青藏高原东北边缘亚高山桦木林种群年龄结构

基于10个典型样地的调查数据,对白桦、红桦、糙皮桦3种天然分布于青藏高原东北边缘亚高山带的主要桦木种群年龄结构进行了测度分析．结果表明,3种桦树的年龄结构较复杂,白桦和糙皮桦均属于增长型(发育的前期)或稳定型(发育的中期),而红桦的不同群丛属于增长型(发育的初期)或始衰型(发育的中后期),不同群落之间差异明显; 聚类分析结果显示,青藏高原东北边缘桦木林年龄结构大致可以分为5类,中华柳—糙皮桦林单独聚为第1类,桦叶荚蓬—白桦林和辽东栎—山杨—白桦林聚为第2类,箭竹—白桦林、糙皮桦纯林、红桦纯林、山杨—白桦林聚为第3类,白桦纯林单独聚为第4类,箭竹—红桦林和青杆—白桦林聚为第5类．出现以上情况,不仅与群落本身的性质有关,而且与人为干扰和地区环境差异有关．因此,为保护该地区桦木林,不但要进行适当择伐,减少人为干扰,而且应对其进行长期的定位监测．

Population age structure of birch forests in the subalpine of the northeastern border of the Qinghai-Tibet plateau

The population age structures of birch forests dominated by Betula platyphylla, Betula albo-sinensis and Betula utilis in the subalpine of the northwest border of the Qinghai-Xizang plateau were studied on the basis of data from 10 typical sample plots. The results showed that the age structure of birth forests diversed, the Betula platyphylla forests and Betula utilis forests took growing or stable types (the earlier and middle stage of development);but the forest of Betula albo-sinensis took on growing or senescent types(the earlier and last stage of development). The differences among communities were significant. The birch forests in the subalpine of the northwest border of the Qinthai-Xizang plateau were divided into 5 groups by the clustering analysis of population age structure, which included the first group (Salix cathayana-Betula utilis forest), the second group (Viburnum betulifolium-Betula platyphylla forest, Populus davidiana-Betula platyphylla mixed Quercus liaotungensis forest), the third group (Fargesia nitida-Betula platyphylla forest,pure Betula utilis forest,pure Betula albo-sinensis forest and Populus davidiana-Betula platyphylla forest),the fourth group(pure Betula platyphylla forest) and the fifth group(Fargesia nitida-Betula albo-sinensis forest and Betula platyphylla-Picea wilsonii forest). The above situations were mainly due to human disturbance and environment differences. Therefore, human disturbance should be reduced and the long-term location monitor should be carried on in order to protect the birch forest in the area.