Tree species richness enhances stand growth in south-east Asian subtropical secondary forests

Background/Question/Methods

A key question in ecology is whether species diversity promotes productivity, and by which mechanisms this occurs. To date, extensive data sets from experimental and comparative studies addressing this question are available for grassland communities. However, much less is known about productivity-diversity relationships in forest, despite the fact that forests are among the most productive terrestrial ecosystems on Earth. The goal of the present study was to assess the relation between diversity and productivity in subtropical secondary forests. We recorded basal area and basal area increase from 2008 to 2010 in twenty-five 30 x 30 m plots in subtropical China. These plots were selected to span diversity gradients and cover different stages of secondary succession. All tree individuals exceeding 10 cm diameter at breast height were identified and their diameter and height measured at the beginning and the end of the observation period. Data were analyzed with general linear models, taking covariates characterizing the plots’ environmental conditions into account. Structural equation models were used to further analyze the relationship between successional stage, diversity, growth, and individual density.

Results/Conclusions

The tree cohort studied (1554 stems) encompassed sixty-nine species and thirty families. Plot richness ranged from three to twenty-one species and densities varied between twelve and 107 stems per plot. Mean standing basal area in 2008 was 27.95 m²/ha (minimum of 1.97 m²/ha and maximum 59.82 m²/ha) and in 2010 it was 29.585 m²/ha (minimum of 1.61 m²/ha and maximum 60.58 m²/ha). Tree richness was positively related to basal area increase (p<0.01). Mortality and in-growth of individuals into the censored cohort were independent of richness and successional stage. Structural equation modeling further indicated that the increased productivity of more diverse stands was due to an increased number of tree individuals rather than to an increased individual size. Overall, our findings suggest that diversity promotes forest productivity during secondary succession, possibly supporting a faster resilience after disturbance.