Succession of the Seedlings of Dominant Species and Diameter-class Structures of Their Populations in Malan Forest Region of the Loess Plateau

The seedlings of several dominant species,Quercus liaotungensis,Pinus tabulaeformis,Betula platyphylla and Populus davidiana,and diameterclass structure of their populations in Malan Forest Region in the Loess Plateau was investigated and this showed that(1) in all the seven typical populations in Malan Forest Region,Quercus liaotungensis seedlings distributed in quantities and renewed well by seed seedling,and different Quercus liaotungensis populations presented different diameter-class structures.They belonged to one stable type in Pinus tabulaeformis and Quercus liaotungensis mixed forest,and one growth type in Populus davidiana forest,Populus davidiana and Betula platyphylla mixed forest,Betula platyphylla forest,Populus davidiana forest and Betula platyphylla and Populus davidiana mixed forest;(2) Pinus tabulaeformis seedlings distributed in quantities in Pinus tabulaeformis and Betula platyphylla mixed forest,Pinus tabulaeformis forest,Pinus tabulaeformis and Quercus liaotungensis mixed forest but the numbers of these seedlings was lean than the numbers of Quercus liaotungensis seedlings in these forests.Of the diameter-class structures of these populations,the diameter-class structure of Pinus tabulaeformis populations belonged to one stable type;(3) Betula platyphylla and Populus davidiana seedlings totaled a small number thus not capable of renewing themselves and the communities mainly composed of Betula platyphylla and Populus davidiana would be gradually replaced by the communities mainly composed of Quercus liaotungensis and Pinus tabulaeformis;(4) Abiotic and biotic factors such as sunshine,water and shrub and herb layers as well as their interactions exerted influences on the distribution and abundance of the seedlings of dominant species in Malan Forest Region.It follows that in Malan Forest Region,the natural vegetation recovery was dominated by Quercus liaotungensis populations,which would consequently play an important role in the natural vegetation recovery.Pinus tabulaeformis populations have played and will play an important role in the vegetation recovery of the region.