**TANABBO Spot spread**

# Spot spread probability

Probability of bark beetle spot spreading is calculated in several steps. (Fig. 2). First of all actual mask of forest stands is calculated. From the mask of forest stand are subtracted all spots of bark beetle appearances.

Spots with bark beetle appearances are aggregate to spatial coherent groups. Group consists all cells of raster that are somehow connected. Groups are numbered by explicit identificators and for every group areaÂ isÂ calculated.

Potential of bark beetle spreading is calculated by multiple linear regression, what express size of spot under current local conditions. Independent values are volume per hectare, slope, vegetation index NDVI and potential of solar radiation. Before the coefficient of multiple linear regression are calculated the range of values of input rasters must be set to range from 0 to 1. Spots of bark beetle appearances are not setting to this range. Multiple linear regression is using all cells values, which are consider to be inside spots.

The range of values of probability of spot spreading is recalculate to range from 0 to 1. The reciprocal value express resistance potential of spruce stands against bark beetle. This is used to calculate the cumulative cost of new outbreaks of spruce bark beetle. Values are recalculated to range from 0 to 1.

Reciprocal value of cumulative cost is recalculated to range from 0 to 1. It express the probability of bark beetle spreading to surrounding forest stands.