Effects of Topographic and Soil Factors on Woody Species
作者: 会同衫木林站 更新时间: 2015-09-28
Floristic composition, structure, and spatial patterns are the fundamental characteristics that reflect species assembly in forests. Species assembly in a forest result from stand development processes [1,2] that are driven by immigration through various means of propagule dispersal  and extinction; these are due to species response to environmental conditions  and biotic interactions, such as competition, erbivores, and predation . Understanding the underlying processes of species assembly in a forest could provide useful information for predicting stand dynamics and for forest management and biodiversity conservation. In general, two approaches may be followed to analyze the processes that affect species assembly. One is a dynamic approach where the factors affecting changes in species richness are nvestigated using data collected from the forests at different successional stages . Another is a statistical approach where the factors are inferred from the existing stand structure and spatial pattern using the data collected in a plot . For example, spatial patterns (aggregation, random, and regular) are usually used to interpret species assembly and coexistence [7,8]. It is assumed that aggregation spatial patterns are a common phenomenon for conspecific trees in order to reduce competitive exclusion and promote a more diverse coexistence of species . Many factors, including functional traits (e.g., growth form, shade tolerance, and dispersal modes), life history strategy , regeneration strategy , disturbances , and habitat heterogeneity , lead to aggregated distribution.Some evidence has indicated that habitat heterogeneity plays an important role in regulating the distribution of species . Previous studies reported that species distribution was correlated with variations in topography or soil in tropical , subtropical [16–18], and temperate forests . However, habitat associations of the majority of species were inconsistent with life stages or vertical layers in tropical and temperate forests [20,21]. Topography and soil variables significantly affected species assembly in China’s subtropics [16,17], but their relative contribution to entire stands and dominant species among vertical layers is poorly understood. Evergreen broadleaved forests in subtropical areas of China are climax vegetation with diverse species, high stability, and productivity . The favorable climate results in diverse evergreen broadleaved forests . However, primary evergreen broadleaved forests had almost disappeared
until now and their total area was less than 5% of the original area as a result of clearance for plantations and the conversion into secondary vegetation, due to sustained human disturbance and a timber-centric forestry policy over past decades . Recently, China has changed its forestry policy from timber production to ecosystem services . Close-to-nature forest management occurred just
as a practical approach to over exploitation and degradation in fragile mountain landscapes. The general aim of close-to-nature management was to formulate diversely structured and uneven-aged forests on a finer scale . For Chinese subtropical areas, remnants of those surviving original evergreen broadleaved forests are considered as templates of sustainable management for natural forest
development. Although numerous studies related to species diversity and coexistence have beenconducted in old-growth forests at remote mountain locations [26,27], information remains limited on floristic composition, stand structure, and spatial pattern, as well as on the driving mechanisms of species assembly in subtropical areas of China.