PARENT SESSION
Contributed Oral Session 34: Polar and Alpine Ecology: Climate Effects; Communities
Monday, August 8, 1:30 PM - 5:00 PM, Meeting Room 524 A, Level 5, Palais des congrès de Montréal

Interactions between plant competition, herbivory, and abiotic stress in an arctic-alpine community.

Mitchell, Matthew^*,1, Hik, David¹, Cahill, James¹, ¹ University of Alberta, Edmonton, AB, Canada

ABSTRACT- Interactions among plants can vary from facilitative to competitive. Prevailing theory suggests facilitation will be most prevalant under stressful conditions, yet there can be significant variation in the net effect of interactions. The local-scale factors that cause this variation are unknown, and were the focus of this study. Specifically, we investigated how herbivory, productivity, and abiotic stresses can influence the net effect of plant interactions within an arctic-alpine community. The alpine meadows of the southwest Yukon are an ideal system for studying these interactions. Small mammal herbivores primarily graze close to talus rock piles, creating a strong herbivory gradient. Productivity and abiotic stress gradients also occur within short distances. Individuals of two species, a perennial herb (Artemisia norvegica) and a sedge (Carex consimilis) were marked and subjected to all combinations of herbivory, competition and water availability. These treatments were imposed through use of the natural herbivory gradient, along with experimental manipulations of neighbour density and water availability. Plant growth was followed for two growing seasons by measuring leaf demography and plant biomass. Both species showed increased growth when released from competition, namely increased leaf births and numbers of live leaves. Distance from talus also had strong effects. Artemisia individuals far from talus increased in stem mass with release from competition, while those plants near the talus did not. Close to talus Carex individuals increased their number of leaves much more than plants far from talus. It is unclear if distance effects are due mainly to herbivory or abiotic differences; far from talus snowmelt averages 6 days earlier, and NO₃ flux and soil depth are greater far from talus. Watering effects were very subtle. Relationships between competition, productivity and community composition have yet to be analyzed. Quantifying stress and predicting the outcome of multiple interactions on plant growth is challenging, especially with the small-scale variability of arctic-alpine systems. What is clear is that in this system, for these two species, that competition and its interactions are important factors in limiting the growth of individuals.

Key words: plant competition, arctic-alpine community, Artemisia norvegica, Carex consimilis