Spatial distribution of tree species in evergreen-deciduous broadleaf karst forests in southwest China

Abstract

Understanding the spatial distribution of tree species in subtropical evergreen-deciduous broadleaf karst forest is fundamental to studying species coexistence and karst species diversity. Here, complete spatial randomness and heterogeneous Poisson process models were used to analyze the spatial distribution patterns of 146 species with at least one individual per ha in a 25-ha plot in southwest China. We used canonical correspondence analysis (CCA) and the torus-translation test (TTT) to explain the distributions of observed species. Our results show that an aggregated distribution was the dominant pattern in Mulun karst forests; the percentage and intensity of aggregated decreased with increasing spatial scale, abundance, mean diameter at breast height (DBH), and maximum DBH. Rare species were more aggregated than intermediately abundant and abundant species. However, functional traits (e.g., growth form and phenological guild) had no significant effects on the distributions of species. The CCA revealed that the four analyzed topographic variables (elevation, slope, aspect, and convexity) had significant influences on species distributions. The TTT showed that not all species have habitat preferences and that 68.5% (100 out of 146 species) show a strongly positive or negative association with at least one habitat. Most species were inclined to grow on slopes and hilltops.

Stand Structure and Abiotic Factors Modulate Karst Forest Biomass in Southwest China

“…MNNR was set up in 1991 to protect the subtropical mixed evergreen-deciduous broadleaf forest ecosystem that developed on a limestone substrate. The topography in this reserve is characterized by steep hills separated by lowland depressions with numerous potholes and caves, and extensive underground streams [7]. The average annual temperature is 19.4 • C and the average annual precipitation is 1500 mm in this area [7].…”

“…Mulun National Natural Reserve (MNNR) and the adjacent Maolan National Natural Reserve in the Guangxi and Guizhou provinces, respectively, preserve the last undisturbed remnants of karst forests in Southwest China, and possibly in the world [7]. Our study was conducted at MNNR (107 • 54 01 -108 • 05 51 E, 25 • 07 01 -25 • 12 22 N), in the Huanjiang County, northwestern Guangxi Province, China.…”

“…The average rock exposure ratio is greater than 60%. All woody stems with a diameter at breast height (DBH) ≥ 1 cm in this plot were identified, tagged, measured, and georeferenced [7]. Important species included Cryptocarya microcarpa, Itoa orientalis, Platycarya longipes, Lindera communis, and Clausena dunniana.…”

“…For each quadrat, seven topographic variables were recorded: elevation, convexity, slope, aspect, rock outcrop ratio (ROR), topographic wetness index (TWI), and vertical distance to channel network (VDCN). The first four topographic factors were computed following the method in Du et al [7]. ROR is a ratio of the rock coverage area.…”

“…Southwest China has the second largest forest region in China [6]. This region also contains the largest karst forest region in China, with an extremely fragile geological background, small environmental carrying capacity, and low tolerance to disturbance [7]. During the past century, a large part of the karst region in southwest China was severely degraded following the destruction of natural vegetation due to human disturbance.…”