Forests and carbon storage: size matters New research from Brazil and Germany indicates environmental concerns are best met by conserving large and entire tracts of forest rather than the the same area of smaller forests.

The conclusion has implications for efforts to reduce carbon emissions, because forest biomass is one way of storing carbon dioxide. The researchers investigated a large number of small forest fragments left over after clearing of most of the Atlantic Forest near São Paulo in Brazil, and found their biomass could be as much as 40% less than in a single large forest.

They said the lower biomass was due to a higher death rate among trees at the edges of forests, particularly large, old trees that had large amounts of biomass. The higher death rate was caused by changes in wind and light conditions at the edge of the forest.

Using forest simulation software developed at the Helmholtz Centre, the researchers modelled different sizes of forest and found that the smaller a patch of forest was, the worse the ratio between its edge and total area.

The simulation results suggested a natural tropical forest in the study area contained about 250 tonnes of above-ground biomass per hectare, a forest fragment measuring 100 hectares had about 228 tonnes per hectare while a one hectare patch of rain forest had only 140 tonnes of biomass per hectare.

"This finding is of great significance for the function of rain forests as a biomass store. It is important to be clear about the fact that we are losing more than just the deforested areas. Even the remaining forest is thinned out as a result," said Dr Jürgen Groeneveld of the Helmholtz Centre.

"It is a mistake to think only in terms of total area. We have to start thinking in terms of the spatial configuration of the remaining forest fragments as well. In terms of carbon storage, it is better to protect 100 continuous hectares than to protect 100 one-hectare patches."

Questions still remain about the stability of the edges of forest fragments and whether fragments regenerate or if the degradation spreads further into the forest, so the researchers say their figures should be viewed as a preliminary estimate.

"But if it is confirmed, it is a really fundamental finding," said Dr Sandro Pütz of the UFZ. "Forest fragments cannot perform in the same way as continuous forests."


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