Veranderingen in de broedvogelbevolking van landgoed Mensinge in 1963-2008
Drentse vogels , Volume 23 - Issue 1 p. 4- 19
Mensinge is an Estate in northern Drenthe, consisting mainly of woodland (80%), planted from 1810 (Fig. 1). Oldest stands are of Oak Quercus robur. Beech Fagus sylvatica and Scot's Pine Pinus sylvestris. Younger stand comist of Norwegian Spruce Picea abies and deciduous species. During the study period the stands became older, more diverse, the proportion of broad leaved trees rose and the understory became much demer. Changes that occurred on a much larger scale like the lowering of ground water level and deposition of several nutrients by air and precipitation took also place in Meminge. The estate borders the village of Roden and recreation became more interne in the course of the study area. Up to 1992 the area was visited twice (mapping method) a year during April and May (c. 5 days each month) by Sjoerd Braaksma. Data of a various but substantial number of nest boxes were incorporated in the study (Tabel 1, Appendix 1). During the last years Braaksma commented that his ears became less semitive. In 2002 and2008 the area was visited about eight times per season by severalpersons. Fig. 2-9 and appendix 2 show the changing numbers of breeding birds. Almost all trends can be explained by the local changes in landscape as mentioned above. In general species of young tree stands, sparse vegetation on the forestfloor and species that breed in woodland but mainlyforage in adjacent agricultural area (Fig. 10), declined or disappeared. Species of old stands and (not moist) deciduous woodland in general increased. Some woodland birds increased, but the increase is entirely by the absence of harsh winters during the last decade (Fig. 9). A few species of young stands initially declined, but found new habitat in the newly appearing understory. Besides habitat preferences, heavy species showed the strongest decline (Fig. 11). Overall, numbers of territories remained quite stable over the years, but biomass decreased twofold.
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