Abstract
Both biodiversity and biomass are important variables in forest ecosystems, and the relationship between them is critical for ecosystem functioning and management. The primary Pinus kesiya forest is increasingly threatened by human disturbance in Yunnan Province. We observed that species richness had a positive impact on aboveground biomass across all forest vegetation layers, and this relationship was strongest in the herb layer. The asymptotic relationship between cumulative species number and aboveground biomass suggested that individual of Pinus kesiya trees with relatively large diameters contributed the majority of the aboveground biomass in the tall tree strata due to their strong competitive advantage over other tree species. Although aboveground biomass increased with stand age in the tall tree strata, climate factors and the soil nutrient regime affected the magnitude of the diversity-productivity relationship. Stand age had no significant effect on species richness and aboveground biomass in the forest understory. The effect of the positive diversity-productivity relationship of the tall trees on the shrub layer was negligible; the diversity-productivity relationship in the forest understory was significantly affected by the tall tree aboveground biomass. The tall trees have increased the strength of the positive diversity-productivity relationship in the forest understory.
Highlights
The relationship between biological diversity and ecosystem functioning has stimulated research on the relationship between terrestrial plant species richness and temporal variation in biomass production during the past two decades[1,2]
The aboveground biomass values of the tall tree, short tree, shrub, herb and liana layers were positively correlated with the species richness of the tall tree, short tree, shrub, herb and liana layers based on the cubic ordinary least squares (OLS) regression, respectively (Fig. 2a–e)
These results differ from those found in a study by Ali and Yan, which indicated that the tall tree layer had negligible effects on the short tree layer in terms of aboveground biomass[14], while our results show that the tall tree aboveground biomass had a negative effect on the short tree aboveground biomass in the primary Pinus kesiya forest ecosystem, which covers a large area of the subtropical zone in Yunnan Province, SW China
Summary
The relationship between biological diversity and ecosystem functioning has stimulated research on the relationship between terrestrial plant species richness and temporal variation in biomass production during the past two decades[1,2]. An increasing number of studies have focused on the relationship between biodiversity and aboveground biomass, as well as the mechanisms resulting in variations in both species functional traits and environmental conditions in tropical, temperate and boreal forest ecosystems[4,9]. Reich et al confirmed that a positive species richness and aboveground biomass relationship across forest strata was found, and the understory species richness is mediated by the indirect effects of the dominant producers on resource availability and heterogeneity in a boreal forest[13]. Positive species diversity and aboveground biomass relationships are mostly found across forest strata that exhibit higher species richness and many trophic levels[2,7], biotic and abiotic factors affect the magnitude and quality of such relationships, and these effects should be considered, especially by increasing the range of variables included in multivariate studies, such as competition intensity, resource heterogeneity and population dynamics[13]. Soil nutrient conditions and stand age are recognized as directly or indirectly affecting the species richness-aboveground biomass relationship, but were rarely explicitly considered because of the instability in environmental conditions[9,12]
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