Plant extinctions erode benefits to humanity

Environment News Service: Scientists are warning that species extinctions could reduce the productivity of plants on Earth by half. In a new analysis, the international team led by University of California researchers shows that humans could lose some of the most important benefits that plants provide.

Plant productivity regulates the absorption of greenhouse gases like carbon dioxide, as well as the ability of habitats to produce oxygen, food, fiber, and biofuels.

Arctostaphylos glandulosa Eastw. ssp. crassifolia, or Del Mar manzanita, is an endangered shrub found in California. (Photo ©J.S. Peterson courtesy USDA)

Both the number and types of species going extinct are changing the "services" that ecosystems provide to humanity, the authors conclude. "The process by which plants grow and produce more plant biomass is one of the most fundamental biological processes on the planet," said Bradley Cardinale, lead author of the paper and assistant professor of biology at UC Santa Barbara.

Dr. Cardinale said experiments to date have probably underestimated the impact of species loss on ecosystems. "We found that as experiments were run longer, they detected increasingly strong impacts of species diversity on plant productivity," he said. "Unfortunately, because most experiments have only been funded to run for a few years at a time, they have probably underestimated the impacts of extinction on natural habitats."

Dr. Bradley Cardinale (Photo courtesy UC-Santa Barbara)

The article will appear this week in the online issue of the "Proceedings of the National Academy of Sciences." The study summarized the results of 44 experiments from around the world that simulated plant species extinction. It shows that ecosystems with fewer species produce up to 50 percent less plant biomass than those with more "natural" levels of diversity.

"Therefore, species extinctions could compromise the benefits that nature provides to society," said Cardinale. In practical terms, this means that diverse ecosystems are likely to be better at controlling pests, breaking down organic matter, and absorbing carbon dioxide.

"Our analyses provide the most comprehensive evidence yet that natural habitats with a greater variety of plant species are more productive," said co-author Michel Loreau of McGill University in Montreal.

"This occurs partly because diverse communities are more likely to contain highly productive species," said Loreau. "But even more important, our analyses show that diverse communities are more productive because plants are complementary in how they use biological resources. In other words, different plant species play unique roles in the environment."

Co-author Andy Hector, an assistant professor at the University of Zurich, said plant communities operate like a soccer team. "Teams are composed of both star players and supporting players," said Hector. "You probably can't win many games if you lose your top striker because she or he is the most productive player and can dominate a game. But strikers cannot win games by themselves. They need great passes from supporting players and solid goal-tending if the team is going to be successful as a whole." The authors say plant communities are also composed of both stars and supporting players.

Until recently, scientists knew much about the causes of global species extinction, but very little about the ecological consequences. This statistical analysis shows that species extinction generally causes ecosystems to become less productive, and less efficient at capturing biological resources.

The authors call species extinction "one of the most pronounced environmental changes of our time," and note that many scientists now argue that the Earth is in the midst of the sixth mass extinction in the history of life. Some estimates suggest that as much as 50 percent of all known species could be extinct by the end of this century.