Climate May Not be Leading Cause of Decomposition: Logs Reveal Key to Carbon Cycling

Climate may not be the primary driver of decomposition. Challenging the long-held assumption, scientists have found that local factors play a far greater role than climate when it comes to wood decomposition rates, and the impacts on regional carbon cycling.

Scientists have long thought that climate is the major factor that controls decomposition. This is because warmer temperatures can increase the activity levels of "decomposer" organisms, such as microbes, that break down dead organic matter. Yet while climate certainly plays a role when it comes to regional and global scales, local-scales may be another question entirely.

"We're reaching the wrong conclusion about the major controls on decomposition because of the way we've traditionally collected and looked at our data," said Mark Bradford, one of the researchers, in a news release. "That in turn will weaken the effectiveness of climate prediction."

In order to assess the local effects on decomposition, the researchers distributed 160 blocks of pine tree wood across five sub-regions of temperate forest in the eastern United States, ranging all the way from Connecticut to northern Florida. Then, the scientists watched the levels of decay that occurred over 13 months. By selection similar forest types, the scientists managed to examine the differences in the effect of climate across the regional gradient.

"Most people would try to make sure everything was as standard as possible," said Bradford in a news release. "We said, 'Well, let's generate as much variation as possible.' So we put some blocks on south-facing slopes, where they would be warmer in the summer, and others on north-facing slopes where it's colder. We put some on top of ridges and others next to streams where it was wetter."

So what did the researchers find? It turns out that local-scale factors explained about three-quarters of the variation in the wood decomposition. Climate, in contrast, only explained about one-quarter.

These findings in particular have implications for climate models and the carbon cycle. In the future, scientists may be able to make more accurate models by knowing exactly what factors come into play when it comes to this decomposition rate.

The findings are published in the journal Nature Climate Change.