Boreal Mixedwoods Conference, Canada 2012

105/27/13
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

205/27/13
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

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Materials and Methods

905/27/13
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)
1005/27/13

1105/27/13
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

1205/27/13
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

1305/27/13
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
BA
RDI =
•Competition index:
- Broadleaf density and relative density index

1405/27/13
Results

1505/27/13
Results: Permanent sample plots
0
2
4
6
8
10
0 1 2 4
Plot radius [m]
PlotestablishDBH[cm]
one island Slocan Prophet
Establishment spruce DBH(± SEM) by plot radius at three forest stands

1605/27/13
Relationship between establishment DBH and aspen density
- Relationship was significant
y = -0.0001x + 6.9944
R
2
= 0.172
0
2
4
6
8
10
0 5000 10000 15000 20000
Aspen density at plot estab. [stems ha
-1
]
DBHatplotestab.[cm]
One island lake

1705/27/13
y = -0.0601x + 5.7533
R2
= 0.0466
0
2
4
6
8
10
1 3 5 7 9 11 13 15
Aspen RDI at plot establishment
DBHatplotestab.[cm]
Relationship between establishment DBH and aspen RDI
- Relationship was not significant
One island lake

1805/27/13
Slocan
y = -5E-05x + 7.0128
R
2
= 0.0055
0
2
4
6
8
10
12
0 2000 4000 6000 8000 10000 12000
Birch desnity at plot estab. [stems ha
-1
]
DBHatplotestab.[cm]
Relationship between establishment DBH and birch density
- Relationship was not significant

1905/27/13
Prophet
y = -0.0004x + 8.8425
R
2
= 0.0618
0
5
10
15
0 2000 4000 6000 8000 10000
Birch density at plot estab. [stems ha
-1
]
SpruceDBHatplot
estab.[cm]
Relationship between establishment DBH and birch density based
-relationship was also not significant

0
0.4
0.8
1.2
0 1 2 4
Plot radius [m]
MGI[cm]
One island Slocan Prophet
2005/27/13
• 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
ii
B
ii
B
ab i
A a
ab
ii
B
b
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

2105/27/13
Results
Temporary sample plots (TSP)

2205/27/13
• Similar spruce DBH up to 4000 stem ha-1
Results: Temporary sample plots
One island lake
0
2
4
6
8
0 1000 2000 3000 4000 5000 6000 7000 > 8000
Aspen density [stems ha
-1
]
Spruceplotestab.DBH[cm]
Spruce Aspen

2305/27/13
• Similar spruce DBH up to 6000 except density group 5000 stems ha-1
Prophet
0
2
4
6
8
10
0 1000 2000 3000 4000 5000 6000 7000 >8000
Birch density [stems ha
-1
]
Spruceplotestab.DBH[cm]
Spruce Birch

2405/27/13
y = -2E-05x + 0.7257
R
2
= 0.1797
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
Aspen density [stems ha
-1
]
MeanannualDBHgrowth
[cm]
• Aspen density ≥ 10000 stems ha-1
siginificantly impacted the spruce DBH growth
One island lake

2505/27/13
• Aspen RDI ≥ 6 siginificantly impacted the spruce DBH growth
y = -0.0442x + 0.8075
R
2
= 0.3227
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 2 4 6 8 10
Aspen RDI
MeanannualDBHgrowth[cm] One island lake

2605/27/13
y = -5E-05x + 0.9124
R
2
= 0.294
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 2000 4000 6000 8000 10000
Birch density [stems ha
-1
]
MeanannualDBHgrowth
[cm]
Prophet
• Birch density ≥ 5000 stems ha-1
siginificantly impacted the spruce DBH growth

2705/27/13
Prophet
y = -0.0304x + 0.8051
R
2
= 0.0678
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 1 2 3 4 5 6 7 8
Birch RDI
MeanannualDBHgrowth
[cm]
RDI ≥ 5 siginificantly impacted the spruce DBH growth

2805/27/13
Conclusion

2905/27/13
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
4 m
 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

3005/27/13
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

3105/27/13
• Funding provided by
Ministry of Forests and Range, British Columbia
FRBC-Slocan Mixedwood Chair
• Technical support provided by
Kyle Runzer
Cindy Baker
Nicole Balliet
Eduardo Bittencourt
Acknowledgements

3205/27/13
Dr. Amalesh Dhar
Mixedwood Ecology and Management Program
University of Northern British Columbia
3333 University Way, Prince George,
BC, Canada V2N 4Z9
Phone: +1 250 960 5778
Fax: +1 250 960 5339
Email: dhar@unbc.ca
Christopher .D.B. Hawkins
Yukon Research Centre
Yukon College
P.O. Box 2799
Whitehorse, YT, Canada Y1A 5K4
Phone: +1 867 456-8627
FAX: +1 867-456-8672
Email: chawkins@yukoncollege.yk.ca
For further communication

3305/27/13

Boreal Mixedwoods Conference, Canada 2012

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