The structure of the forest landscape - a potential determinant of forest fires?

Forest fires in Poland are a serious disturbance of forest ecosystems, generating large natural, social and economic losses. For this reason, it is very important to identify and quantify the factors that may affect the occurrence of fires in the forest environment.

In this paper, it was hypothesized that the structure of the forest landscape significantly affects the occurrence of forest fire. In order to verify this thesis, basic landscape metrics were calculated, reflecting the features of the structure of forest areas in Poland (number of patches, average and median area of patches, length and density of patch edges, patch shape) in relation to three characteristics of forest stands: age class, moisture type and trophic type (data from Poland National State Forest). The analyzes were carried out both at the landscape level and at the level of selected classes. Two approaches were tested to statistically test the impact of landscape structure on forest fires:

1. The metrics were calculated with reference to the test set (A), which was the areas of buffer zones with a radius of 1000 m established around the occurrences of fires from 2015 in one of the Polish voivodeships (Lubelskie voivodeship), registered by the National Forest Fire Information System (NFFIS). The control sets were buffer zones of the same radius, established around randomly placed points: allowing (set B) and not allowing (set C) the overlapping of buffer zones. It was assumed that finding a statistically significant difference between set A and sets B or C allows the acceptance of a research hypothesis in relation to the features of the landscape structure expressed by the analyzed metrics. Therefore, statistical analysis was performed using the Kruskal-Wallis test and the Wilcoxon test for paired observations.

2. The indicators were calculated in relation to the test set (A), which was the areas of buffer zones with a radius of 1000 m established around the occurrences of fires from 2007-2017 in Poland registered by the National Forest Fire Information System (NFFIS). The control set consisted of buffer zones of identical radius established around randomly selected points (selected by stratified random sampling). It was assumed that finding a statistically significant difference between the two groups allows for the positive verification of a research hypothesis in relation to the feature of the landscape structure expressed by the analyzed indicator. For this purpose, statistical analysis was performed using the Mann-Whitney U test.

Preliminary results allowed to identify statistically significant differences between the features of the forest structure in the vicinity of fire sites and the surroundings of control groups, regardless of the method of selection of control groups. This may indicate the important role of the forest structure in shaping the fire risk. Further studies are planned to confirm this conclusion. The research is carried out as part of the PRELUDIUM project no. 2019/35/N/ST10/00279, funding by the National Science Centre Poland.