Soil Carbon Storage in Tropical Montane Forests is Insensitive to Warming
The effects of warming on soil carbon storage remain poorly quantified because assessing temperature effects below ground is complicated. To address this issue, a research team lead by PSW scientists examined soil carbon storage and whole ecosystem carbon storage across a highly constrained 5 degrees Celsius (41 degrees Fahrenheit) mean annual temperature gradient in tropical montane wet forest in Hawaii. Across this gradient, vegetation composition, disturbance history, soil type, parent material, and soil moisture are all relatively constant across the gradient. As such, it represents an important advance over previous temperature gradient studies. The team documented an increase in productivity across the gradient, including higher total litterfall rates and higher total below ground carbon inputs with increasing temperatures. They conclude that, previous assumptions about a positive soil carbon cycling feedback on warming are unlikely to be correct. While decomposition and storage will respond strongly where ecosystem carbon is unprotected. When ecosystem carbon is protected, as soil organic carbon often is via soil aggregation and organo-mineral associations, reduced access to carbon by decomposing organisms results in little temperature sensitivity. In the long-term, warming in tropical montane forests will accelerate below-ground carbon cycling, but is unlikely to cause net losses of soil carbon.