The effect of biotic interactions on boreal conifer recruitment at alpine treeline in central Newfoundland

Abstract

Treeline, the ecotone between forest and alpine or tundra ecosystems, is perceived as the thermal limit to tree growth, reproduction, and survival and in a warming world, we expect treelines to shift to higher elevation and latitudes. Despite increases in temperatures, there has been no ubiquitous change in treeline position. Shifts in treeline position will be dependent on increased recruitment, the production or dispersal of viable seed followed by germination and seedling establishment and survival, at treeline. To examine how biotic interactions constrain or facilitate black spruce and tamarack recruitment at alpine treeline, we conducted a series of observational and experimental studies along an altitudinal gradient in central Newfoundland, Canada. We found treeline population to be simultaneously seed and establishment limited, however if seedlings become established we found seedling survival to be high. Our results highlight the need for multiple factors to align temporally for recruitment to occur.