TF写作真题第018套（gm008）

GM_008

Native to Europe and Asia, cheatgrass is an invasive species of grass that is causing problems in North American fields. The plant quickly dominates fields that it has invaded and drives out other plants. This can cause, among other problems, severe damage to animal habitats and to scenic areas. Several solutions to the cheatgrass problem have been proposed by ecologists.

One option is to encourage animals such as cattle to feed on cheatgrass. Cattle and other livestock are known as grazers because they graze, or eat, small portions of grass or other plants throughout the day. If grazers were released in fields where cheatgrass is prevalent, the cheatgrass would be reduced. That would create room for native species to reestablish themselves and flourish. This plan is appealing because cheatgrass is most prevalent in areas of North America where cattle and other livestock are raised.

Another option is to burn the cheatgrass off the fields with controlled fires. This plan has the advantage of eliminating vast amounts of cheatgrass in a short time. Cheatgrass, it turns out, is a highly flammable plant: it burns much more easily than the native plant species that have been crowded out. Strategically set fires could burn away the cheatgrass where it has come to dominate, creating space so the newly cleared fields could be reseeded with native grasses and other plants.

Still another option is to introduce a fungal parasite that specifically attacks cheatgrass. In Europe and Asia, where cheatgrass is a native species, there is a species of fungus that has the ability to prevent cheatgrass from reproducing. Introducing this fungus in North American fields where cheatgrass has proliferated could slow the spread of cheatgrass, making it possible for native species to better compete against cheatgrass.

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