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綜合寫(xiě)作

The Russian thistle has an unusual method of spreading its seeds. It lives for a year, and when it dies, the top part of the plant dries up and separates from its roots. This dried tangle of leaves and branches—known as a tumbleweed—is blown along the ground by the wind, releasing seeds as it travels. Russian thistle is not native to the United States but has become established there as an invasive species. Invasive species are often considered harmful, but some scientists point out that this plant offers a number of benefits.

Food for Farmers’ Animals

First, Russian thistle can grow in dry areas where many other plants cannot, and it can survive long periods of little or no rain. It also has some nutritional value and can be eaten by large animals such as cows. In times of drought, when other plants cannot grow because of lack of rain, farmers can sometimes help their animals get enough nutrition by feeding them Russian thistle.

Habitat Creation

Second, Russian thistle can grow up to a meter high. As it often grows in regions with no trees, its size sometimes makes it the largest plant in the area. It thus creates valuable habitats for animals that would otherwise have no place to live. Small mammals and birds can take shelter under Russian thistles.

Soil Improvement

Finally, Russian thistle can grow in damaged soil where many native plants cannot. Once Russian thistle begins to grow in damaged soil, a fungus sometimes infects its roots. This fungus does two things. It weakens the Russian thistle, and it benefits certain native plants. As the fungus spreads in the soil, it supports the return of native plants to damaged areas, where they can then grow and flourish in the soil again, thanks to the fungus.

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