Spatial distribution of larch caterpillar and its driving factors

Larch caterpillar (Dendrolimus superans Butler) is one of the most common defoliators in the forests of Great Xing’ an Mountains. Modeling the spatial distribution and elucidating its occurrence mechanisms at landscape scales are of high importance for regional prevention and management of this forest pest. In this research, we analyzed the historical larch caterpillar occurrence data observed during 2008-2012 at the stand level across three forestry bureaus of Great Xing’ an Mountains. We used generalized linear model (GLM) and maximum entropy model (MaxEnt) to predict spatial distribution of larch caterpillar under the influences of a suite of environmental variables representing site conditions and forest stand structure. We also assessed the marginal effect and relative importance of those environmental variables. The results showed that both GLM and MaxEnt models produced good predictions. Although the spatial distribution patterns of the potential larch caterpillar occurrence probability derived from the two models were similar, there were clear differences in pest-prone areas when setting various probability thresholds. Elevation, stand age, soil thickness and larch proportion in a stand were important environmental variables in determining larch caterpillar distribution. Our results indicated that the larch caterpillar might have the highest occurrence probability in the area where the elevation was around 300 m and forest was young or in the middle-age group. The occurrence probability tended to be higher in the stands with a thinner soil layer. Larch proportion in a stand exhibited a positive but nonlinear relationship with the pest occurrence probability.