Changes in the natural dynamics of Nothofagus dombeyi forests: Population modeling with increasing drought frequencies

Abstract

Drought-induced episodes of tree mortality can determine forest dynamics and structure, particularly in forests dominated by single species. Short-and mid-Term climate projections indicate that strong changes in annual precipitation may strike more often in northern Patagonia. Data for recruitment, growth, and survival of Nothofagus dombeyi tree individuals were collected at several sites across the Nahuel Huapi National Park in Argentina. We combined mathematically all these different demographic stages into an Integral Projection Model to simulate 100-yr projections of simulated stand structure under different frequencies of extreme drought episodes. We projected total basal area and the number of individuals for three different initial stand types (i.e., young, medium, and old) and for varying drought frequencies (i.e., from 1 to 5 drought events every 100 years). Recruitment into the dbh ≥; 10 cm size class under normal conditions (i.e., without drought) was higher than under episodic drought conditions. In addition, survival under normal conditions was higher than under drought conditions, especially for small trees. Differences in growth were also important, with trees growing more vigorously under normal than under drought conditions. Our simulations predicted that N. dombeyi populations would experience a reduction in tree density in the mid-Term if, as predicted by the IPCC projections, the frequency of future drought events increased. The simulations also showed that in those cases, young stands should suffer the most. Drought-mediated changes may induce a decline in the development of N. dombeyi forests in the mid-and long term by a drastic reduction in tree density.