BEAVERS, known for their ingenuity at damming small streams using branches, are unwittingly contributing to global warming (New Scientist, Vol 142, No 1931).

Beaver ponds flood low-lying areas and, like wetlands, cause the decay of submerged vegetation, which produces the greenhouse gases methane and carbon dioxide. But Joseph Yavitt and Timothy Fahey of Cornell University in New York have now found that the methane emissions from beaver ponds in the northern temperate forests are 10 times higher than from a wetland of the same size. Thought the reason for this is still not clear, Yavitt believes the beavers may be adding extra organic matter in the pond, which could accelerate the production of these gases.

Nonetheless it implies that northern forests are a net methane producer. The carbon dioxide generated by the ponds also means that the carbon dioxide absorption capacities of the northern forests should be reduced by 7 per cent.