TOEFL統合ライティング

📖 読解文章

The concept of rewilding—restoring ecosystems to their pre-human state by reintroducing apex predators and keystone species—has gained traction as a powerful conservation tool. Proponents argue that rewilding can restore ecological balance, enhance biodiversity, and mitigate climate change. First, the reintroduction of wolves to Yellowstone National Park in 1995 demonstrated a trophic cascade: wolves reduced elk populations, allowing overgrazed willows and aspens to recover, which in turn supported beavers, songbirds, and fish. This shows that apex predators can regulate herbivore numbers and promote vegetation regrowth. Second, rewilding projects often involve large herbivores like bison or horses, which create heterogeneous habitats through grazing and trampling, increasing niche diversity and supporting a wider array of species. For instance, in European rewilding sites, the presence of Konik horses and Tauros cattle has led to a rise in insect and bird populations. Third, rewilded landscapes with healthy forests and grasslands act as carbon sinks, sequestering more CO2 than degraded lands, thus contributing to climate mitigation. The Oostvaardersplassen reserve in the Netherlands, despite controversies, shows that natural grazing can enhance soil carbon storage. Therefore, rewilding offers a feasible, cost-effective strategy for large-scale ecological restoration.

🎧 リスニング講義

Now listen to the following lecture by a professor of ecology, responding to the reading passage. Although the reading paints a rosy picture of rewilding, the scientific evidence is far less supportive. First, the Yellowstone example is oversimplified. While wolves did reduce elk numbers, the recovery of willows and aspens was also influenced by other factors, such as a series of wetter years and reduced human hunting. Moreover, in many ecosystems, apex predators fail to produce the same cascading effects because herbivores are not easily controlled or because vegetation is limited by soil and climate. Second, the claim that large herbivores enhance biodiversity is misleading. In practice, overgrazing by rewilded herbivores often leads to soil compaction, erosion, and the loss of sensitive plant species. For example, in the Oostvaardersplassen, the absence of natural predators resulted in overpopulation, leading to mass starvation of animals and severe damage to the ecosystem. Third, the carbon sequestration benefits are questionable. Rewilding may actually release carbon if it involves converting grasslands to shrublands or if herbivore activity disturbs soil organic matter. Moreover, the time required for carbon gains is long, and in the interim, ecosystems may become net sources of greenhouse gases. In short, rewilding is not a one-size-fits-all solution; it often fails to achieve its promised benefits and can even cause ecological harm.