Functional diversity and identity effects on forest soil carbon stocks
depend on climate contexts
1. Soil carbon plays an important role in mediating global climate change and sustaining environmental quality
. Although experimental studies have established that higher biodiversity can lead to greater soil C storage, uncertainties remain concerning the relationships between tree diversity and soil carbon stocks in natural forests, as well as the climatic factors that drive their directions and magnitudes.
2. Using Canada’s National Forest Inventory data, we tested the relationships between soil carbon stocks to tree functional diversity and identity, and how these relationships varied with climate gradients in the organic horizon and mineral horizon.
3. We found that climatic factors were the most important model predictors with the largest and constant impacts. Compared with climatic factors, tree diversity and composition were relatively poor predictors of soil carbon stocks. Importantly, the effects of functional diversity on soil carbon stocks were climate-dependent, shifting from negative in warm or moist climates to positive in cold and dry climates. In addition, forest communities with acquisitive resource utilization strategies had higher, while those with conservative resource utilization had lower mineral horizon soil C stocks in warmer sites than in colder sites.
4. Synthesis. Our results provide large scale evidence that tree diversity and identity effects on soil carbon are dependent on climatic context and suggest that converting high functionally diverse natural forests to monoculture plantations can decrease soil carbon stocks of colder and drier sites in boreal and temperate forests.