The distribution of diameter class

stand canopy

and undergrowth plant diversity in Robinia pseudoaeacia plantation with different densities in the hilly area of the Loess Plateau were analyzed.Results show that the breast diameter class of stands presents a normal distribution when density of young-aged stands is 2 800 trees per hectare and a nearly normal distribution when density of young and middle-aged stands is 700~900 trees per hectare.Under the condition of the same stand age and site

leaf area index increases

while transparency and diversity and evenness index of plant species beyond forest canopy decrease with increased stand density.