Tropical vegetation benefits less from elevated atmospheric CO2 than previously thought

Carbon sequestration from the atmosphere in tropical vegetation has been suggested as a mitigating factor for elevated atmospheric CO2 levels from an anthropogenic perspective. A new study now shows that over the long term, humidity change actually plays a bigger role than atmospheric CO2 in determining tropical woody vegetation change. The research findings have broad implications for the development of effective climate mitigation strategies and are now published in Science.

Tropical vegetation forms an important part of the global carbon cycle as it contributes substantially to global net primary productivity and through this sequesters large amounts of carbon dioxide from the atmosphere. Previous research on individual plants or forest patches has suggested that tropical vegetation may be a mitigating factor for anthropogenic elevated atmospheric CO.2 levels: i.e. when more CO2 is released into the atmosphere, the vegetation will absorb more CO2 and thus reduce the impact of this greenhouse gas.

Landscape scale

The study recently published in Science, led by Dr William Gosling of the Institute for Biodiversity and Ecosystem Dynamics at the University of Amsterdam, has for the first time been scaled to enable change in tropical vegetation at the landscape scale and over time scales relevant to ecosystem change. considered. The international research team from the Netherlands (University of Amsterdam and Wageningen University & Research), the United States and the United Kingdom, combined different data sources. “We combined evidence of past environmental changes extracted from sediments recovered from Lake Bosumtwi in Ghana, with simulated past climate conditions and the global atmospheric CO record.2 change obtained from ice cores over the past 500,000 years,” says Gosling.

Sediments from Lake Bosumtwi revealed information on woody cover, fire history, herbivore activity and moisture availability. This information was combined in a model with temperature and atmospheric CO2 The data. Gosling: “The model allowed us to identify the relative strength of the relationships between the different drivers of vegetation change.

Humidity, fire and herbivore

This new research approach has shown that atmospheric CO2 is less important than moisture availability, fire, and herbivory in determining tree cover change in rainforest-savannah transitions. “Based on small-scale experiments, large-scale vegetation models have predicted that woody cover in savannas will increase due to increased atmospheric CO2 The data. Our results show that these models need to be redesigned,” says Frank van Langevelde, professor in the Wildlife Ecology and Conservation Group at Wageningen University and Research and co-author of the paper. Gosling: “What’s new in our data is that when you go down to the landscape scale, the resources available and the processes that occur in that landscape are more important than the CO2 fertilization effect. Simply put, we have shown that no matter how much CO2 is in the atmosphere if there is not enough water, or if there are fires every year, or if all the seedlings are eaten by animals, you are not growing a forest.’

“Although we have a data set spanning 500,000 years, we only have one study site. It is possible that the relationship between CO2 and the vegetation elsewhere in the tropics is different,” says Gosling. “In any case, efforts that promote carbon sequestration in tropical vegetation must carefully consider the roles of moisture, fire, and herbivores if they are to be successful.”

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