Expansion dynamics and performance of the dwarf shrub Empetrum hermaphroditum (Ericaceae) on a Subarctic sand dune system, Nunavik (Canada)

Abstract

Many tundra plant species rely more heavily on clonal propagation than on sexual reproduction. However, if reproduction bottlenecks are alleviated, shifts in the balance between these strategies can occur. To better understand the colonization and expansion dynamics of clonal dwarf shrubs in a rapidly changing environment, we monitored a crowberry population (Empetrum hermaphroditum) on a sand dune system in subarctic Québec. Our objectives were to quantify survival, recruitment, and growth and to determine whether performance varied across a topographic and successional gradient. In 2012, we resurveyed a 6-ha plot where all individuals had been counted in 2007. Along the successional gradient, we measured vegetation cover, soil characteristics, shoot elongation, and seed germination. Over the 2007-2012 period, the population continued to experience abundant recruitment, fast growth, and low mortality, resulting in a 40% increase in population size and a 244 m 2 increase in cover. Performance patterns did not match the dune successional gradient; instead, individuals at intermediate positions showed better growth and produced more viable seeds. The ability of crowberry to successfully establish from seed might have been enhanced by the regional warming observed since the 1990s and seems to be part of a dual strategy allowing crowberry to fill gaps while continuing to spread efficiently on the dune system via clonal growth.