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Forest fragmentation alters global carbon cycle

Careful measurements show how roads and other disturbances affect moisture and the ability of fungi and bacteria to break down dead wood

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Forest fragmentation has a big impact on the carbon cycle. bberwyn photo.

By Summit Voice

FRISCO —Logging roads, clearcuts and other disturbances that fragment forests can slow the decay of dead wood and significantly alter the cycling of carbon and nutrients in woodland ecosystems, according to a new study.

Scientists with Earthwatch and the University of Exeter (UK) took a hard look at global forest fragmentation, starting the well-known fact that the edge effect influences temperature, moisture and other elements of forest microclimates. But the effect on the carbon cycle is less understood, so the researchers used on-the-ground experiments combined with modeling to try and fill the gaps.

Wood blocks were placed in Wytham Woods near Oxford at various distances from the forest edge, and left to decay over two years. The measured decay rates were applied to a model of the surrounding landscape, to allow comparison between the current fragmented woodland cover and decay rates in continuous forest.

The research, published today in the journal Global Change Biology, shows that wood decay rates in the southern UK are reduced by around one quarter due to fragmentation. This effect is much larger than expected due to variation in temperatures and rainfall among years.

“We were surprised by the strength of the edge effect on wood decay, which we believe was driven by reduced moisture at the forest edge impairing the activity of saprotrophic fungi – those that live and feed on dead organic matter,” said Dr. Dan Bebber, of the University of Exeter.

Wood decay, and the recycling of other biological matter like leaf litter, is driven by fungi and by microbes that are sensitive to temperature and moisture. The difference between the absorption of carbon dioxide via photosynthesis by trees, and the release of carbon by microbes, determines the overall carbon balance of the forest.

“Saprotrophic fungi control the cycling of carbon and nutrients from wood in forests, and their responses to changes in microclimate driven by fragmentation, and also climate change, will influence whether forests are a carbon source or sink,” said Dr. Martha Crockatt, of Earthwatch.

The southern UK has a temperate climate with moderate temperatures and rainfall. Similar studies in different parts of the world, from the warm tropics to the cooler boreal regions, are needed to understand how edge effects on decomposition vary globally.

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