Functional responses of white spruce to snowshoe hare herbivory at the treeline

Herbivores can modify the rate of shrub and treeline advance. Both direct and indirect effects of herbivory may simultaneously interact to affect the growth rates of plants at this ecotone. We investigated the effect of snowshoe hare herbivory on the height of white spruce at two treeline locations...

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Published in:PloS one 2018-06, Vol.13 (6), p.e0198453-e0198453
Main Authors: Olnes, Justin, Kielland, Knut, Genet, Hélène, Juday, Glenn P, Ruess, Roger W
Format: Article
Language:English
Subjects:
Animals
Bayes Theorem
Biology
Biology and Life Sciences
Browsing
Climate Change
Earth Sciences
Ecology and Environmental Sciences
Ecosystem
Emergency preparedness
Global warming
Growth rate
Hares - physiology
Herbivores
Herbivory
Influence
Models, Biological
National parks
People and places
Picea - growth & development
Picea glauca
Seedlings
Snowpack
Snowshoe hare
Spruces
Treeline
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Summary:Herbivores can modify the rate of shrub and treeline advance. Both direct and indirect effects of herbivory may simultaneously interact to affect the growth rates of plants at this ecotone. We investigated the effect of snowshoe hare herbivory on the height of white spruce at two treeline locations in Alaska, USA. White spruce is expanding its distribution both upwards in elevation and northward in latitude because of climate warming, and snowshoe hares are already present in areas likely to be colonized by spruce. We hypothesized that herbivory would result in browsed individuals having reduced height, suggesting herbivory is a direct, negative effect on spruce treeline advance. We found an interactive effect between browsing history and spruce age. When young (under 30 years old), individuals that were browsed tended to be taller than unbrowsed individuals. However, older seedlings (over 30 years old) that had been browsed were shorter than unbrowsed individuals of the same age. Hares suppress faster growing individuals that are initially taller by preferentially browsing them as they emerge above the winter snowpack. This reduced height, in combination with increased mortality associated with browsing, is predicted to slow the advance of both latitudinal and altitudinal treeline expansions and alter the structure of treeline forests.
ISSN:1932-6203
1932-6203
DOI:10.1371/journal.pone.0198453