Previous research has shown that fires burn certain land cover types disproportionally
to their abundance. We used quantile regression to study land cover proneness to fire
as a function of fire size, under the hypothesis that they are inversely related,
for all land cover types. Using five years of fire perimeters, we estimated conditional
quantile functions for lower (avoidance) and upper (preference) quantiles of fire
selectivity for five land cover types - annual crops, evergreen oak woodlands, eucalypt
forests, pine forests and shrublands. The slope of significant regression quantiles
describes the rate of change in fire selectivity (avoidance or preference) as a function
of fire size. We used Monte-Carlo methods to randomly permutate fires in order to
obtain a distribution of fire selectivity due to chance. This distribution was used
to test the null hypotheses that 1) mean fire selectivity does not differ from that
obtained by randomly relocating observed fire perimeters; 2) that land cover proneness
to fire does not vary with fire size. Our results show that land cover proneness to
fire is higher for shrublands and pine forests than for annual crops and evergreen
oak woodlands. As fire size increases, selectivity decreases for all land cover types
tested. Moreover, the rate of change in selectivity with fire size is higher for preference
than for avoidance. Comparison between observed and randomized data led us to reject
both null hypotheses tested (
= 0.05) and to conclude it is very unlikely the observed values of fire selectivity
and change in selectivity with fire size are due to chance.