The paper presents results of studies concerning the effect of environmental conditions expressed in terms of forest site type on thinning intensity. The volume of timber harvested from various site types was compared for types of tending interventions (early thinning for positive selection and late thinning for positive selection). Based on the conducted analyses it was shown that thinning intensity in coniferous forest sites was greater that in broadleaved forest sites. Forest sites also had an effect on the intensity of thinning interventions performed within a given forest site group (broadleaved vs. coniferous forest sites). In broadleaved forest sites the greatest volume of timber was harvested at the fresh mixed forest site (BMś – 27.05 m³/ha), while it was lowest at the fresh coniferous forest site (Bśw – 23.66 m³/ha). In broadleaved forest sites the greatest timber volume was harvested in the moist mixed broadleaved forest (LMw – 20.07 m³/ha) and it was smallest in the fresh broadleaved forest site (Lśw – 9.65 m³/ha). The greatest thinning type ratio in broadleaved forest sites was lower than the lowest thinning intensity in coniferous forest sites. Analysis of the type of conducted silvicultural measures showed that a greater thinning type ratio is observed at late thinning for positive selection. Only in the BMw site a greater volume was harvested during early thinning for positive selection than it was at late thinning for positive selection.

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