六级冲刺练习：阅读（133）

　　Logically, therefore, research to solve problems is a major job of the Forest Service. It covers the whole forestry field, including the protection and management of forests, related rangelands, and water-sheds; utilization of forest products; and the economic aspects of forestry. The Services regional forest and range experiment stations and its Forest Products Laboratory are constantly making new forestry studies throughout the United States and announcing new forestry facts.

　　Redeeming the American Chestnut. Scientists have long been seeking ways of bringing back that valuable and storied tree, the American chestnut. Attacked by a blight brought in from Asia about 1900, practically all of our native chestnuts were killed. Their gaunt white skeletons are a reminder of a tree whose range extended from New England to Alabama and Louisiana. But there is a glimmer of hope. Forest Service scientists have found a few individual trees that seem to be resistant to the disease. Buds or branches from 28 of these tough survivors have been grafted to other root stocks for multiplication and the chance for further study of their resistance. Forest research may yet make the American chestnut once again tempt the palate , and also help supply the nations timber needs.

　　Can Lightning Fires Be Prevented? Foresters have a hard job making people careful with fire in the forests. At the same time, some of them are trying to make Nature cut down the number of fires she starts with her most powerful fire-starting weapon, lightning.

　　A little white cloud, peeking up over a Montana mountain, is quickly found by a mobile radar unit. It is tracked as it gets bigger and starts its journey with the winds. Finally, any lightning storm which develops in it is analyzed. This cooperative research project, known as Skyfire, has also made experiments in cloud seeding to reduce lightning occurrence. It is too early for positive conclusions, but scientists believe their findings will lead to a better preparedness and quicker attack on lightning-caused fires. Foresters may eventually be able to prevent lightning fires more easily than those caused by man.

　　Getting More Seed from Better Trees. Would you believe that healthy trees that have been deliberately wounded will produce more seed than undamaged trees? Thats what happened when foresters partly girdled some longleaf pines in Louisianathey produced twice as many cones as did ungirdled trees. In Montana, they tried it with five-year ponderosa pines. These experimental trees bore 26 cones as against one cone on the ungirdled control trees. In the South where slash pine is chipped for turpentine, the chipped trees produced 50 per cent more cones than comparable unchipped trees.