Burn severity influence on post-fire vegetation cover resilience from Landsat MESMA fraction images time series in Mediterranean forest ecosystems.

Fernandez-Manso, A., Quintano, C., Roberts, D.A. (2016) - Burn severity influence on post-fire vegetation cover resilience from Landsat MESMA fraction images time series in Mediterranean forest ecosystems. - Remote Sensing of Environment / Elsevier

Mediterranean ecosystems are adapted to recurrent forest fires by having regeneration mechanisms that overcome
the immediate effects of fire. However, the increasing frequency of fires in most European Mediterranean
countries is challenging the natural regrowth capability of these ecosystems. In this context, monitoring post-fire
vegetation recovery is a priority for forest management and soil erosion control. In this work, a 13-year series
(1999–2011) of Landsat 5 Thematic Mapper (TM)/Landsat 7 Enhanced Thematic Mapper (ETM+) data was
used to model post-fire vegetation recovery as a function of burn severity and to quantify post-fire resilience
as a measure of vegetation cover regrowth. We evaluated a large forest fire located in Spain that burned approximately
30 km2 of Pinus pinaster Ait. in August 1998. 88 field plots of four burn severity levels (unburned, low,
moderate and high) were measured in the field a year after the fire. As a variable representative of vegetation,
we chose the shade normalized green vegetation fraction image (SGV) obtained by applying Multiple
Endmember Spectral Mixture Analysis (MESMA) to the original Landsat TM/ETM+ images. The SGV values
were extracted for the 88 field plots and, after performing a one-way analysis of variance (ANOVA), a Fisher's
Least Significant Difference (LSD) test allowed us to estimate resilience of vegetation cover as the number of
post-fire years exhibiting a statistically significant difference between burned and unburned areas. Next, SGV
values were referenced to unburned control plots values and the vegetation recovery index (VRI) was defined.
The evolution in time curve of VRI for low, moderate and highly fire affected vegetation was fit using trend
models (specifically, an exponential trend for VRI in high and moderate burn severity levels; a linear trend for
low burn severity level, Root Mean Square Error, RMSE = 0.18, 0.13, and 0.09, respectively). We observed that
vegetation cover affected by lowseverity fire recovered to its original state after 7 years, and vegetation cover affected
by moderate severity recovered after 13 years. Vegetation affected by high severity fire was estimated to
recover after 20 years.Weconclude that VRI time series based on multi-temporalMESMAfractions from Landsat
data can be considered a valuable indicator of the post-fire vegetation cover recovery. Its temporal evolution represented
post-fire vegetation cover regrowth adequately and facilitated the estimate of vegetation cover resilience
in Mediterranean forests.

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