西双版纳不同森林类型的树洞密度及其特征

树洞是森林生态系统的重要组成部分,它能为许多动物提供栖息、筑巢、繁殖和躲避天敌的场所。因而,树洞的密度和特征通常被认为是限制树洞巢居动物多样性和丰富度的主要因子,然而目前国内外对热带森林的树洞密度和洞口特征研究较少。选取西双版纳20 hm~2热带森林动态监测样地(包括热带季节雨林和热带山地常绿阔叶林)为研究对象,采用地面观测法调查了所有胸径≥5 cm的活体乔木上的树洞,分析其树洞密度和特征(高度、洞口大小、类型和洞口方位,并探讨树洞在不同森林类型间的差异)。结果表明:(1)热带季节雨林和热带山地常绿阔叶林的树洞密度不存在显著差异;(2)两种森林类型的树洞均以高度较低、洞口较小、干中部洞口为主,受盛行风的影响洞口朝向主要集中在东北方向;(3)树洞高度、类型和洞口方位在两种森林间的分布差异显著(P0.01),而洞口大小不存在明显差异。结果表明森林类型会影响树洞的特征,因而加强森林生境异质性的保护对维持树洞巢居动物的需要具有重要意义。

Cavity density and characteristics in different tropical forest types in Xishuangbanna, southwest China

Tree cavities are important components in forest ecosystems, as they can provide habitats for roosting, nesting, breeding, or shelters for many animals. Thus, cavity density and characteristics have been generally considered as limiting factors for cavity-dependent fauna. However, limited studies on tree cavity density and characteristics have been conducted in the tropics to date. In this study, we aimed to analyze cavity density and characteristics (height, size, type, and orientation) in tropical forests and determine potential differences across different forest types. A ground-based observation was conducted in 20 hm² forest dynamic plots of tropical seasonal rain and montane evergreen broad-leaved forests in Xishuangbanna, southwest China. We found that the cavity densities did not differ between the two forests. Most of the cavities in the two forests occurred at a lower height from the ground, with a narrower entrance diameter, and were located in the main trunk. In addition, the orientation of cavity entrances was mainly toward the northeast, which was influenced by the prevailing wind. In contrast to similar cavity sizes between the two forest types, the height, type, and orientation of cavities were significantly different (P < 0.01). Together, these results indicate that cavity characteristics were influenced by forest types, and highlighted the importance of forest heterogeneity in providing resources for cavity-dependent fauna.