PARENT SESSION
Poster Session 19: Biodiversity
Wednesday, August 10, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Community- and species-level consequences of competition in an unproductive environment: an experimental approach using boreal forest understory vegetation.

Treberg, Mike^*,1, Turkington, Roy¹, ¹ University of British Columbia, Vancouver, BC, Canada

ABSTRACT- There are contrasting opinions on how important competition is in structuring plant communities in unproductive environments. Some suggest that competition plays no role in these systems while others argue that competition is as important in unproductive systems as it is in productive ones. A major problem in resolving this debate has been the use of experimental procedures that examine the responses of only a few species while ignoring the community response as a whole. We conducted our experiment near Kluane Lake in the Yukon Territory, Canada, during 1999-2002 in a boreal understory community known to be nutrient limited. We tested the hypotheses that competition is important in structuring this unproductive community and that species-level responses are not necessarily consistent with community-level responses. This experiment used a community density series, which varied the density of the entire community while keeping the relative proportions of each species constant. This technique has been successful in simpler annual plant communities; however, this is the first time it has been applied to a perennial plant community. The nine most common species of the understory vegetation (representing 94 % of the total plant cover) had their densities manipulated to as low as 1/16 times the natural density (where it is assumed that competition will have minimal impact) to x2 the natural density. Three levels of fertilizer were applied to vary the productivity. At the community level, density was important in determining structure indicating that plant competition was important in this unproductive environment, however fertilizer treatments had no effect. At the individual species level, increasing community density decreased the abundance of 3 of the 9 species and fertility increased the abundance of 2 species and decreased the abundance of 2 others. Two species showed no response to either density or fertility. These results indicate that experiments using only species-level responses may not be consistent with patterns observed at the community level.

Key words: plant competition, community density series