Alternatives for creating early seral forest openings

Andrew Gray

What is an early seral forest?

• Early seral=Successional stage after disturbance and before tree canopy closure

• Concept of succession developed from studies of abandoned fields and glacier retreat

• But stand development rarely starts from “bare ground”

• How much disturbance?• What needs to be disturbed?• How long will it remain open?

Important disturbance characteristics

• Disturbance size• Disturbance severity

(residual structure and composition: over- and under-story)

• Available resources: light, soil moisture, nutrients

• Disturbance frequency

Experimental design

Control 1.0 0.6 0.4 0.2

WIND RIVER EXPERIMENTAL FOREST

H.J. ANDREWS EXPERIMENTAL FOREST

Old Growth- McRae Creek ~500 yrs

Gap Size Ratio

x

Old Growth- Trout Creek ~500 yrs Mature- Panther Creek 150 yrs Mature- Martha Creek 95 yrs

Eugene

Spokane

Olympia

Location of 4 stands in study

X

X

Primary set

Secondary set

GAP SIZE =GAP DIAMETER ÷ TREE HEIGHT

Each stand has 2 sets of gap sizes + controls, secondary set was used only for fisheye photographs (and other studies)

Experimental Design

DIAMETERHE

IGH

T

HJA old-growth Trout Ck. old-growth

Panther Ck. mature Martha Ck. mature

Gap light and moisture patterns

N

Light

Soilmoisture

Gap Sizecontrol 0.2 0.4 0.6 1.0

PA

R Q

uant

a (m

ol/m

2/d

ay)

0.0

2.5

5.0

7.5

10.0

12.5

15.0

17.5

20.0 NorthCenterSouth

a a a

a a a a aa

b

b

b

b

abab

Mean daily PAR (+SE), sunny summer days (n=4)

Month and Year of Soil Moisture Sample96959493929190

A S M J J A S O M J J A S O M J J A S O A S S

Soi

l Moi

stur

e (%

vol

umet

ric)

15

20

25

30

35control 0.2 0.4 0.6 1.0

Trends in soil moisture at gap centers, 0-15 cm depth

Fig. 4. Average differences in soil moisture between the clearcut and the forested areas during spring (April-June), summer (July-September), and fall (October-November), 1960-1980. Positive values indicate higher soil moisture in the clearcut area. Solid data points represent significant differences (t~ = 0.05, t-test of inequality) between the clearcut and forested areas.

P.W. Adams et al. 1991. For. Ecol. Manage. 41: 249-263

Soil moisture is temporarily more abundant after clear-cutting

Change in species richness by gap size

5.0

5.5

6.0

6.5

7.0

7.5

8.0

8.5

9.0

9.5

10.0

1990 1991 1992 1993 1994 1995 1997

Year

Mea

n s

pec

ies

rich

nes

s p

er m

icro

plo

t (0

.25

m2)

0

0.2

0.4

0.6

1

Gap sizes

Changes in cover of residual and invader species

0

1

2

3

4

5

6

1990 1991 1992 1993 1994 1995 1997

Year

0

0.2

0.40.6

1

Invader Species

30

40

50

60

70

80

90

100

1990 1991 1992 1993 1994 1995 1997

0

0.2

0.4

0.6

1

Residual SpeciesM

ean

of s

umm

ed c

over

by

spec

ies

grou

p

Residual plants can take the heat

Density of natural regeneration after 3 growing seasons

Den

sity

(#/

m2 )

0.0

0.5

1.0

1.5

2.0

2.5

3.0Douglas-fir

SouthCenterNorth

Gap size

0.0 0.2 0.4 0.6 1.00

10

20

30

40

50

60

70western hemlock

Hemlock in old-growth only.Density in mature stands=0.

Tree canopy closure was faster in old-growth stands

Where’d my early seral go?

Blue River Landscape Study:based on natural-disturbance regimes

Landscape area 1 (N. Fk. Quartz)

Forb species in BRLS study

Landscape Area

Stand type Rank Species Cover SE Species Cover SE Species Cover SE Species Cover SE

1 Mature 1 POMU 3.24 1.68 XETE 0.70 0.44 CIAR4 1.24 0.90 XETE 1.45 0.962 XETE 2.21 1.10 CIVU 0.30 0.21 ANMA 0.61 0.57 CIAR4 1.24 0.803 LIBO3 2.03 1.06 PTAQ 0.09 0.09 XETE 0.58 0.30 PTAQ 0.95 0.644 VISE3 1.00 0.69 CIAR4 0.09 0.08 CIVU 0.47 0.26 POMU 0.56 0.37

2 Mature 1 ATFI 6.52 6.52 ATFI 2.13 2.13 ATFI 6.76 6.762 POMU 5.41 3.08 PTAQ 1.20 1.01 PTAQ 2.56 1.943 PTAQ 3.72 2.72 GATR3 0.43 0.29 POMU 1.28 0.974 LIBO3 2.37 0.71 ADBI 0.35 0.31 CHAN9 1.00 0.60

2 Old-growth 1 LIBO3 3.82 1.50 LIBO3 0.38 0.19 LIBO3 3.83 2.532 COLA3 1.06 0.44 XETE 0.33 0.24 CHAN9 3.13 0.743 POMU 0.55 0.45 VISE3 0.19 0.08 SESY 1.67 0.994 VISE3 0.53 0.17 TRBO2 0.07 0.05 TITR 1.13 1.13

3 Mature 1 ACTR 2.68 0.952 VAHE 2.63 1.243 LIBO3 2.38 1.144 VISE3 1.35 0.26

Pretreatment Year 0 Year 2 Year 4

Teakettle study: burn and/or thin?No thin CASPO thin Shelterwood

No burn

Burn

0

10

20

30

40

50

No thin CASPO Shelterwood No thin CASPO Shelterwood

Mea

n o

f su

mm

ed c

ove

r b

y g

rou

p

herbshrub

Understory response to thinning and burning

No burn Burn

No burn Burn No burn Burn

white fir incense-cedar

Jeffrey pine sugar pine

Is NFMA a barrier to enhancing early-seral forest?

"... all forested lands in the National Forest System shall be maintained in appropriate forest cover with species of trees, degree of stocking, rate of growth, and conditions of stand designed to secure the maximum benefits of multiple use sustained yield management in accordance with land management plans.”

Seral conditions on private lands

Conclusions

• Relatively small gaps or light thinnings in the overstory create local hot-spots of early seral plants, may be beneficial to many organisms.

• Understory density and disturbance affects composition and the speed of crown closure.

• Light prescriptions can be counterproductive; severe or repeated disturbances may be important for maintaining high-quality early seral conditions.