Development of Outbreaks of Forest Insects on Different Spatial Scales

Abstract

This work is dedicated to discussing the possibilities of describing the dynamics of forest insect outbreaks on different spatial scales. The properties of outbreaks are considered on a microspatial scale, where the distribution patterns of individuals across different food sources within the boundaries of a local territory or a stand are analyzed and, on a macrospatial scale, where the focus of the analysis are the indicators of the removal of the photosynthetic apparatus (leaves or needles) over the entire territory of the locus, including primary, secondary, and migratory loci. When analyzing the microspatial distribution of caterpillars on trees within loci on different stages of gradation, the model of the distribution of individuals on fodder trees is used as a second-order stage transition. The macrospatial processes that occur during the outbreak development include, first, the growth of an existing outbreak and the emergence of new connected damaged areas of the forest, and, second, the emergence of new unconnected secondary foci. To characterize the outbreaks, their fractal dimension D and the characteristics of the “viscous fingers” on the border of the outbreaks are used. Remote sensing data are used to calculate these characteristics. The proposed approaches can be used to predict the development of a forest insect outbreak. When constructing and verifying the models, we used data from the Siberian silk moth census and the tree colonization rate in the outbreak zone, as well as the remote sensing data on the areas and shapes of the foci in the districts of Krasnoyarsk krai during an outbreak of the Siberian silk moth Dendrolimus sibiricus Tschetv. in 2015–2019.