关键词: 最小面积, 二元指示种分析, 种 - 面积曲线

AbstractThe portion of the Yangtze River valley between Chongqing and Yichang is known as the Three Gorges Reservoir Area (TGRA). The total area of TGRA is approximately 54,000 km². Located in the central sub-tropical zone in China, TGRA has a humid subtropical monsoon climate. Originally, the flora in this area was subtropical evergreen broad-leaved forests dominated by Castanopsis, Cyclobalanopsis, Quercus, Phoebe and Cinnamomum. However, as a result of long-term human activity, such as widespread agriculture, the forest vegetation below 1,000 m a.s.l. has been almost completely destroyed, and the current land cover is dominated by secondary masson pine (Pinus massoniana) forest, cypress (Cupressus funebris) forest, and crop lands. The evergreen broad-leaved forest in Shiping Forest Park (SFP, 29º47′40″N，107 º37′40″E) is the remaining evergreen broad-leaved forest typical of TGRA. Although the forest in SFP is not completely ma-ture or in a steady state, it is a valuable gene bank of native plant species. For the conservation of these for-ests, a good understanding of their biodiversity is needed. We established an 1.0 hm² permanent plot in SFP, and then divided it into 100 subplots. In the plot, 195 species of vascular plants were recorded, belonging to 142 genera and 73 families. Of these, 12 families, 16 genera and 18 species are pteridophytes; 2 families, 2 genera and 2 species are gymnosperms, and 59 families, 123 genera and 174 species are angiosperms. Among the angiosperms, dicotyledon has 49 families, 104 genera and 152 species, and monocotyledon has 10 families, 20 genera and 23 species. The families, ranked by the number of species, are Caprifoliaceae (10), Lauraceae (8), Myrsinaceae (8), Fabaceae (7), Rubiaceae (7), Fagaceae (6), Theaceae (6), Vitaceae (6), Lili-aceae (6), Ericaceae (5), Rosaceae (5), Euphorbiaceae (5), and Gramineae (5). The genera ranked by the number of species are Viburnum (7), Eurya (5), Symplocos (4), and Ardisia (4). In the flora of 61 seed plant families, those of cosmopolitan distribution contribute 34.43%, those of tropical and subtropical distribution contribute 45.90%, and those of temperate distribution contribute 18.03%. In the flora of 126 seed plant gen-era, total tropical distribution elements compose 52.94% of the total, while total temperate distribution ele-ments contribute 45.38%. Thus, the flora of the forest is tropical in nature and has strong temperate affini-ties. According to Raunkiaer′s classification system of life forms, phanerophytes are the most abundant in this community, epiphytes, hemicryptophytes and geocryptophytes come next, while chamaephytes and therophytes are rare. Considering leaf form, 78.35% have simple leaves, while 21.65% have compound leaves. Considering leaf size spectra, microphyllous contributes 48.97%, followed by mesophyllous (41.75%), macrophyllous (6.19%), and nanophyllous (3.09%). In leaf texture spectra, the plants with her-baceous leaves compose 57.22%, while those with leathery leaves compose 30.41%, thick leathery 10.82%, and membranous 1.55%. The plants with entire leaf margins account for 51.03% of the total spe-cies, while those with non-entire leaf margins are 48.97%. As the structure of the stand, from the aerial top to the forest floor, there are three distinct layers, namely tree layer, shrub layer and herb layer. The tree layer can be further subdivided into three recognizable sub-layers: upper, middle and lower tree layers. The upper tree layer is dominated by Castanopsis carlesii, as well as C. fargesii and Liquidamber formosana. Phoebe zhennan, Elaeocarpus decipiens, E. japonicus, Pinus massoniana, Choerospondias axillaris, and Cornus controversa also appear in the upper tree layer. In addition to species appearing in the upper tree layer, Viburnum betulifolium, Camellia oleifera, Cinnamomum wilsonii, Ilex szechwanensis and Turpinia affinis are common in the middle tree layer. Most species of the lower tree layer also appear in the upper two layers, except for a few small trees such as Cornus macrophylla, Viburnum brachybotryum, Pithecel-lobium lucidum, Rhododendron hypoglaucum, Itea chinensis, Pittosporum truncatum, Symplocos stapfi-ana, and S. stellaris.