Amazon rainforest likely to become savannah due to burning, deforestation, climate change

by Jeremy Hance A new analysis shows that the heavily-deforested Amazonian region of Mato Grosso is particularly susceptible to ‘savannization’ due to repeated burning that has likely depleted the region’s soils of precious nutrients. According to the study, published in the Journal of Geophyscial Research, savannization, or the process of tropical ecosystems shifting to savannah, is likely in northern Mato Grosso even if no more further deforestation occurs. Dr. Marcos Costa, one of the study’s authors, describes the savannization tipping point in an ecosystem as such: “the coupled atmosphere-biosphere system would shift from the present rainy climate-rainforest situation to an alternate drier-savanna situation…It involves the coupled vegetation-atmosphere-ocean system, but the evolution of this system apparently depends on other feedbacks that are usually neglected. These feedbacks are associated with the deforestation and agricultural practices, like soil nutrient limitation and fires.” These feedback systems, soil nutrients and fires, are particularly important to an area like Mato Grosso, where large-scale burning has been used for decades by settlers seeking more land for ranching and agriculture. The repeated burning causes a direct loss of soil nutrients in the ecosystem. “Frequent fires volatilizes significant stocks of [nitrogen], provoking a co-limitation of this nutrient in forests recovering from repeated fire,” the authors write. “Nutrients in the remaining ash might be lost by ash transport, and leaching to surface and groundwater.” The authors point to previous study which showed that tropical forests suffering from repeated burning—five or more times—“accumulate biomass at an average rate lower than 50% of forests that burned only once, and are more susceptible to further burning.” Why is the loss of soil nutrients through burning important? “Any plant must capture nutrients from the soil to grow,” explains Costa. “If soil nutrients are depleted, trees grow at a slower rate, because they can’t use efficiently the light and water available.” … According to the study: “over northern Mato Grosso, the rainforest does not recover on the timescale of 50 years, no matter how much is deforested.” …

Amazonian region likely to become savannah due to burning, deforestation