Community Character And Their Environmental Interpretation Of Cerasus Stipulacea — Betula Albosinensis Mixed Forest In The Middle Part Of Qinling Mountains

To investigate the influence of environmental factors on species distribution, biodiversity and natural regeneration of Cerasus stipulacea — Betula albosinensis mixed forest, the importance value and biodiversity of species were calculated and 17 environmental factors,including topography, forest characteristics and soil-litter, were obtained based on field experiment in Qinling Mountains. Redundancy analysis(RDA) and canonical correspondence analysis(CCA) were used to examine relationship between species distribution and environmental factors. Partial RDA and CCA were used to calculate the gross and net effects on species distribution for each environmental factors, and regression analysis was used to discuss the influence of environmental factors on species diversity. The main results showed that:(1) Cerasus stipulacea — Betula albosinensis mixed forest community plant species were abundant. There were 126 species were recorded by investigating 34 plots, belonging to 44 families and 94 genera. Among those there are 1 family, 1 genus and 1 species of Pteridophyta piants, 2 families 5 genera and 7 species of Gymnospermae piants, 41 families, 88 genera and118 species of Angiospermae piants. Divided by life forms, tree layer has 44 species of plants,shrubs layer(including vines) has 36 species of plants, herbs layer has 46 species of plants.(2) The diameter-class distribution of the Cerasus stipulacea—Betula albosinensis mixed forest community present the inverted "J" type, close to the ideal structure. The constructive species Pinus armandii and Betula albosinensis are approximately normally distributed(or single peak curve), with fewer plants in smaller diameter class, as decliend population. The height-class distribution of community and constructive species Pinus armandii and Betula albosinensis presents normal distribution, medium-sized trees were abundant, while trees with small and large diameter were less.(3) At all layers of community, Patrick index showed that: herb layer> tree layer> shrub layer, Simpson index and Shannon-Wiener index showed that: tree layer> shrub layer> herb layer, Pielou index showed that: shrub layer> tree layer> herb layer. The aspect is the main environmental factors for the tree layer species diversity; elevation, slope-position, pH, and litter thickness is the main environmental factors foe shrub layer species diversity; stand density and shrub cover is the main environmental factors for herb layer species diversity.(4) In the middle of Qinling mountains, 17 environmental variables totally explained62.5%, 60.6%, 62.8% in species distribution of tree layer, shrub layer and herb layer ofCerasus stipulacea — Betula albosinensis mixed forest respectively. Overall, available potassium and available nitrogen is key environmental factors for tree species distribution,available potassium is key environmental factors for herb species distribution. The net effect of all environmental factors on the species distribution of shrubs were not significant, but the gross effect of altitude, aspect, slope-position, slope, stand density, shrub cover, organic matter,total phosphorus, total potassium, pH value and litter thickness in shrub species distribution were significant.(5) Cerasus stipulacea—Betula albosinensis mixed forest tree species in the regeneration layer recorded 42 species, including 42 seedlings and 35 saplings, belonging to 13 families and 26 genera. Environmental variables totally explained tree seedlings 50.12% and saplings49.68% in species distribution of Cerasus stipulacea—Betula albosinensis mixed forest. The net effect of all environmental factors on the species distribution of seedlings and saplings were not significant. Seedling species were abundant while sapling were less. The natural regeneration of Betula albosinensis is better than Cerasus stipulacea.