环境因子对桂西南蚬木林下植被物种多样性变异的解释

探索林下植被分布格局及其影响因素, 对于天然林保护和森林生物多样性维持机制研究具有重要意义。本文以桂西南喀斯特地区不同蚬木(Excentrodendron tonkinense)天然成熟林为研究对象, 采用植物群落样方调查、单因素方差分析、Pearson相关分析和冗余分析(RDA)等方法, 研究了8个县市蚬木天然成熟林林下植被物种多样性的变异及其对土壤、地形和光照等环境因子的响应。结果表明, 林下植被中灌木层优势种主要有越南槐(Sophora tonkinensis)、鹅掌柴(Schefflera heptaphylla)、毛果翼核果(Ventilago calyculata), 以及乔木层幼苗如蚬木、广西澄广花(Orophea anceps)、岩樟(Cinnamomum saxatile)、金丝李(Garcinia paucinervis)等, 主要来自豆科、五加科、鼠李科、椴树科、番荔枝科、樟科、藤黄科和大戟科等; 草本层优势种主要有肾蕨(Nephrolepis cordifolia)、石山棕(Guihaia argyrata)、崖姜(Pseudodrynaria coronans)、柔枝莠竹(Microstegium vimineum)、水蔗草(Apluda mutica)、沿阶草(Ophiopogon bodinieri)等, 主要来自肾蕨科、棕榈科、槲蕨科、禾本科、百合科、铁角蕨科和鳞毛蕨科等。土壤pH值、土壤含水量(SWC)、土壤全钾(TK)、土壤全磷(TP)和坡度(SLO)是林下植被物种多样性的主要影响因素, 它们分别解释了林下植被物种多样性32.3%、16.1%、9.7%、8.6%和8.6%的变异。灌木丰富度、灌木多样性指数与TK、SWC、土壤pH值和TP显著负相关, 而草本丰富度、草本多样性指数则与TK显著正相关; 灌木密度、灌木盖度与土壤pH值显著正相关, 草本密度与SWC和TK显著正相关, 草本盖度与TP、TK显著正相关, 与坡度显著负相关。土壤和地形因素是影响林下植被物种多样性变异的最主要因素, 而林分冠层结构的影响较小, 土壤各因素对林下植被物种多样性的影响高于地形因素。

Effect of environmental factors on understory species diversity in Southwest Guangxi Excentrodendron tonkinense forests

Exploring how distribution patterns of understory vegetation are affected by environmental factors is of great importance for natural forest protection and biodiversity conservation. Natural and mature Excentrodendron tonkinense-dominated forests on karst terrains were studied in eight counties of Southwest Guangxi. One-way ANOVA, Pearson correlation and redundancy analysis (RDA) were used to investigate the variation in species diversity and understory structure along a gradient of environmental factors including soil, topography, canopy structure and light. The results showed that the shrub layer was dominated by Sophora tonkinensis, Schefflera heptaphylla and Ventilago calyculata, as well as seedlings of species from the tree layer, such as Excentrodendron tonkinense, Orophea anceps, Cinnamomum saxatile and Garcinia paucinervis, etc. These species mainly represented the Leguminosae, Araliaceae, Rhamnaceae, Tiliaceae, Annonaceae, Lauraceae, Guttiferae and Euphorbiaceae families. Within the herb layer, the dominant species were Nephrolepis cordifolia, Guihaia argyrata, Pseudodrynaria coronans, Microstegium vimineum, Apluda mutica and Ophiopogon bodinieri, which mainly represent the Nephrolepidaceae, Palmae, Drynariaceae, Gramineae, Liliaceae, Aspleniaceae and Dryopteridaceae families. Soil pH, soil water content (SWC), soil total potassium (TK), soil total phosphorus (TP) and slope (SLO) were the main influencing factors, respectively explaining the variation in understory species diversity by 32.3%, 16.1%, 9.7%, 8.6% and 8.6%. Shrub richness and the shrub diversity index were significantly and negatively correlated with TK, SWC, soil pH and TP, while herb richness and the herb diversity index were significantly and positively correlated with TK. Shrub density and shrub coverage were positively linked to soil pH (P < 0.05), and herb density was positively associated with SWC and TK (P < 0.05). Herb coverage was positively correlated with TP and TK, and negatively correlated with slope (P < 0.05). Soil and topography were the most important factors affecting species diversity in the understory, while canopy structure had little effect on it. Edaphic factors were found to affect understory species diversity more than topographical factors.