托福official63综合写作环境类Integrated Writing范文+题目解析

Now listen to part of a lecture on the topic you just read about.

Professor: The methods mentioned in the reading are not likely to work very well in controlling cheat grass.Here’s why.

First, cheat grass is not a plant that grazers prefer. This means that if grazers are released in a field that has a lot of cheat grass, but that also has other kinds of plants, the grazers will eat the other kinds of plants first. The grazers might eat some of the cheat grass, but only after the native grasses and plants, the grasses and plants that we are trying to protect, have been destroyed. So releasing grazing animals into fields with cheat grass with probably have the opposite effect of the one intended. There will be fewer native grasses, but plenty of cheat grass still around.

Second, fire will destroy cheat grass plants on the surface, but that doesn’t mean cheat grass won’t quickly come back. Cheat grass produces many many seeds. The seeds can germinate even a few years after falling to the ground. Many seeds get pushed down into the soil below the surface. If the seeds are below the surface, Fire cannot harm them. So after the fire has burned away cheat grass plants and seeds on the surface of a field, the seeds that are buried in the soil below the surface sprout and give rise to new plants, and the field is soon again filled with cheat grass.

Third, the fungi parasite. Here you have to understand that cheat grass and the fungi parasite have lived together in their native habitats for thousands of years. During this time, cheat grass plants have been able to develop some resistance against the fungus, so while the fungus has the ability to harm cheat grass, in reality it only harms cheat grass plants that are already weak or sickly. The healthy and strong cheat grass plants can usually resist the fungi infection.

So introducing the fungi parasite into North America will probably not be efficient.