| Description |
In January 2007, large areas of the Šumava mountain range was affected by hurricane named Kyrill, which caused wind damages to forest stands on several tens of square kilometres. The ample territorial documentation was after the Kyrill hurricane added windthrow maps with the intensity of damage in three categories. The available map documentation was used to create a geodatabase, which was subsequently subjected to special-purpose analyses in order to find out mutual relations between the characteristics of environment and forests on the one hand, and the territorial occurrence of windthrows on the other. The analyses differed in the integration rate of environmental knowledge, resp. in the scope of information describing the correlation between windthrows and environment. The simpliest analyses were focused on the investigation of geostatistic relations among individual factors of natural environment or stands and the rate of damage to forest by wind breakages during the Kyrill hurricane. Parameters of natural environment and forest stands subjected to the analysis of the factor/windthrow relation were as follows: slope gradient, slope aspect, soil depth, site humidity, altitude, forest stand density, age and species composition. A possible relation between the respective factors and the volume of windthrow damages was formulated into a working hypothesis and the analysis was made in such a way that the hypothesis would be either corroborated or declined. Analyses of relations between the individual factors and the size of windthrow damages showed that a relatively loose relation exists between them (i.e. between the given factor and the measure of damage due to windthrows), and a majority of working hypotheses were completely eliminated due to the results of individual analyses. Demarcation of plots with a different rate of susceptibility to windthrow damages in the studied territory offered itself for a more complex form of analysis. Demarcation of the plots of differentiated risk with respect to windthrows dwells on a preliminary hypothesis that although the individual factors may alone contribute to or reduce the risk measure, a combination of otherwise rel. harmless individual factors may increase the risk. The demarcation of risk areas was based on the ball evaluation of relevant environmental factors (slope, aspect, soil depth, site humidity) by means of a 0-3 point scale and by the aggregation of partial evaluations in the locality. The sums were then divided into 5 risk categories. Territories of individual risk categories were then analyzed for their relation to windthrow damages. Not even this analysis demonstrated a significant measure of relation between the values of integrated risk and the windthrow damage to forest. Much better results were provided by the analysis of weighed risk when the territory assessment was entered by individual factors weighed by the measure of the concentration of values (excess) in the division. Thus, the following parameters obtained different weights in the evaluation (according to the 1-3 scale): slope, aspect, relief curvature, distance below the divide, soil depth, site humidity, wind direction, wind velocity, forest stand age, measure of forest stand naturalness, forest stand density and tree diameter. Here it was shown that a narrow measure of relation exists between the occurrence of severe losses due to windthrows and the risk level of individual localities. The second objective of the multivariable analysis of the territory consisted in the research of optimum hauling tracks to collect the windthrown timber from affected plots for conversion. Factors entering the evaluation of the territory and the selection of optimum hauling tracks were as follows: slope gradient, soil carrying capacity, current road pattern and the surface size of windthrows. Optimum tracks for individual hauling technologies were established by using the Distance Tools procedure in ArcGIS SW.
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