Inter-annual climatic variability modulates biotic interactions on early Nothofagus pumilio community development

ABSTRACT Background: Despite extensive efforts to understand how biotic interactions and community dynamics respond to changes in environmental conditions many knowledge gaps remain. Assessing biotic interactions involving little studied organisms, such as the biological soil crust (BSC), can widen our understanding of ecosystem functioning. Aims: (1) to quantify the effects of two pioneer communities, one of shrubs and the other of BSC, on the survival and early growth of Nothofagus pumilio tree seedlings on land exposed after glacier retreat, and (2) evaluate how these biotic effects changed according to variations in environmental conditions. Methods: We conducted seedling transplants, at four glacier forelands in the Patagonian Andes across a precipitation gradient in three microsite types: bare soil, soil-covered BSC, low-stature vegetation cover by the creeping dwarf-shrub Empetrum rubrum (ER). Results: N. pumilio seedling survival was related to inter-annual climatic variations, with higher survival in cool-wet years. These effects depended on microsite conditions, with a tendency towards highest survival in BSC. Conversely, microsite type was the dominant factor affecting seedling leaf area, with a trend towards bigger leaves in bare soil. Conclusions: At regional scales, inter-annual climatic variability modulates N. pumilio colonisation. However, microenvironmental differences imposed by cover type introduce important variations. Accounting for interactions between climate and pre-existing communities is essential for predicting climate change impacts on plant community development.