Forest carbon cycling: Insights gained from radiocarbon measurements

Background/Question/Methods

Radiocarbon dating has proven to be an instrumental tool for estimating rates of soil carbon turnover and for characterizing distinct carbon pools that differ in turnover rate. Although radiocarbon-based turnover estimates are very useful for describing soil carbon dynamics, one potential limitation is they generally represent long-term averages over timescales of decades to millennia, and shorter-timescale dynamics can be missed. However, radiocarbon is an extremely versatile tool with largely unrealized potential to detect responses to rapid forest changes. Here we present results from several studies showing the large spectrum of time across which soil carbon dynamics can be characterized with radiocarbon, from multi-decadal timescales to immediate responses following fire, harvest, and changes in biota.

Results/Conclusions

Radiocarbon estimates of decadal and longer soil carbon turnover show great geographical variation, as demonstrated by a recent study of AMERIFLUX forest sites across the U.S. Patterns could not be explained by any single factor, but radiocarbon data showed that soil carbon storage can be sensitive to singular site-specific factors, such as the presence of earthworms, site hydrology, or parent material. Radiocarbon studies of forest fire show that disturbance can alter the number, types, and turnover times of soil carbon pools. We also show that radiocarbon measurements of soil CO₂ flux can be used to detect changes in the relative amounts of old soil carbon decomposed over the course of a growing season. Used in a variety of ways, radiocarbon measurements can provide a powerful tool for testing soil responses to environmental change, or for constraining models of soil carbon dynamics.