Biotic interactions and plant colonisation in the high Arctic

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Biotic interactions both positive (e.g. mutualism, facilitation) and negative (e.g. competition, herbivory) are major structuring forces in natural communities. However, the role of positive interactions still needs to be better defined and integrated in these models. In a rapidly changing environment, species response to change will depend not only on their specific adaptations but also on the biotic interactions involved that can promote or prohibit plant growth and establishment. The present consensus is that with increasing environmental stress the relative importance of positive biotic interactions should increase. In the Arctic, abiotic constraints strongly affect plant community structure and it is generally implied that facilitation may play an important role, especially in plant establishment. Yet, biotic interactions have been rarely quantified in this system. The Arctic offers a rare untapped opportunity to test predictions on the relative importance of positive biotic interactions in structuring plant communities under stressful abiotic conditions.     My long-term objective is to contribute to the development of general ecological theory explaining the dynamics of vegetation change. I focus on high arctic vegetation as a model system in which biological interactions are slowed and environmental constraints more pronounced than at lower latitudes. My previous work revealed that facilitation promotes establishment in cushion plants and biological soil crusts in the High Arctic.  These two nurse-protégé systems promote different species (herbs vs shrubs) and thus can alter to various degree the community structure. My program proposes to initiate unique large scale seed addition experiments with biological soil crust removal to test: 1) the relative importance of seed shortage and safe site limitation; and 2) the balance between competition and facilitation in plant colonisation in two contrasting nurse-protégé systems of the High Arctic. First to address such theoretical questions in this system, this work will also be a significant contribution to the understanding, conservation and future management of Canada's northernmost biome.