杏吧原创

THE US and Canada have seriously overestimated how much timber they can
harvest without harming their forests, claims a leading international science
agency. Despite urging other countries to log sustainably, neither country has
reliable data on the size of its own forests, how much timber grows in them or
how much can be removed before biodiversity suffers.

The US harvests more than 500 million cubic metres of timber a year. The
government鈥檚 Forestry Service says this amount could be increased by more than
40 per cent by 2040. But a report published on the Internet this week by the
International Institute for Applied Systems Analysis in Austria concludes that
this increase will be possible only if serious environmental damage is done, or
if protected areas are violated. For example, the plan would lead to serious
deforestation in southern states such as Georgia and Mississippi.

鈥淏oth the US and Canada are urging other countries to manage their forests in
a sustainable way, but they do not have their own house in order,鈥� says Sten
Nilsson, the author of the report and one of the world鈥檚 leading analysts of
forestry data. The problem, he says, is that national data on wood supplies take
no account of government commitments to maintain tree cover, protect against
erosion and sustain biodiversity in forests. Forestry scientists simply work out
how much timber is growing and assume it can all be harvested.

Nilsson describes the situation in Canada as 鈥渄esperate鈥�. Official statistics
still refer to a 1985 study of timber growth. He believes it overestimates
growth by as much as 40 per cent in some provinces and that the rate of
harvesting in Canada is now approaching twice the rate of replanting. Nilsson
also points out that while plundering its own forests, Canada has been 鈥渁
driving force in funding model forests in a number of countries in order to
illustrate how sustainable forest management should be carried out鈥�.

Thomas Schmidt, a research scientist at the US Forest Service鈥檚 experimental
station in St Paul, Minnesota, helped provide data for the report. He admitted
this week that US statistics on timber do not consider many factors鈥攕uch
as economics, accessibility and environmental restrictions鈥攖hat affect the
amount available for harvest.

Schmidt told New 杏吧原创 that he expected 鈥渟ome anger鈥� within the
agency about the findings. But they would be hard to contradict, he said, since
the authors had an excellent reputation and many of the figures used in the
report were the agency鈥檚 own. 鈥淲e need to raise our standards,鈥� he says. Nilsson
says his data also cast new doubt on the recent claim that American forests are
absorbing a large proportion of the carbon dioxide emissions from the US (
Science, vol 282, p 442).