Agenda - 09-29-1999 - 9e - Laserfiche WebLink

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grow underneath the pines. Eventually these hardwoods become tall enough to reach the canopy, and the shade - intolerant pines die. Aker 100 -150 years most of the pines have fallen. The remaining forest has a canopy with a variety of hardwoods and an understory of shade - tolerant shrubs and herbs, as well as seedlings and saplings of the hardwoods in the canopy. When trees in the canopy die or are blown over by storms, these saplings from the understory respond to the additional light and grow to fill the gap. The prevalence of pines in the forests of Hickory leaves Orange County is a result of human intervention and thus is a rela- tively new feature of our forests. As a consequence, most of our native species of wildlife have adapted for life in hardwood forests and only a few make much use of young forests of pine. During the summer of 1998, a preliminary study of birds in Orange County forests confirmed that mature hardwood forests harbor more species of our native birds than other habi- tats (Appendix D. Birds are an easy group of species to survey and provide a convenient assay for the quality of habitats for wildlife in general. SIZE OF A FOREST IS IMPORTANT The importance of a forest as a habitat for wildlife increases disproportionately with its size. Studies throughout eastern North America have repeatedly confirmed that many forest- inhabiting species do not inhabit tracts of forest below a certain size. Species vary in their sensitivity to forest area. In Maryland, for instance, the chance of finding a Pileated Woodpecker at a randomly chosen point in a forest is greatest for forests over 3000 hectares in size (7000 .� a.a�A .'.a - Red - Shoudered Hawk acres). This 1•' study includedY 3 16 species of birds that are known to be sensitive to the area of forests and that also occur in Orange County (Table 1). Eight of these 16 species are most likely to be encountered in forests over 7000 acres in size. Biologists do not completely understand the reasons why each of these species is sensitive to the area of forests. The explanations probably differ from species to species. In some species, the minimal size of a forest needed for breeding is larger than the area that one nesting pair usually occupies. Possibly the edges of a forest do not provide the habitats that these species need. Edges might have more human disturbance and more small predatory mammals and birds (raccoons, crows, jays) or nest parasites (brown - headed cowbirds which lay their eggs in other species' nests). A small forest has a greater proportion of its total area near an edge than does a large forest. Consequently, species that avoid edges would have more individuals for a given acreage of forest in larger tracts. In other words, forest - interior species are often also area - sensitive species. Usually only so many individuals of one 5