| The gap is the indispensable factor in the long-term change of forest ecosystem, its form and change compose shifting mosaic of forest landscape. To study gap has both theoretic significance and important utility value.Through field investigation of 96 gaps in some permanent plots of mid-subtropical evergreen broad-leaved forest in Wanmulin Nature Reserve of Fujian Province, this paper dealt with gap characteristics and their natural disturbance. The results showed that the area percentage of expanded gap (EG) and canopy gap (CG) in the forest landscape were 50.86% and 16.66% respectively. The natural disturbance frequency for EG and CG were 0.85%·a-1 and 0.28%·a-1 respectively, the return interval of canopy gaps was about 357a. The most popular manner of gap formation in the forest was stem breakage (58.04% of the total), and the second, uprooting (33.48%). Most gaps were formed by two trees, averaging 2.33 trees per gap. The size of most expanded gaps was in the range of 100~300m2, the gaps of 200~300m2 occupied the biggest percentage in area, and those of 100~200m2 occupied the biggest percentage in number. The size of most canopy gaps was under 100m2, the gaps of <50rn2 had the biggest percentage in area and number. The diameter at breast height of most gap makers was 20~30cm.Based on investigation in gaps and non-gaps stands in mid-subtropical evergreen broad-leaved forest in Wanmulin Nature Reserve of Fujian Province, the quantitative characteristics of tree species in gaps and non-gaps stands, the regeneration responses of the major tree species to gaps size were analyzed. The results showed that the quantitative characteristics of tree species were significantly different in gaps and non-gap stands. The responses of 6 main tree species to gap size were different, regeneration densities of Symplocos sumwtia peaked at the gap size of about 100m , regeneration densities of Schima superba peaked at the size of 300~400m2, while those of the other 4 species peaked at the size of 100~200m2.The height niche breadth and the height niche overlaps of main tree species in gaps and non-gaps were studied. The results showed that the height niche breadth of Litsea subcoriacea and Cinnamomum chekiangense in gaps and in non-gap were biggest. The height niche overlaps were greater between those species that had similar biological and ecological characteristics, and vice versa. In gaps, the height niche overlaps between Symplocos sumuntia and Symplocos anomala were the biggest, and comparatively small between Litsea subcoriacea and Adinandra mellettii, Litsea subcoriacea and Distyliopsis dunnii, Cinnamomum chekiangense and Distyliopsis dunnii Distyliopsis dunnii. While in non-gaps, the height niche overlaps between Symplocos sumuntia and Adinandra mellettii were the biggest, and comparatively small between Litsea subcoriacea and Distyliopsis dunnii, Litsea subcoriacea and Adinandra mellettii.The species diversity was measured by means of sjpecies richness, diversity index, species evenness and ecological dominance index, then the relationship between species diversity and gap size was studied. The results showed that the species diversity in gaps was bigger than that of non-gap's, the tree species diversity changed with gap size, revealing a bimodel, the species diversity peaked at the gap size of 200-300 m and about 500 m2; the shrub tree species diversity changed with gap size, revealing a unimodel, the species diversity peaked at the gap size of 400-500 m2.To research the species diversity change in gap gradient , the change of species diversity in gap gradient with different gap sizes with the data from gaps and non-gap. The results showed that species richness and species diversity gradually decreased from the gap center area to non-gap; the change of the tree number and ecological dominance were high in the center and low on edges; the change of species evenness was high on edges and low in the center. The species diversity of all areas of gap got the maximum when the gap size was 200~300m2.The log s... |
