填空题：Can We Replant the Planet's Rainforests? It's hard not to be

Can We Replant the Planet's Rainforests?
It's hard not to be impressed by rainfurests. Towering, aged trees called emergants stretch almost 250 feet (76 meters) into the air, surpassing the interwoven canopy that both covers and houses more than half of the world's species. Though rainforests contain nearly half of all the planet's trees, they only cover about 7 percent of the surface of the land.
Despite the importance of rainforests, deforestation practices continue. Though the term can apply to natural causes like forest fires, it's commonly linked to human activities, like logging, agriculture and mining--all important for our economy. But by stripping (剥夺 ) the land of these resources, we must accept the consequences of our actions. Chopping down rainforests increases the likelihood of soil erosion, landslides and flooding. It also decreases biodiversity and medical resources. More than 25 percent of modern medicine is derived from rainfurest plants, and only 1 percent of rainforest plant species have been studied for potential medicinal uses. Deforestation also destroys the homelands of indigenous cultures and affects the livelihoods Of millions of other people, many of whom live in the world's poorest regions.
In an effort to counteract this destruction, conservation efforts are blossoming across the globe. Among these are reforestation projects, aimed at increasing the amount of living trees and physically linking remaining forests together, to combat habitat loss and prevent species extinction.
There arc many challenges facing these projects. Firstly, rainforests arc full of ancient, gigantic trees; these aren't the saplings you buy at your local nursery. Much of the action of a rainforest's ecosystem takes place in the lofty upper reaches,which can present problems for reforestation efforts since towering trees take decades to grow. Secondly, rainforest trees closely rely on their evolutionary playmates--the surrounding flora and fauna--to create the delicate conditions needed to sustain functions such as nutrient cycles and pollination.
So while rainfurests provide a flourishing (欣欣向荣的) habitat for life, the success of that habitat relies on a fragile balance of ecological factors. Take away the trees and you have a major problem. But if the soil's bacteria and other microorganisms (微生物 ), which break down the nutrient-rich organic matter that tumbles to the dark forest floor, arc also eliminated, the rainfurest is destroyed. If the insects and birds that act as critical pollinators go extinct, life will falter.
So, can we push up our sleeves, grab a shovel, dig in and just start replanting the rainforests? To a certain extent, we can.
However, while efforts at reforestation have significant value, they're usually not as crucial as preserving existing rainforests.
Rainforest conservation is just as important as trying to reforest other areas.
Reforestation can be accomplished by nature, by humans or through a combination of the two. Some reforestation efforts focus on growing forests quickly because these woodlands are key to many of Earth's natural cycles, such as the carbon and water cycles. Replanting deforested land with quick-growing exotic tree species, like eucalyptus or Australian acacia, can help solve immediate problems such as soil erosion and elevated carbon levels.
However, exotic trees may make the land unsuitable for future rainforest cultivation by changing the soil's original characteristics. Scientists need to study individual situations to determine what type of impact each foreign species will make on the area's microbial life, and what the appropriate choices are for reforestation. On a positive note, fast-growing secondary forests and tree farms can replace primary forests as a source for agricultural and energy needs. A primary forest is basically one that's undisturbed by humans and has suffered very few ecological disruptions ( ep~l ). There are several other names for a primary forest, such as old growth and primeval forest. A secondary forest is one that has regrown after a destructive event, like a fire or logging. Primary forests usually have much higher levels of biodiversity than secondary ones, which is part of the reason conservationists are trying to save old growth.
In areas where deforestation is severe, remaining patches of primary forests are often located at great distances from other surviving rainforests or reforested regions. This makes animal survival and recolonization, as well as plant cross-pollination, difficult and can impede efforts to sustain actual rainforest ecology. Although the parcels of vegetative land can increase the chance of some species' short-term survival, researchers say the species are likely doomed to extinction over the long tema.
One-way conservationists seek to protect rainforest species is to reforest the corridors of trees that lie between rainforest parcels. This gives plants and animals access to a larger habitat and the chance to mix with other populations, which can boost their genetic diversity and help prevent extinction through isolation for most species. Conservationists can help cultivate these arboreal arteries into supportable rainforest habitats by working to have these corridors widened. The wider the corridors are, the safer they become for migrating animals to use.
It's also important to reforest and enlarge areas adjacent to these surviving parcels. This provides an easy means for species to inhabit new territory and expand viable rainforest ecology.
Researchers are exploring several options for improving and easing reforestation efforts. One inventive method involves bats. Installing man-made bat roosts in deforested areas can encourage these uniquely flight-enabled mammals (like the spectacled flying fox) to spread seeds and begin the process of rainforest regeneration. Activities like installing bat roosts are examples of how people are a part of natural reforestation efforts.
Reforestation efforts are sprouting up all around the world. Numerous conservation groups are working to preserve, enlarge and connect the world's rainforests. Let's take a closer look at some of those projects.
Rwanda's government and various ecological groups are paying special attention to the Gishwati Forest Reserve. Once a vast rainforest, activities such as deforestation and refugee resettlement reduced it to a fraction of its original size around the turn of the century. Since then, reforestation has somewhat increased the size of the forest, but it remains a sliver of its original size.
A project called the Rwandan National Conservation Park is gaining momentum, and those people involved with the project are working to bring the rainforest back and connect it with larger, surviving rainforests nearby. These individuals and organizations are looking to accomplish this through the use of wide tree corridors. They also plan to increase the acreage of the core forest and study the ecology of the forest's animals, particularly its chimpanzees.
According the passage, what activities destroy the rainforests?
[A] All human activities,
[B] Forest fires, farming and mining.
[C] Logging only.
[D] Soil erosion, landslides and flooding.