土壤肥力及地形因子对桂西南喀斯特山地木本植物群落的影响

Effect of soil fertility and topographic factors on woody plant communities in the karst mountains of Southwest Guangxi,China

基于对桂西南喀斯特山地植被的典型群落抽样调查,运用聚类分析和除趋势对应分析(DCA)对样方内胸径≥1.0 cm的木本植物进行数量分类和排序,运用除趋势典范对应分析(DCCA)探讨了土壤肥力及地形因子对木本植物群落空间分布的影响。结果表明:1)聚类分析将森林群落划分为4个类型。2)DCCA第一排序轴突出反映了土壤全氮、碱解氮含量及坡度的变化趋势,第二排序轴主要反映了海拔和全钾的变化趋势,各植物群落类型沿第一排序轴呈有规律的分布。3)在影响植物群落空间格局的因素中,土壤肥力因子对群落格局的解释能力为32.82%,地形因子的解释部分占22.54%,8.98%是土壤与地形因子耦合作用的结果,两者未能解释的部分占53.62%。群落物种多度分布主要受生物之间的相互作用和人为干扰等随机因素所影响。

Southwest Guangxi in China has a well-developed karst geomorphology. Shrubs are predominant and secondary forests and Fengshui woods have a patchy distribution in this area because of disturbance and vegetation degradation.However,little is known about the main environmental factors that affect the spatial distribution of woody plants in this area. To investigate the spatial patterns of woody plant communities and explore how the soils and topography influence them,woody plants with diameter at breast height ≥1. 0 cm,nine soil parameters（ pH,total nitrogen,total phosphorus,total potassium,alkali-hydrolyzable nitrogen,available phosphorus,available potassium,exchangeable calcium and soil organic matter） and five topographic factors（ percentage of covered rock,elevation,slope,aspect and position） were investigated in 44 sample plots in a typical karst region in southwest Guangxi. Multivariate statistical analysis techniques,such as cluster analysis,detrended correspondence analysis（ DCA） and detrending canonical correspondence analysis（ DCCA） were employed in the study. The results clearly demonstrated that： 1） The 44 sample plots were classified into four communities by cluster analysis： Vitex negundo ＋ Cipadessa baccifera ＋ Alchornea trewioides（ I）,V. negundo ＋ Litsea glutinosa ＋ Mallotus philippensis（ II）,Lysidice rhodostegia ＋ Canthium dicoccum（ III） and Excentrodendron hsienmu（ IV）according to the importance values of woody plants. 2） DCA ordination revealed that the compositions of communities I and II were very different from those of communities III and IV,but the composition and structure of community III was similar to that of community IV. 3） DCCA ordination showed that the first axis was significantly positively correlated with soil total nitrogen（ 0. 729）,alkali-hydrolyzable nitrogen（ 0. 713） and slope（ 0. 704）. Soil organic matter（ 0. 671）,percentage of covered rock（ 0. 665） and elevation（ 0. 450） were also significantly positively related to the first DCCA axis. The second axis was significantly correlated with elevation（-0. 614）,total potassium（ 0. 558）,available potassium（ 0. 481） and pH（ 0.410）. The first axis accounted for the largest fraction of variation and mainly showed a gradient of soil total nitrogen,alkali-hydrolyzable nitrogen and slope. The second axis mainly showed variation due to elevation and soil total potassium.Along the first axis,the patterns of communities ranged from shrub communities to secondary forests dominated by E.hsienmu and L. rhodostegia,respectively,accompanied with an increase in altitude,slope,percentage of covered rock and major soil nutrients. The distribution of major woody species with important values ≥1. 0 in the DCCA two-dimensional ordination diagram showed that V. negundo,C. baccifera and A. trewioides were mainly distributed at the bottom of slopes where soil was barren and human disturbance was intensive. Arbor species that were dominant or subdominant in secondary forest,such as E. hsienmu,Walsura robusta and Sapium rotundifolium,mainly existed on the upper slope with a high percentage of covered rock and steep slope gradients where soil was fertile. 4） Effect of soils,topographic factors and their interaction on the spatial patterns of woody plant communities was quantitatively partitioned and it was found that soils accounted for 32. 82% of the variation,topographical factors accounted for 22. 54% and interaction between soils and topography accounted for 8. 98%. Undetermined factors accounted for 53. 62% of variation. This indicated that the distribution of species abundance was mainly affected by biological and anthropogenic factors in the study area.