天山云杉天然林不同林层的空间格局和空间关联性

天山云杉(Picea Schrenkiana)林是天山林区的重要针叶林。研究调查了分别代表天山云杉增长型种群和成熟型种群的两块标准地,应用Ripley's K系数法研究了天山云杉更新层、低林层、中林层和高林层的空间格局和不同林层的空间关联性,并应用Moran's I系数法研究了不同林层的林木高度的空间自相关性。结果表明:所有林层的天山云杉活立木都是显著聚集的,只是发生聚集格局的强度和聚集尺度不同。更新层天山云杉具有最大的聚集强度,从更新层到低林层,聚集强度急速降低。两块标准地中天山桦(Betula tianschanica Rupr.)、天山柳(Salix tianschanica Rgl.)和天山云杉活立木的空间关联性的表现不同。研究结果表明:增长型种群中天山桦、天山柳在所有尺度上都抑制天山云杉的生长;而成熟型种群中天山桦、天山柳在1-10 m尺度内对天山云杉种群的生长没有影响,10-40 m表现出正相关,40 m以上没有表现出明显的关联性;同时天山桦、天山柳基本上在所有尺度都抑制天山云杉的更新。在更新层和低林层间表现出正相关;而更新层和枯死木之间的空间关联性为正相关。

Spatial distribution pattern of different strata and spatial assocations of different strata in the Schrenk Spruce Forest, northwest China

Forests often show clear vertical structure, which has significant influences on a series of structural and functional properties of forest ecosystems, such as seed dispersal ability, canopy radiation condition, photosynthetic capacity, and seedling growth. However, how forest vertical structure changes with horizontal scale has been less studied. The schrenk spruce (Picea schrenkiana) forest is the most wide-spreaded forest type in Xingjiang Province, northwest China. It has profound significance in soil and water conservation, timber harvesting, and climate regulation to the region. Analyzing the horizontal spatial patterns of different tree height classes can provide important insights into understanding the responsible processes that have generated the pattern. We conducted an across-scale analysis of forest structure to characterize the spatial characteristics of two contrasting Schrenk Spruce experimental forests in the campus of Xinjiang Agriculture University. All trees were mapped within a 2.4hm² rectangular plot for the establishing and the mature experimental forests. Species within each plot were identified, and the number of species, tree height, tree age, and DBH (diameter at breast height) were recorded for each individual tree. Based on these measurements, we categorized all the tree individuals into four height classes: the upper, intermediate, lower and sapling classes. The spatial distribution patterns and spatial associations of trees among different height classes were first analyzed using a point pattern analysis method, the Ripley's K statistic. Then, the Moran spatial correlograms were constructed to quantify the spatial pattern of tree height. Our results showed that: i) Schrenk Spruce tree individuals in different height classes distributed in an aggregative fashion. All tree-classes were clumped but at different distances. Bigger trees showed clumped distributions at greater distances. The sapling height class was the most clumped strata and had a positive association with other tree species; ii) Intra- and inter-species spatial associations of Schenk Spruce varied with the height of other tree species and the scale of analysis. Betula tianschanica Rupr. and Salix tianschanica Rgl. inhibited the regeneration of Schrenk spruce at all scales in the establishing population plot, whereas positive associations occurred between the scales of 10 to 40 m in the mature population plot; The intermediate height class and upper height class were spatially independent of Betula tianschanica Rupr. and Salix tianschanica Rgl; iii) Different spatial interactions existed between different height classes and also varied with the scale. Dead Schrenk spruce trees were spatially dependent of other trees at larger scales but independent at smaller scales. Negative repulsion interactions were found between saplings and lower living trees,whereas positive attraction interactions existed between saplings and dead trees.. Saplings were negatively associated with adult trees at almost all scales, iv) The correlogram analysis revealed the spatial gradients for different height classes. The distances of high positive autocorrelation values were 50 meters in both plots. Three distinct peaks of significant positive spatial autocorrelation were found for the sapling height class in the mature population plot, but no particular spatial autocorrelation in the establishing population plot. Negative spatial autocorrelation occurred above the 60m scale for both the intermediate height class and the upper height class, reflecting trees at upper strata tend to occure in larger patches.