青海仙米林区云杉矮槲寄生空间分布格局及其与环境的关系

Spatial distribution pattern of Arceuthobium sichuanense and its correlation with environment in Xianmi forest region of Qinghai,northwestern China

以青海省仙米林区受矮槲寄生侵染的云杉林为对象,选取有代表性的小班进行样带调查,统计分析发病率后,发现云杉矮槲寄生在小班内从下坡至顶坡危害逐渐加强。按矮槲寄生病级(DMR)分级系统统计样带内所有寄主病级,从柱状图中分析发现,云杉矮槲寄生优先分布于寄主下层树冠,而后不断向上扩展。在整个仙米林区设置标准样地40块,采用Canoco 4.5软件对标准地内病情指数、寄主平均胸径、寄主平均树高、林分类型、混交度、草本盖度、苔藓厚度等响应变量,以及郁闭度、坡度、坡位、海拔等环境因子进行冗余分析(RDA),发现郁闭度、坡度、坡位、海拔和林分组成是影响云杉矮槲寄生在林间发生的主要因子,其中郁闭度与矮槲寄生的病情指数呈显著负相关,坡度、海拔与矮槲寄生的病情指数呈显著正相关,林分组成影响矮槲寄生在林间的发生且在混交度较高的林分内矮槲寄生危害较轻。

Our research focused on Arceuthobium sichuanense and its host in Xianmi forest region, Qinghai of northwestern China, and transect survey method was chosen to investigate the typical sub-compartment. By analyzing the disease incidence, it was found that the hazard of A. sichuanense in the sub- compartment gradually increased from foot to the top of hill. Then all crown-third DMR（ dwarf mistletoe rating） distribution of the host was counted in transect, it was figured out that A. sichuanense preferred to distribute from lower to the upper crown of the host. Forty standard samples were set in Xianmi forest region, taking DMI（dwarf mistletoe idex）, mean DBH, mean height, stand type, mingle index, herb cover, moss depth as response variables, taking canopy density, slope, elevation as environmental factors. It was ascertained that crown density, slope, slope position, elevation and stand type were main factors which had an effect on the outbreak of A. sichuanense by using RDA analysis, in which the canopy density had a significantly negative correlation with the incidence of dwarf mistletoe; the slope and elevation had a significantly positive correlation with the incidence of dwarf mistletoe; the stand composition had an effect on the occurrence of dwarf mistletoe, and the dwarf mistletoe was less harmful in the higher mingling forest.