Figure 1.
Study area corresponds to mainland Portugal located in the Iberian Peninsula, Europe.
Figure 2.
Land cover map (right) and spatial distribution of fire perimeters (left).
The land cover map is based on a simplification of the COS90 legend. Annual crops correspond to 10% of the study area, whereas evergreen oak woodlands, account for 18% of the study area. Forests are mostly
plantations (Eucalypt, 6%) and
stands (Pine, 15%). Shrublands and grasslands account for 16% of the study area. The fire perimeter map represents the annual fire perimeter distribution per year between 1990–1994. Areas that burned twice during the study period account for 2.5% of the overall burned area.
Table 1.
Number of fires and burned area per year.
Figure 3.
Example of the delineation of used and available area.
The used area corresponds to the area actually burned by the fire (grey). The available area (dashed) corresponds to the used area plus the area of a surrounding buffer (white). The buffer is delineated to have the size of the original fire, therefore the available area is twice the used (burned) area.
Figure 4.
Example of one of the 500 maps showing the distribution of randomly placed fire perimeters (grey) overlapping observed fire perimeters (red).
Each observation corresponds to a fire and its associated buffer, which is subjected to a random translation and rotation.
Figure 5.
Jacobs' selection index with values of 0, 1 and −1 corresponding to indifference, preference and avoidance, respectively.
Boxplot represents the 25th percentile (lower end of box) and 75th percentile (upper end of box). The median (50th percentile) is represented by the bar inside the box. Whiskers represent extreme observations and horizontal lines represent outliers - an observation is considered outlier if it is larger than q3w(q3
q1) or smaller than q1
w(q3
q1), where w, q1 and q3 are the whisker length, the 25th and 75th percentiles, respectively.
Figure 6.
Quantile regression for the first significant upper and lower quantiles ( = 0.05) between fire size and fire selectivity (Jacobs' index).
Significant quantiles in the avoidance region (lower) varied between 50th and 10th quantile in evergreen oak woodlands and shrublands, respectively. In the preference region all land cover types presented significant regressions for the 90th quantile. Estimated parameters and significance for each model are presented in Table 2.
Table 2.
Linear regression coefficients for the estimated quantile functions.
Figure 7.
Expected distribution of the mean value of Jacobs' index and slope associated with significant ( = 0.05) lower/upper linear regression quantiles after randomly re-assorting fire perimeters 500 times.
The histograms have common scale in the x-axis for all land cover types and the same scale in the y-axis for the three variables - mean fire selectivity and slope of avoidance/preference regressions. Arrows indicate the position of the real (observed) p-value in the randomized distribution. P-value is calculated as the ranking position of the observed value in the simulated distribution.