问答题

The Forest Service is responsible for the forests on public lands in the United States. It supervises almost seventy-eight million hectares of forests, grasslands, rivers and lakes. It is an agency of the Department of Agriculture. Forest Service officials say there are four major threats to forests and wild lands in America. The first is the threat of fire and fuel. This year, forest fires have burned more than three million hectares of land. That is almost two times as much as the ten-year average. Fires are a natural part of forest growth, but they can also threaten lives and property. Fuel is dead plant material and small plants that grow under tall trees. As much as forty-nine metric tons of fuel can build up on every hectare of forest floor. The Forest Service estimates that up to one-fourth of the forests it supervises have dangerous levels of fuel. Sometimes foresters set controlled fires to remove the fuel. Other times the fuel must be cleared by hand. Another threat to forests is from invasive species. These are non-native plants and animals that push out native kinds. They can cause a lot of economic damage. Some invaders are insects like the Asian longhorn beetle (长角甲虫). Some are diseases like white pine rust blister (锈蚀庖). Others are plants like the fast-growing kudzu vine (野葛藤). The Foreign Service has hundreds of experts who try to develop ways to deal with invasive species. The agency says another threat to the health of wild lands is the loss of open space. It says over one hectare of forest or grassland is lost to development every minute. Development also leads to the division of large natural areas into smaller ones. Many animals need wide open spaces. Also, building near wild lands increases the risk to homes from forest fires. The fourth threat to public lands is what the Forest Service calls unmanaged recreation. People can hunt, fish and camp in many national forests. But careless use of motor vehicles and other actions can be destructive. On November second, the Forest Service released a new rule on the use of motor vehicles on public lands. The rule requires each national forest to identify roads and paths that are open to motor vehicles. Vehicles will be banned from other areas. The ban, however, will not affect snowmobiles (雪上汽车). ________will not be banned from areas other than authorized roads and paths.