Differential effects of climate variability on forest dynamics along a precipitation gradient in northern Patagonia

Summary 1.  The understanding of the impacts of climate anomalies on demographic processes involved in forest dynamics is becoming a major global change research objective, as climate‐driven demographic changes have the potential to alter ecological processes and change the composition of existing communities. 2.  Here, we test whether the effects of climatic variability on Nothofagus dombeyi forest dynamics differ along the W–E precipitation gradient of northern Patagonia, Argentina, due to different controlling factors along the gradient. 3.  Using a dendroecological approach, we sampled six N. dombeyi stands along the gradient. Tree death, growth release and sapling birth dates were obtained and used to reconstruct stand mortality, canopy disturbance and establishment patterns in each stand. Discrete extreme climatic events were obtained by applying thresholds to meteorological time series. Bivariate event analysis was performed to examine the temporal relationships between climate events and forest demographic and canopy disturbance patterns. 4.  In the xeric region, forest dynamics is driven by drought/heat and humid events. Following drought/heat events we observed standing‐dead tree mortality, releases in growth, and tree establishment episodes. Regional synchrony of these events was coincident with droughts registered for northern Patagonia. However, successful establishment was related to wet periods that occurred after drought events, showing the dependence on favourable periods for growth. For wet regions, demographic patterns showed a temporally uniform pattern but with synchronies at the regional and local scales. Canopy openings produced by fallen trees, and consequent release in growth and establishment, were related to both drought and snowy/windy years. The effect of drought in wet region forests was related mainly to the extreme 1998–99 drought in northern Patagonia. 5.   Synthesis . Climate in northern Patagonia influences N. dombeyi forest dynamics differentially along a precipitation gradient. In xeric forests, strong but relatively short climatic fluctuations impact forest structure through direct effects on tree demography. In wet forests, climatic‐induced mechanical disturbance prevails, driving mortality and subsequent growth and establishment. Considering that recent extreme droughts have the strongest negative impact on N. dombeyi populations at the eastern distributional limits, a change in distribution of this species as a consequence of projected climate change is expected.