Vegetation and fire dynamics during the Holocene in the Southwest Nothofagus forest- steppe ecotone (Argentina)

SOTTILE, GONZALO; BAMONTE, FLORENCIA; MANCINI, M.V; BIANCHI, M. M.

Bariloche

Congreso; VI Southern Connection Congress; 2010

Fire regimes strongly influence structure and functioning of ecosystems. Spatial and temporal patterns of fire activity affect plant communities including floristic and life-form composition, diversity and productivity. The aim of the present study is to reconstruct fire and vegetation dynamics of the Southwest of Santa Cruz province during the Holocene. Pollen and macroscopic charcoal analysis from two peatbogs located at Cerro Frías (50ºS, 72º42’W) and Ea. La Tercera (49ºS, 72º22’W) were carried out. The first bog is located in the forest-steppe ecotone and the second one is placed in the grass-shrub steppe ecotone, eastward of the forest limit. Charcoal records show moderate values in charcoal accumulation rates (CHAR) and CHAR Background up to 6500 cal yrs BP. Between 5000-4000 cal yr BP there is a sharp decrease in fire frequency and CHAR. By 3000-4000 cal yrs BP, the highest CHAR, peak magnitude, and CHAR Background values are recorded. This is associated with a Nothofagus decline (at 50ºS) and a vegetation turnover from a shrubby to a grass steppe (at 49ºS). Around 1000 cal yrs BP fire frequency decreases again and fire activity slightly increases up to the last 400 cal yrs BP. The periods showing low fire frequencies are related to low background values suggesting low biomass availability or fuel discontinuity on the eastern steppe communities. In forest communities at the west, this kind of fire regime seems to be linked to very high or very low precipitation values.