During recent years, the Dutch State Forestry has privatised its forestry operations, which has led to a considerable increase of timber extraction during the breeding season. The impact of felling has been quantified in the Forestry of Smilde. Breeding birds in two adjacent plots (old Pinus sylvestris, an undergrowth of mainly Quercus robur, Betula sp. and Sorbus aucuparia, and a dense carpet of Deschampsia flexuosa and Empetrum nigrum on the forest floor) were mapped and as many nests as possible were located and controlled. In Plot A (4.5 ha) large-scale felling was carried out during mid-May, but not in Plot B (5.6 ha). A significantly larger number of nests failed in Plot A than in Plot B (Table 1), entirely as a result of forestry operations. Moreover, only 8 out of 45 dead standing trees with a diameter at breast height of > 14 cm were spared during felling and timber extraction. Significant damage was inflicted on the undergrowth, particularly as a result of deliberate destruction of undergrowth during harvesting and during timber extraction with a tractor. It is suggested that forestry operations should be restricted to the winter period, i.e. safeguarding breeding birds (and other fauna) between 1 March and 1 September. Dead trees should be retained, especially when still standing.