Dynamics of aspen and Calamagrostiscompetition and implications to white spruce

growth

Phil ComeauDept. of Renewable Resources,

Univ. of Alberta

Major factors limiting growth and survival of planted white spruce

• Short growing season (soil & air temperatures)

• Cold injury (winter/chinook, frost)

• Drought• Flooding• Competition

– adverse effects of two plants that utilize the same resource (one species or both affected).

• Competition– Light– Water– Nutrients– Physical damage– Delayed soil warming

(Calamagrostis)

• Aspen (deciduous) and Calamagrostiscanadensis are the two most prominent competitors

Are aspen and Calamagrostisequal in competitive effects?

Judy Creek Mixedwood Experiment(Pitt, Comeau, Mihajlovich and MacIsaac)

• Objective: To evaluate benefits of woody only vs complete vegetation control, and to test and demonstrate some different approaches for growing mixedwood stands

• Submesic-Mesic site – located in the Swan Hills• Harvested March 2002• Sw planted June 2003• 8 Treatments

– Radial (2 m radius) • RWC - Radial woody control (2002) (triclopyr) (9 reps)• RCC2 -Radial complete control 2 years (glyphosate 2002, and 2003) (7 reps)• RCC4 - Radial complete control 4 years (glyphosate 2002, 2003, 2004 and 2005) (9 reps)

– Reference treatments (3 reps)• BCC - Complete removal of all competition with white spruce (glyphosate annually)• BHC - Complete removal of herbaceous competition only (handweeding and glyphosate)• BWC - Complete removal of woody competition (including aspen) (triclopyr 2002)• Untreated - No competition control• Aspen without competition control or white spruce

• Spruce - Radial treatments planted at 400 sph; – Reference treatments planted at 1600 sph

• Plots 45 x 45 m for response surface and 25 x 25 m for reference treatments

Effects of aspen and understory on spruce growth

VI2006=0.0208 x (Ht2005**2.1973) x exp(-0.3362xLAIo-0.3443xLAIu) n=360 R2=0.817

(3 lines show trends for different values of LAIu; ht2005=50 cm)

0

20

40

60

80

100

120

140

160

180

200

0 1 2 3 4

LAI overstory (LAIo) (m2 m-2)

Stem

vol

ume

incr

emen

t 200

6 (c

m3 y

-1)

vinc2006 0 2.5 5

VI2006=0.0208 x (Ht2005**2.1973) x exp(-0.3362xLAIo-0.3443xLAIu) n=360 R2=0.817

(3 lines show trends for different values of LAIh; ht2005=50 cm)

020406080

100120140160180200

0 1 2 3 4 5 6

LAI understory (LAIu) (m2 m-2)

Stem

vol

ume

incr

emen

t 200

6 (c

m3 y

-1)

vinc2006 0 2 4

Ht2005, LAIo and LAIu all significant in this model (p<0.01)Competition (LAIo and LAIu) accounts for 68% of the variation in growthLAIo (aspen) alone accounts for <25%

VI2006=0.0208 x (Ht2005**2.1973) x exp(-0.3362xLAIo-0.3443xLAIu) n=360 R2=0.817

(for line shown LAIu=LAIo=0)

0

50

100

150

200

250

300

350

0 10 20 30 40 50 60 70 80

Height 2005 (cm)

Stem

vol

ume

incr

emen

t 200

6 (c

m3

y-1)

Commensalism (facilitation) [one plant benefits from presence of another]

• Aspen– Reduce winter

(chinook) injury– Reduce summer frost

injury– Reduce Calamagrostis

cover/lai– Reduce weevil injury

Combining effects of aspen and grass

LAIu vs LAIo for broadcast treated plots only

y = -0.1847x2 + 0.1214x + 3.5763R2 = 0.2068

01234567

0 1 2 3 4 5

LAIo

LAIu

Stem Volume 2006 vs LAIo 2006V2006=110.6*exp(-0.642*LAIo-0.334*LAIu) n=625 R2=0.72

[trees of good vigour only]

020406080

100120

0 1 2 3 4 5

LAIo 2006 (m2/m2)

Stem

vol

ume

2006

(c

m3 )

P V2006 (0 grass) P V2006 (+ grass)V2006 Actual (avg) V2006 BCC Actual (avg)P2 (0 grass) P2 (+grass)

Development of vegetation cover in untreated and BWC at Judy Creek

5.5 4.3 5.1 10.319.4

44.360.4

67.9

25.8 30.2 28.331.5

3.7

6.4

4.75.9

14.617.3 15.8

16.4

1.2

1.4

1.41.1

34.8

50.147.6

49.7

1.5

1.9

0.80.9

0.0

20.0

40.0

60.0

80.0

100.0

120.0

SWNC SWNC SWNC SWNC SWWC SWWC SWWC SWWC

2003 2004 2005 2006 2003 2004 2005 2006

% C

over

grasses forbs shrubs decid trees

Do competitive effects change from year to year?

Model predictions of stem volume increment for a 30 cm tall seedling -each year. (2006+u - based on relationship between LAIu and LAIo)

0

5

10

15

20

25

30

35

40

0 1 2 3 4

LAIo (m2 m-2)

Stem

Vol

ume

Incr

emen

t (c

m3 y

-1)

2006 2005 2004

05

10152025303540

0 2 4 6 8

LAIu (m2 m-2)St

em V

olum

e In

crem

ent

(cm

3 y-1

)2006 2005 2004

2004 R2=0.7802005 R2=0.8332006 R2=0.817

Competitive effects of aspen vary between sites and age classes

(Pritchard 2003, Voicu and Comeau 2006, Filipescu and Comeau [in press])

• Other competitors• Site, soil and

microclimate (differences in environment)

• Variation in importance of facilitative effects or benefits (frost and winter/chinook injury, suppression of understory)

• Other factors?

Some promising treatment options

• Spot treatments• Thin aspen• Herbicide treatment in strips or bands• Successional management• Preharvest aspen control

Plant spruce and thin aspen (age >4)

• Provides protection of spruce from frost and winter injury

• But – grass and shrubs may be a problem and will be difficult to deal with

Spot treatments for mixedwood stands

• Spot site prep (glyphosate or imazapyr)

• Plant and spot tend (herbicide or brush)

• Can enhance early growth of white spruce

Treatment options (Judy Creek)(end of 4 growing seasons)

2006 Untreated BWC RWC RCC2 RCC4 BCC Height (cm) 2006 40.1 c 39.9 c 45.4 b 49.7 a 52.4 a 43.5 bcDiameter (cm) 2006 0.54 e 0.69 d 0.84 c 1.15 b 1.32 a 11.33 a Volume (cm3) 2006 10.7 e 22.1 d 31.5 d 61.6 c 83.7 a 72.6 b LAIu (m2/m2) 2.97 b 3.64 a 2.81 b 1.38 c 0.53 d 0.11 e LAIo (m2/m2) 1.79 a 0.03 b 0.04 b 0.03 b 0.06 b 0.05 b

(largest; smallest)

Treatments – Broadcast herbicide – create spruce dominated stand

• Consider risk of chinookfrost, and weevil injury, need to control both grass and aspen– Best on North aspects in

areas with winter snow cover

• Or• Delay treatments until

after age 4 when spruce are less vulnerable to chinook and frost

Patch or banding treatments to create a “mixture”

• Patch Plant plus 1 or 2 herbicide treatments –patches

• Banded treatments

• ? Optimum dimensions of bands or patches? (Voicu and Comeau 2006 - 15 m width?)

• ?Timing?

Successional Management – Understory Protection

• Harvest aspen at 60+ years and protect/release advance regeneration of white spruce

• Underplant if needed to increase spruce stocking

• Aspen (with understory) –Mixedwood – Aspen

• Need reasonable aspen densities and low understory cover

• Snowshoe hare browsing a problem in some areas and some years

Preharvest aspen control

• Preharvest aspen control using hack and squirt treatments has been found to reduce aspen densities to <2500 stems/ha following harvesting of CD stands

• Preharvest girdling of aspen in conifer dominated stands can also reduce post harvest aspen densities

Conclusions• Competition develops rapidly on boreal mixedwood sites

– need to continue measurement at JC to see what happens in futureyears, need to look at other sites.

• During summers with reasonable precipitation – Aw and C. canadensis exert similar competitive effects, but grass develops more LAI than Aspen and therefore can have a larger impact

• Ignoring understory competitive effects can result in incorrect conclusions regarding aspen competition (flat line response)

• Controlling only aspen and not the grass may limit growth responses (result in no benefit and maybe even reduced growth)

• South facing or exposed sites in chinook prone areas may be problematic for establishing spruce during low snowfall years unless aspen or shrub cover is retained

• Spot, patch and banding treatments show promise for improving early growth of spruce in regenerating mixedwood stands – need to continue to look for ways to do this at reasonable cost

• Yield and Economic implications of these different treatments need to be explored (What are the long term implications of early growth gains?)

Acknowledgements• Funding for various projects: AFPA;

MWMA; WESBOGY; Alberta Plywood; Blue Ridge Lumber Ltd.; Canadian Ecology Centre - Forestry Research Partnership; CANFOR; Dow AgroSciences; Millar Western Forest Products Ltd.; Monsanto Canada; Tolko Industries; Weyerhaeuser; NSERC; CFS

• Milo Mihajlovich, Doug Pitt, Dan MacIsaac and Susan Humphries

• Mihai Voicu, Cosmin Man, Francesco Cortini, Sheelah Griffith