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Tropical forests affected by habitat fragmentation store less biomass and carbon dioxide in the long term

Conserving continuous forests is important for mitigation of climate change

Deforestation in tropical rain forests could have an even greater impact on climate change than has previously been thought. The combined biomass of a large number of small forest fragments left over after habitat fragmentation can be up to 40 per cent less than in a continuous natural forest of the same overall size.

This is the conclusion reached by German and Brazilian researchers who used a simulation model on data from the Atlantic Forest, a coastal rain forest in the state of São Paulo, Brazil, around 88 per cent of which has already been cleared. The remaining forest fragments are smaller, so the ratio between area and edge is less favourable. The reason for the reduction in biomass is the higher mortality rate of trees at the edges of forest fragments, according to the results published by researchers from the Helmholtz Centre for Environmental Research and the University of São Paulo in Ecological Modelling. This reduces the number of big old trees, which contain a disproportionately high amount of biomass.

Terms of use
Altered wind conditions and light climate lead to a general change in the microclimate at the forest edges. Big old trees are particularly vulnerable to these factors. With the help of FORMIND, a forest simulation software developed at the UFZ, the researchers modelled different sizes of forest patches left over after landscape fragmentation. The smaller a patch of forest is, the worse is the ratio between edge and area. Simulation results suggest that a natural tropical forest of our study area contained approximately 250 tonnes of aboveground biomass per hectare, a forest fragment measuring 100 hectares has around 228 tonnes of biomass per hectare, while a patch of rain forest measuring one hectare has only 140 tonnes of biomass per hectare. In other words, the biomass in the forest remnants in this study fell by as much as 40 per cent. "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. 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," says Dr Jürgen Groeneveld of the UFZ, explaining the significance of the study for climate policy. As well as the biomass yield per hectare, these fragmentation-related spatial (edge) effects also have impacts on climate balance and biodiversity, i.e. on several dimensions of sustainability.

The simulation integrated results from other researchers who are conducting unique long-term experiments on fragmentation in Amazonas. However, a large number of questions remain unanswered: Are the edges stable? Can the forest regenerate or does the degradation continue inwards? The researchers therefore view the figures as a preliminary, cautious estimate. "But if it is confirmed, it is a really fundamental finding," adds Dr Sandro Pütz of the UFZ. "Forest fragments cannot perform in the same way as continuous forests." The researchers therefore intend to investigate the long-term effects over the coming years to find out how the rain forest remnants develop in the long term. The results of this study will also have fundamental consequences for forest conservation, at least in terms of the carbon balance: "In any case, in terms of carbon storage, it is better to protect 100 continuous hectares than to protect 100 one-hectare patches," says Jürgen Groeneveld.

The data used in the model come from the tropical coastal rain forest in the state of São Paulo, Brazil. The Atlantic Forest was severely deforested in the second half of the 19th century for construction timber, charcoal and grazing and arable land. Although only around an eighth of the original forest area remains, these remnants are still regarded as international biodiversity hot spots, since they are home to an as yet not fully recorded, but impressive number of endangered animal and plant species that are not found anywhere else. Since 2003, Brazilian and German researchers have therefore been investigating the long-term effects of landscape fragmentation on habitats in the Atlantic Forest, which used to stretch along the whole of Brazil’s east coast and is today one of the most endangered rain forests in the world.

The new findings from the ecological modelling experts led by Andreas Huth and Klaus Henle are also relevant for negotiations at the UN climate conference in Copenhagen. Under the heading REDD (Reducing Emissions from Deforestation and Degradation), the conference will be discussing a mechanism for including the forests in climate protection. Forests bind carbon dioxide. Deforestation or degradation of forests leads to a further release or less fixing of carbon dioxide per unit area, thereby increasing the greenhouse effect. Around 20 per cent of total global CO2 emissions comes from the destruction of forests.

Tilo Arnhold

J. Groeneveld, L.F. Alves, L.C. Bernacci, E.L.M. Catharino, C. Knogge, J.P. Metzger:
S. Pütz, A. Huth (2009): The impact of fragmentation and density regulation on forest succession in the Atlantic rain forest. Ecol.Modell. 220 (19), 2450-2459

M.C. Ribeiro, J.P. Metzger, A.C. Martensen, F.J. Ponzoni and M. M. Hirota (2009):
The Brazilian Atlantic Forest: How much is left, and how is the remaining forest distributed? Implications for conservation. Biol. Conserv. 142, 1141-1153

More information
Dr. Jürgen Groeneveld/ Dr. Christoph Knogge/ Dr. Sandro Pütz / Dr. habil. Andreas Huth
Helmholtz centre for Environmental Research (UFZ)
Telephone: +49 341 235-3213, -1706, 1719
Dr. Jürgen Groeneveld
Dr. Christoph Knogge
Dr. Sandro Pütz
Dr. habil. Andreas Huth
Dr. Jean Paul Walter Metzger
University of São Paulo, Instituto Biociencias, São Paulo, Brazil
Telephone: ++55 11 3818.7564
Jean Paul Walter Metzger
University of São Paulo, Instituto Biociencias, Docentes
Helmholtz Centre for Environmental Research (UFZ)
Press office
Tilo Arnhold
Telefon: +49 341 235 1269
Weiterführende Links
Biodiversity: Biodiversity's bright spot. Nature 462, 266-269 (2009)
Research project Mata Atlantica:
FORMIND: an individual based forest model:
At the Helmholtz Centre for Environmental Research (UFZ) scientists research the causes and consequences of far-reaching environmental changes. They study water resources, biological diversity, the consequences of climate change and adaptation possibilities, environmental and biotechnologies, bio energy, the behaviour of chemicals in the environment and their effect on health, as well as modelling and social science issues. Their guiding research principle is supporting the sustainable use of natural resources and helping to secure these basic requirements of life over the long term under the influence of global change. The UFZ employs 930 people at its sites in Leipzig, Halle and Magdeburg. It is funded by the German government and by the states of Saxony and Saxony-Anhalt.

The Helmholtz Association helps solve major, pressing challenges facing society, science and the economy with top scientific achievements in six research areas: Energy, Earth and Environment, Health, Key Technologies, Structure of Matter, Transport and Space. With 28,000 employees in 16 research centres and an annual budget of around EUR 2.8 billion, the Helmholtz Association is Germany’s largest scientific organisation. Its work follows in the tradition of the great natural scientist Hermann von Helmholtz (1821-1894).

Tilo Arnhold | EurekAlert!
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