Abstract: This study examined the relationship between environmental factors and composition and richness of the understory species in three typical low-function forests (Pinus tabuliformis, Robinia pseudoacacia and Platycladus orientalis) in Beijing low mountain areas, to explore the response of species to the environmental factors in shrub and herb layers and confirm the primary factors determining the species richness. A total of 34 plots were established for investigation. Canonical correspondence analysis (CCA) was used to elucidate the relationship between species composition and environmental factors (altitude, slope aspect, slope position, slope, and canopy density), partial CCA to calculate the respective importance of environmental factors in species composition, and grey correlation degree analysis to fit the response of species richness to each environmental factor. Our results indicated that the net effects of altitude and slope on species composition in shrub layer were significant (P<0.05), and that of canopy density in herb layer was significant (P<0.05). Slope had the greatest effect on species richness in shrub layer with the grey correlation value 0.734, and altitude showed the highest correlation degree with a value of 0.700 in herb layer. Species composition and richness in each layer responded distinctly to the same environmental factor. Altitude and slope were the main factors affecting species composition in shrub layer among the five factors, and canopy density was the main factor in herb layer. Slope and altitude were the main factors affecting species richness in shrub and herb layers, respectively.

Key words: alpine meadow, saturation threshold., climate warming, nitrogen addition, community production, biomass allocation