林隙对太白山牛皮桦-巴山冷杉混交林内草本植物多样性的影响

Effects of forest gap on herbaceous plant diversity in mixed birch-fir forest of Taibai Mountain

采用CCA梯度排序和随机排列(random permutation)检验方法,分析了太白山牛皮桦-巴山冷杉混交林林隙内草本植物组成随林隙梯度变化的分布特征,以及个体数≥5的55种草本植物分布与凸度、坡度、土壤全N、全P、速效N、有效P、pH值和有机质8个林隙生境变量的关联性.结果表明:太白山牛皮桦-巴山冷杉混交林中,林隙面积占林分总面积的19.8%,林隙密度为20.7个.hm-2,其大小在25.6～279.1 m2,平均面积为93.7 m2.林隙面积扩大可以增加草本层物种丰富度,但林隙内69种草本植物中,大部分在所有林隙中都有分布,有8个物种仅出现在面积>120 m2的大林隙,即草本植物的分布未呈现出沿林隙大小梯度连续变化的规律.个体数≥5的55种草本植物中,27.3%的物种与生境变量显著相关.林隙面积对物种丰富度的增加作用具有随机性.

To better understand the effects of forest gap on the herbaceous species community in a mixed birch-fir forest of Taibai Mountain in Qinling,CCA ordination and random permutation test were employed to analyze the distribution pattern of the species composition across a gradient of gap size,and the relationships between the distribution of 55 herbaceous species with ≥5 individuals and the habitat variables（convexity,slope,and soil total N,total P,available N,available P,pH,and organic matter）.In this forest,gap area occupied 19.8% of the total land area,gap density was 20.7 per hm^2,and gap size varied from 25.6 to 279.1 m^2,with a mean of 93.7 m^2.The species richness in herbaceous layer in gaps was significantly positively correlated with gap size,but of the 69 herbaceous species identified in the gaps,most species were found across all gap sizes,and only eight species were found in larger gaps（ 〉120 m^2）.No successional change was observed in the herbaceous species distribution with gap size.The CCA ordination and random permutation test also showed that 27.3% of the 55 species with abundance ≥5 had significant association with the eight habitat variables.It was concluded that gap size contributed to the species richness,but determined the diversity constitution in random.