中国西藏南部乔松林自然更新特征及影响因子

Regenerational Characteristics and Its Impact Factors of the Pinus wallichiana Forest in Southern Xizang

以我国西藏南部的乔松林为研究对象,采用典型样地法,选取17个环境因子,探究影响乔松林天然更新的主要因素。结果显示:(1)幼苗更新密度与坡度呈极显著负相关(P<0.01),与最暖季平均温呈显著负相关(P<0.05),与最干季降水量和地形湿度指数呈极显著正相关(P<0.01);(2)CCA(典型相关分析,canonical correlation analysis)排序表明,最干季降水量和最湿季降水量是影响幼苗更新的主要因子,最湿季降水量和最暖季平均温是影响幼树更新的主要因子;(3)幼苗存活率与群落灌木层盖度呈显著正相关(P<0.05),与乔木平均树高呈显著负相关(P<0.05);(4)中林窗下幼苗更新密度、幼苗高度和幼树更新密度均显著高于其余林窗类型(P<0.05),中林窗下幼树高度略低于小林窗,但仍然高于大林窗与非林窗。

Thorough the typical plot survey in southern Xizang,China,the infleucial factors on natural regeneration of the Pinus wallichiana forests were studied by 17 environmental factors.The results showed that:(1)The seedling density was significantly negatively correlated with the slope(SLO)(P<0.01)and the mean temperature in the warmest season(TWQ)(P<0.05).It was significantly positively correlated with the driest season precipitation(PDQ)and topographic wetness index(TWI)(P<0.01);(2)The CCA(canonical correlation analysis)indicated that precipitation in the driest season(PDQ)and precipitation in the wettest season(PWQ)were the main factors affecting the renewal of seedlings,and the precipitation in the wettest season(PWQ)and the average temperature in the warmest season(TWQ)were the main factors affecting the renewal of saplings;(3)The seedlings’survival rate was significantly positively correlated with the shrub coverage(P<0.05),and was significantly negatively correlated with the averagetree height(P<0.05);(4)Seedling density,seedling height and sapling density in the middle-size forest gaps were significantly higher than other types of gaps(P<0.05).The height of saplings in the middle-size forest gaps was slightly lower than that of small-size gaps,but it was still higher than large-size forest gaps and dense forest.