Characteristics and spatial distribution of forest gap in a northern tropical karst seasonal rainforest in Nonggang, Guangxi, South China
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 tropical karst seasonal rain forest dynamic plot in Nonggang National Nature Reserve, Guangxi.Total 305 gaps were identified, ranging in size from 10 to 371with 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.