ALUR 1975-76

The Impact of Fire on Forest and Tundra Ecosystems Final Report 1975

K. A. Kershaw Department of Biology

W. R. Rouse Department of Geography

McMaster University Hamilton, Ontario

© Pub I ished under authority of the Hon. Judd Buchanan, PC, MP, Minister of Iridian and Northern Affairs, Ottawa, 1976. QS-8117-000-EE-A 1

The research was carried out and the report was prepared under contract for the Arctic Land Use Research Program, Northern Natural Re­sources and Environment Branch, Department of Indian Affairs and Northern Development. The views, conclusions and recommenda­tions expressed herein are those of the author and not necessarily those of the Department.

ALUR 75-76-63

UBRAR~ usvws

Anchorage

List of Tables

1-- ·- ·!~,1

"' Contents

List of Figures

Section I

Section II

Section III

Section IV

Overall Group Objectives Introduction Geographical Location of the work

Plant Ecology Introduction Ecological objectives in 1974 The research area Methods

Aging of burned areas Sampling procedure Data analysis

Results Discussion

Microclimate Introduction Methods

Research sites Snow survey Temperature, humidity, precipitation, wind Radiation and surface temperatures Soil temperature Soil moisture Evapotranspiration

Results Snow survey Temperature, precipitation, humidity, wind Radiation Soil temperatures Soil Moisture Evapotranspiration

Discussion

General conclusions and recommendations

Acknowled,~emen ts

Literature cited "'·

PAGE

i

ii

1 1 1

3 3 4 4 6 6 6 9 10 24

28 28 32 32 32 32 33 33 34 34 36 36 36 40 40 45 45 45

50

52

53

List of Tables

2.1 Mean percentage cover values for all species present within 5 the sample data.

2.2 The age determinations for each replicate fire scar examined in 7 the 17 sites sampled.

2.3 Correlation and regression coefficients between the environmental 11 measures. Non-significant regressions or correlations at the 5% level, are marked with an asterisk.

2.4 Correlation and regression coefficients between the more abundant 25 & 26 species in the sample and the environmental measures. Non-significant regressions or correlations at the 5% level, are marked with an asterisk.

3.1 Average depths, densities and ~vater equivalents of snow at the 37 different sites.

3.2 Measured radiation fluxes for mainly clear days in July and August. 41

3.3 Radiative surface temperatures during July and August. 42

3.4 Average subsurface soil temperatures at different depths. 46

- i -

1.1

2.1

2.2

2.3

2.4

2.5

2.6.

2.7

2.8

2.9

List of Figures

The location of the research site.

The distribution of the sample plots over the Abitau-Dunvegan Lake drumlin field.

Ordination of the total plot data with the ages of the burns overlayed. The six PHASE I plots have markedly lower loadings on Axis 2 than the remainder of the sample.

Ordination of the total plot data with the plot percentage cover values of Polytrichum piliferum overlayed. High cover values of Polytrichum are very characteristic of PHASE I of the recovery sequence.

Ordination of the sample plots from burns greater than 23 years of age, with the ages overlayed. The three further recovery phases are clearly loaded on Axis 2.

Ordination of the sample plots from burns greater than 23 years of age, with the percentage cover of Stereocaulon paschale over­layed. The abundance of Stereocaulon is closely correlated with Axis 1 but the dominance of Stereocaulon in PHASE III loaded on Axis 2, is clearly evident.

Ordination of the sample plots from burns greater than 23 years of age, with the percentage cover of ·cladonia stellaris overlayed. The abundance of Cladonia stellaris is loaded on Axis 2 and decreases steadily from PHASE 2 to PHASE 4.

Ordination of the sample plots from burns greater than 23 years of age, with the percentage cover of Cetraria nivalis overlayed. The abundance of Cetraria shows a general correlation with the second recovery phase.

Ordination of the sample plots from burns greater than 23 years of age, with the percentage cover of Ptilidium ciliare overlayed. Ptilidium is only abundant in the last recovery phase where the tree canopy has closed.

Ordination of the sample plots from burns greater than 23 years of age, with the percentage cover of Vaccirtium vitisidaea. The abundan~e increases in the later phases of recolonization.

2.10 The correlation between number of trees and age of the burn showing a marked positive relationship (p<.OOl). --

- ii -

2

8

12

13

14

15

16

17

18

19

20

2.11

2.12

2.13

2.14

3.1

3.2

3.3

3.4

List of Figures cont'd.

The correlation between peat depth and age of the burn showing a marked positive relationship (p<.OOl).

The strong negative correlation between tree distance and age of the burn (p<.OOl).

The marked positive correlation between peat depth and number of trees (p<.OOl).

The change of percentage cover of six of the most abundant species, during the recovery sequence following fire. The marked drop of cover of Polytrichum piliferum (PHASE I) coincides with a marked increase in cover of Cetraria nivalis and Cladonia stellaris (PHASE II). Subsequently Stereocaulon paschale dominates the recovery sequence (PHASE III), finally being replaced by moss and vascular plant species (PHASE IV).

Map showing location of research sites and instrumentation.

Map of the snow survey showing sampling points, snow depths, densities and water equivalents for April 9, 10, 11, 1975.

Air temperature, vapour pressures, rainfall and wind speeds during the 1975 growing season.

Soil temperatures at all sites and depths during the 1975 growing seaso~T represents the soil temperature at a given site and depth averaged between June 4 and August 15.

21

22

23

27

30

31

35

38 & 39

3.5 (a) Average soil moisture for different depth intervals at each site 43

3.6

3.7

(b) Maximum seasonal change in soil moisture for different depth intervals at each site.

The seasonal patterns of soil moisture, precipitation and cumulative evapotranspiration at each site.

The time sequence of surface and subsurface soil temperature, net radiation and evapotranspiration from the mature lichen woodland phase through various stages of burning back to the mature lichen woodland phase.

- iii -

44

47

Section 1

Overall Group Objectives

To study the recovery of burnt surfaces characteristic of the region to the east of Great Slave Lake, in terms of vegetation develop­ment, soil properties, microclimate, and the interaction between these facets of the central problem of fire damage.

Introduction

Extensive examination of the air photo coverage available for the area bounded by Taltson River in the west, Great Slave Lake to the North, latitude 60°N to the south, and longitude 105°W to the east, showed considerable variation of vegetation as might be expected. The area is dominated by spruce-lichen woodland which develops on a wide range of land forms. (cf region B27 of Rowe, 1972). Eskers, gravel/sand-outwash areas, drumlins, and river alluvial plains were all dominated exclusively by lichen woodland. Where these formations graded into areas of bedrock terrain, spruce-lichen woodland remained the dominant vegetational type.

Since the defined objective is to study the chronological develop­ment following fire, geomorphological variations will confound the primary effects and are clearly undesirable. Accordingly, it was essential that a single land form type of fairly constant structure be selected allot·Ting reliable replication: over the area. A field survey in the summer of 1973 showed the marked variability of many of the areas of spruce-lichen woodland and quickly eliminated them as suitable systems. A large drumlin field in the Abitau-Dunvegan Lakes area was finally chosen for detailed study and offers a number of advantages. The high frequency of symmetrical drumlins in the area enables any required level of sampling replication to be readily achieved. Their relatively constant size, form and orientation eliminates the problems of additional variables obscuring the main fire recovery sequence under study. The lichen-woodland is clearly very fire-susceptible and the abundance of caribou trails indicate it is an important overwintering area for large numbers of caribou.

During the 1973 field season a central camp site was selected and cleared for use. At the same time a small plot of mature woodland was burnt as a 1 year old experimental reference point for the micro-climate and soil work.

Geographical location of the research camp

The research camp is situated approximately 85 miles N.E. from Uranium City (Figure 1.1) at 60° 2l'N, 106° 54'W and is placed more or less centrally in the drumlin field which covers approximately 1200 sq. miles. The base camp is located on the end of a drumlin burnt 50 years ago, opposite to the main research burn 24 years of age,and has a large number of drumlins readily accessible from it. The general vegetation of all the drumlins seen

1

J

N.W.

Territories

Abitau

~· e RESEARCH

SITE

Alberta

in the Dunvegan-Abitau Lakes area is spruce-lichen woodland which is also characteristic of the eskers and sandy glacial outwash areas. The wetter margins of each drumlin are also exlusively dominated by black spruce but with a moss/shrub understory. Several drumlins immediately adjacent to camp are covered with extremely patchy black spruce woodland and examination this summer confirmed our previous interpretation that the low density patches of black spruce in fact represent an old burn set in woodland of even more mature standing.

Section II

Introduction

The effectsof fire in conifer forest ecosystems of western and northern North America have been studied by foresters and ecologists for many years. In most of the earlier vegetation studies, which are contained in the comprehensive reviews of Lutz (1956) and Ahlgren and Ahlgren (1960), the recovery of vegetation following firecould not be set in an accurate framework of time. Only recently, through the development of accurate techniques in fire chronology, has. the dynamic nature and time scale of

3

the fire factor gained appreciation. Tree-ring analyses, the most important of which is the fire-scar method (Spurr, 1954; Frissel, 1973), allow the dates and extents of fires up to three or four hundred years in the past to be identified. In,addition, an extension of the fire history to the more distant past is possible through 14c analysis of charcoal in soils (Bryson et al, 1965) and the analysis of pollen and charcoal in lake sediments (Swain, 1973).

Heinselman (1973) and Kilgore (1973) use these methods to give detailed accounts of past fires in conjunction with general vegetation descriptions to establish the importance of fire in controlling the structure and composition of the vegetation in Minnesota and Sierra Nevada, respectively. However, unique geomorphological, climatic and floristic characteristics of different geographic areas complicate the primary effects of fire. Before generalizations applicable to widespread fire affected regions can oe made, the separate consideration of the effects of fire in each region is necessary in order to determine which features are common to all.

This study was designed to examine the chronological development of vegetation following fire in southern NWT where open spruce-lichen woodland is the dominant vegetation type. The study was restricted to black spruce­lichen woodland dominated drumlins due to their relatively constant size, shape and orientation in relation to the highly variable nature of other geomorphological features in the area. In addition, the abundance of drumlins in the area facilitated high levels of sampling replication.

Recently, much interest has been directed towards the contention that fire is a contributing factor in the decline in numbers of barren­ground caribou in Northern Canada through destruction of slow growing lichen forage (Scatter, 1964). The study area is within the winter foraging range for large numbers of caribou, as indicated by an abundance of trails and previously shed antlers, thus making the information particularly relevant.

Ecological objectives in 1974

A previous report in this series (Kershaw, Rouse and Bunting, 1975) has considered the initial stages of recovery, describing two major phases dominated by Polytrichum piliferum and Cladina spp respectively. The current years objectives were to amplify and extend the initial Y70rk, and to characterise the post 50 year fire recovery sequence.

The Research Area

The research camp is situated in the Abitau-Dunvegan Lakes area in N.W.T. approximately 85 miles NE of Uranium City, Saskatchewan at 60° 2l'N, 106° 54' Win the center of a large field of drumlins (Figure 1.1). The drumlins are generally uniform in size, shape and substrate. They are approximately 3 km long, ~ km wide, rise steeply from wet flat margins, which are often extensive, to a height of 30 m and have soils of sand mixed with gravel. Boulder filled sink-holes are present on many of the drumlin crests. In addition, sandy eskers, rocky outcrops, small streams and · numerous lakes, generally long and narrow, are present in the area. The pattern of water drainage and the orientations of the drumlins and lakes indicate that movement of glacial ice was in a NE to SW direction. Thus the topography of the area is rugged with steep-sloped drumlins separated by long narrow lakes and wet "lowland" areas.

Black spruce (Picea mariana) -lichen woodland is the dominant vegetation type on the drumlins. Larix laricina and Populus tremuloides are extremely rare in the study area. The only other components of the tree canopy of importance are Betula papyrifera and Pinus banksiana. The latter, although thinly scattered on most drumlins, can be found in pure stands on some drumlins SW of camp and on the eskers. Betula is restricted mainly to woodland less than 70 yearsold. Dense stands of stunted Picea are present in the wet margins of the drumlins.

The.ground vegetation on the drumlins is always dominated by lichens with a few species of mosses and shrubs making up the balance (Table 2.1). The wet "lowland': areas are much richer in species with Ledum groenlandicum, Myrica gale, Chamaedaphne calyculata, Empetrum hermaphroditum, Vaccinium oxycoccus and Rubus chamaemorus growing on extensive carpets of mosses, primarily Sphagnum ~ ---

4

5

Table 2.1

a) Lichens

Species Mean % Cover Standard Deviation

Cladonia stellar is 17.31 9.78 Cladonia uncia lis 8.48 5.34 Cladonia amaurocraea 4.17 3.80 Cladonia gracilis 2.15 2.98 Cladonia mitis 0.73 2.09 Cladonia botrytes 0.10 0.33 Cladonia gonecha 0.83 0.82 Cladonia cristatella 0.11 0.35 Cladonia cornuta 1.46 1.43 Cladonia coccifera 0.78 0. 71 Cladonia macroEhylla 0.39 0.43 Cladonia subulata 0.04 0.10 Cladonia crisEata 1.50 1. 71 Cladonia rangiferina 1.01 1.77 Cetraria islandica 1.54 1.37 Cetraria nivalis 9.16 9.37 Stereocaulon Easchale 22.03 24.13 Peltigera aEhthosa 0.08 0.22 Peltigera scabrosa 1.06 1.38 NeEhroma arcticum 0.10 0.36 Lecidea uliginosa 0.85 1. 94 Biatora granulosa 1.40 2.80

b) Mosses, Liverworts and Lycopods

Ptilium crista-castrensis 0.26 1.22 Polytrichum piliferum 4.13 13.62 Polytrichum juniperinum 0.87 1.93 Dicranum spp. 0.46 1.06 Hylocomium splendens 0.31 0. 72 Pleurozium schreberi 1.26 2.79 Ptilidium ciliare 4.40 6.02 Lycopodium ~ 0.09 0.36

c) Vascular Plants

Arctostaphalos uva-ursai 0.08 0.35 Ledum groenlandicum 2. 77 2.85 Vaccinium vitis-idaea 15.26 7.19 Vaccinium uliginosum 1.85 2.57 Vaccinium myrtilloides 0.58 1.10 Geocaulon lividum 0.98 1.34

d) Remainder

twigs and litter 19.75 10.32 bare ground 3.39 11.32

6

The influence of fire is most evident on the drumlins, where it has created a mosaic ofvariou&o/ aged patches of woodland whose irregular boundaries are often quite distinct due to differences in tree density and ground vegetation. The low wet margins surrounding the drumlins have limited the size of most burned areas, although drumlins which have been completely burned by past fire are not uncommon.

From climatic data from Uranium City based on the period 1931-1960, the area has a mean annual temperature of -5°C and a mean annual precipitation of 77.2 em.

Methods

1. Aging of burned areas

Prospective burns were chosen with the aid of aerial photography and by aerial survey and their ages estimated primarily through fire scars. (Spurr, 1954; Frissel, 1973). Several live scarred trees were located either on the perimeter of each burn or within "stringers", unburned patches within a burned area. To eliminate problems imposed by other agents of scarring such as bears, rodents, freeze damage and windthrow, several criteria were established. An increase in annual ring width immediately following the fire, charcoal on the scar wood, a triangular shaped scar and replicate scars on the same side of several trees, all indicate fire damage.

Cross-sections through the scars were made using a McCulloch chain saw and the number of years since fire damage was determined for each, by counting the number of annual rings from the scarred ring to the bark. The ages of the scars frequently fell into age sets indicating fire recurrence. Thus the time since the most recent fire was estimated from a mean of the elements of the youngest age set, and only after a high degree of agreement between cross-sections had been obtained (see Table 2.2).

Fire scarred trees were absent for a very recently and completely burned area. Since Salix ~ reestablish themselves very rapidly from basal sections of stems or underground roots (Lutz, 1956; Tucker and Jarvis, 1967), the age of the burn was estimated at 3 years from age determinations of such Salix shoots on the burned site.

Two additional areas of woodland could not be aged through fire scars. The absence of fire-scarred trees was probably due to the death of first generation trees since peat depth, abundance of mosses and size and density of trees were comparatively very high. An estimate of the minimum age of each of tl)ese burn's was made from the age maximum of the 15 largest trees, determined from annual ring counts taken using a Swedish increment borer.

-----2. Sampling procedure

The sampling procedure was designed to examine the ground vegetation

No. of Sample Plots

1

1

4

6

3

4

2

5

4

2

4

6

3

4

5

4

No. of Sample Plots

3

4

Table 2.2

Time Since Fire Damage

3*

12 12 11 12 12 12 12

25 22 23 24 23 23 23 23 23

30 33 32 31 32 32

40 43 45 42 38

44 45 48 45 42 44

45 47 47 47 47 48

52 48 50 48 49 49

69 67 67 67 67

71 70 72 73 72

74 83 83 81 73 76

93 89 92 92 93

98 98 94 98 99 98

139 138 134 139

140 148 150 150 155 155

219 215 213 215 217 214 212 218

Scarred Trees Absent - Ages of Oldest Trees (Yrs)

178 163 164 173 119 161 179 187 168 152 178 163 182 186 188

164 187 184 171 166 168 182 184 149 174 177 190 161 186 185

* from age determinations of Salix ~

Estimated Age of Burn (Yrs)

3

12

23

32

42

45

47

49

67

72

78

92

97

138

150

215

Estimated Age of Burn (Yrs)

>188

>190

7

8

Figure 2.1

SCAbE.

5

liiii ~;=;:~~0

~~~~5

====1

:0

~~~~15

~ Miles Kilometres 5 0 5 10 15 20 25

of the burns at two level5of detail while treating the trees as an independent variable. To allow for comparisons between burns of different ages, seventy 10 m2 sample plots were distributed over 19 burned areas for which ages had been determined (Figure 2.1). Replicate sample plots were positioned well within the perimeter of each burn, away from stringers and whenever possible on the top, NW and SE facing slopes of each drumlin. Measurements of slope, using an inclinometer, and total number of trees were recorded for each plot. Other measures were derived from quadrat data (see below).

To allow for comparisons within burns, twenty replicate 1 m2 quadrats were placed randomly within each of the seventy 10 m2 plots. Percentage cover, as determined from 50 random point samples, was used as a measure of abundance of each species within each quadrat. At the same time, the depth of peat to the underlying sand and gravel was measured from an exposed profile. The distance from the center of each quadrat to the nearest tree, circumference of its trunk at ground level and length of its lowest live branch were measured with a tape measure. In addition, a core sample from the closest tree was taken for each quadrat and the ages of those trees were subsequently determined from an annual ring count in the laboratory using light microscopes. All data were averaged over quadrats to give 10 m2 plot mean values.

3. Data Analysis

The analysis of data was primarily made using principal component analysis, an ordination technique which has been shown to be extremely efficient in summarizing large bodies of data. Its applicability as an ecological tool has been illustrated by a number of workers (Gittins, 1964; Orloci, 1967; Kershaw, 1968; Neal and Kershaw, 1973a,b; Kershaw and Rouse, 1973; Larson and Kershaw, 1974). The analysis operates on a matrix of correlation coefficients derived from the raw cover data in which the value of each coefficient is indicative of the similarity in species composition of a pair of sample areas. The results of the analysis are presented graphically (Kershaw and Shepard, 1972) with each sample area having coordinates on three orthogonal axes representing linear uncorrelated components in the solution of the matrix. The first axis accounts for the greatest proportion of total variance in the data. Successive axes account for decreasing amounts of variance.

The analysis was carried out using mean cover values for the seventy 10 m2 plots to examine variation between burns. The resulting ordination showed that 20% of the total variation was attributable to six plots from the youngest burns. Hence these plots were removed and the analysis repeated.

In addition, environmental and cover data for the 10 m2 plots were further analysed through linear regression analyses, the calculation of correlation coefficients and class mean histograms.

9

Results

Previous data from the Dunvegan-Abitau Lake drumlin field had established two recovery phases during the first 50-60 years following fire (Kershaw, Rouse and Bunting, 1975). Within twelve years Polytrichum piliferum forms an extensive cover and largely characterizes the mature stage of PHASE I. Cladonia cristatella, ~· botrytes, and Biatora granulosa are equally characteristic of PHASE I but never reach high cover values. Equally the general absence or very low cover of Cetraria nivalis, ~· islandica, Cladonia uncialis, and ~· stellaris are typical of PHASE I. PHASE II commences 25-30 years following the fire and is characterized by high cover values of Cladonia stellaris, ~· uncialis and Cetraria nivalis together with very reduced cover of Polytrichum piliferum and virtual absence of Cladonia cristatella and ~· botrytes.

10

The analysis of the current data confirms the very distinct floristic differences in PHASE I (Figures 2.3 and 2.4) and the initial importance of Cladonia stellaris in PHASE II. Of particular importance, it also establishes PHASE III dominated almost exclusively by Stereocaulon paschale and a final phase of closed canopy woodland where Stereocaulon is eliminated and replaced by mosses and vascular plants.

Thus the ordination of the total data separates the PHASE I samples on Axis 2 (Figure 2.2). Five of these plots are dominated by Polytrichum piliferum (Figure 2.3) and contrast markedly with the remainder of the sample. The sixth plot is from a 3 year old burn characterised by a large proportion of bare ground, typical of the very early stages of PHASE I.

The reanalysis of the data after the removal of these sjx PHASE I plots shows a clear correlation of Axis 2 with increasing age of burn (Figure 2.4), while Axis 1 is closely correlated with the cover of Stereocaulon paschale (Figure 2.5). This emphasises the strong non-linear relationship between Stereocaulon and age of burn. Thus although Stereocaulon contributes the most variance to the data set and is thus strongly correlated with Axis 1, it is also very strongly correlated with PHASE III and only with PHASE III, in the recovery sequence (cf Figures 2.4 and 2.5). Conversely Cladonia stellaris is linearly correlated with Axis 2 (Figure 2.6), the cover values progressively decreasing from PHASE II (30-45%) to less than 10% in PHASE IV, where under closed canopy conditions Stereocaulon paschale is eliminated. Cetraria nivalis (Figure 2.7) is correlated with both Axis 2 and Axis 3, the high cover values being restricted to PHASE II and III only (see also Figure 2.14). This distribution has been interpreted as a result of the dual role of this species; it is characteristic of the early stages of lichen colonization of burnt woodland, but it is also a very abundant and active colonizer of heavily grazed areas of ~tereocaulon woodland and thus appears abundantly in some sample p!ots from PHASE III. The domination of the final closed canopy woodland (PHASE IV) by moss and vascular plant species is demonstrated well by the ordinations of Ptilidium ciliare (Figure 2.8) and Vaccinium vitis­idaea (Figure 2.9) and call for little comment. ~

The linear regression results for environmental measures are summarized in Table 2.3 and the more important correlations are presented in

Table 2.3

Intercept Slope x variable y variable a SEa Ta b SEb Tb r

quadrat-tree distance burn age (yrs) 86.34 4.50 19.18 -0.28 0.04 -6.92 -0.64 (in.) tree age (yrs) burn age (yrs) 59.79 9.31 6.42 0.34 0.08 4.07 0.44 trunk circum.(in.) burn age (yrs) 10.40 1.01 10.30 0.03 0.01 3.41 0.38 peat depth (em) burn age (yrs) 0.66 0.47 1.41* 0.03 0.004 7.79 0.68 no. trees burn age (yrs) 2.35 2.00 1.18* 0.17 0.02 9.47 0.75 quadrat~tree distance no. trees 76.39 4.22 18.09 -1.09 0.18 -5.85 -0.58 (in.) tree age (yrs) no. trees 81.73 8.14 10.04 0.83 0.36 2.30 0.27 trunk circum. (in.) no •. trees 11.64 0.83 14.11 0.11 0.04 2.95 0.34 peat depth (em) no. trees 0.61 0.34 1. 78* 0.17 0.02 11.37 0.81 quadrat-tree distance (in.) tree age (yrs) 68.88 6.94 9.92 -0.13 0.07 -1.99* -0.23 trunk circum. (in.) tree age (yrs) 6.06 0.86 7.08 0.08 0.01 9.47 0.75 peat depth (em) tree age (yrs) 2.02 0.73 2. 77 0.02 0.01 2.68 0.31 quadrat-tree distance (in.) trunk circum. 54.79 7.51 7.29 0.11 0.49 0. 23)~ 0.03

(in.) peat depth (em) trunk circum. 2.78 0.39 7.04 0.08 0.01 5.58 0.56

(in.) peat depth (em) quadrat-tree 8.13 0.70 11.60 -0.70 0.01 -6.72 -0.63

distance (in.)

Figure 2.2

23 3 23 12

23

-

12

ORDINATION OF BURN AGES

G7

23

I 23

32n

92

92

97 4L

150 150

I= Phase I ~ 23 years H= >23 years

~~ 138

II

13

Figure 2.3

ORDINATION OF POLYTRICHUM PILIFERUM

'Zli

!i(; 0 30 (;8

7

30

68

17

0

---I (f)

H X a

3 ~

0

~ 0

B 10 l!J1

0

0 0

II

0 0 Q 0

o o8 o13fb10 3 o o 10 0

0 0

3

7 0

0 2

0 0 0

1 (; l9 3 0 1

0

0

0(

I

0

oo 0

1 0

0

I=~ 10% cover ll= >10% cover

i'

i:'.li I'

' .. jl ,,

14

Figure 2.4

ORDINATION OF BURNS >23 YEARS OF AGE

32 32

494~5 7'll9

4945

4-7

47 32

32

67 42 92

llS

49215

.1.50

&7 s2

.1.50 1.50 92

l.50 97 9273

97:

78 78 9<:9'3

97 671.5

4-5

~ (j)

H X C[

lo .190

11.M§:m 0 4-9

2.1.5 .188 49 .138 .188

1.90 .188

.1.38

45

I= Phase II ll= Phase ill 51-100 years m= Phase nz: >100 years

4-7 4-9 llS

4-1~9 llS.

704-9 ~

S7

.1.50

1.50

3~5 "U6.ts.fsus .1.90.1.38 21.5

.188 45 .188

.188 .138

92 S7

1.3818 .1.S%2

42 42

42 S7 .150 92

45 32

78

s;8 9~8 78 92

2 s7 s7

.1.50

.t3~~LW jmJ) -;__1~1P:W 1.a18l8

2.15

32

32 32 32

32

32 I 32

32

15

Figure 2.5

ORDINATION OF STEREOCAULON PASCHALE

0

G 0 4-00

0 4-3 .1..1.

1. 5 9

3 4-4-

I 0 4-

1.7 32

II 26

37 4~5

ill 4-24-5

47

N s

0 0

~s?v 3 .1.7

0-t 5

o0B 0!. 0 0

0 0 5 8

H

2.1

.1.

9

.,----i (f)

H X CI

0

0

7

~ 38 389 4-2

32 45

4S

50

54 Sai9

ss S-4&7

3

4-

4-

0

0 0 Q Q 0

34° 0

no 0%

s-4 i 0 0 0 g 5 0 1.

3 7

.1.7 9 21.

25 21.

37 32zs 3816

45 39 32

4-5 42 46 40

54 5~5 s~9 47

9 S4- ss

&7

4

4

I = ~ 1 Oo/o cover n = 11-30% cover m = 31-50o/o cover

Ill= > 50% cover

.1..1. 4 9 0

4

42

:I

'.1'1

~II· 1'!;,•,1.·.' :111

'I ill

li

~ .. '1:.1' 1,1

Figure 2.6

16

ORDINATION OF CLADONIA STELLARIS

20

I

~~2 u..!..5

8

~s

.1.3

.1.5 H

14

i39

.1.3 ~28

35

3.1.

I

~ (f)

H X a:

~ I

,'8 46 34

I=~ 19% cover H=l>19% cover

2 ~s ;?

~a: a ~5 : s

3.1. 28 28 21

I I I I \

I

. I I I I u.:

u :19 I

~0\ I I I I I I

20

\ \ \

\ \

\ 22 \ \

\ I 2.1.

\\ 2-4[ \

\~5 ' '

3d1 20 3~4 .1Ji :~s ~§a 8 13

.1.5 ~8 .1.5

3-4

l.1.

22

~8

7 3.1.8

s H.1.5

~-41.~ 232o

s ~s

.1.0 s H 16

I

22 ~2

11

2~

s 25 24

Figure 2.7

.1.0 4

.1.7

22 3~5

42 38

H

~s~ \Ai-

17

ORDINATION OF CETRARIA NIVALIS

3

0 8

2

2 55 9S

2 ~2

23 3 s

26

.1.2

H ~8

8 s ~a

2521. 1.8

v 1.0 1.~

z 2 z sg

1.7

Z2

1.

------1 (f)

H X CI

50 0

4 2 2 2 0 3

1. .1.

I=<. 10% cover n = 11-20% cover m= > 21 o/o cover

s 9 2\ ~;LZ ions

1. 2 & 4 0

1. 34 2

3

0

2

1.8

25

35

38

42

Z2 .1.

1.3 1. 4

s 3

8 4 1.7

3 2 8 1.5

1.5

I

2S

ill

cS 23

35 Z&

38

Figure 2.8

0 0

0 0

0 0

0

0

---

18

ORDINATION OF PTILIDIUM CILIARE

l.

0

.1

02

0 0

0

0

0

0

3

0 4-

.10

8

0

7 0

3

.10

.1 0 0

s7~

>-i (f)

H X CI

2 0 B

.1.1 .13 H l.5

0 0 0

8 .19

.1.1

9 63 7

.17

0 z 0

3

.1 Oo

0

0

0

0

0

0

0

a a 3

7

I=< 5% cover n= [> 5% cover

_to ~ 0 ° 3 zozs

3 H 15 .13

0 15

0 19 .1.1

0 7

.i .10a 69

2 3 1

.17 7 3 0

0 80

-11 1l

0 1

0

s s.11

7 sv-~z3 7 9 .1.1

.15

II 0 0

0

I

0 0

0

0 0

0 0

19

Figure 2.9

ORDINATION OF VACCINIUM VITIS-IDAEA

i7

i921

i5

121.~ eno

131.4 i5 1.3 cc

9 i5 i2 17

ll 98

i3 co 1.4

6 9 6

cc 5

i!o 8 9

14

6 1.2 711.

ll 1.013

l.c

ll

~ (f)

H X a

2 s 24

2s~~ 23 iS

24 2i

1.8 iS

23

18 .ll5 30

i5

1.9

i2 13

s 23

i522

5 1.aa co 6

1.0 1.5

1.5 so 22 i3

12

711.

1.0 ll

13

i3 1.)5 30 c7l.~a <£!

ec c5z3 l.s1-6

2 38

s

.139 §

9

H

i3

II 9

I

iS

9

l.~ s

I=< 15o/o cover n= > 15% cover

8 13

9 17 iS

H

8

/f~)' s2

20

Figure 2.10

60 • •

21

Figure 2.11

12 •

•

• •

.. .. • -E

(.) - .. .. J: ~ a.. • • w c ~ • • .. • <C w a.. • • .. • •

A MAee • • .. .. . ..- •• .. A • .. • • • . . ...

·--·-----------------------·------------------------------------0 215 BURN AGE (yrs)

22

Figure 2.12

•

•

• • • • .. w • u • 2 • <( • 1- • • (/J -c • • • •

i w • II w .. .. • • • II

a: • • • 1- • • • • • I,

II ••• • • •

• • • • • Iii .. • • ill • • • • • • • • • • ..

• • .. ... •

0 215 ";.

BURN AGE (yrs)

23

Figure 2.13

12 •

••

• •

• •• •

- • E (..) -

:I: • • • • .... a.. w • • • c

~ •• ••• w a..

• • • •• •

. ..... .. .. . ..

.......... • • •

........ •

·---·----------------------------------------------------------~ 0 60 NUMBER OF TREES

Figures 2.10-2.13.

There is a steady linear increase in the number of trees per plot with increase of burn age (Figure 2.10)and with a concurrent increase in peat depth (Figures 2.11 and 2.13). The regular pattern of the developing Picea trees and thus the complete eventual closure of the canopy, is demonstrated by the linear decline of the inter-tree distance (Figure 2.12). The regression of the more abundant species represented in the sample against the environmental measures largely confirmsthe ordination results presented above (Table 2.4). ·

Discussion

The fire scar method has been used in conjunction with a detailed vegetation examination to establish the post-fire recovery sequence of black spruce-lichen ~.roodland on drumlins in the southe;rn N. W. T. There is directional change in species composition of the ground layer vegetation with increasing burn age. This change is accompanied by increases in depth of peat, which will primarily affect surface soil moisture characteristics (Rouse and Kershaw, 1971) and the development of the spruce canopy through increases in the age, size and density of trees, which will affect the general surface microclimate (Wilson, 1973, Kershaw, Rouse and Bunting, 1975). In addition, a considerable degree of variation is evident within the sequence. This variation may be due to a number of factors which will affect the actual recovery of vegetation following a fire, such as intensity of the fire, type of vegetation burned, climate for a number of years following the burn, extent of the burn and the time of year of the fire which will largely determine the quantity of seed available for recolonization. However, the effect of any one of the factors is often difficult to determine.

The ground vegetation is dominated by a number of species each with a unique temporal distribution. The moss Polytrichum piliferum is most abundant on burns less than 25 years old. Cetraria nivalis and Cladonia stellaris rise to maximum levels of abundance on burns which are 25 to 75 years old while Stereocaulon paschale is at a maximum on 75 to 100 year old burns. Ptilidium ciliare and Vaccinium vitis-idaea reach maximum levels of abundance on burns greater than 150 years of age.

Ahti (1959) and Bergerud (1971) recognize a five-stage recovery sequence for lichen woodland in Newfoundland. The sequence involves primarily Cladonia lichens and the shrubs Kalmia angustifolia, Vaccinium angustifolimn and Rhododendron canadens.e. The final stage, dominated by Cladon.ia stellaris, connnences 80 yea11;s following fire. In northern Ontario, Shafi and Yarranton (1973) distinguish four phases in a post....,fire recovery sequence primarily involving vascular plants and covering less than 60 years. In addition, Scatter (1964) working in northern Saskatchewan (50° to 600N, 1040 to 106°W) only lOG-miles to the southwest of the Abitau Dunvegan lakes area, establishes a three phase sequence of recolonization following fire. Scatter's first phase and the first 25 years of the recovery sequence presented here are in good agreement, but Cetratodon purpureus is rare in our study area. However, comparisons of his second and third phases with the remainder of this sequence show distinct differences. The most outstanding is that Scatter

24

Table 2.4

Species Environmental Intercept Slope % cover measure a SEa Ta b SEb Tb r

C1adonia stellaris burn age (yrs) 19.32 2.24 8.61 -0.02 0.02 -0.91* -.11 Cetraria nivalis burn age (yrs) 14.45 2.10 6.91 -0.05 0.02 -2.68 -.31 Vaccinium vitis-idaea burn age (yrs) 8.32 1.37 6.06 0.07 0.01 5.98 .58 Stereocaulon Eascha1e burn age (yrs) 17.98 5.18 3.47 0.01 0.05 0.31* .04* yo1ytrichum piliferum bur.n age (yrs) 12.65 3.08 4.10 -0.08 0.03 -3.00 -.34 Ptilldium ciliare burn age (:lrs) -2.14 1.04 -2.04 0.07 0.01 7.49 .67 c. ste11aris peat depth (em) 19.30 1.97 9.81 -0.46 0.42 -1.10* -.13* c. nivalis peat depth (em) 14.86 1. 74 8.53 -1.38 0.37 -3.74 -.41 v. vitis-idaea peat depth (em) 7.96 1.38 5.76 2.10 0.29 7.17 .65 s. paschale peat depth (em) 32.43 4.14 7.83 -3.36 0.88 -3.83 -.42 P. Eiliferum peat depth (em) 9.15 2.81 3.25 -1.16 0.60 -1. 94* -.23* -P. ciliare Eeat deEth (em) -1.58 0.83 -1.90* 1.62 0.18 9.15 .74 c. ste11aris no. trees 18.02 2.03 8.86 -0.02 0.09 -0.28* -.03* c. niva1is no. trees 14.40 1.84 7.83 -0.26 0.08 -3.17 -.36 v. vitis-idaea no. trees 8.01 1.08 7.41 0.37 0.05 7.84 -.69 s. pascha1e no. trees 28.35 4.48 6.33 -0.49 0.2.0 -2.48 -.29 P. piliferum no. trees 11.27 2.80 4.02 -0.35 0.12 -2.86 -.33 P. ciliare no. trees -2.28 o. 77 -2.96 0.37 0.03 10.89 .80 c. ste11aris quadrat-tree 18.28 2._92 6.27 -0.01 0.05 -0.26* -.03* c. niva1is (in.) 3. 71 2.74 1.35* 0.11 0.04 2.39 .28 v. vitis-idaea 21.74 2.02 10.15 -0.11 0.03 -3.51 -.39 s. Ease hale distance 10.18 6.62 1.54* 0.16 0.11 1.52* .18* P. piliferum -11.29 3.69 -3.06 0.29 0.06 4. 77 .50 P. ci1iare 11.53 1.58 7.30 -0.12 0.03 -4.86 -.51 c. stellar is tree age (yrs) 18.86 2.67 7.01 -0.01 0.03 -0.54* -.06* c. nivalis tree age (yrs) 4.70 2.53 1.86* 0.05 0.02 2.19 .26 v. vitis-idaea tree age (yrs) 10.11 1.81 5.58 0.06 0.02 3.20 . 36 s. pascha1e tree age (yrs) 6.80 5.94 1.14* 0.14 0.06 2.46 .29 P. Eiliferum tree age (yrs) 17.67 3.50 5.05 -0.14 0.03 -4.11 -.44 P. ci1iare tree age (yrs) -0.37 1.54 -0.24* 0.05 0.02 3.54 .39

cont'd . . . N Ln

Table 2.4 corit'd

Species Environmental Intercept Slope % cover measure c SEa Ta b SEb Tb r

c. stellar is slope (0) 19.19 1.87 10.25 -0.28 0.25 -1.10* -.13* c. nivalis slope (0) 10.01 1.83 5.47 -0.03 0.25 -0.12* -.01* v. vitis-idaea '·~ slope (0) 13.59 1.40 9.74 0.29 0.19 1.54* .18* s. Easchale slope (0) 25.16 4.25 5.92 -1.01 0.57 -1. 76* -.21* P. Eiliferum slope (0) 5.39 2.75 1.96* -0.10 0.37 -0.28* -.03* P. ciliare slope (0) 3.00 1.16 2.58 0.27 0.16 1. 71* .20*

* not significant at p ::::: .05 level

Figure 2.14

50 POLYTRICHUM PILIFERUM

40

30

20

10

?

r 0

50 CLADONIA STELLARIS

40

a: w > 0 (.)

30 w (!)

~ 2 w 20 (.) a: w D..

10

40 VACCINIUM VITIS-IDAEA

30

20

10

oL--o~~-5~---r--r-~--~~r--r2-0~1-225 26-50 76-100 126-150 176-200

BURN AGE

26-50

CETRARIA NIVALIS

? ___,____

STEREOCAULON PASCHALE

PTILIDIUM CILIARE

126-150 201-225

176-200

27

28

makes no mention of extensive Stereocaulon paschale cover. Thus the contrast between these four recovery sequences with respect to rates of recovery and species involved emphasizes the importance of considering the effects of fire in different geographical regions separately.

Although Scatter and Thomson (1966) report the presence of Stereocaulon paschale in N.W.T. and Ahti et al (1967) rep~rts its presence in Ontario, Manitoba and locally in B.C. and Newfoundland, the importance of Stereocaulon-spruce woodland as a vegetation type has not been commented upon. ~· paschale is the most abundant component of the ground vegetation in our area forming extensive carpets on burns between 75 and 100 yea~old. Unique sets of variables undoubtably control the development of this woodland and its subsequent disappearance on burns greater than 150 years old, but these have yet to be examined and work is proceeding along these lines. Of additional interest is the abundant evidence of caribou grazing of these mats. This is in agreeme~t with Kareev (1968) who notes the importance of~· paschale as a winter fodder for caribou in Russia. This observation, coupled with the importance of arboreal lichens and Cladina species as sources of winter fodder (Bergerud, 1972; Scatter, 1967) suggests that fire is in fact, necessary to maintain a plentiful supply of lichen forage for caribou.

Thus with the reburn cycle largely maintained at less than 100 years, a closed canopy woodland dominated by mosses and vascular plants fails to develop. Spruce-lichen woodland is accordingly dependent on fire for its maintenance.

Section III

Microclimate

Introduction

In the summer of 1973 a research site was selected where a large 22 year old burn was contiguouswithfully-vegetated spruce-lichen woodland subsequently dated at 80 years since the last fire. In the same year a small plot was burned which by the summer of 1974 was 1 year old. In June 1974 another small plot was burned so that a time sequence of 0, 1, 23 and 80 year burns was attained. Inadvertently the 1 year burn caught fire while the 0 year plot was being fired thus creating a more thorough burning of the surface. As well as disrupting the time sequence this showed that if any fuel remains a newly burned area is quite susceptible to reburning.

Measurements of air temperature, precipitation, wind, components of the radiation balance, soil temperature, soil heat flow and soil moisture were inaugerated in early July, 1974, and maintained through to mid-August for a maximum period covering 43 days for the general meteorological measurements and a mi~um period of 34 days for soil moisture measurements. Detailed site descriptions, methods and results are reported in Kershaw, Rouse and

29

Bunting (1975).

The results can be generalized as follows. The 1974 measurement period had normal atmospheric temperatures but was extremely wet with more than double the normal rainfall recorded. The highest net radiation was recorded over the fresh burn (0 Yr.) and the lichen-woodland (80 Yr.) which meant that more energy was available for heating the soil and the air and for evapotranspiration. Soil heating was small relative to the available radiant energy. For the lichen woodland most of the net radiation appeared to be expended in evapotranspiration and while evaporation was still an important process in the new burns, it was of lesser magnitude and the sensible heat flux achieved greater magnitude. It was conjectured that the relatively low net radiation over the 23 yr. burn must serve to slow the growth processes during that phase of revegetation particularly as it was accompanied by a low soil water availability.

The 1974 results indicated that the soil thermal environment during initial revegetation was one of extremes which was not modified significantly until trees formed an important part of the vegetation canopy. High surface temperatures in the 0 and 1 yr. burns· came closest to the optimum temperature range for the germination of black spruce seeds in controlled laboratory experiments. The main differences between the 0 and 1 yr. burns in this initial measurement period seem to arise from the increased removal of the surface litter through the reburning of the 1 yr. plot. This led to higher soil temperatures but to a lesser retention of surface soil moisture. The rate of tree growth was clearly important since the' development of mature trees enhances lichen growth quite possibly as a result of their conservation of surface soil moisture. Although the study was not made in a permafrost zone the results indicated that burning over permafrost would create strong summertime melting for periods in excess of 23 years as shown by the substantially higher soil temperatures of the 0, 1 and 23 year burns in comparison to the lichen woodland.

In 1975 initial research into the nature of the snow cover was carried out in early April and soil temperatures were also measured at this time. The main research period commenced in early June with the burning of a large plot adjacent to previous burns to create a burning time-sequence of 0, 1, 2, 24 and 81 years. The 2 yr. burn represents a very intensive burn as a result of its reburning the previous year which removed much of the organic layer. Measurements were initiated on June 4 and continued through August 15 to encompass a period of 72 days which began shortly after final snowmelt in the lichen woodland, spanned the summer solstice and encompassed the bulk of the growing season. Direct measurements during this period included screen air temperature and humidity, precipitation and wind; incoming solar short-wave and infrared long-wave radiation; net radiation over each of the 5 surfaces; soil temperature profilesto a depth of 160 em at all sites; soil moisture profiles to a depth below 1 m for each site. Derived measurements included surface temperature and evapotranspiration.

The objective of this part of the study was to gain an overall under­standing of the primary microclimatic changes which accompany the cycle

RESEAR SITES AND

INSTRUMENTATION

BOUNDARYS ----····· ..... ooooooo

·-·-INSTRUMENTATION

O*- Net radiation

Site

Sile Site Site Site

A

B c D

E

K+- Incoming solar radiation u- lncom ing long- wove radiation

M- Temperature, humidity, wind p -Precipitation s -Soil moisture T- Soil temperature

CONTOUR INTERVAL-20m.

SCALE 1: 5460

LAKE

. -·

40

., .---.) '-·-'/ ..,.,.. . .,.,.. .

LAKE

Datum - 0 m.

w 0

DETAILED TOPOGRAPHY AND SAMPLING POINTS

• SAMPLING POINT --BOUNDARY OF BURNS --CONTOUR INTERVAL=3m.

SCACE. I' 5460

SNOW DENSITIES (g cm3)

,..,,.ISOPLETH INTERVAL=0·4g cni3

-CONTOUR INTERVAL=Gm.

DATUM ' 0 METRES

SNOW DEPTH (em)

,,.,.,,,ISOPLETH INTERVAL' 5 em -- CONTOUR INTERVAL= Gm

SNOW WATER EQUIVALENTS (em)

.,.,,ISOPLETH INTERVAL= 2 em _CONTOUR INTERVAL=G m. --BOUNDARY OF BURNS.

LAKE

Figure 3.2 Map of sampling points, snow depths, densities and water equivalents for the snow survey 1975.

32

from mature lichen-woodland through initial burning, and various stages of recovery back to the lichen-woodland phase. This is a period which covers in excess of 50 years as noted earlier in this report and as such the big changes which occur in the microclimatic regime have long-term environmental impacts and also widespread environmental impacts due to the ubiquitous nature of fire in subarctic areas.

Methods

1. Research sites

The position of the research sites and plots of instrument locations are shown in Figure 3.1. The 0 yr. burn, unlike previous burning, was carried out without felling the trees so that the situation was quite natural. The fire was fairly hot though like most burns in this area it was more intense in some places than others. The coniferous needles were completely destroyed and the ground lichen cover was completely burned, except where caribou trails or human foot prints had compacted the surface, in which case, it went unscathed. The 1 yr. burn had noticeably lost some of its blackness from the previous year whilst the 2 year burn was not changed noticeably. Revegetation by widely-spaced vaECular plants nota.bly Vaccinium spp., Ledum groenlandicum and a few spruce seedlings was better­developed on the 1 than on the 2 yr. burn. The 24 yr. burn was dominated by Polytrichum spp. which form a mat about 2-3 em thick. The remaining ground cover was comprised of lichen species. Vaccinium spp., Ledum groenlandicum, Biatora granulosa and bare ground. The arooreal vegetation of the mature lichen woodland in the vicinity of the measurement site is composed exclusively of black spruce trees, Picea mariana, averaging 14 m in height with each tree located an average 3 m from its nearest neighbour. The ground flora was comprised largely of Stereocaulon, Cladonia, and Cetraria lichen spp.

2. Snow survey

Snow depths and densities were determined at the sampling points of the systematic grid shown in Fig. 3.2 for the period April 10-12 inclusive. Snow depths at each point represent an average of three measurements with a metre stick. Snow weights were determined by weighing with a spring balance a snow core taken in an M.S.C. tube sampler, again using an average of 3 samples at each point. Density was derived from the weight of the core divided by the depth measured with the metre stick which avoided problems of compaction in the tube sampler. A total of 64 sample points represented the open woodland environment, 10 sample points the one and two·year old burns, which were largely sheltered from the wind by the surrounding woodland for all but rare north-easterly winds, and 24 sample points represented the 24 year burn whichwasopen to wind erosion from all directions.

3. Temperature, humidity, precipitation, wind

Air temperature and humidity were recorded continuously on a thermo-

33

h~ograph housed in a Stevenson Screen. Temperature comparison checks with an electrical resistance thermometer gave an accuracy of ± 5% while checks of the hair hygrometer in the h~graph unit against wet and dry bulb thermocouples indicated an accuracy of ± 15%. The relative humidity measured by the hygcrograph is changed to vapour pressure according to the reduction formula

= p H sv R

(3.1)

where Pv is ambient vapour pressure, Psv is saturation vapour pressure at ambient temperature and HR is relative humidity expressed as a decimal fraction. Precipitation was measured with standard 10 em diameter rain gauges and represents an average of 9 gauges spaced randomly over the experimental site. Wind speed was derived as a daily average from a standard totalizing anemometer.

4. Radiatien and surface temperatures

The radiation balance Q* can be expressed in terms of incoming solar radiation K~, surface albedo a, incoming long-wave radiation L~ and outgoing long-wave radiation Lt in the form

Q* K~(l - a) + L~ - Lt (3.2)

Q* was measured over each surface with a net radiometer, K~ and L~ were measured at one site with a pyranometer and pyrgeometer respectively while a = Kt/K~, where Kt is reflected solar radiation, was also measured directly for each surface with up-facing and down-facing pyranometers. Lt was derived as a residual in eq. (3.2) and the surface radiative temperature T0 was calculated from Lt in the form

= ~Lt (3.3)

where E is surface emissivity assumed to be unity for all surfaces and cr is the Stefan-Boltzmann constant. In reality the emissivity will not be unityJ but, as it is an unknown quantity for these surfaces, it is reasonable that all fire surfaces, being natural, will have similar emissivities, which will approach the unity representative of a perfect black body. For the 0, 1 and 2 yr. burns, where there is no vegetation, T0 will give a pretty accurate representative of the soil surface temperature. For the 23 and 80 yr. burns it is an integrated temperature for the soil surface and shallow vegetated mat in the former caseJand the soil surface, lichen mat and spruce canopy in the latter case.

5. Soil temperature

Beneath the surface, soil temperature was measured at 5, 10, 20, 40, 80, 160 em depths with single-junction thermocouples potted in brass cylinders and referenced to an ice bath. The thermocouples in the 0 yr.

burn were installed two days after the burning and measurements were commenced on June 8, six days after burning.

6. Soil moisture

34

Soil moisture was measured with a neutron probe at 2, 4, 4, 5 and 12 sites in the 0, 1, 2, 24 and 8lyr. burns respectively. In the 0 yr. burn the tubes were positioned and measurements were made prior to firing. The tubes were protected during the firing and measurements were made in the post­fire period. In the 1, 2 and 24 yr. burns the sites were located at random usual~y where the greatest depth for the access tubes could be achieved. In the 81 yr. burn the probe tubes were positioned in a grid, each tube being approximately 3m from its nearest neighbour. In this manner a representative sampling of the spruce lichen woodland was achieved close to the sites of radiation, soil temperature and soil heat flow measurements. Where possible, measurements were made at depths of 5, 10, 20, 30, 40, 60, 80, 100, 120 em. A soil basket 10 em thick and 30 em in diameter was placed over each access tube in order to give reliable near-surface measurements, by temporarily deepening the soil column and preventing the escape of neutrons. This basket was housed in the soil surface during non-measurement periods, so that it could maintain the moisture characteristics of the surrounding surface soils.

7. Evapotranspiration

An approximation to evapotranspiration from the 24 and 81 yr. burns and evaporation from the 0, 1, and 2 yr. burns can be derived from the calculation of soil water loss SHL where

SWL P - L':.Sm (3.4)

where P is precipitation and L':.Sm is the change in soil moisture between measurement periods (negative when soil moisture decreases). In turn

Sl>TL = E + r + V (3.5)

where E is evapotranspiration, r is surface runoff and V is deep seepage across the terminal depth of measurement. There was no surface runoff during the experimental period in 1975 hecause the rains were always of low intensity and were readily absorbed by the porous surface soils. In order for deep seepage to occur across the terminal depth of measuremen~ the moisture gradient must decrease with depth so that the hydraulic gradient is directed downward. The calculations of total .soil moisture were carried out in a manner where the terminal depth of~a measured moisture profile was set at the lowest point where the soil moisture increased downward across the terminal depth. This gave a hydraulic gradient which was directed upward in opposition to the gravitational flow, so that it is safe to assume that V in eq. (3.5) is minimal and evap~anspiration can be approximately expressed in the form

Figure 3.3

3·5 WIND SPEED ( m I sec) SEASONAL AVERAGE WIND SPEED = l·e5 m/sec

3·0

2·5 ... ~ 2·0

-f\11{ ~ 15

10

05 ----------' 2·0

1·5 RAINFALL (em)

~10 ~ !l SEASONAL- -,_~~TA-L-= -~~~--e-m-. -~]

~ r '1 r., n 0 rJ ~ ! {

.0

E

(.)

0

0·5

0 ..~.-_...-· _...L.:L .. _-._fl! _ __.., ....... _. ~~----"'""·"-'~~, .... L~.......J·-----'1&1""! . .._. i;J_,""[ij""~_,a..._ __ l~ : :'1_..-• .., __ 18

14

1: I

SEASON/H. AV::Ril.GE = ~

~I ------'

----------------------------·------., AIR TEMPERATURE (•c l SEASO!';AL AVERAGE

30 ---DAILY M1\X. 18·3 •c

25 ....... DAILY MIN. 7·1 •c

~

20

15

10

. 5

'" ,, I I' ~, A (; ;i V\t'"-''1 't' ...1

1

I I \ I \~ 1, I I~ v \

~- \/ :·.-·\ i\.. ........ :.. i\ .·1 vI

~: ·. .. .. : .. : i : ; ...... ··~ .. ... ... : ·..... .. . ~· . · . ... . ·.: . ~ ..... ··

O..l---r--r-r-r-r--r-.-.r--r--r-.--r-r-.--r-~--r--r-r-r-r-r-r-r-r-r--r--r-r-r-r-r-r-r--,-------' 12 16 2o ' 24 ' 28 2 6 10 14 IB 22 26 30 3 7 II 15 8

JUNE JULY AUGUST

Figure 3.3 Air temperature, vapour pressures, rainfall and wind speeds during the 1975 growing season.

35

36

E = S"\AJL = P - LlSm (3.6)

If the above assumptions are in error the greatest moisture flow will occur early in the season when the soils are very wet. As will be seen in the results there is no evidence that this was ever the case in 1975.

Results

1. Snow survey

Isopleth maps of snow depths, densities and water equivalents are presented in Fig.3.2,and the average data are summarized in Table 1. The period of measurement in mid-April represented the period of maximum snow accumulation according to evidence from Uranium City. Snow depths in the protected 1 and 2 yr. burns were, on average, only 88 percent of those in the open woodland, whereas in the exposed 24yr.hurn this fell to 76 percent. Since the snow densities in all the environments were approximately the same, the equivalent water depths were less over the burns, in almost the same proportion as for the snow depths.

If it is assumed that there was no wind erosion over the 1 and 2 yr. burns and that the lesser accumulated snow water equivalent is due to enhanced solar radiation load, then from Table 1 one can ascribe an 11 percent melting of the snow cover in the burns to the sun and an additional 11 percent depletion in the 24 yr. burn to wind erosion. Since the soil is still frozen this melt water is lost as runoff to the low lying areas and surrounding lakes.

2. Temperature, precipitation, humidity, wind

Maximum, minimum and mean daily temperatures are plotted in Fig. 3.3. The thermal regime during the experimental period can be divided into three periods; an early summer period to June 20 when the mean temperature was 8.2C and the air temperature sank close to freezing on several occasions; a mid-summer period from June 21 to July 19 with a mean temperature of 15.8 and maximum temperature exceeding 30C on three occasions; a late summer period after July 19 with an average temperature of 11.9C, the maximum temperature never exceeding 22C and the minimum temperature again approaching freezing near the end of the period. The temperature regime agreed closely with the long-term average for this area and was almost exactly the same as the coincident period in 1974 as reported by Kershaw, Rouse and Bunting (1975).

The daily vapour pressures shown in Fig. 3.3 follow a similar course to the air temperatures, the humidity going up during the periods of high evaporation and decreasing during cold periods with low evaporation. The average vapour pressure of 10.1 mb~ain agrees very closely with the long term av~e for this area. It does point to a relatively dry summertime atmosphere when compared to more southerly locations like Vancouver, Winnipeg and Ottawa which have average vapour pressures around 14 mb over the same

TABLE 3.1

Site

Mature Woodland

1-2 Yr. Burn

24 Yr. Burn

Burns Combined

37

Average depths, densities and water equivalents of snow at the different sites.

Depth (em) Density (g em-3) Water Equivalent (em)

Burns/Woodland(%) Burns/Woodland(%) Burns/Woodland%

59.4 0.294 17.4

52.3 88 0.297 1.01 15.5 89

45.3 76 0.299 1.02 13.5 78

47.4 80 0.298 1.02 14.2 82

Figure 3.4

a. :::;: w ......

u

a. :::;: w ......

~

C!. :::;: w ....

25~-------------------------------------------------------------.

20

15

10

5

0

To = 15·1

=r; = 15·3

T2 = 17·1

f24 = 13·8

5 CM

25,-~---------------------------------------------------------.

10 = 13·4 10 CM

2~----------------------------------------------------~------,

20

15

10

5

0

-5

10 = 12·4

=r; = 13· a T2 = 14·9

Yz4= 12·2 "f81 = 9·1

20 CM

10 1:1 20 2:1 30 5 10 15 20 25 30 5 10 15 20 25 30 5 l) 13 20 25 30 5 10 15

APRIL MAY JUNE JULY AUGUST. GOOO 0•0000 0 ••.... ,~I

------- •2

YR. BURN. YR. BURN .

YR. BURN. -·-·-·- 24 YR BURN.

81 YR. BURN.

38

0

a.. :::!: w 1-

a.. :::!: w 1-

25~-----------------------------------------------------------,

20

15

10

5

0

-5

1'0 :.10·8

: 12·2

: 14·3

40 CM

25~--------~------------------------------------------------~

20

15

JO

5

0

25

20

15

10

5

0

T0 = 8·5

1j :: 9-6

1'2 = 102

=9·2

"fo ~ 6·1

.1! : 5·4

T2 = 6·0

T24 =5·9

T~;1 =3-1

---------------------

eo CM

160 CM

10 15 20 25 30 !I 10 15 20 25 30 !I 10 15 20 25 30 !5 10 15 20 2!5 30 !I 10 1!5

APRIL

oooooooo 0 YR. BURN

I YR. BURN 2 YR. BURN

-·-·-- 24 YR. BURN 81 YR. BURN

MAY JUNE JULY AUGUST

39

40

time period.

Average daily wind speeds were moderate and gave the same values as for the comparable period in 1974. This is only about one-half of the long­term mean wind speed recorded at nearby meteorological stations which probably reflects the exposed airport location of these latter stations as much as anything. It does indicate though that winds are a gentle environmental factor during the growing season.

The rainfall was slightly above average in 1975. The total of 11.5 em during the experimental period compares with the long-term average of 9.4 em and the total excess occurred during the early summer period to June 20. The precipitation in 1975 was only 45% of the comparable very wet period of the 1974 research period.

In summary, the meteorological conditions during the 1975 research season were fully normal when compared to the long-term averages. The measurement period fully spanned the frost free period between June 9 and August 15 and comprised early summer, mid-summer and late summer elements in terms of the thermal regime. Rainfall was double normal for the early summer period but was fully average during the middle and late summer periods.

3. Radiation

As shown in Table 3.2 burning leads to a reduction in summertime net radiation of from 15 to 19 percent. Since the albedos of the 0, 1, 2, 24 and 81 yr. burns average 5.0, 6.5, 9.0, 15.6 and 20.4 percent respectively, it is evident that differential surface heating, which directly influences the out­going long-wave radiation, plays a large role in influencing the radiation balance. Thus, the low albedo of freshly burned surfaces does not lead to an increased net radiation as is commonly assumed.

4. Soil temperatures

Soil surface temperatures as computed from eq. (3.3) are given in Table 3.3. The removal of the tree canopy by fire createsan immediate increase in soil surface temperatures of some 60 to 70 percent in the mean the maximum and the minimum temperatures. Even after a quarter century surface temperatures of the burns remain from 30 to 40 percent hotter. The maximum temperatur~on the 0, 1, and 2 year burns rise as high as 65°C during dry high sun periods such as July 10 and the average diurnal temperature ranges are extreme at about, 46°C for the 0, 1, and 2 year burns compared to 37 and 28°C for the 24 and 81 yr. burns.

Subsurface soil temperatures are plotted in Figure 3.4 from April 10 to August 15 for the six different measurement depths at each plot. Curves between measured values on April 10 and June 4 are interpolated in a manner where the temperature is allowed to increase linearly when the snow disappears from the ground. Since the snow persisted 8 days longer in the lichen woodland than in the burned areas there is a lag in the curve for the 81 yr. hurn. The mean te~atures plotted in Figure 3.4 are calculated for the period June 4 to August 15. It is evident in the data from the 0 yr. burn that there is a very rapid upward adjustment in subsurface soil temperatures immediately after

41

TABLE 3.2 Measured radiation fluxes (ca~ cm-2 day) for mainly clear days in July and August. Data include daily totals of Q* for 5 sites and the ratio of Q* for each of the burns to Q* for the mature lichen woodland (Q*s/Q*lw)

Date I Period (hrs.) K+ L+ Q* Q*s/Q*lw(%) I

I 0 i 2 24 81 0 1 2 24 81 i

July 101 04-18 671

I 494 337 337 329 334 410 82 82 80 81 100

I July 161 04-19 i 639 514 321 315 300 318 384 84 82 78 83 100

I July 17j 04-18 407 445 243 232 203 218 272 89 85 75 80 100

I

July 311 04-19 479 l 469 250 261 249 267 312 80 84 80 86 100

I J

Aug. 1 04-19 484 500 262 258 233 262 293 89 88 80 89 100

Aug. 4 04-20 I 603 502 295 290 279 280 352 84 82 79 80 100 I

I Aug. 9 04-20 I 431 523 253 256 260 239 282 90 91 92 85 100

I I !

Ave I i 530 492 280 278 265 274 329 85 85 81 83 100

I

I

I I '

42

TABLE 3.3 Radiative surface temperatures for the daily interval (0400-2000 h) during July and August. All values in °C. The ratio of surface temperature for the burned surfaces to that for the lichen woodland is given in (T0 B/T0 lw)

Date Mean Daily Daily Max. Daily Min

0 1 2 24 81 0 1 2 24 81 0 1 2 24

July 10 48.5 47.6 46.5 41.8 29.3 65.1 64.3 62.7 52.6 39.4 19.6 19.6 19.6 20.8

July 16 43.9 44.0 46.3 37.4 25.9 62.7 61.1 68.2 52.6 36.4 14.6 15.8 15.8 13.2

July 17 35.6 36.4 38.5 33.6 23.7 50.8 49.9 53.4 43.3 32.2 15.8 15.8 17.1 15.8

July 31 35.5 33.3 33.2 28.2 19.6 '56 .9 55.2 54.4 ~3.3 33.2 9.2 8.0 9.5 9.5

Aug. 1 32.9 32.4 34.0 28.6 20.9 52.6 53.4 55.2 41.4 39.4 2.2 2.2 2.2 0.8

Aug. 4 36.3 34.2 35.3 31.4 20.8 57.9 57.0 57 .o 49.0 32.2 2.2 2.2 2.2 0.8

Aug. 9 26.4 25.3 23.4 23.3 15.8 49.9 49.0 45.2 40.4 27.8 2.2 2.2 2.2 2.2

Ave. 37.0 36.2 36.7 32.0 22.3 56.6 55.7 56.6 46.1 34.4 9.4 9.4 9.8 9.0

T0

8/T0

lw 1.7 1.6 1.6 1.4 1.0 1.6 1.6 1.6 1.3 1.0 1.5 1.5 1.5 1.4

81

13.2

10.6

10.6

6.4

0.8

0.8

2.2

6.4

1.0

Figure 3.5

w2o~-------------------------------------------------, 3 (a) _J 0 > 1-'­z tJ 15-0:: w 0..

w 0:: :::> 1- 10 (f)

0 :::: _J

0 C/) 5-

w (.!) <: a: w ~

SURFACE TOP 40 CM TOTAL PROFILE

12·~-----------------·-------------------------------~

II

E!3 0 YR. BURN. !:'ZZa I YR. BURN.

tZ2il 2 YR. BURN. c::J 24 YR. BURN.

10 (33!; 81 YR. BURN.

~ 7 w 0 a: ~ 6

:g 5 z <l: :I: 0 4

w a: ~ 3 C/)

0

::::: 2 _J

0 C/)

. .

. . . . . . . . . . . . . . . . . .

[

I' I

It

·.·

SURFACE

. . .

. . .

. . . .

. . . . . . . . . . .

TOP 40 CM

. . . .

TOTAL PROFILE

(b)

I .,

43

0

I~ c.. c"' zo fT1

c.. c

1\) 01

01 0

01

0

t(u;

~ D I> D I> D

0

I> D c5 I> DO :; I> D 0 :

1>1> D 0 ;,® 1>1> 0000 ••• -;

1>1> 0 o o ~· 1 I> D 0° ••• •"rf,

·l> DO .·r I> D 0 ••• I I> D 0 l I I> D 0 .• t>D <V d.

tf' D ' /" I> D •• • /

I> o ••• 0 I ~ g·g ~ 1> /D 0 I 1>•0 0/ t>." D

00@5

I>: o r I> • D • t i oto/ t> e. 0 I> ~ D

~i I> \ D /0 I> • 0 0 1>". ilo

f~g § I ~go ®1>0 0

"'i I> • 1J 0 (.II I> .. /0 0

'> \(!;£] 0 1> ;ro 0

l>

01 0

c Cl(JI

~ -i

0

0

I> .. ~ 0 ~ i 10 o t> :J.,oo <6 I> ~ 0 0 I> "j D 0 I>~ D 0 I>~ 0 0

iij :;:;

SOIL

Cii lii 1\) 0

Q) "'"' - 0 ~~-< ~-< ::o;o~. ;o

1\) 1\) ~

MOISTURE (%VOLUME)

.., CUMULATIVE WATER LOSS (CM)

0 ~

'-.... ···~Po ............... ••••. ·n.._ . ......"'®-...

............ . ..... .... ····· ...... , ····· .. :"-, .... ' ····'~ ····®

'~·, .. ®::.· ..

~

ct'f'j8: I I 0 • ®t>DO: cor->"'-o -.I> -<-<-<-<-< ;o~;o.::o;u

'\ ............ ·· .. ',

0 -:" 1\)

0 6 RAINFALL (CMl

'9o ' 0 , .ooo

---,.ooo -- oo

' 0 ' 0 'o \" ~

·.. ,, ··. ',

•••• ®,

... "' ..... \1 ... ··.... \ ·· .. \

•• ® . . .

1-:!:j !-"•

OQ c: ti CD

w . 0\

.j::­

.j::-

45

burning, so that, they more closely reflect the 1 and 2 year burns than the mature lichen-woodland. As is evident in Table 3.4 the subsurface temperatures for the burns are warmer than for the lichen woodland in a similar degree to the radiative surface temperatures although the 0 yr. burn still shows some influence from its prior cool forested heritage.

5. Soil moisture

There was no measurable difference in the soil moisture pre- and post­fire at the 0 yr. burn. As this was a relatively hot fire totally burning the surface vegetation, the conclusions is, that the heat of the fire has no substantial effect on the soil moisture.

Figure 3.5(a), gives a comparison in seasonal average soil moisture and soil moisture change between the five stages of burn. The average soil moisture is not greatly different between surfaces. However, the 81 yr. burn stands out as having wetter soils at all depths, whereas the soils of the 24 yr. burn are driest at all depths. The other feature is the wetness of the 0 yr. burn in the surface layers.

Figure 3.5(b) g1v1ng the seasonal change in soil moisture shows more pronounced seasonal patterns. At the soil surface the 0, 24, and 81 yr. burns show the greatest variability in time, whereas at other depths, it is the 0 and 81 yr. burns which show the greatest range, a range that exceeds the inter­mediate aged burns by around 100 percent.

The temporal pattern of the seasonal changes in soil moisture is shown in Figure 3.6. The 0 and 81 yr. burns were substantially wetter than the other burn soils at the beginning of the measurement period on June 8, but after a period of two months, they lost sufficient moisture that they were drier than all but the soils of the 24 yr. b~rn.

6. Evapotranspiration

In Figure 3.6 all sites show the same constant evaporation and evapo­transpiration to the end of June when there is a rapid and substantial divergence, the 0 and 81 year burns maintaining much the same evaporation rate through to the end of the measurement period, whereas the 1, 2 and 24 yr. burns all behaved the same, and showed a large decrease in the evaporation rate during July and August.

Discussion

Since the 1975 season was climatically normal and the measurements spanned most of the growing season the data presented in the report can be accepted as representing the usual effects which accompany burning. Figure 3.7 plots the temporal changes in net radiation, evapotranspiration surface soil temperatures and subsurface soil temperatures, from the mature lichen woodland phase, through initial burning, to partial revegetation, and back to the mature lichen woodland phase, a sequence which covers a time span of approximately 80

TABLE 3.4 Average subsurface soil temperatures (°C) at different depths.

Depth (em)

5

10

20

40

80

160

Ave.

Ts/T:tw

The ratio of temperature for the burned surface to that for the lichen woodland is given in (TB/Thr)

0 Yr. 1 Yr. 2 Yr. 24 Yr.

15.1 15.3 17.2 13.8

13.4 15.1 16.3 13.5

12.4 13.8 14.9 12.2

10.8 12.2 14.3 11.4

8.5 9.6 10.2 9.2

6.1 5.4 6.0 5.9

11.1 11.9 13.2 11.0

1.5 1.6 1.7 1.4

46

81 Yr.

10.2

9.6

9.6

7.9

5.1

3.1

7.6

1.0

0 z <t ...J 0 0 0 ~

2 UJ J: u ...J

UJ cr ::::> 1-<t ~

""" 2 cr ::::> m

0 1-<t cr

47

Figure 3.7

1·80 .-----------------------------------,

1·60

1·40

1·20

1·00

0·80

0·60

0* Net Rodlatloll·

E Evopotronsplralion

To Surface Soil Temperature

'-......._ Ts Subsurface Soli Tomperotura

.................. .......

.................. ..........

................. .................. -...-... -................. 7:. ........ ~

........ 70-... -... -......;:

-......::::::

-;;:::~"""""

~ -·-.. :-:,:-:.-:-~·-.:· ~ ----.... l ----- ····· ~ ----a;--- ·········· !h -------- ········ : \...--------------..--·----- E········ ........ ······· ... ······ .... ~- ........................ •••••• ••••• w •••••••••

0·40~--,-------.------T-----r------~-------r-----~----~------~

0

MATURE

LICHEN WOODLAND

10 20 30 40

YEARS SINCE

50 flO

BURNING

70 80 MATURE

LICHEN WOODLAND

48

years. Perhaps the most striking feature is the decrease in net radiation which accompanies burning and lasts for long periods. This has very important implications in a number of respects. From the energy-balance equation where Q* is partitioned between the latent heat of evapotranspiration LE, sensible heating of the atmosphere H and heating of the subsurface layer G in the form

Q* = LE + H + G (3.7)

it is evident that a reduction in Q* must be accompanied by an equivalent reduction in the terms on the right side of eq. (3.7). Most soil temperatures when the soil is frozen prior to snow-melt, do not differ significantly between the different surfaces, so that the high soil temperatures which are achieved in the early summer in the burns must be accompanied by a large G. This is only an early summer phenomenon, however, and does not persist into the mid-summer period as shown by Kershaw, Rouse and Bunting (1975). Also, since winter soil temperatures are much the same, the strong early suwmer soil heating is matched by a late summer cooling so that over the year G tends to zero. Now the evaporation rate decreases substantially after the first year of burning, due to a lesser soil moisture supply which is largely a result of the early melting of the snow cover over the burns, and due to a lack of transpiring vegetation, which could tap the deeper soil layers. Because the decrease in evaporation which accompanies burning is greater than the decrease in net radiation, it means that the sensible heat flux over burned surfaces is greater than over mature lichen woodland. This would also be expected from the very large temperature gradients which develop between the burned surfaces~and the overlying atmosphere. It is visually evidenced by the dust devils which form frequently over the burned surfaces on hot summer days. These results have important environmental implications. \~ere there are large areas which have been completely burned, the hot dry atmosphere will exert a strong influence on non-burned areas downwind, particularly increasing the summertime moisture stress through an advective heat input which increases the evaporative demand. In a region of interspersed lakes and land surfaces such as the Thor Lake area, burning of the terrestrial areas will greatly increase the evaporation from downwind lakes and ponds and the shallower ones will dry up more quickly.

It is apparent that in subarctic areas burning is a widespread phenomenon and its pronounced effects on the energy-balance are felt for long time periods. As a result the most important microclimate changes which accompany burning should be parameterized as part of land impact and land capability studies. This is particularly important if any program of controlled burning is planned. It is questionable whether large areas of wildfire should be left uncontrolled to burn themselves out, since they will affect not only the immediately burned area, but also large areas downwind. Small fires of limited areal extent are to be preferred. Burning in the early summer is probably best for both seed germination and vegetation regrowth since high soil temperatures combine with more ab~nt soil moisture as evidenced in the 0 yr. site of this study. From

a soil temperature, soil moisture, evaporation standpoint, the intensity of burning does not apparently much matter as shown in the similar behaviour of the 1 yr. and 2 yr. burns.

49

50

Section IV

General Conclusions and Recommendations

The additional field work in the 1975 season firmly established the continued vegetational sequence tentatively outlined in the previous report of this program (Kershaw et al, 1975). Following the two phases of succession dominated initially, by the moss Polytrichum piliferum and then by the lichen Cladonia stellaris, the 75 year old burns are dominated by the lichen Stereocaulon paschale, constituting a phase which lasts up to 150 years when the lichen cover is replaced by a carpet of mosses and herbaceous plants typical of the final recovery phase. This Stereocaulon phase has quite typically an almost pure mat of Stereocaulon paschale; such Stereocaulon woodland does not appear to have been previously reported. It is very fire susceptable, burning at frequent intervals and probably only rarely does it mature to the final closed canopy spruce woodland. Thus the widespread occurrence of Stereocaulon woodland in this region, S.E. of Great Slave Lake, owes its existence to fire. In the absence of forest fires, it would develop into spruce-moss woodland.

Concurrently with the development of the Stereocaulon woodland there is a continued increase in tree density, tree size and peat depth. This leads to the final spruce-moss woodland which characteristically is a closed canopy woodland with large over mature (35m) trees, an abundance of fallen timber following death of the older trees, and a thick layer of peat.

It is significant that caribou grazing is restricted to the Stereocaulon phase, with fire essential to the maintenance of such prime grazing habitat in this area. The wide variance between our results and previous studies of post fire recovery sequences in other parts of Canada, demonstrates the considerable element of geographical uniqueness inherent in all post-fire recoveries and it is clear that generalisations from the N.W.T. situation are not valid.

Burning of the lichen woodland leads to long term microclimatic changes which are of considerable magnitude for periods in excess of a half century in this environment. Net radiation is reduced by 20 percent immediately after burning and this decrease remains at least 10 percent after 50 years. The magnitude of evaporation is reduced by 30 percent, one year after burning, and by about 20 percent after 50 years of the post-fire recovery sequence. The increase in soil temperatures, both surface and subsurface, is in the order of 70 percent immediately following the fire and temperatures are still about 30 percent higher a half century later. Thus burning is accompanied by a hotter soil and a hotter, drier atmosphere for a period exceeding 50 years and if large areas are burned this will exert a strong desiccating influence on non­burned areas downwind which will amongst other things greatly increase evaporation from ponds and small lakes and could lead to a drying up of the shallower ones.

51

The following recommendations are proposed:

1) The only obvious natural resource of the area appears to be caribou which are dependent on the excellent winter grazing of this area. Accordingly it is recommended that the forage utilization, the growth of Stereocaulon mat and the environmental control of this growth should be examined in relation to the management of this area.

2) The degree of uniqueness of fire recovery sequences necessitates similar survey studies to be made in other areas to enable an overall sensible fire policy to be established. Thus, if similar findings were available for Spruce-Cladonia woodland, a level of generality would be established, essential to the development of an overall policy.

3) If controlled burning is planned, fires of limited areal extent are preferable and burning in the early summer is recommended.

4) It is questionable if large-scale wildfires should be left uncontrolled to burn themselves out since they affect not only the immediate environment but will lead to an increased desXcation of areas downwind.

Acknowledgements

It gives us considerable pleasure to acknowledge the dedicated assistance of Eugene Maikawa, Herb Deruyter and Mrs. Margaret Webber in the botanical program and Peter Mills, Rick Bello, Steve Fuller and Bob Van Dijken in the climatic program.

-

52

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Ahti, T. and R.L. Hepburn. (1967). Preliminary studies on woodland caribou range, especially on lichen stands in Ontario. Ontario Dept .

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53

Bryson, R.A., W.N. Irving and J.A. Larson (1965). Radiocarbon and soil evidence of former forest in the southern Canadian tundra. Science 147 (3653): 46-48.

Cayford, J.H. (1970). The role of fire in the ecology and silviculture of jack pine. Proceedings Annual Tall Timbers Fire Ecology Conference, 10: 221-224.

Frissel, S.S. Jr. (1973). The importance of fire as a natural ecological factor in Itasca State Park, Minnesota. Quat. Res. 3: 397-407.

Gannutz, T.P. (1969). Effects of environmental extremes on lichens. Bull. Soc. Bot. Fr. Hem., 1968, Colloq. Lichens, 1967. pp. 169-179.

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Harris, G.P. (1971). The ecology of coricolous lichens. II. The relationship between physiology and the environment. J. Ecol. 59: 441-452.

Heinselman, M.L. (1973). Fire in the virgin forests of the Boundary l.Jaters Canoe area, Minnesota. Quat. Res. 3: 329-382.

Kayll, A.J. (1968). The role of fire in the boreal forest of Canada. Canada Department of Forestry and Rural Development Forestry Branch, Petawawa Forest Experiment Station Information Report, PS-X~7.

Kershaw, K.A. (1968). Classification and ordination of Nigerian savannah vegetation. J. Ecol. 56: 467-482.

Kershaw, K.A. and W.R. Rouse. (1973). Studies on lichen-dominated systems V. A primary survey of a raised-beach system in northwestern Ontario. Can. J. Bot. 51: 1285-1307.

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Kershaw, K.A. and R.W. Shepard.---(1972). Computer display graphics: principal­component analysis and vegetation ordination studies. Can. J. Bot. 50: 2239-2250.

Kilgore, B.M. (1973). The ecological role of fire in Sierran conifer forests. Quat. Res. 3: 496-513.

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Larson, D.W. and K.A. Kershaw. (In press) Studies on lichen dominated systems. XIII. Seasonal and geographical variation of net COz exchange of Alectoria ochroleuca (Hoffm.) Massal.

Lutz, H.F. (1956). Ecological effects of forest fires in the interior of Alaska. U.S. Dept. Agr., Tech. Bull: 1133.

Maikawa, E. and K.A. Kershaw. (1975). The temperature dependence of thallus nitrogenase activity in Peltigera canina. Can. J. Bot. 53: 527-529.

Neal, M.W. and K.A. Kershaw. (1973a). Studies on lichen-dominated systems. III. Phytosociology of a raised beach system near Cape Henrietta Maria, Northern Ontario. Can. J. Bot. 51: 1115-1125.

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Scatter, G.W. (1971). Fire, vegetation, soil and barren-ground caribou relations in Norther.n Canada. In "Proceedings, Fire in the Northern environment -a symposium." (c-:w. Slaughter, R.J. Barney, and G.M. Hansen, Eds.) pp. 209-230. U.S. Dept. Agr. Pac. N.W. For. and Range Expt. Stat., Portland, Oregon.

54

Smith, D.W. and J.H. Sparling. (1966). The temperature of surface fires in jack pine barren. I. The variation in temperature with time. II. The effects of vegetation cover, wind speeds, and relative humidity on fire temperatures. Can. J. Bot. 44: 1285-1298.

Spurr, S.H. (1954). The forests of Itasca in the nineteenth century as related to fire. Ecology 35: 21-25.

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