Effects of Pinus massoniana plantation stand density on understory vegetation and soil properties

By using plot investigation and sampling analysis methods,the understory vegetation and soil properties of Pinus massoniana plantations with different stand density in subtropical area were studied in Daqingshan,Guangxi Province.In the P.massoniana plantations after 14-year natural growth,the understory species diversity index of shrub layer increased with the increase of stand density from 1050 trees·hm-2 to 1800 trees·hm-2,but decreased when the stand density further increased to 2250 trees·hm-2.Herb species diversity index was not sensitive to the stand density change.With increasing stand density,shrub biomass had the same variation trend as that of shrub species diversity index,while herb biomass decreased with increasing stand density.Significant differences(P0.05)were observed in the soil(0-20 cm)physical and chemical properties between the plantations with different stand density.The soil nutrient contents except those of total P and available K and P had the same variation trend with that of the understory species diversity index of shrub layer.Soil available K and P contents fluctuated with stand density,whereas soil total P content was higher when the stand density was 2100 trees·hm-2.In the plantations with moderate stand density(1800 trees·hm-2),soil water-holding capacity and soil porosity were higher,and soil bulk density was lower.