the Recommendations

The major assumption of these recommendations was that the 1990s outbreak was an

essentially natural event, and could be used as a model for silviculture that more closely

Recommendations

48

reflects natural disturbance7. It is acknowledged that other hypotheses concerning the

underlying cause of the recent WHL outbreak have been proposed (e.g. Zammuto

(1995)).

The second major assumption was that the effects observed during this event are

characteristic for WHL outbreaks in this area (or that there is a reasonable degree of

correspondence between successive WHL events). Numerous severe WHL events have

occurred in other areas of B.C. since 1913 (Parfett et al. 1995). The only other recorded

WHL outbreak in the Robson Valley was, however, only of light severity (Hoggett

unpublished-c, Parfett et al. 1995). In other words, while the 1950s outbreak was of

similar extent to the 1990s outbreak, its effects were much less intense.

Evidence for the validity of these two assumption was, at the time of this report,

circumstantial. They remained untested. There were no definitive answers to the

questions of periodicity, spatial extent, and the degree of correspondence between the

effects of successive events. Nor were the cause(s) of successive WHL outbreaks within

the Robson Valley known. The third stage of the project was designed to attempt to

address the first three of these questions.

The third assumption was that any silviculture actions at the stand level would take place

in the context of, and in agreement with a higher-level forest management plan. It is

assumed that this plan has taken into account the full range of values (both commodity

and amenity) at a landscape scale, and that timber production is one of these aims.

Finally, it is assumed that actions associated with timber production will occur consistent

with the goals of ecosystem management. The primary driver in the following

recommendations was the development of silviculture that mimics the effects of a natural

disturbance agent. It was not the provision of any particular set of commodity and/or

7 The existence of a large WHL event in the 1950s proved that WHL events have occurred in the past in the RobsonValley. The 1950s event also occurred in an area that was relatively remote from intensive human managementpractices (at the time that it occurred). This suggested that there have been essentially natural WHL outbreaks in theRobson Valley in the past.

Recommendations

49

amenity values. If other concerns are of overriding importance, selection of silviculture

actions may need to be extended to incorporate a greater range of silviculture

possibilities. A general discussion of the utility of various silviculture systems in BC has

been provided by Weetman (1996). A concise aid to silviculture decision making in the

ICH using a broader range of silviculture possibilities has been presented in Peterson et

al. (1998c).

A Framework for Recommendations

Natural disturbance can be classified based on the disturbance agent (or the cause), and

the effects of the disturbance agent. Effects include (Oliver and Larson 1996, Pickett et

al. 1987):

• the intensity of the disturbance event (which is reflected in the amount of existing

forest, forest floor vegetation, forest floor, and soil removed)

• the frequency of disturbance

• and the size and shape of the area disturbed.

The third stage of this project will attempt to deal with periodicity. Stage 1 and data

analyzed in this report can offer information on spatial scale and intensity. In other

words, the information outlined below deals with the effects of a WHL outbreak when it

occurs. It does not address the critical issue of how often these events visit the landscape.

Disturbance Scale

Stage 1 of this project identified boundaries for areas that had been disturbed with

moderate to severe intensity during the 1990s outbreak (Hoggett unpublished-c). The size

range of polygons identified in Stage 1 and the proportion of damage in each size class

has been included as Table 3.

Recommendations

50

Table 3: Size range of polygons showing moderate to severe intensity of disturbance

following the 1990s WHL outbreak.

Polygon Size (Ha) <10 10 to <50 50 to <250 250 to <1000

Number of Polygons 2 16 6 2

Total Area in this Class (Ha) 10 575 1218 1976

% Total Area of WHL Damage 0.26 15.22 32.23 52.29

One important characteristic of this data was that non-natural features (such as roads,

logging boundaries, ecological classification boundaries) caused breaks in contiguity that

were treated as polygon boundaries. For example, if the disturbance straddled a major

road, the two sides of the road were treated as separate polygons. This tended to reduce

the size of polygons.

A second feature was that this data did not deal with areas of light mortality. A decision

was made to concentrate on those areas where tree mortality was likely to trigger

significant changes in ecosystem composition and/or structure8. Areas of light WHL

severity may also offer a model for management. It is important to state, however, that

the light damage occurred in addition to more severe damage. The effects were, therefore,

cumulative rather than substitutive.

With these features in mind, it was apparent that polygon sizes varied by several orders of

magnitude. Some polygons were under 10 hectares while others were close to 1000

hectares. The number of polygons of greater than 250 hectares was low, but they

represented over half of the total area of moderate to severe disturbance. Almost 85% of

the disturbance area was in polygon sizes of greater than 50 hectares.

8 This was a pragmatic decision. Areas of moderate to high disturbance severity were most likely to be useful fordetermining the differences between the effects of major disturbance types (an important goal of Stage 2 of the project).They were also most likely to offer models that would be easier to integrate with current management practices.

Recommendations

51

Disturbance Intensity

The intensity of disturbance has been described in detail earlier in this report. It effects

have been briefly summarized in Table 4 in terms of two major descriptors: structure (or

horizontal and vertical arrangement of elements, and composition (the species of tree and

understorey plants). The purpose of this summary was to succinctly set the stage for the

silviculture options outlined below.

Silviculture Options

It is apparent that silviculture options exist for: (1) treating the area affected by the 1990s

outbreak, and (2) directing future silviculture activities outside of the current area.

In either case, the range of options span from preserving (for (1)) or mimicking (for (2))

the post disturbance structure and composition, to ignoring it. Four points (called

Scenarios) in this continuum that offered a logical reference for discussion were:

1. Mimic precisely the post WHL spatial scale as well as the internal structure and

composition of disturbed patches.

2. Mimic precisely the post WHL spatial scale, leave the internal structure largely in

tact, but influence species composition.

3. Mimic precisely the post WHL spatial scale, but modify the internal structure and

influence the species composition.

4. Do not consider the post WHL spatial scale and substantially modifying both

structure and composition.

Scenario 4 was the default management strategy at the time of the study. Any similarity

between its effects and those of WHL would be purely coincidental. It has not been

considered further here.

Recommendations

52

Table 4: Summary of the effects of WHL outbreak on a range of ecosystem elements

Element Arrangement Compositon

Canopy

Trees

Multilayered.

Essentially randomly distributed at scales of lessthan 50 m, but did show distinct boundaries insome variables at scales of 100 m.

High proportion of canopy space currentlyoccupied by dead trees.

No observed spatial pattern in the distribution ofeither live or dead trees (mortality random atscales of less than 50 m).

Mixed species.

Dominated by western redcedar and westernhemlock which occur in relatively equalproportions (in terms of basal area).

High proportion of the basal area of livetrees decayed.

High proportion of trees displaying theeffects of other damaging agents.

Regeneration Aggreated into clumps.

Higher densities found with higher levels ofcanopy cover.

Lower densities where with increasing densityof second understorey layer .

Dominated by western hemlock, with asubstantial proportion of western redcedar.

Minor component of subalpine fir.

Spruce virtually absent.

Majority of saplings showing signs of decay

Understorey Two layered, with second layer more variable interms of total cover.

Increasing development of a the second layerwith decreasing live cover of live overstorey(increasing mortality).

Mixed species.

Layer 2 with major component of speciesnormally associated with disturbance andknown to be strongly competitive with treeregeneration.

Dead Woody

Material

High volumes of coarse woody debris.

CWD generally in advanced stages of decay.

High basal areas of snags (greater than 50% oftotal basal area).

Majority of snags in early stages of decay.

All species contributing to both the snag andCWD pool in proportion to their overallrepresentation in the ecosystem.

Forest Floor

and Soil

Moderate forest floor depths, showing noconsistent spatial pattern and no relationship toother ecosystem features.

Both soil and forest floor remained essentiallyundisturbed.

Recommendations

53

Scenarios 1 and 2 would be considered inappropriate by almost everyone as a direction

for silviculture in forest stands outside the outbreak area. The information in Table 4

suggested that, even within the outbreak area, the use of WHL as a model for silviculture

presents considerable problems. Many of the more obvious features of WHL disturbance

would be undesirable from both production and amenity perspectives. For example

extensive areas of dead standing trees or brush dominated ecosystems would not be

desirable from either a forest production or preservation perspective. It is also

acknowledged that the current management environment (operational and regulatory)

would prohibit the retention or development of many of these features. For example

patchy regeneration overtopped by dense brush would not meet free growing standards,

and working in stands with a significant component of standing dead and mostly decayed

timber would present a severe safety hazard.

This clearly demonstrated the requirement for interpretation when considering the goals

of ecosystem management. If a perfect mimic of natural disturbance is inappropriate,

what level of dissimilarity is acceptable? Ecosystem management requires that a decision

be made on the degree to which silviculture reflects natural processes. The underlying

criterion for this decision is the sustaining of ecosystem composition, structure and

function (Christensen et al. 1996). There was, at the time of preparing this report, no

objective method for determining the degree of dissimilarity at which this criterion would

no longer be met.

A decision tree for silviculture activities has been developed with these constraints in

mind. The tree has been presented in Diagram 2. It is appropriate for all areas that are to

be considered for harvesting in the ICHwk3 of the Robson Valley.

Recommendations

54

Diagram 2: Decision tree to assist in determining appropriate silviculture actions

Is stand within area disturbed

by WHL?

Is harvesting desirable?

Create treatment units of spatial scales

and spatial frequencies that

approximate WHL

Pursue actions consistent

with Scenario 3

Is stocking of surviving stems

and regeneration of sufficient

number and suitable

distribution to provide for

continuous canopy cover in

the medium term ?

Is the quality of

regeneration adequate?

Is harvesting practical?

Pursue actions

consistent with

Scenario 1

Pursue actions consistent

with Scenario 2

Y

Y

Y

Y

Y

N

N

N

N

N

Recommendations

55

The discussion below does not explicitly consider operational or regulatory constraints.

Rather, it suggests spatial distributions, and ecosystem structures and compositions that

reflect, to varying degrees, conditions following disturbance by WHL. The intention was

to describe a range of forest ecosystem possibilities. Local forest managers are more

familiar with the social, economic, operational and regulatory environments in the

Robson Valley. They are, therefore, in a far better position to determine the degree to

which these features can be usefully incorporated in day to day silviculture design and

implementation. The more of the features of WHL that can be built into silviculture

prescriptions, the more closely management will reflect WHL disturbance.

Though the discussion of scenarios has a quantitative foundation, the prediction of

scenario outcomes is largely qualitative. It was based on the authors experience in the

ICHwk3 and on a range of references that consider the silviculture and dynamics of ICH

ecosystems (Anon. 1996, Arsenault 1998, Camenzind 1989, Cameron 1998, Cameron

undated, Coates 1998, Jull et al. 1999, Peterson et al. 1998a, Peterson et al. 1998b,

Peterson et al. 1998c, Robinson and Moss 1990, Weetman et al. 1990).

Scenario 1: No Action

Description

This scenario may be appropriate for areas of the 1990s outbreak where the existing

canopy condition and natural regeneration were considered adequate for the purposes of

future management. The definition of adequate would have to be made in the light of the

management objectives for the area of forest in question. An area that was being

managed primarily for visual or habitat values would have different regeneration

objectives to an area that was being managed for the eventual production of saw- or

veneer logs.

This scenario would require no silviculture action beyond an assessment of the canopy

and regeneration. Scenario 1 would maintain the spatial distribution of WHL, as well as

its internal compositional and structural features. Its likely longer-term consequences

have been outlined in Table 5.

Recommendations

56

Table 5: Prognosis for Scenario 1

Element Prognosis

Canopy Trees • Enhancement of within stand structural diversity with long term persistence of a highdensity of snags, a moderate density of live canopy trees, a second understorey layerand gradual in-filling of canopy from regeneration pool.

• Clumped distribution of regeneration and competition with understorey will probablyresult in relatively low densities of live canopy trees. These trees will have relativelyhigh live crown ratios and relatively highly tapered stems.

• Composition of mainly western hemlock and western redcedar. Other species can onlybe expected in relatively low proportions.

• Majority of trees will display relatively high proportions of decayed basal area.

Regeneration • Continued initiation and development of advance regeneration aggregated into clumps.

• In-filling mainly consisting of those species capable of surviving under low lightconditions and regenerating on undisturbed forest floor.

• Higher densities found with higher levels of canopy cover.

• Lower densities where with increasing density of understorey layer 2.

Understorey • A phase of continuing development of the second understorey layer and totalunderstorey cover.

• Increasing proportion of species normally associated with disturbance within theunderstorey.

• The eventual reduction in understorey cover as trees regain dominance over the site.

Dead WoodyMaterial

• Long term persistence of a relatively high density of snags

• Increasing volumes of coarse woody debris at the expense of the density of snags

• Initial phase of a large proportion of this CWD in early stages of decay.

Forest Floorand Soil

• Potential change in forest floor depth and humus form resulting from the changes intype and amount of litter input.

• No soil or forest floor disturbance

Risks

There was a range of risks inherent in this treatment. The most important related to the

quantity and quality of regeneration. Current and future regeneration will eventually fill

canopy positions.

The quality of regeneration present on site was poor and known to be of clumped

distribution. The species composition was also restricted to a subset of species that were

Recommendations

57

present in pre-outbreak stands. The regeneration that was present will face considerable

competition from the developing upper understorey layer. Evidence from the examination

of ICHwk3 stands regenerated by fire in the early twentieth century indicated that

understorey can suppress the development of a full canopy for over 100 years9. Finally,

regeneration will face significant risk of damage when the overstorey of dead tress begins

to disintegrate. At some stage the large number of DC 3 snags will fall. Field observation

suggested that this process was just beginning for the most decayed western hemlock.

The process could continue for decades10.

With all these factors at play, it was considered likely that a proportion of the current

outbreak area will take a considerable time to regain a full tree canopy. Trees that fill

canopy positions will be primarily decayed western hemlock and western redcedar. This

option was only considered suitable where management objectives other than the

production of timber are of primary concern, or where the regeneration at the time of

assessment can be demonstrated to be of suitable quantity and quality.

Another potential risk was that of fire hazard. It has been suggested that large areas of

dead timber present a significant fire hazard. Fire hazard is mainly related to the

accumulation and disposition of fine fuels. Field observation did not reveal any

significant accumulation of fine fuels at ground level. Input of fine fuels from dead trees

appears to be gradual and quickly incorporated into the forest floor layer. The relatively

dense blanket of deciduous understorey in those areas with highest mortality may actually

act to reduce fire hazard.

9 This evidence was gathered in a separate part of the Stage 2 of this study.

10 Field observations of early rapid decay of hemlock snags agreed with observations by reported in the literature(Engelhardt 1957, Johnson et al. 1970). A separate part of this study revealed that a moderate density of westernredcedar snags from fire early in the twentieth century were still standing in 1999. This disparity between the decay andpersistence of the different species present within the plots suggested that input into the CWD pool will start shortlyafter an outbreak and continue for many decades.

Recommendations

58

Scenario 2 – Influence Composition Only

Description

This scenario could be appropriate for areas of the 1990s outbreak. It would maintain the

spatial distribution of WHL disturbance, as well as its internal structural features.

Intervention to modify species composition would be undertaken in order to increase tree

species diversity and improve average tree stem quality.

Tactics

Tactics could include:

• Planting spot preparation

• Planting

• Brush control

• Fertilizing

A range of tree species could be planted including western redcedar, spruce, Douglas-fir,

subalpine fir and lodgepole pine (Pinus contorta var. latifolia) (Anon. 1996). The

continued persistence of western hemlock will be ensured by natural regeneration.

Planting in clumps of less than 6 m diameter would be appropriate, and may be one

method of allowing persistence of a second understorey layer without compromising a

full tree canopy in the long term. Initial brush control will almost certainly be required in

some areas. Selection of larger planting stock and spot fertilization at time of planting

would enhance seedling growth and the ability of seedlings to overtop competing

vegetation.

The likely long-term compositional and structural consequences have been outlined in

Table 6.

Recommendations

59


Element Prognosis

Canopy Trees • Enhancement of within stand structural diversity with long term persistence of ahigh density of snags, moderate density of surviving canopy trees, somedevelopment of a second understorey layer and the well stocked development of aregeneration layer.

• More even regeneration that Scenario 1 should ensure relatively rapid tree crownclosure over most of the treated area. Some patchiness resulting from understoreycompetition and falling snags will be present. Future canopy trees will have lowerlive crown ratios and more cylindrical height to diameter ratios than those inScenario 1.

• Composition shifted from dominance by western hemlock. Moderate components ofother species.

• Majority of future canopy trees will display low proportions of decayed basal area.They may have a range of other defects associated with mechanical damage causedby falling snags.

Regeneration • Initial high regeneration densities of a mix of species following planting distributedrelatively evenly across treatment area.

• Long period of relatively low regeneration success once planted and currentlyexisting regeneration achieves canopy closure (as stands enter the stem exclusionphase (sensu Smith (1986)).

• Gradual in-filling of any residual unoccupied patches by those species capable ofsurviving under low light conditions and regenerating on undisturbed forest floor.

Understorey • An initial and general, but not complete reduction in the development of the secondunderstorey layer and total understorey cover associated with control measures.

• The more rapid exclusion of understorey cover than Scenario 1, coincident with theonset of stem exclusion. Some patches of understorey will be retained as a result ofsuccessful understorey competition and falling snags.

Dead WoodyMaterial

• Long term persistence of a relatively high density of snags

• Increasing volumes of coarse woody debris at the expense of the density of snags

• Initial phase of a large proportion of this CWD in early stages of decay.



• Little or no disturbance to soil or forest floor.

Recommendations

60

Risks

The primary risk for this scenario relates to investment. The proposed silviculture tactics

would be expensive, would not be offset by timber harvesting, and would be carried for

the full rotation (assuming harvesting in the future). Their success, measured by the rapid

achievement of a full canopy of relatively high quality trees, would also not be a foregone

conclusion. The risks of understorey competition and damage to regeneration present in

Scenario 1 were also present in this scenario. It is important to note that understorey

control measures can only reduce understorey competition.

Finally, though planting will reduce the risk of perpetuating the decay cycle 11, new trees

will exist in a dense matrix of decayed trees, increasing their exposure to decay agents.

This risk of the perpetuation of decay will also be increased if regeneration was damaged

by falling snags.

With these features in mind, Scenario 2 was best considered as a rehabilitation operation,

funded from outside of a normal operating budget and its associated investment

constraints. Some damage to regeneration, and some degree of regeneration failure would

have to be expected.

Scenario 3 – Influence Composition and Structure

A decision concerning the appropriate silviculture system was important once

intervention that was more active was considered. Silviculture demands a long-term view

because of the long-lived nature of its primary object (the tree) and the generally slow

dynamics of the forest ecosystem in which it resides. The silviculture system has been the

traditional framework for silviculture actions. In essence, the silviculture system provides

a mechanism for linking treatments in time, and for linking treatments to management

goals.

Recommendations

61

Where timber harvesting will occur, a heavily modified clear-cutting silviculture system

(what Nyland (1996) terms heavy removal cutting) was considered the most effective

method of preserving a range of features of stands disturbed by WHL (as outlined in

Table 4).

Shelterwood or seed-tree methods were not considered appropriate as they imply the

removal of any retained overstorey at some stage in the future. This generally occurs

before the residual overstorey begins to have an appreciable effect on the growth of

regeneration (Nyland 1996). There was no evidence to suggest that trees that survived the

WHL outbreak would be removed by some natural process once regeneration was

secured.

Selection methods (either group of single-tree) have had demonstrated success in the

northern ICH (Coates 1998, Jull et al. 1999). They were not considered appropriate as

methods for preserving or mimicking the effects of moderate to severe disturbance

caused by WHL. Selection systems do not remove all the trees in one area at one time

(Nyland 1996), as WHL had done in some areas. They imply the development of a

heavily regulated age class structure. They also require systematic thinning through the

range of age classes. The aim of thinning is to maintaining full site occupancy, structural

and compositional stability, and promote the growth of all residual trees to maturity

(Nyland 1996). This regulation requires frequent, relatively light, and relatively

homogeneous interventions. The result of selection silviculture applied at both the stand

and landscape scales, would be much more homogeneous and structured that the

observed effects of WHL. The incorporation of a legacy from a previous stand, though

possible, would also be more problematic than with other systems.

Clear-cutting, on the other hand, has an impact that is generally severe, but occurs

relatively infrequently. Its severity can legitimately be substantially modified in the

11 Both western redcedar and western hemlock can be grown on rotations of less than 100 years without dramatic lossto decay (Robinson and Moss 1990). This indicated that, providing the tree was free of decay early in its life cycle,there was a reasonable chance of it escaping dramatic loss to decay within a conventional timber rotation.

Recommendations

62

pursuit of non-timber objectives (Anon. 1995, Florence 1996)12. The retention of a

uniform or patchy distribution of trees and other ecosystem elements within clearcuts of a

range of sizes was considered most likely to preserve or mimic the range of ecosystem

features promoted by WHL.

The size class range of polygons suggested the approximate limits on the size of

treatment units and the appropriate proportions of units in each polygon size class (see

Table 3). Plot data has been used to provide a preliminary approximation of the

appropriate proportions of retention levels. Four of the thirteen plots (~30%) had

conditions that approximated clearcutting with little or no retention (basal area and

canopy cover survival of less than 15%)(see Graphs 1 and 2 in Appendix 7). The same

proportion had conditions that approximated heavy retention (basal area survival and

canopy cover survival of 50-75%). The remainder (~40%) had conditions that

approximated clearcutting with moderate retention (basal area survival of 15-50% and

live cover survival of between 15-65%)13. The size of retained patches within the

harvesting area could not be clearly stated from the data from this study. An appropriate

starting point (pending closer examination of pattern at larger scales) would be patches

with a shortest dimension (through the centre) of between 50 and 100 m. These

considerations form the basis for the scenario outlined below.

Description

This scenario could be appropriate for areas of the 1990s outbreak, and for areas outside

the outbreak. It would maintain or create patches within the size distribution of those that

result from WHL disturbance. It would involve the modification of both structure and

12 For example, Bunnell et al. (1998) provides a rationale for changing forest management for a large forestmanagement tenure on Vancouver Island to include this type of silviculture.

13 Smith (1986) defined clearcutting as a treatment in which virtually all vegetation is removed and almost all of thegrowing space becomes available for new plants. It is acknowledged that the areas of moderate retention levelssuggested here would move ecosystem conditions away from those conventionally associated with clearcutting. Smithdefined similar operations as heavy removal cutting. His terminology, however, has not been universally adopted.Irrespective, the proposed system has more in common with a single-cut clearcut, than with multi-cut even- or uneven-aged silviculture systems. Areas with high levels of retention are essentially reserves.

Recommendations

63

composition within patches of disturbance. Intervention to modify structure and species

composition would be undertaken in order to substantially influence tree species

composition, improve average tree stem quality, and promote the rapid growth of trees.

The silviculture system would be clearcutting with reserves.

Tactics

Tactics would include:

• Delineating between no retention, moderate retention and reserve areas

• Harvesting the overstorey in no- and moderate-retention areas

• Falling to waste non-merchantable trees (with or without subsequent stacking and/or

burning) in areas where they are not required as reserves

• Site or planting spot preparation

• Planting

• Brush control

• Fertilizing

A general guide to the selection and treatment of retention areas has been provided in

Table 7.

Recommendations

64

Table 7: Relative proportions of retention types for Scenario 3

No Retention Moderate Retention Reserves

Percent of HarvestingArea

30 40 30

Tactic Complete harvest Complete harvest withretained live trees

No harvesting –retention of all

ecosystem elements

Percent Live BasalArea Retention

0 30 100

Retention of DeadBasal Area

0 0 100

Distribution ofRetained Basal Area

None Uniform Not applicable

Control of competingvegetation

As required As required None

Target Areas withthese features (if theyexist)

High mortality Moderate mortality Low mortality

The range of tree species that could be planted is the same as for Scenario 2. The

continued persistence of western hemlock will be ensured by natural regeneration, even

without the protection of advance regeneration. Planting in clumps of less than 6 m

diameter would still be appropriate, though more regular planting patterns could be used.

Where possible, substantial volumes of CWD should be left throughout the harvesting

area. In areas that have been damaged by WHL, the arrangement of patches of different

retention levels should attempt to follow mortality patterns. In areas outside the outbreak

area they should be arranged relatively randomly. Minimum patch sizes should be

approximately 1 hectare.

Its likely long-term compositional and structural consequences have been outlined in

Table 8.

Recommendations

65


Element Prognosis

Canopy Trees • The creation of a horizontally stratified mix of structure types will maintain a largeproportion of within stand structural diversity.

• Long term persistence of a moderate density of snags, moderate density of survivingcanopy trees, some development of a second understorey layer and the rapiddevelopment of a regeneration layer.

• Rapid tree crown closure over the treated area. Some patchiness resulting fromunderstorey competition and falling snags in the reserve areas.

• Composition shifted from dominance by western hemlock. Moderate to highcomponents of species selected for planting.

• Future canopy trees will have lower live crown ratios and more cylindrical height todiameter ratios than those in Scenario 1. Majority of future canopy trees will displaylow proportions of decayed basal area.

Regeneration • High regeneration densities of a mix of species following planting. Regenerationdistributed relatively evenly across treatment area. Planting excluded from reservepatches.

• Long period of relatively low regeneration success once planted and currentlyexisting regeneration achieves canopy closure (as stands enter the stem exclusionphase).

• Gradual in-filling of any residual unoccupied patches in high retention areas thosespecies capable of surviving under low light conditions and regenerating onundisturbed forest floor.

Understorey • Development of the second understorey layer intentionally restricted to reserve areasonly.

• Understorey development in other areas would be suppressed once canopy closurewas achieved.

Dead WoodyMaterial

• Long term persistence of a moderate density of snags restricted to reserve areas.

• Large CWD loads in retained patches, with an attempt to maintain relatively highlevels of CWD throughout the remainder of the harvesting area.


• Levels of soil and forest floor disturbance associated with normal harvestingoperations.


Recommendations

66

Risks

Some of the risks associated with Scenarios 1 and 2 would be alleviated in this scenario.

Regeneration success should be easier to guarantee. The potential for damage from

falling dead timber would be removed.

The risk of perpetuating the decay cycle would similar to that of Scenario 2.

The moderate levels of retention may pose some wind-throw hazard, but windthrow has

not proven to be a feature of other attempts at partial cutting in the ICH (Coates 1997,

Jull et al. 1999).

Incremental Silviculture

Incremental silviculture actions (thinning, pruning, fertilizing) will be unlikely to be

financially sensible in either Scenarios 1 or 2. There were no inherent features of WHL

disturbance that would prompt these types of action in Scenario 3. Decisions on

incremental silviculture would best be made on a stand by stand basis. The primary

decision criterion should be their respective merits in achieving stand management goals.

Monitoring the Implementation of Silviculture

These silviculture recommendations are provisional, based on existing knowledge at the

time of preparation of this report. Ecosystem management requires that an adaptive

approach be adopted when implementing management decision (Christensen et al. 1996).

This means that (Christensen et al. 1996):

• management must be based on the best current understanding of the ecosystem to be

managed

• the expectations of management actions must be clearly stated in operational terms

Recommendations

67

• and the results of management actions must be monitored and compared with

expectations.

Monitoring the fate of surviving ecosystem elements and regeneration should be

undertaken in all implemented treatments as an ongoing part of management. The results

of monitoring must be used to inform future management decisions.

Research Recommendations

A range of research recommendations follow from the analysis of this section of the

project’s data. These are:

• More accurate mapping of the 1990s WHL event to enable landscape analysis.

Analysis of the pattern of WHL disturbance should attempt to assess the validity of

the hypotheses advanced by Zammuto (1995).

• Search for pattern for ecosystem variables at larger scales than those examined in this

study. An appropriate starting point would be at scales of around 100 m. This would

be most efficiently achieved for many features (such as overstorey survival) by

careful analysis of existing large scale aerial photography.

• Completion of Stage 3 of the project. This stage will attempt to quantify periodicity

of WHL events, to assess similarity between events, and to place WHL in the context

of other forms of disturbance within the ICH of the Robson Valley.

Conclusion

68

Conclusion

It is apparent that the 1990s WHL outbreak had a large impact on a range of ecosystem

elements. This impact varied from stand to stand and even in relatively short distances

(less than 100 m) within stands.

It was also apparent that silviculture could be designed to preserve or create a range of

features associated with disturbance caused by WHL. The effects of WHL can be used as

a basis for silviculture that meets the requirements of ecosystem management. The

scenarios proposed in this report attempt to satisfy these requirements to varying degrees.

Associated with each were inherent risks and potential consequences for the provision of

both production and environmental values.

This report represents the best information concerning the effects of WHL on ecosystems

in the ICHwk3. It must be strongly emphasized, however, that it was based on just one

event. The similarity of this event to previous WHL outbreaks has not been assessed

(except superficially with an event in the 1950s). The study also contained no information

concerning periodicity of WHL (return interval for disturbance). The report could make

no recommendations on appropriate average level of annual forest disturbance. It was

strongly recommended that Stage 3 of this study be pursued in an attempt to address

these deficiencies.

The report contains information from only a part of data collected for this project.

Improved information will continue to become available as data analysis continues.

Conclusion

69

Acknowledgements

The author would like to thank:

• Forestry Renewal BC, Zeidler Forest Industries, and State Forest of New South Wales

(Australia), all or which contributed to the funding of this research work.

• Staff at the BC Ministry of Forests Robson Valley office for frequent assistance and

support.

• Professor Emeritus Gordon Weetman of UBC for his comments on a draft of this

report.

• Tania Parkinson for innumerable hours of technical, administrative and editing

assistance.

70

Appendix 1 – Variables Measured in Each Plot

Plot Subplot VariablesIntensive Whole Trees:

• Species• Diameter• Height• Height to live crown• Canopy position• Decay class• Lean• Location (distance and direction from a known point)• Evidence of damaging agents (Using a rating system outlined

in Appendix 2)• Wildlife tree classification (using classification listed in

Appendix 3)Other features:• Type• Decay class• Size• Location

5 contiguous 5x5msubplots

Understorey:• Number of layer• Species in each layer• Percent cover by species in each layerSaplings:• Species• Status (live or dead, vertical or leaning)• Diameters (at 0.3 and 1.3 m)• Height• Location

11 contiguous 2x2msubplots

• Percent cover by moss species• Number of seedlings by species (seedling was considered any

individual of tree species of less than 1 cm diameter at 0.0mheight)

Randomly selectedsubsample of treesand saplings

Trees:• Diameter at 0.3 m height• Depth to decay in two directions• Core for growth increment measurements• Canopy width in four or three directions depending on canopy

positionSaplings:• Diameter at 0.0 m height• Depth to decay in two directions• Disc for growth increment measurements

71

Plot Subplot VariablesIntensive

ctd.Four twenty metrelong transects

Coarse woody debris (>10cm diameter at point of line):• Species• Diameter• Alignment• Slope• Presence of charcoal• Decay class

Extensive Whole plot As for intensive plot only no recording of evidence of damagingagents or wildlife tree classification

Nineteen 2x2msubplots placed at 5m intervals startingat x=5, y=0

Number by species of seedlingsCover of mossLive saplings:• Species• Diameter at 0.3 m height

Nineteen 5x5msubplots placed at 5m intervals startingat x=5, y=0

Understorey vegetation cover by layer

Nineteen pointsplaced at 5 mintervals starting atx=5, y=0

Canopy cover estimated by four readings from a canopydensiometerForest floor depth, estimated from four depth measurements on a 1metre long excavationCharcoal amount and continuity estimated for length of a 1 metrelong excavation

72

Appendix 2 – System for Classifying Evidence of

Damaging Agents

D F V Disease - conk visible

Bl Blind or swollen knot – pronounced swelling around knot, most often onhemlock

R Root

L Foliage

E Bole or branches external bark/sapwood only

It Bole or branches internal

K * Canker – caused by fungi, look for repeated callous growth, staining, resinimpregnation and fruiting bodies

I Df Insect - defoliation

T Bud damage

Ex Stem or branch damage including exit holes

Fi * Fire - scar

C W Co Charcoal on woody debris common

Is Isolated

G Co Charcoal in soil profile/forest floor common

Is Infrequent

We Up Weather – uprooted wind

B Broken wind

P Windthrown

Z * Lightning

X Frost

M * Mechanical – including falling trees, logging, rock

Up Uprooted

B Broken

P Knocked over whole

Bi * Biological – damage by woodpeckers, bears, deer, rodents, beavers etc.

U * Unknown

Xs Sh Shallow soil

Wt Wet soil

* S O Su Scar – open surface – exposed wood, damage to bark and cambium

De Deep – damage to wood below bark and cambium

Cl Closed – light to pronounced indentation, or pronounced scar tissue orcallous growth

B Broken

Mlt Multiple leader – list number of leaders

73

Appendix 3 – Summary of System for Classifying

Wildlife Tree Types14

Type Description Comments

WT1 Hard outer woodsurrounding decaysoftened inner wood

Substrate for excavating cavities for reproduction/resting for strongerexcavators – woodpeckers.

WT2 Outer and inner woodsoftened by decay

Substrate for excavating cavities for reproduction/resting for weakerexcavators – woodpeckers, chickadees, nuthatches.

WT3 Small excavated or naturalcavities (<6cm)

Small existing cavities for reproduction/resting – chickadees,nuthatches, swallows bats.

WT4 Large excavated or naturalcavities (6-12cm)

Large existing cavities for reproduction/resting – ducks, owls,bluebirds, swallows, bats, squirrels, mustelids.

WT5 Very large natural cavitiesand hollow trees (>12cm)

Very large existing cavities for reproduction/resting – swifts, owls,bats mustelids.

Hollow trees need some form of entrance to be included in this class.

WT6 Cracks, loose bark ordeeply furrowed bark

Other types of existing cavities for reproduction/resting – creepers,bats.

Must be sheltered from above.

WT7 Witches brooms Large open-nest supports and other non-cavity sites forreproduction/resting – diurnal raptors, owls, squirrels, mustelids.

WT8 Large branches, multipleleaders or large diameterbroken tops

Large open-nest supports and other non-cavity sites forreproduction/resting – herons, diurnal raptors and owls.

Platform needs to be in upper half of canopy height.

WT9 Arthropods in wood orunder bark

Feeding substrates – woodpeckers.

Only classify if fresh signs of insect feeding are present.

WT10 Open structured trees in oradjacent to open areas

Hunting perches – diurnal raptors, owls.

WT11 Large concealed spaces Large concealed spaces for reproduction/

resting/escape – grouse, hare, woodrat, porcupine, fox cats, somemustelid, bears.

Should be able to fit two fists into space.

WT12 Small concealed spacesabove ground level butbelow 1.3 m height

Small concealed spaces for reproduction/ resting/escape –salamander, toad, treefrog, snakes, wrens, shrews, voles, deer mouse,ground squirrel, chipmunk, jumping mice, weasels

14 From Keisker (1999)

74

Appendix 4 – Coarse Woody Debris Classification

System15

Class Description

Character 1 2 3 4 5 6

Bark Intact Mostlyintact

Sloughingor absent

Detached orabsent

Detached orabsent

Branchsystem

Currentyeartwigspresent

Largertwigspresent,branchsystementire

Largebranchespresent,longer thanlogdiameter

Branch stubspresent, shorterthan log diameter,branch stubs pullout

Absent

Structuralintegrity

Sound Sapwoodsomewhatdecayed;heartwoodmostlysound

Heartwoodmostlysound;supports itsownweight

Heartwood rotten,does not supportown weight, crosssection of the boleoval, branch stubspull out

None; woodresembles redpowder, withlittlediscerniblestructure orsigns of rings.

As for 5 onlygreater thanhalf verticaldiameterbelow surfaceof forest floor

Colour Original Original Original toreddishbrown

Reddish or lightbrown

Red-brown todark brown

Invadingroots

Absent Absent Sapwoodonly

Throughout Throughout

Veget-ation

None Coniferseedlingsgerminatebut do notsurvive

Tsuga <2m height;someshrubs andmosses

Tsuga < 15 cmdbh; smallershrubs; moss

Tsuga up to200 cm dbh;shrubs, somelarge; moss

15 From Triska and Cromack (1980)

75

Appendix 5 - Classification for Snags16

Stage Features Fallen Analog

1 Live

2 Declining

3 Recently dead – branch structure including fine branches still largely

intact

I

4 Loose bark – bark loose, branches <3 cm generally absent II

5 Clean – no bark, generally only branch stubs II, III

6 Broken – top broken off III

7 Decomposed – bole starting to disintegrate due to biodeterioration,

chunks of bole broken off

IV

8 Down material – bole almost completely disintegrated, down

material partly to largely submerged

V

9 Stump – only stump obvious, fallen material submerged V

16 From Caza (1993)

76

Appendix 5 – Correlation Between Variables at the Plot Level

Dea

d B

asal

Are

a pe

r Ha

Mea

n %

Dea

d C

over

Tot

al B

asal

Are

a pe

r Ha

% B

asal

Are

a Su

rviv

ing

Out

brea

k

Mea

n %

Liv

e C

over

Mea

n %

Gap

Mea

n %

Mos

s C

over

Den

sity

of W

T1

Tot

al D

ensi

ty o

fR

egen

erat

ion

Mea

n %

Und

erst

orey

Cov

er L

ayer

1

Mea

n %

Und

erst

orey

Cov

er L

ayer

2

Mea

n D

BH

of L

ive

Tre

es in

Can

opy

Lay

er 1

Mea

n H

eigh

t of L

ive

Tre

es in

Can

opy

Lay

er 1

Mea

n H

eigh

t of L

ive

Cro

wn

Tre

es in

Can

opy

Lay

er 1

Density of WT1 -0.630 0.674 -0.611

Total Density of Regeneration 0.705

Mean % Understorey Cover Layer 2 0.667 0.709 -0.608 -0.651 -0.634 -0.736

% Decayed Basal Area in Canopy Layer 1 0.670 -0.740 0.630

% Decayed Basal Area in Canopy Layer 2 -0.704 -0.872 0.640

Density of Tress in Canopy Layer 1 0.861

Mean DBH of Live Trees in Canopy Layer 1 -0.670 0.664

Mean Height of Live Trees in Canopy Layer 1 -0.694 -0.716 0.644

Mean Height to DBH Ratio for Trees in CanopyLayer 1

-0.851 -0.619

Mean Height of Live Crown Trees in Canopy Layer 1 0.629 0.633 -0.613 0.665

Mean Live Crown Ratio of Trees in Canopy Layer 1 -0.646 0.639 0.618 0.698 -0.609

Variables that displayed a simple correlation of greater than 0.600 when plot level results were analyzed. Those correlations that were

considered trivial have been omitted from the table. Variables considered in the analysis have been listed below.

77

Correlation Between Variables ctd.

Wes

tern

Red

ceda

r Tot

alB

asal

Are

a(H

a)

Wes

tern

Hem

lock

Tot

alB

asal

Are

a(H

a)

Wes

tern

Red

ceda

r Liv

eB

asal

Are

a(H

a)

Wes

tern

Hem

lock

Liv

eB

asal

Are

a(H

a)

Total Live Basal Area (Ha) 0.880

Total Basal Area (Ha) 0.912 -0.606 0.771

% Total Basal Area Surviving 0.720

Western Redcedar Total Basal Area (Ha) -0.872 -0.621

Western Hemlock Total Basal Area (Ha) -0.872 -0.745

Mean % Canopy Cover of Live Trees 0.625

Mean % Canopy Cover of Dead Trees -0.642

Mean % Moss Cover -0.651 0.790

Mean Density of WT1 -0.779 0.742 -0.723

Mean Density of Regeneration 0.795

Mean % Understorey Cover Layer 1 0.658 -0.601

% Decayed Basal Area in Canopy Layer 1 0.762 -0.697

% Decayed Basal Area in Canopy Layer 2 -0.867

% Decayed Basal Area in Canopy Layer 3 -0.651

Mean DBH of Live Trees in Canopy Layer 1 0.686

Mean Height of Live Trees in Canopy Layer 1 0.621 0.731

Variables that displayed a simple correlation of greater than 0.600 when plot level results

were analyzed. Those correlations that were considered trivial have been omitted from

the table. Variables considered in the analysis have been listed below.

78

Variables Considered in the Simple Correlation Analysis

• Dead, Live and Total Basal Area per Hectare

• Mean percent Basal Area Surviving WHL Outbreak

• Total and Live Basal Area for Western Redcedar and Western Hemlock

• Mean percent Live, Gap and Dead Cover

• Mean Forest Floor Depth

• Mean Moss Cover

• Mean Volume of CWD per Hectare

• Mean Density per Hectare of WT1, WT2, WT6, WT8, and WT11

• Total Density of Regeneration per Hectare

• Mean percent Cover Layer 1, and Layer 2 Understorey

• Density per Hectare, Mean DBH, Mean Height, Mean Height to Daimeter Ratio of

Dead Trees in Canopy Layer 1

• Density per Hectare, Mean DBH, Mean Height, and Mean Height to Diameter Ratio

of Dead Trees in Canopy Layer 1

• Density per Hectare, Mean DBH, Mean Height, Mean Height to Diameter Ratio,

Mean Height to Live Crown, and Mean Live Crown Ratio of Live Trees in Canopy

Layer 1

79

Appendix 6 – Examples of Results of the Three Different

Types of Spatial Analysis

Descriptive Analysis

Appendix 7: Graph 1 - Canopy cover by class at 5 m intervals along a 100 m

transect

80

Appendix 7: Graph 2 – Live and dead basal areas for all trees at 5 m intervals along

a 100 m transect

81

Appendix 7: Graph 3 - Understorey cover by layer at 5 m intervals along a 100 m

transect

82

Appendix 7: Graphs 4 and 5: - Plots of tree location and height for trees > 10 cm

dbhob in the extensive plot. Diameter has been indicated by the relative size of the

triangle. Grey triangles represent dead trees, and green live.

83

Correlation Analysis

Appendix 7: Graph 5 - Correlation between the basal area of subcanopy trees and

all other variables

84

Appendix 7: Graph 7 - Correlation between the average height of canopy trees and

all other variables

85

Intensity Analysis

Appendix 7: Graph 8 - Intensity of subcanopy trees along a 10x100m plot

86

Appendix 7: Graph 9 - Intensity of regeneration along in a 5x25m subplot

87

K-Function Analysis

Appendix 7: Graph 10 - K-function analysis for western hemlock trees showing

evidence of clustering

The simulated pattern lines in the k-function analysis represent the minimum and

maximum values given by the random pattern simulations for each distance. In this case,

25 simulations were used. The minimum value plotted for any distance was the lowest

value of khat for that distance from the 25 point pattern simulations that were conducted.

Observed values of k that fall above the upper line indicate aggregation at that scale when

compared to a random point pattern. Values that fall below the lower line indicate

regularity when compared to a random point pattern.

88

Appendix 7: Graph 11 - K-function analysis for all canopy trees in IN06. The plot

shows evidence of regular distribution

89

Appendix 7: Graph 12 - K-function analysis for saplings showing evidence of

clustered distribution at distances of less than 4 m.

90

Appendix 7: Graph 13 - K-function analysis for saplings showing evidence of

clustered distribution at distances of less than 6 m.

91

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