Fire and Fabiana imbricata shrubland dynamics in northwestern Patagonia

LUCIANA GHERMANDI, N. DUDINSZKY, F.ODDI AND M. DE TORRES CURTH

Campos de Jordao, Brasil

Congreso; 2009 Latin American IALE Conference; 2009

In northwestern Patagonia landscape, environmental heterogeneity and fire regime create a vegetation mosaic of grasslands and Fabiana imbricata shrublands. These environments are economically important because they are used for stockbreeding and forestry. Due to the fact that F. imbricata is an unpalatable shrub, their invasion could decrease grassland productivity. Environmental heterogeneity, like outcrop presence and hare density, increases landscape patchiness and changes the F. imbricata shrublands dynamics. We monitored postfire shrub recruitment and cover in northwestern Patagonia and we studied the long term population dynamics under different environmental conditions trough a matrix model, exploring different fire frequencies and spring precipitation regimes. Direct field observations coupled with aerial photography interpretation and remote sensing data were used to identify the landscape patterns of F. imbricata shrublands.  From the lower to upper zones of the hillside topographic gradient, the vegetation changes from grasslands to F. imbricata shrublands, followed by open Austrocedrus chilensis woodland and ending in rock outcrop.  We hypothesized that F. imbricata acts as a firebreak that creates an Austocedrus chilensis refuge in the upper part of the topographic gradient. This patter could be related to the horizontal fuel discontinuity due to the low cover of the herbaceous layer in the F. imbricata shrublands. If fires are not very intense, the fuel discontinuity would stop the spread of fire coming from the grassland. Dendrochronology techniques were used to determine the age of the shrubland and Landsat TM images coupled with aerial photos were analyzed to determine the pre and post- fire vegetation. The climate change models predict an increase in the frequency of El Niño Southern Oscillation phenomena that could causes more coupled fires - rainy springs in northwestern Patagonia, and consequently, more shrub recruitment windows.  The field monitoring, the results of model and the landscape pattern analysis seem to confirm the close relationships between shrublands presence and fire, though the environmental heterogeneity could act as a filter to the shrubland invasion.