A linear positive relationship between tree species diversity and forest productivity across forest-dominated natural reserves on a large spatial scale

Abstract

Exploring diversity-productivity relationships (DPRs) of various ecosystems is essential to forest management and conservation, as it can inform us about the dynamics and future trend of forest productivity and carbon sequestration under the change of species diversity. However, the DPR of natural reserve and its formation mechanisms are poorly understood, although such ecosystem plays a key role in protecting species diversity and maintaining carbon sink and other ecological service functions. By integrating ground survey data of 113,007 trees of 163 tree species from 1029 plots and remotely sensed vegetation data, we investigated the DPR features as well as the mechanisms behind them of 25 forest-dominated national natural reserves across the large part of northeastern China. We found a significant (P < 0.01) positive relationship between species diversity index and aboveground biomass across the analyzed natural reserves on a large spatial scale. In addition, the species diversity index and aboveground biomass obtained from the ground survey data were significantly (P < 0.01) and positively correlated with satellite-derived enhanced vegetation index linked to forest productivity, further confirming the robustness of the linear positive DPR observed. These results indicate that forest productivity and carbon sequestration would probably decline if a decrease in tree species number, highlighting the importance of species diversity protection in natural reserves. A structural equation modeling analysis suggested that heat-related and water-related climate factors played predominant roles in modulating species diversity index and aboveground biomass respectively and hence DPR across the natural reserves studied. Meanwhile, geographical location (i.e. latitude and longitude) can indirectly affect DPR by regulating the climate factors above. The findings of this study can contribute to understanding the DPR and predicting the future trends of forest carbon sink under climate change and thus to sustainable forest management for our study region as well as other similar natural reserves.