Abstract
Although trait analyses have become more important in community ecology, trait-environment correlations have rarely been studied along successional gradients. We asked which environmental variables had the strongest impact on intraspecific and interspecific trait variation in the community and which traits were most responsive to the environment. We established a series of plots in a secondary forest in the Chinese subtropics, stratified by successional stages that were defined by the time elapsed since the last logging activities. On a total of 27 plots all woody plants were recorded and a set of individuals of every species was analysed for leaf traits, resulting in a trait matrix of 26 leaf traits for 122 species. A Fourth Corner Analysis revealed that the mean values of many leaf traits were tightly related to the successional gradient. Most shifts in traits followed the leaf economics spectrum with decreasing specific leaf area and leaf nutrient contents with successional time. Beside succession, few additional environmental variables resulted in significant trait relationships, such as soil moisture and soil C and N content as well as topographical variables. Not all traits were related to the leaf economics spectrum, and thus, to the successional gradient, such as stomata size and density. By comparing different permutation models in the Fourth Corner Analysis, we found that the trait-environment link was based more on the association of species with the environment than of the communities with species traits. The strong species-environment association was brought about by a clear gradient in species composition along the succession series, while communities were not well differentiated in mean trait composition. In contrast, intraspecific trait variation did not show close environmental relationships. The study confirmed the role of environmental trait filtering in subtropical forests, with traits associated with the leaf economics spectrum being the most responsive ones.
Highlights
In recent years, community ecology has made much progress in understanding how the trait composition in a community changes along environmental gradients [1,2,3]
Statistical analyses We mainly focused on the contribution of interspecific trait variation on trait-enviroment relationships, and used leaf trait values averaged per species
An inverse strong relationship to successional stage was encountered to number of individuals, caused by decreasing tree densities with ongoing succession, and to the proportion of deciduous individuals in a plot, because the evergreen trees and shrubs became more abundant with successional time, while the amount of photosynthetically active radiation decreased and the red:far-red ratio increased
Summary
Community ecology has made much progress in understanding how the trait composition in a community changes along environmental gradients [1,2,3]. As a result of environmental filtering, mean values of a trait will differ among communities along an environmental gradient, while, as a result of competitive exclusion, trait value distribution within communities will be divergent. Environmental filtering might select for a trait that at the same time confers competitive superiority or the ability to facilitate other members of the community [12] In this case, it might be considered to broaden the definition of environmental trait filtering and to lump together abiotic environmental filters and those brought about by biotic interactions [11]. Few studies have attempted to relate shift in community mean trait values to environmental changes along forest succession series. Elevation, inclination and aspect can be considered proxy variables for these unmeasured environmental variables that are difficult to assess in a field study
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