Interaction between disturbances and their effects on the recovery of a
heterogeneous Mediterranean landscape in South America
Abstract
Fires and droughts are important drivers of disturbance in Mediterranean
forests. Despite this, there is a gap of knowledge of the effect of
climate change and particularly the interaction of longer periods of
drought with other disturbance processes in remnants of native forests.
As the frequency of these events is expected to increase in the future,
it is important for forest managers to understand recovery patterns and
the response of vegetation to these interactions. The objective of this
work is to quantify the effects of the interaction of drought and fires
in the recovery of Mediterranean-type forests at a local scale in South
America using field data, satellite images, and trend analysis. These
forests have experienced significant reductions in their extension and
fragmentation, and in recent years have been subjected to the longest
drought since there are records and that occurred between 2010 and 2020.
Using a time series of Landsat satellite images (1986-2020) and the fire
registry of the National Forestry Corporation (CONAF) we evaluate the
relationship between the Normalized Difference Vegetation Index (NDVI)
and other vegetation indices with characteristics measured in the field
to evaluate the recovery after a fire event. We quantify the temporal
trends of the NDVI to discover the location, direction, and timing of
the change. In addition, we evaluate the interaction of climate, soil,
and topography by forest type. We observe that the NDVI recovery slope
is less steep in burned areas in the periods after 2015, exacerbating in
topographic conditions of northern exposure (of the southern
hemisphere). Even for the time period analyzed, some areas were reported
where recovery levels still do not show a significant positive trend. We
also observed a difference in the recovery of areas that experienced
high severity fires versus low or intermediate severity fires in a
period of drought, the recovery of areas exposed to a high severity fire
takes twice as long to recover. These results indicate that the
vegetation recovery processes can be negatively affected by the drought
that occurs before, during, and after fires. Our analysis identifies
spatially explicit patterns of short- and medium-term trends in these
“new” regimes of prolonged droughts and fires, providing insight into
forecast warmer and drier weather conditions so that our results can
serve as a general framework for the resource management of these highly
stressed areas, which can be applied to similar Mediterranean
ecosystems.