Abstract: We analyzed the effects of stand and soil factors on shrub and herb diversity across seven stand densities (700-900, 900-1200, 1200-1500, 1500-1800, 1800-2100, 2100-2400, and 2400-2700 trees·hm^-2) of Robinia pseudoacacia plantations in the Caijiachuan watershed. The results showed that, among the seven stand densities, the species richness of understory plants was highest at 900-1200 trees·hm^-2(16.00), being significantly higher than the average richness (12.50) at other stand densities. The coefficience of correlation between stand factors and shrub and herb diversity was 0.739, which had a stronger influence than soil factors (0.671). The influence of stand factors (0.751) was more pronounced at densities of 700-1500 and 1800-2700 trees·hm^-2. However, at the density of 1500-1800 trees·hm^-2, soil factors (0.660) dominated the influence on shrub and herb diversity. The average crown width and stand density were the key stand factors affecting understory shrub diversity, while the average tree height and the average diameter at breast height were the key stand factors influencing herb diversity. Total phosphorus was the key soil factor affecting both shrub and herb diversity. We recommended to set stand density R. pseudoacacia plantation at 900-1200 trees·hm^-2, which would contribute to higher stability and diversity.

Key words: Robinia pseudoacacia; plant diversity; stand factor; soil nutrient factor; grey correlation degree