Herbaceous vegetation in the understory of the boreal forest: Does nutrient supply or snowshoe hare herbivory regulate species composition and abundance?
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Authors: E. John, and R. Turkington
Date: 1995
Journal: Journal of Ecology
Volume: 83
Number: 4
Pages: 581-590
Summary of Methods: John and Turkington investigated the impact of nutrient addition and mammalian exclosures on the above-ground biomass and species composition of the understory vegetation of the boreal forest of southern Yukon in three field experiments. Experiment 1 was run from 1990-1992 during which time the major herbivore, the snowshoe hare (Lepus americanus), declined dramatically in numbers. It combined the addition of nutrients with the exclusion of herbivores in a 2 X 2 factorial design. Experiment 2 was run over an eight-week period in 1991, and tested the effects of exclosures on above-ground plant biomass at a range of snowshoe hare densities. Experiment 3 examined the effects of long-term (6-yr) exclosures, erected in 1987, on understory species composition. At natural densities the impact of herbivores on vegetation is low compared with the effect of fertilizers. Fertilizer resulted in some species increasing in abundance while others decreased. Where herbivores were at artificially high densities their impact was greater. There is a natural dynamic to the system as some species changed in abundance in control plots during the experiment. The results suggest that both the composition and abundance of herbaceous vegetation in the boreal forest are determined more by the productivity of the site than the activities of mammalian herbivores.
Article Summary / Main Points: None
Vegetation Types:
MLRA Ecoregions:
Agrovoc Control Words: Riparian zones Rangelands Wildlife
Article Review Type: Refereed
Article Type: Experimental Research
Keywords: boreal forest, herbaceous vegetation, herbivory, nutrient addition, snowshoe hare cycle, lepus americanus
Annotation: Experiment 1 was conducted on two sites with sixteen 5 m X 5 m plots at each site randomly divided among four treatments: control, fence only, fertilizer only, and fence with fertilizer. Fertilizer was applied mid May and early June,Surveys of plant cover were done on June 10 and August 18, 1990, June 14 and August 16, 1991, and June 15 and August 11, 1992. Experiment 2 had four paired plots that were set up at each of five sites on May 24, 1991. Live-trapping was done from March-April of each of the years 1990-1992. On July 15-20, 1991, all living above ground biomass was harvested from plots. Experiment 3 had two 4-ha hare-proof exclosures erected in 1987 and 1988. In July of 1992, the vegetation inside and outside each exclosure was sampled. Grazing intensity is not specified.
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