Litter Production and Nutrient Return in Three Kinds of Plantations in the Upper Reaches of the Jialing River

Litter production and nutrient return studies in three plantations of Pinus eliottii Engelm,Robinia pseudoacacia,mixed stand of Pinus eliottii and Robinia pseudoacacia in the low hills rainstorm district of Guangyuan City have shown that the annual amount of litter of the three plantations ranges from 3 609.6 kg·hm-2·a-1 to 4 917.6 kg·hm-2·a-1,and in addition to Robinia pseudoacacia stand,the leaf litter production of the Robinia pseudoacacia stand and Pinus eliottii and Robinia pseudoacacia stand is the most,with respective 87.45% and 55% shares of their total volume.The litter production of the Pinus eliottii stand displays three peak values,and the Robinia pseudoacacia stand and the mixed stand of Pinus eliottii and Robinia pseudoacacia have two peak values in a year.Annual return production of N and P of the Robinia pseudoacacia stand is the largest,and that of the Pinus eliottii stand is the least.The nutrient return of leaves is the most in each component.Comparison is made among three kinds of forest,which exhibits that the total amount of litter in Pinus eliottii stand and mixed stand of Pinus eliottii and Robinia pseudoacacia is obviously larger than that in Robinia pseudoacacia stand,but their nutrient return amounts are different.Robinia pseudoacacia plantation and mixed stand of Pinus eliottii and Robinia pseudoacacia are significantly higher than that of Pinus eliottii stand,thus indicating that broad-leaved forest has a good the ability of maintaining soil fertility,and needle-leaved and broad-leaved mixed forests have a bigger ability to improve soil fertility.