Contrasting climate influences on Nothofagus pumilio establishment along elevational gradients

Abstract

Abstract Predicted warmer temperatures and more frequent extreme climatic events in the southern Andes will affect the dynamics of the Patagonian forests. These environmental changes may differentially alter the probability of Nothofagus pumilio establishment across its altitudinal range of distribution. We monitored fruit rain, seedling emergence and survival at the lower and upper elevation boundaries of N. pumilio forests in Santa Cruz (49° 22'S − 72º 56' W), Argentina. From 2012 to 2018, recruitment and mortality were evaluated biannually in the field. Seedling establishment was tested in relation to drought, based on the SPEI (Standardized Precipitation Evapotranspiration Index), and changes in elevation. Fruit rain was consistently higher at low elevation and the abundance of fruits was not affected by drought intensity. Seedling emergence was ~ 11 to 19 times larger at the upper forest boundary, in particular during years characterized by warm-dry climatic conditions in spring-early summer. In contrast, seedling abundance was ~ 3 times larger at low elevations during relatively cold-wet growing seasons. Over the period 2012 to 2018, dominated by dry-warm spring and summers, survival probability curves for seedlings and juvenile trees were higher at upper than lower elevations. Our results show contrasting effects of climate on tree establishment at the elevation limits, with positive and negative drought effects at high and low elevations, respectively. Predicted increase of extreme drought events during the XXI century could be detrimental for N. pumilio establishment at dry, low-elevation forests.