Structural resistance and functional resilience of the Chaco forest to wildland fires: an approach with MODIS time series

Abstract

Forests have resistance that allows them to resist fires without changing to another state, and resilience that allows them to recover after disturbance. These properties are determined by many structural and functional determinants that interact between them. Despite the importance of structural resistance and functional resilience to wildland fires, few studies have evaluated the combined effect that structural and functional determinants have on them. Our goal was to assess the structural resistance and functional resilience to fire using remote sensing information. We specifically assessed the combined effect of pre-fire vegetation characteristics, burn severity, and post-fire precipitation on forest structural resistance and functional resilience to fire. Eighty-five forest plots of 250 m × 250 m were selected in areas that burned in 2003. For each burned plot, a paired unburned control plot of 250 m × 250 m was selected outside the burned areas. We measured burn severity and post-fire precipitations (2004–2011). We analysed MODIS time series in order to calculate the following pre- (2002) and post-fire (2011) phenological parameters: minimum level of photosynthetic activity per year; maximum level of photosynthetic activity per year; length of growing season per year; integral of annual photosynthetic activity; relative seasonality of photosynthetic activity. Also we detected plots that changed into a shrubland eight years after the fire. Fifty three per cent of burned plots changed from forest into a shrubland state. Results show that the forest structural resistance to fire depends on the balance between the level of severity and the parameters related to pre-fire aboveground net primary production. The impact of pre-fire vegetation characteristics on functional resilience ability was driven by burn severity and it’s interactions with pre-fire productivity and seasonality. Results suggest that changes in forest species composition and aboveground net primary production reduced forest structural resistance and functional resilience to fire.