Community-level consequences of harsh environmental constraints based on spatial patterns analysis in karst primary forest of southwest China

Abstract

Karst region has a high rate of rock exposure, shallow and discontinuous soil, and a fragile ecological environment. However, these special habitats encompass a large area of forest with strong original nature-karst deciduous broad-leaved and evergreen mixed forest. So far, very limited information is available on the spatial patterns and internal maintenance mechanism of this community. To fill this gap, the spatial distributions together with spatial correlations of both the live and dead trees in the karst primary forests of the Maolan National Nature Reserve in China were explored by using univariate as well as bivariate g(r) functions. The results revealed that: (1) the habitat heterogeneity of the karst primary forest has insignificant influence at a larger scale (>10 m); (2) the decline in aggregation with the increasing size classes from saplings to adults suggests self-thinning process, proving that negative density constraints occurred in early life stages; (3) positive spatial correlation was found in live trees with similar diameters, which related to the microsite heterogeneity; (4) the aggregation of dead trees and non-attraction of dead and surviving trees indicated scramble competition; (5) mortality analysis indicated the absence of random mortality, favoring positive density-dependent effects; (6) strong initiation sprouting regeneration was one of the main self-renewal strategies, and regeneration was more likely to occur at the edge of the gap rather than under the gap. Our results support the view that the mechanisms underlying the observed spatial patterns were related to certain ecological processes and their interaction. These were the positive and negative density dependence, scramble competition, and microsite heterogeneity.