Spatiotemporal dynamics of plant occurrence in an urban forest fragment.

摘要

The study area is an urban forest remnant in the city of Tampere (Finland). The presence of vascular plant species were surveyed in 1980 and again in 2000 within the 5x5 m grid cells covering the whole forest. The forest fragment has been influenced by three types of urban pressure: general ecological conditions (such as eutrophication due to increase of nitrogen), edge effect and local human disturbance. A general and spatially even eutrophication was reflected in the frequencies of C- and S-strategists as a shift towards to the C-point in the CSR triangle. The total number of native species (83 in 1980, 89 in 2000), typical Vaccinium type (VT)-forest species (32 in 1980, 31 in 2000) and aliens (57 in 1980, 68 in 2000) did change, but only to a moderate extent. The number of typical VT-forest species and native species were more common in central parts of the fragment. In terms of the number of species, the forest has been relatively resistant to date to major changes. However, the average number of native plant species per grid cell increased from 13.7 to 14.4, the average number of aliens increased from 2.0 to 4.2 and the average number of typical VT-forest species decreased from 5.5 to 5.0. Natives were spatially concentrated in the centre in 1980, but in 2000 they were more evenly distributed. The edge has offered habitats for new species, but the typical VT-forest species of the original sub-xeric forest are slowly diminishing.