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A dirty way to fight climate change

A promising strategy: Store carbon in the soil.

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Switch to compact fluorescent light bulbs and plant a tree – these are the most popular strategies for mitigating climate change today.

Yet world leaders gathering for the climate-change summit in Bali, Indonesia, next week should consider an alternative. It's one of the most overlooked yet most effective and inexpensive strategies available: Store carbon in the soil.

This is one way the earth has managed carbon since it began. The earth's soil contains the second-largest quantity of carbon, where it has been the most stable and least vulnerable to fires and climate changes. (The largest amount is dissolved in oceans.)

Planting trees sounds like a flawless solution: Trees absorb carbon, after all. But it can actually be quite harmful, even dangerous. Soil needs "riches" such as carbon, organic matter, and mineral nutrients, and they come in part from the "litter" left by plants that grow and die annually on the land. By planting trees in soils that were created by other, more productive plants (e.g., prairie and wetland plants that used to occupy some of today's farmland), less litter is produced. That means less carbon and organic matter are contributed to the soil, causing it to deteriorate.

In some areas, planted trees can dewater the soil. They can also release nitrogen and phosphorous in runoff that enters rivers, lakes, and estuaries and hurts water quality. More worrisome, some forested areas are becoming more vulnerable to wildfires, because changing precipitation patterns and the associated drying effects are creating a tinderbox. These changes appear to be resulting in bigger and more frequent fires (e.g., very recently in California).

Ecological lesson No. 1 is that we should plant trees only where the soils will benefit from it.

The corollary, lesson No. 2, is not to plant trees where inappropriate, for example, in farmland that used to be wetlands and grasslands. Native, deep-rooted plants should be grown in those areas instead, since they enrich the soil – with carbon, among other things – more quickly.

Lesson No. 3 is that, in the face of drought and increased wildfires, rebuilding soils is a safer strategy for storing carbon.

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