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

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.

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

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)

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

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

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.

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

Species Richness (2014)

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P=0.1766

Species Diversity (2014)

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P=0.0305

b a b b

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

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

Trembling Aspen Density (2014)

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a c b c

P

White Spruce Survival (2014)

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P=0.2480

White Spruce Height (2014)

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P=0.7400

White Spruce Diameter (2014)

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P=0.0531

b b ab a

MGM Yield Forecasts – Age 90

25 http://www.rr.ualberta.ca/Research/MixedwoodGrowthModel.aspx

164.9

3.1 68.6

200.8 295

246.9

299 340

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?