广西弄岗北热带喀斯特季节性雨林林隙特征与空间分布

Characteristics and spatial distribution of forest gap in a northern tropical karst seasonal rainforest in Nonggang, Guangxi, South China

关键词:  喀斯特季节性雨林, 林隙, 空间分布格局, 空间关联, 生态因子

Key words:  karst seasonal rain forest, forest gap, spatial pattern, spatial associations, ecological factors

摘要:

林隙是森林中一种普遍存在的小尺度森林干扰形式,对促进森林更新和循环演替具有重要作用。对热带喀斯特森林的林隙干扰目前还了解不多。该文采用Worldview-3高空间分辨率遥感影像结合地面调查,对弄岗喀斯特季节性雨林15 hm²样地林隙干扰特征及其空间分布规律进行了研究。结果表明:样地内共解译到305个林隙,林隙的密度约为每公顷20个,林隙大小的变化范围为10～371 m²,平均大小为52.3 m²,林隙面积占森林面积的10.6%; 林隙在0～50 m尺度整体表现出聚集分布格局; 林隙空间分布与大树(DBH≥10 cm)存在显著空间关联,与小树(DBH<10 cm)和枯立木无显著空间关联; 不同生态因子对林隙的数量分布和基本结构影响不同,对林隙数量分布影响最显著的包括凹凸度、干旱度指数、丰富度,而坡向、海拔、丰富度对林隙大小有显著影响,海拔、岩石裸露度、地形湿润度指数、干旱度指数、多度等5个生态因子对林隙周长有显著影响。研究结果表明林隙在喀斯特季节性雨林普遍存在,林隙的空间分布与特征存在着地形分异特征,是喀斯特独特的地质地貌和生境条件与喀斯特森林自身生物学特性综合作用的结果。

Abstract:

Forest gap is the dominant form of disturbance in many forest ecosystems. Gaps play an important role in forest helping to maintain forest regeneration and dynamics. Little is known about the gap pattern and characteristics of karst seasonal rain forests. In this study, high-spatial-resolution Worldview-3 satellite imagery was coupled with field data to assess gap disturbance regime and its pattern in a 15 hm² northern tropical karst seasonal rain forest dynamic plot in Nonggang National Nature Reserve, Guangxi. Total 305 gaps were identified, ranging in size from 10 to 371 m² and with mean size 52.3 m². The canopy gap fraction was 10.6%, and gap density was about 20 per hectare. The spatial pattern of gaps was clustered at scale 0-50 m. Significant association was found between gaps and big trees(DBH≥10 cm), and null associations between gaps and small trees(DBH<10 cm)and between gaps and standing dead trees. The prevailing ecological factors had different influence on gap distribution and gap characteristics. Convexity, altitude above channel(AAH)and tree species richness had significant effect on the gaps distribution. Gap size was significantly influenced by slope, mean elevation and tree species richness. Gap perimeter was mainly affected by mean elevation, rock-bareness rate(RBR), topographic wetness index(TWI), AAH and tree species abundance. These results indicated that gap disturbance was very frequent in karst seasonal rain forests, and there were topographic differentiation in spatial distribution and characteristics of gaps resulted by the combination effects of unique special karst geological conditions, habitats and the biological characteristics of karst forest.