Carbon offsetting initiatives could be improved with new insights into the make-up of tropical forests, a study by researchers at British universities has shown.

Scientists studying the Amazon Basin have revealed unprecedented detail of the size, age and species of trees across the region by comparing satellite maps with hundreds of field plots, said a statement from the University of Edinburgh.

The findings will enable researchers to assess more accurately the amount of carbon each tree can store, a key factor in carbon offset schemes, in which trees are given a cash value according to their carbon content, and credits can be traded in exchange for preserving trees.

Existing satellite maps of the area have estimated trees' carbon content based largely on their height, but have not accounted for large regional variations in their shape and density.

Researchers from the Universities of Edinburgh and Leeds, who led the research, said their findings could help quantify the amount of carbon available to trade in areas of forest, which could help administer carbon offsetting more accurately, and improve understanding of how much carbon is stored in the world's forests, which informs climate change forecasts.

Scientists studied a database of thousands of tree species, taken from more than 400 hectare-sized plots across the Amazon Basin including Brazil, Bolivia, Colombia, Ecuador, Guyana, Peru, Suriname and Venezuela among others.

The survey was developed as part of a sister project, known as RAINFOR, involving more than 200 researchers across the region.

The research found that forests in the basin's northeast on average stored twice as much carbon as those in the southwest, as a result of soil, climate and species variation. The northeast has slow-growing, dense-wooded species, while the southwest is dominated by light-wooded trees with faster turnover, which highlights the need to recognize that carbon is not distributed uniformly in the forest, said scientists.

Funded by the Natural Environment Research Council, the study was published in Global Ecology and Biogeography.

Dr. Ed Mitchard of the University of Edinburgh's School of GeoSciences said, "Satellite maps of the world's forests don't contain enough information about their carbon content. Developing our understanding of this aspect of forests, in the Amazon and elsewhere, could be hugely important for our climate."

Professor Oliver Phillips from the University of Leeds' School of Geography, who co-led the study, said, "Satellites can't see species, but species really matter for carbon. This is the big challenge for the next generation of satellite and field scientists. New satellites will be launched soon that will be more sensitive to forest structure and biomass, but we must ensure we have sufficient ecological ground data to correctly interpret and use them."

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