Boreal Mixedwoods Conference, Canada 2012

104/10/23

Christopher D.B. Hawkins and Amalesh Dhar Mixedwood Ecology and Management Program

University of Northern British Columbia, BC

Impact of variable broadleaf density on spruce growth near Dawson Creek and Fort Nelson in northern

British Columbia

Mixedwood Ecology and Management Program (UNBC) | Christopher D.B. Hawkins & Amalesh Dhar

204/10/23

Outline

1. Traditional woodlands (forest) management in central BC

2. Why Mixedwoods?

3. Objectives

4. Materials and Methods

5. Results

6. Conclusion

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Introduction

Traditional woodlands (forest) management in central BC:

• Historically BC reforestation policies and regulations are conifer-biased

• Broadleaves species (birch, aspen) are routinely removed from plantations

- maximize conifer tree growth

• Maintaining BC’s free-to-grow standard (BC Ministry of Forests 2000 )

“a stand of healthy trees of a commercially valuable species, the growth of

which is not impeded by competition from plants, shrubs or other trees”

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Introduction

Traditional woodlands (forest) management in central BC:

• Stands may only be declared free to grow when 2/3 years have passed since chemical or manual brushing treatment applied

• Avoid administrative delays to revert stand management responsibility back to Crown

• Broadleaf species must be less than 1000 stems ha-1

• Practice has been consistently applied across much of Canada

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Introduction

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Mechanisms for increased complex stand productivity:

b) Complementary interactions (Species that differ in shade tolerance, height growth

rates, crown structure, phenology and rooting depth)

- Rate inter-specific competition is lower than intra-specific

Betula – Picea mixtures in Scandinavia

• Forest health [WPW attack reduced at increased deciduous density (Hawkins et al.2012)]

• better able to deal with disturbances and have greater ecological stability than pure stand

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Objectives

• examine the growth response of spruce to different brushing treatments

as well as varying levels broadleaf (birch & aspen) densities

• test the effectiveness of current BC free-growing criteria

Objectives

804/10/23Mixedwood Ecology and Management Program (UNBC) | Christopher D.B. Hawkins & Amalesh Dhar

Materials and Methods

904/10/23

Site: Fort Nelson (Prophet & Slocan)

Location: Northeastern British Columbia

Zone: BWBS mw2-Dominated by broadleaf (Birch) – conifer (Spruce)

forests and conifer forests

Climate:

Snow: Any time

Mean annual precipitation: 330 – 570 mm (30-40% falls as snow)

Mean annual temperature: -1.4 °C (extremes -51.7 °C, 36.7 °C)

Site : Dawson Creek (One Island Lake)

Location: Northern BC

Zone: BWBS mw1

- Dominated by broadleaf (Aspen) – conifer (Spruce) forests and conifer forests

Climate:

Precipitation: 556 mm (35% falls as snow)

Temperature: 1.8°C (extremes – 43.8°C, 34.5 °C)

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1104/10/23

Temporary sample plots (TSP): One island lake & Prophet

•A systematic grid point was established on each stand at 100 meter interval - the closest undamaged spruce was selected as a target tree and plot centre or- go to nearest spruce in cardinal direction

• Plot radius of TSP: 1.78 m (area: 0.001ha or 10 m2)• Measure what is there (no treatments were initiated)• Height and DBH of target spruce were measured from each TSP• All TSP’s were re-measured in 2009

Experimental design and data collection Two types of sample plots were established

1204/10/23

Permanent sample plots (PSP) (all three sites)

A single tree variable brushing radius experiment was established• target spruce tree was selected as like TSP• a brush-free radius of 0 m, 1 m, 2 m or 4 m was

established around each spruce• prior to brushing, all broadleaf and spruce stems within

the radius were measured (height and DBH)•All PSP’s were re-measured in 2009

Control / 0m radius

1m radius

2m radius

4m radius

1304/10/23

Establishment year

Area Target species

Competitive species

TSP PSP Stand Age

Re-measurement

2007 One Island Lake Spruce Aspen 82 66 14 2009

2007 Slocan Spruce Birch 0 68 17 2009

2007 Prophet Spruce Birch 72 79 16 2009

Relative density index: often used to determine the growth of trees (Ducey & Larson 2003)

Where,

Where, BA = Basal area m2 ha-1, QDM = quadratic mean diameter in cm, 0.4 = a single slope coefficient from Curtis (1982).

4.0)(QMD

•Competition index:

- Broadleaf density and relative density index

Results

Results: Permanent sample plots

0 1 2 4

Plot radius [m]

one island Slocan Prophet

Establishment spruce DBH(± SEM) by plot radius at three forest stands

1604/10/23

Relationship between establishment DBH and aspen density

- Relationship was significant

y = -0.0001x + 6.9944

R2 = 0.172

0 5000 10000 15000 20000

Aspen density at plot estab. [stems ha-1]

One island lake

1704/10/23

y = -0.0601x + 5.7533

R2 = 0.0466

1 3 5 7 9 11 13 15

Aspen RDI at plot establishment

Relationship between establishment DBH and aspen RDI

- Relationship was not significant

One island lake

Slocan

y = -5E-05x + 7.0128

R2 = 0.0055

0 2000 4000 6000 8000 10000 12000

Birch desnity at plot estab. [stems ha-1]

Relationship between establishment DBH and birch density

- Relationship was not significant

Prophet

y = -0.0004x + 8.8425

R2 = 0.0618

0 2000 4000 6000 8000 10000

Birch density at plot estab. [stems ha-1]

Relationship between establishment DBH and birch density based

-relationship was also not significant

0 1 2 4

Plot radius [m]

One island Slocan Prophet

• MGI same at 0 (control), 1 and 2 m radii and increased in 4m radius

• MGI growth - significantly differed at One island & Slocan

- not significantly different at prophet

Mean annual DBH increment (± SEM) by plot radius at three forest stands

Site F P(F) R2

One Island 5.132 0.003 0.20

Slocan 3.861 0.013 0.15

Prophet 2.296 0.085 0.28

Results

Temporary sample plots (TSP)

• Similar spruce DBH up to 4000 stem ha-1

Results: Temporary sample plots

One island lake

0 1000 2000 3000 4000 5000 6000 7000 > 8000

Aspen density [stems ha-1]

] Spruce Aspen

• Similar spruce DBH up to 6000 except density group 5000 stems ha-1

Prophet

0 1000 2000 3000 4000 5000 6000 7000 >8000

Birch density [stems ha-1]

m] Spruce Birch

y = -2E-05x + 0.7257

R2 = 0.1797

0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000

Aspen density [stems ha-1]

• Aspen density ≥ 10000 stems ha-1 siginificantly impacted the spruce DBH growth

One island lake

• Aspen RDI ≥ 6 siginificantly impacted the spruce DBH growth

y = -0.0442x + 0.8075

R2 = 0.3227

0 2 4 6 8 10

Aspen RDI

One island lake

y = -5E-05x + 0.9124

R2 = 0.294

00.20.40.60.8

11.21.41.6

0 2000 4000 6000 8000 10000

Birch density [stems ha-1]

Prophet

• Birch density ≥ 5000 stems ha-1 siginificantly impacted the spruce DBH growth

Prophet

y = -0.0304x + 0.8051

R2 = 0.0678

00.20.4

0.60.8

1.41.6

0 1 2 3 4 5 6 7 8

Birch RDI

RDI ≥ 5 siginificantly impacted the spruce DBH growth

2804/10/23

Conclusion

2904/10/23

Conclusion

Broadleaf competition not as severe as previously thought

DBH unaffected across a range of deciduous densities

MGI was same at control, 1 and 2 m brushing radii and only increased at

It assumed threshold densities much greater than the hypothesized

(>1000 stem ha-1) density that significantly reduced crop tree growth

Greater structural and species diversity

3004/10/23

Consequence of current policy Administrative vegetation control

Unnecessary cost for density management Reduced diversity Potential productivity reduction brushing does not remove all broadleaf (Hawkins et al. 2012)

Conclusion

Final recommendations Leave more broadleaf competition

May reduced management cost Potential productivity increases Greater structural diversity Greater species diversity If risk is considered, mixed stands are a viable investment

3104/10/23

• Funding provided byMinistry of Forests and Range, British ColumbiaFRBC-Slocan Mixedwood Chair

• Technical support provided byKyle Runzer Cindy BakerNicole BallietEduardo Bittencourt

Acknowledgements

3204/10/23

Dr. Amalesh DharMixedwood Ecology and Management ProgramUniversity of Northern British Columbia3333 University Way, Prince George, BC, Canada V2N 4Z9Phone: +1 250 960 5778Fax: +1 250 960 5339Email: dhar@unbc.ca

Christopher .D.B. HawkinsYukon Research CentreYukon CollegeP.O. Box 2799Whitehorse, YT, Canada Y1A 5K4Phone: +1 867 456-8627FAX: +1 867-456-8672Email: chawkins@yukoncollege.yk.ca

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