In Washington, scientists excluded elk from rainforest plots for 36 years; shrubs became 5 to 6 times more abundant, while 46 plant species disappeared

A fence built deep in the rainforest of Washington has uncovered an unexpected revelation about forest functioning. The objective of the researchers was to determine the effects of the absence of elk, which is one of the largest herbivores in the territory, on the vicinity of plants over a longer time. The scientists thought that plants would regenerate in the absence of herbivores, but the case turned out to be more complicated than anticipated.

After 36 years without elk, shrubs became far more common inside protected plots, with researchers reporting a several-fold increase in their abundance compared with areas where elk remained present. The long-term monitoring began in 1979 and continued until 2015, allowing researchers to observe how decades without elk altered plant communities. At the same time, many smaller plants disappeared. Researchers found that 46 of the original 74 plant species were lost from the fenced areas, showing that removing a large animal can reshape an entire plant community. The U.S. Geological Survey study examined long-term vegetation changes in rainforest plots in Washington after researchers excluded ungulates, including elk, beginning in 1979.

A forest experiment that lasted decades


The research was conducted in the temperate rainforests of Washington's Olympic Peninsula, an area naturally populated by Roosevelt elk that roam through the forests and feed on a variety of plant species. However, instead of looking at several different forests located in different ecologies, the scientists decided to look into the controlled plots of land with already established conditions for vegetation. They built fenced plots to keep the elk out and maintained all other relevant environmental conditions. Over more than three decades, they were able to study the development of shrubs, herbs, grasses, and other plant species.

The surprising cost of removing elk

At first, the removal of elk seemed to be beneficial for various species of plants. Without animals feeding on them, several plants were able to grow more freely. However, over time, fast-growing shrubs expanded and began taking up more space. Their increased growth has resulted in limiting light and nutrients available to smaller plants. Researchers found a decline in herb cover by about 15 percent to 20 percent, while grass-like plants almost disappeared. Instead of enriching the flora, the removal of elk allowed only some plants to grow and resulted in less diversity of species growing together in the area.

Why browsing mattered

The study showed that elk influence forest ecosystems in ways more complex than simply consuming vegetation. The elk feeding behavior ensures that some specific plant species are harmed and that others could dominate the surface of the forest in the desired locations. The elk create suitable conditions for other plants to grow by eating certain shrubs or young vegetation. Additionally, their movements and feeding habits act as natural processes regulating competition between plant species. Additional observations were made outside the enclosed areas to understand broader vegetation changes.

Why large animals matter in ecosystems

The results challenge the idea that removing grazing animals always improves natural areas. In certain ecosystems, plant eaters may serve to preserve biodiversity. But large herbivores like elk are part of a network of relationships involving plants, soil, insects, and other wildlife. Their presence can affect which plants survive and how forests develop over time. The results serve as a reminder to conservation managers that animal issues are best managed within a broader ecological context. Conservation of forested lands may require understanding the role of animals that have shaped those landscapes for generations.

How elk shape forest communities

The Washington rainforest experiment is just one example of how researchers are investigating the ways shifts in populations reverberate through ecosystems. These effects from one level of the food chain to other levels are often called trophic cascades. Investigations with large herbivores have shown that animals such as deer and elk can affect plant distribution, nutrient cycles, and habitats for other species across different ecosystems. These links can be used by ecologists to determine how changes in wildlife populations will affect forests in the long run. The experiments on the Olympic Peninsula are especially valuable because of the slow rate of many of the changes in ecosystems. Decades of data offer scientists clues to help inform future decisions about managing wildlife populations and conserving forests.