Interference On Grassland Bird Community Structure In The Formation Of Impact

The author studied the influences on grassland bird communities caused by disturbance in the Dagang forestry center in Jilin province during the period from April to July in 2001 and 2002. The contents include: The influences on grassland bird communities structure caused by human activity in big scale; The influences on grassland bird communities structure caused by grazing disturbance; The influences for grassland bird communities structure caused by grazing disturbance; The influences on grassland bird communities structure caused by habitat fragmentation. The main results are as follows:1. The landscape types of grassland changed greatly for the reason that human settled down and developed all kinds of activity, the landscape types of grassland include: village, manpower forest, shrub, farmland and so on, and which increasing the heterogeneity of grassland in big scale. The grassland bird species diversity is higher and the grassland bird community structure is more complicated than before, because there are different bird communities within different landscape type.The bird communities take on successional law in different aged manpower forests in grassland area. The bird community composed by the birds that nest on the ground only in younger manpower forest, and the bird community on ground replaced by birds that nest on trees following the increase of tree age.2. Both the grazing frequency and different number of herd influence the species composition of bird community, the bird species increasing following the decreasing of grazing frequency; and the biomass decreasing following the increasing of grazing frequency, the bird species increasing following the decreasing of the number of herd; thebiomass of bird community decreasing following the increasing of thenumber of herdThe grazing disturbance influences bird community structure by two ways: one way is that grazing disturbance influences bird community directly; the another way is that grazing disturbance influences bird community indirectly by changing vegetation structure and habitat structure. The influences on bird species caused by grazing disturbance are not parallel, because different population has different quantity.3. Habitat fragmentation can lead to forming a new birds community, there are more bird species in community in bigger patches, and 42.8 percent bird species' habitat selection relate to the factor of area. The vegetation structure is an important factor that influences bird community besides area.4. Parts of grassland birds can use post-fire grassland to breed, they need little nest-materials and their nests are simple, or need smaller nest-site area and canopy of vegetation than other birds; but the birds that need more nest-materials with fine nests and nest in areas with higher canopy do not select post-fire grassland to breed in the same year.5. There exists resource partition in nest-site selection among grassland birds, there are three guilds: nesting in higher and denser grass birds guild; nesting in lower and more sparser grass birds guild; middle type birds guild. The nest-selection of birds within same guild is different in some degree. The main factors that influence grassland bird nest-site selection are the height and density of herbage, and the density of Armerniaca sibiric.