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Impacts of single and repeated glyphosate herbicide applications
on plant community diversity in
an Alberta spruce plantation
Phil Comeau1, Erin Fraser2 and Susan Humphries1
1Department of Renewable Resources, University of Alberta,
Edmonton, Canada
2Alberta Agriculture and Forestry, Edmonton, Canada
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Outline
• Background • Project Objectives • Methods • Results •
Conclusions • Acknowledgements
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Background
• Alberta operates under a Sustainable Forest Management
system.
• Forest operators are required to fully reforest every
harvested opening.
• Generally, operators are expected to regenerate the forest
type that was removed.
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Background
• Alberta reforestation standards mandate two assessments to
evaluate reforestation success: – 4 – 8 years post-harvest; and –
11 – 14 years post-harvest.
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Photo: Marty O’Byrne
• The first assessment is the first and best opportunity to
identify any early issues. Evaluates: – Site occupancy; – Species
composition; and – Seedling height.
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Background • If early reforestation assessment identifies:
– Too few trees – Undesirable species composition – Trees are
too short
• Follow-up action is required. • Several options available,
depending on the
issue and management objectives.
5 http://srs4158clemson.blogspot.ca/2012_05_01_archive.html
Photo: Marty O’Byrne
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Background
• Re-treatment could include implementing a vegetation
management program.
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Background
• Herbicide is a common tool used to control competitive
vegetation.
• Herbicide usage in Alberta:
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Background
• Two of the most common vegetation species that compete with
coniferous seedlings:
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Trembling aspen (Populus tremuloides)
Marsh reed grass (Calamagrostis canadensis)
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Background
• Herbicide has been shown to be effective for reducing the
cover of broadleaved trees, shrubs, herbs and grass.
• However, questions remain:
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– Alberta-specific results?
– Impacts of application timing?
– Longer-term (>10 yr.) plant community impacts?
– Impacts of one vs. two applications? Photo: Marty O’Byrne
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Project Objectives
• Examine the longer-term effects of herbicide (glyphosate)
application timing and frequency on: – Plant community diversity
and development; – Trembling aspen density and size; and – Planted
white spruce survival and growth.
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Methods • Four cutblocks harvested in winter 2003/2004. •
Planted in July 2004 with white spruce. • Mesic-subhygric soil
moisture. • Medium-rich soil nutrient regime.
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• Sites near Calling Lake, Alberta
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Methods
• Four treatments: 1. Untreated (control). 2. Herbicide in first
growing season after harvesting. 3. Herbicide in third growing
season after harvesting. 4. Herbicide in both the second and fourth
growing
seasons after harvesting.
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• All herbicide treatments were aerially applied glyphosate at a
rate of 2.1 kg active ingredient per hectare.
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Methods
• Randomized Incomplete Block Design. • Each of four treatments
replicated 3 – 5 times
across the four harvested areas. • Treatment plots at least 100
x 200 m. • One 30 x 30 m measurement plot established
in a representative area near the centre of each treatment
plot.
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Methods
Measurements were completed in 2004, 2005, 2006, 2008, and
2014.
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Vegetation assessment in quadrant 1 Four – 3.99m radius tree
plots 36 repeatedly measured planted white spruce
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Species Richness (2014)
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P=0.1766
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Species Diversity (2014)
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P=0.0305
b a b b
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Species Composition
• Some differences in vegetation community composition were
observed among treatments.
• Major differences were:
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Paper birch (Betula papyrifera)
Cover
Trembling aspen (Populus tremuloides) Cover & frequency
Woodland horsetail (Equisetum sylvaticum) Cover &
frequency
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Marsh Reed Grass Cover
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Trembling Aspen Cover
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Trembling Aspen Height (2014)
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a b ab b
P=0.0078
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Trembling Aspen Density (2014)
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a c b c
P
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White Spruce Survival (2014)
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P=0.2480
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White Spruce Height (2014)
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P=0.7400
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White Spruce Diameter (2014)
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P=0.0531
b b ab a
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MGM Yield Forecasts – Age 90
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http://www.rr.ualberta.ca/Research/MixedwoodGrowthModel.aspx
164.9
3.1 68.6
200.8 295
246.9
299 340
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Untreated Control
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Treated in Third Growing Season
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Treated in Second + Fourth Growing Seasons
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Conclusions
• Herbicide did not reduce vegetation species richness or
diversity. But – some changes to vegetation community composition
were observed.
• Herbicide application significantly reduced trembling aspen
cover, height and density. No long-term impact to marsh reed grass
cover.
• White spruce height and diameter were highest in areas treated
twice.
• Herbicide can be a useful forest management tool, especially
where the goal is to accelerate the development of a spruce stand
type.
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Acknowledgements
• Funding was provided by: – Alberta Forest Products Association
– Alberta Agriculture and Forestry
• Treatment application was supervised by Vanderwell
Contractors.
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Thank you….Questions?
Impacts of single and repeated glyphosate herbicide applications
on plant community diversity in an Alberta spruce
plantationOutlineBackgroundBackgroundBackgroundBackgroundBackgroundBackgroundBackgroundProject
ObjectivesMethodsMethodsMethodsMethodsSpecies Richness
(2014)Species Diversity (2014) Species CompositionMarsh Reed Grass
CoverTrembling Aspen CoverTrembling Aspen Height (2014)Trembling
Aspen Density (2014)White Spruce Survival (2014)White Spruce Height
(2014)White Spruce Diameter (2014)MGM Yield Forecasts – Age
90Untreated ControlTreated in Third Growing SeasonTreated in Second
+ Fourth Growing SeasonsConclusionsAcknowledgementsThank
you….Questions?