PARENT SESSION
Contributed Oral Session 36: Late Breaking and Newsworthy Research: Distribution; Disturbance
Monday, August 8, 1:30 PM - 5:00 PM, Meeting Room 524 C, Level 5, Palais des congrès de Montréal

The importance of plant interactions along a disturbance gradient in French coastal dunes.

forey, Estelle^*,1, Touzard, Blaise ¹, Lortie, Chris², Michalet, Richard¹, ¹ Université Bordeaux 1, Talence, France² York University, Toronto, Canada.

ABSTRACT- Positives interactions have been predicted to become more predominant with increasing stress (Bertness et Callaway, 1994) and disturbance (Brooker and Callaghan, 1998). It has also been shown that biotic interactions could be insignificant in very constrained conditions, because of a low vegetation biomass or to increase competition. However there is a lack of studies in harsh and disturbed habitats. In this experiment we studied variation in the importance of facilitation versus the environment along a sand deposition gradient. Four dominant plant communities were selected from disturbed (fore dunes) to stabilized (rear dunes) coastal dunes, using a COA performed on 800 relevés sampled across 280 Km of Atlantic coast. The four dominant species (Ammophila arenaria, Helichrysum stoechas, Corynephorus canescens, Elymus farctus ) were transplanted within the four communities, with and without neighbours. The experiment was repeated twice, from April to September 2003 during a dry year, and from October 2003 to September 2004 to include the sand deposition events occurring in winter. In both experiments, we measured plant survival and growth of all transplants. We observed strong differences in species responses between the two years. Survival was higher in the fore dunes in the first experiment, likely because of the low disturbance regimes and the severe drought, whereas survival was much higher in the stabilized dunes in the second experiment for converse reasons. In contrast, the effects of neighbours were very low both years, as compared to the effect of stress and disturbance. Only the survival of some target species was higher in the presence of neighbours in the stabilized dunes during the first experiment. Species strategy, related to their position along the natural gradient, strongly determined their performance during both experiments. Hence, the abiotic environment was very important in explaining patterns of responses along disturbance gradients in stressful conditions likely due to the low facilitative effect of potential nurse species.

Key words: Dunes, biotic interactions, disturbance, vegetal community