The paper presents analysis of tree damage after early thinning in lowland spruce stands. Percentage of tree with damage and weighted damage index (WDI) were considered. Three different thinning operations were analysed, in which different cutting method was applied. The smallest level of damage was observed when short wood system (SWS) was used. There were no significant differences between frequency of damage when full tree (FTS) and long wood (LWS) systems were compared.
The paper studies tree damage after late thinning operation in lowland spruce stands. The research was done in the 4th age class stands, where three different methods of timber harvesting were applied: full tree system (FTS), long wood system (LWS), short wood system (SWS). The lowest level of damage was observed in SWS.
The paper compares the proportion of damaged stands managed under group cutting system (group clear cutting and group shelterwood cutting) with the analogous stands where cuts had not been performed. The empirical material came from the database of the State Forests Information System and covered all forest districts located in Polish lowlands. To evaluate the group cutting a test of differences between the fractions of the elements distinguished in the population was used. The first population involved sawtimber stands in which no group cuts had been per− formed in the past decade. The number of damaged stands was determined for this population and their percentage share was established. A similar procedure was applied to the second pop− ulation of stands in which the group cutting was employed. A damaged stand was assumed to be one in which the volume of windbroken and windfallen trees and deadwood harvested in the past 10 years exceeded the volume set in the given for− mula (1). The performed analysis shows that after several years, the proportion of damaged stands in which gaps were established is significantly higher (57.2%) than in the stands without cut patches (32.9%). Stands with patches demonstrate a significant, statistically greater suscep− tibility to damage from abiotic and biotic factors. The proportion of damaged stands managed under the group shelterwood cutting (60%) is larger than that under the group clear cutting (55.4%). Spruce is the most vulnerable to damage, while alder − the least vulnerable. On average, the higher proportion of damaged forests, mainly pine and oak forests is in the territory of the Bialystok Regional Directorate of the State Forests (RDSF) (tab. 2) being lower in the territory of the Warsaw RDSF where damaged pine stands are more frequent (tab. 3). In areas with a high probability of damage to stands group cut should be limited, and in spruce stands – totally abandoned. Time regimes should also be established applying the group cutting by shortening the period of reconstruction of the entire forest stand.
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