Functional diversity and identity effects on natural forest soil carbon stocks depend on baseline climate

Xinli Chen, Faculty of Natural Resources Management, Lakehead University, Thunder bay, ON, Canada, Masumi Hisano, Natural Resources Management, Lakehead University, Thunder bay, ON, Canada, Anthony R. Taylor, Canadian Forest Service, Natural Resources Canada, Fredericton, NB, Canada and Han Y. H. Chen, Faculty of Natural Resources Management, Lakehead University, Thunder Bay, ON, Canada

Background/Question/Methods
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. 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.

Results/Conclusions
We found that the effects of functional diversity on soil carbon stocks were climate-dependent, shifting from negative in warm or moist climates to positive in cold or dry climates. In addition, tree species with acquisitive traits, such as high specific leaf area, leaf nitrogen content and phosphorus content, increased mineral horizon soil carbon stocks in warmer sites, but decreased those in colder sites. Our results suggest 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.