Evergreen broadleaved forests, widely distributing from 22° to 40°north and south in latitude, are mainly dominated by species of Fagaceae, Lauraceae, Theaceae and Magnoliaceae, etc. The largest and most typical one is in China, occupying over 2.5 million square kilometers, across more than ten latitudes. Evergreen broadleaved forests are precious in China for their great ecological, economical and social benefits.
Three Gorges Reservoir Area (TGRA), extending from Yichang in Hubei province to Banan district in Chongqing Municipality, involving 20 counties, is about 54000 km². On the northern border of the middle subtropical zone in China, it is affected by subtropical monsoon climate. So the zonal vegetation would be the evergreen broadleaved forests. However, the zonal vegetation in this area has been destroyed enormously due to agricultural activities.
The Castanopsis forest in Shiping Forest Park in Fengdu county, Chongqing municipality, is the remaining typical evergreen broadleaved forest in TGRA. It is the secondary evergreen broadleaved forest which was restored through mountain closure after clear cutting in 1958.
The research plot was located in Shiping Forest Park (29°47′40″N，107°37′40″E). The 1.0 hm² permanent plot was established in 2001, and was divided into 100 subplots. All the trees whose stems are over 2.5 cm in DBH were identified, measured, tagged, and mapped.
The community totally maintained of 39 woody plant species, belonging to 22 families and 29 genera (Tab.1). The dominant families were Lauraceae，Fagaceae, Symplocaceae and Coprifoliaceae. There were total 650 trees in the tree layer. Evergreen spices made up 67.8% of Importance Values, and deciduous trees were 33.2%. Castanopsis carlesii, Castanopsis fargesii and Liquidambar formosana were dominant species.
The size-class distribution of C. carlesii and C. fargesii showed positive pyramidal type (Fig.1), indicating that both of them had rich saplings banks and regenerated well. The mid-size trees of the two Castanopsis species were few. It was supposed to result from the inter- and intra-specific competition. The size-class distribution of L. formosana showed negative pyramidal type, indicating that it lacked saplings banks and regenerated poorly.
Distribution pattern was analyzed using David and Moore’s index, Lloyd’s index and Morisita’s index on plot size of 10 m×10 m (Table 2). Each of the three dominant populations was divided into five classes asⅠ:height<33cm, Ⅱ:height>33 and DBH<2.5 cm, Ⅲ：DBH 2.5～7.5 cm, Ⅳ：DBH 7.5～22.5 cm and Ⅴ：DBH>22.5cm. The distribution patterns of adult trees in the three dominant populations were clumped pattern as a whole, and those of C.carlesii and C.fargesii changed from clumped pattern to random pattern during their upgrowth. While those of L. formosana altered from random pattern to clumped pattern. The results show significant correlation between the distribution pattern and number of trees.