The Development of Outbreaks of Forest Insects on Different Spatial Scale

Abstract

The work is dedicated to the discussion of the possibilities of describing the dynamics of the forest insect outbreaks development on different spatial scales. The properties of outbreaks were 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 were analysed, and on a macrospatial scale, where the focus of the analysis were the indicators of the photosynthetic apparatus (leaves or needles) removal over the entire territory of the locus, including primary, secondary and migratory loci. When analysing the microspatial distribution of caterpillars on trees within loci on different stages of gradation, the model of the individuals’ distribution on fodder trees was used as a second order stage transition. The macrospatial processes that occur during the outbreak development include, firstly, the growth of an existing outbreak and the emergence of new connected damaged areas of the forest, and secondly, the emergence of new unconnected secondary foci. To characterise the outbreaks, their fractal dimension D and the characteristics of the “viscous fingers” on the border of the outbreaks were used. Remote sensing data were used to calculate these characteristics. The proposed approaches can be used to predict the development of forest insects outbreak. When constructing and verifying the models, we used data from the Siberian silkworm census and the trees colonisation rate in the outbreak zone, as well as the remote sensing data on the areas and shapes of the foci in the regions of the Krasnoyarsk Territory during an outbreak of the Siberian silk moth Dendrolimus sibiricus Tschetv. in 2015–2019.