秦岭松栎混交林群落的稳定性

松栎混交林是秦岭最为典型的森林类型之一,其稳定性程度对于秦岭生物多样性维持、水碳平衡及气候调节等至关重要。以秦岭火地塘林区松栎混交林28个样地为研究对象,对28个群落指标进行调查,通过主成分分析,得出稳定性综合指数值(F)并进行Ward聚类,采用Mantel-最优聚类簇数分析确定最优聚类簇数,对通过F值聚类的样地进行分组划分,确定稳定性等级。结果表明:松栎混交林的稳定性分为3个等级,稳定性高的样地:F值在0.66—1.13之间,平均林龄58a,占样地总数的39.3%;稳定性中等的样地:F值在-0.28—0.34之间,平均林龄46a,占样地总数的42.8%,稳定性低的样地:F值在-2.34—-1.26之间,平均林龄42a,占样地总数的17.9%。前3个主成分中灌木层、草本层多样性指数、海拔、土壤水分物理指标,林分密度和优势树种胸径荷载较大,是影响群落稳定性的主要因子。F值与乔木层Shannon-Wiener指数、灌木层Simpson指数、草本层物种丰富度线性拟合均达到极显著水平(P0.01),与海拔和坡度多元曲线拟合达到极为显著的水平(R2=0.786,p0.0001)。在海拔1212—1708 m,坡度31—49°的生境,松栎混交林的稳定性较大,在海拔1900 m以上的生境,松栎混交林稳定性较低。

Community stability analysis for the oak-pine mixed forest in Qinling Mountains

Oak-pine mixed forests is one of the most typical types of forest in Qinling Mountains, and it''s stability plays an important role in the biodiversity maintenance, carbon and water balance, and climate regulation in the Qinling Mountains. Common constructive tree species of oak-pine mixed forests in Qinling region include Pinus tabuliformis, P. armandi, Quercus aliena var. acuteserrata, and Quercus acutissima. Community stability of the pine-oak mixed forests is of great importance to their eco-functions regarding biodiversity maintenance, water-carbon balance, climatic regulation, and water-soil conservation in the vast area of Qinling Mountains. However, quantitative evaluation for the community stability of pine-oak mixed forests is presently lacking. The aims of the present study included: (1) to evaluate community stability of oak-pine mixed forest; (2) to explore the relationship between community stability and biodiversity of pine-oak mixed forest; and (3) to clarify spatial distribution pattern of oak-pine mixed forest community stability. Twenty-eight forest plots were selected from a typical oak-pine mixed forest community in the Huoditang Forest Area in Qinling region and surveyed based on the theory of multi-indicator multi-factor comprehensive evaluation. 28 community indicators were investigated in 28 plots, and were analyzed by PCA to get stability index values (F) in Huoditang forest region of Qinling Mountains. F values were clustered by Ward clustering method, and the cluster groups were cut by Mantel- optimal number of clusters (Ward clustering). Stability classes were classified according to the cluster groups. The results showed that: the stabilities were divided into three grades: high stable plots: F value was from 0.66 to1.13, average stand age was 58, accounted for total plot of 39.3%, medium stable plots: F value was from -0.28 to 0.34, average stand age was 46, accounted for total plots of 42.8%, low stable plots: F value was from -2.34 to -1.26, average stand age was 42, accounted for total plots of 17.9%. Among first 3 main components, diversity indexes of shrub and herb layer, elevation, soil moisture physical properties, stand density and DBH of dominant tree species undertook large load, and were key factors that influenced community stability. F value was significantly negatively linear fitted Shannon-Wiener index of the tree layer, and positively linear fitted with of Simpson index of shrub layer and species richness of herbaceous layer (P < 0.01). Multivariate curve fitting reached significant levels between F values and elevation and slope (R²=0.786, P < 0.0001). Greater stability of pine-oak mixed forests was in the habitats at the elevation of 1212-1708 m, and slope of 31-49°, if elevation was above 1900 m, stability of oak-pine mixed forest would be sharply decreased.