Analysis Of Impact Factors On Larch Caterpillar’s Occurrence In Great Xing’an Mountains

Larch caterpillar is a most common defoliator in the Great Xing’an Mountains,affecting the output of forest trees, and abating the forest carbon sinks, and destroying the forest ecological balance. To explore the meteorological conditions, site conditions, and the stand structure influencing on larch caterpillar are of high importance for regional prevention and management of this forest pest. We built a stepwise regression approach to obtain the best model based on the Akaike Information Criterion(AIC) with the occurrence data of larch caterpillars on forestry bureaus and meteorological data from Meteorological stations in the Great Xing’an Mountains. We also built the generalized linear model(GLM) and the maximum entropy model(MaxEnt), using the historical larch caterpillar occurrence data observed during 2008–2012 at the stand level and the site conditions, forest stand structure. So we got the key meteorological factors under different scales, and analyzed their marginal influences on larch caterpillars’ population. The results are showed as follows:We used a stepwise regression approach to obtain the best model based on the Akaike Information Criterion(AIC) at the forest bureau scale. We also identified the key meteorological factors based on relative weight. Our modeling results showed that meteorological conditions during the young larva stage and breeding season played the key role in regulating larch caterpillar’s population. In contrast,meteorological conditions during the middle larva stage and old larva stage had a weaker effect. Specifically, the mean daily relative humidity in young larva stage; the accumulated daily temperature less than-22°C during young larva’s overwintering stage, and the total rainfall in breeding season were the key meteorological factors regulating the population of larch caterpillar, with the first and the third meteorological factors had a positive influence and the second a negative role.We predicted spatial distribution of larch caterpillar under the influences of asuite of environmental variables representing site conditions and forest stand structure at the stand level scale. We also assessed the marginal effect and relative importance of those environment variables. The results showed both GLM and MaxEnt models produced good predictions with the modeling accuracy evaluation criterion AUC(i.e.,area under the receiver operating characteristic curve) being as high as 0.837 and0.862 respectively. Elevation, stand age, soil thickness and larch proportion in a stand were important environmental variables in determining larch caterpillar distribution.Our results indicated the larch caterpillar might have the highest occurrence probability in the area where the elevation is around 300 m and forest is 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.