Disturbance History and Dynamics of an Old-Growth Nothofagus Forest in Southern Patagonia

The identification of disturbance events using disturbance chronologies has become a valuable tool in reconstructing disturbance history in temperate forests worldwide; yet detailed reconstructions of disturbance history and their effect on the structure and dynamics of the old-growth Nothofagus forests in the southern Patagonia are scarce. We reconstructed forest dynamics and disturbance history of an old-growth N. pumilio forest in the Toro River Valley, Santa Cruz, Argentina using dendroecological techniques. Since a variation in the disturbance regimes was expected with changing elevation, we sampled at different elevations. We found distinct differences in forest structure, dynamics, and disturbance history with changes in the elevation. The disturbance chronologies provided robust evidence that forests in the study area have been subjected to multiple disturbance events over the last 200 years. Yet, recognizing the agent of disturbance could be difficult in these montane forests and further studies are required. Moreover, disturbances might have varied from frequent, moderate- to high-severity events to less frequent and more severe events. This study represents the first of its kind for the temperate forests of Patagonia.

Short-term effects of wildfire on Patagonian headwater streams

In March–April 2015, the El Cristo fire burned 1228 ha of mixed Nothofagus forest in Los Alerces National Park (Argentine Patagonia). We compared physicochemical variables and community structure of burned and unburned headwater streams. Sampling began shortly after the fire was extinguished and comprised periodic water quality assessments and four visits to collect periphyton and invertebrate samples (May, August, October and December). Water temperature, total dissolved solids, total suspended solids and specific conductance were significantly higher in burned sites, whereas nutrient and oxygen concentrations exhibited no major differences. Chlorophyll a (used as a surrogate for autotrophic periphyton biomass) also did not differ significantly. Macroinvertebrate richness, abundance and diversity showed no differences across sites, but taxonomic composition and densities of sensitive taxa were markedly lower at burned streams. Oligochaetes and amphipods, however, were significantly more abundant in the disturbed reaches. Analysis of functional feeding groups revealed that the relative abundances of shredders and collector-filterers were lower at burned sites, possibly reflecting a shift in detrital input.