Over the last two decades, there has been growing concern that very high rates of modern extinction -- loss of plant and animal species due to habitat destruction, overharvesting and other human-caused environmental changes -- could reduce nature’s ability to provide goods and services that people need, “like food, fuel, carbon storage, clean water, and habitat,” says the University of Vermont’s Carol Adair.
But it’s been unclear how these species losses stack up against other human-caused environmental changes that affect ecosystem productivity.
Now, a new study in the journal Nature provides a sobering answer: extinction of plant and animal species appears to damage ecosystem health as much as climate change, pollution and other major forms of environmental stress.
The study -- led by an international research team, including UVM’s Adair -- was published May 2.
Species matter
The study is the first comprehensive effort to directly compare the impacts of biological diversity loss to the anticipated effects of a host of other human-caused environmental changes.
The results highlight the need for stronger local, national and international efforts to protect biodiversity and the benefits it provides, according to the researchers, who are based at nine institutions in the United States, Canada and Sweden.
“The take-home message is that loss of species is as important as climate change and pollution,” says UVM’s Adair, an expert on global change in the Rubenstein School of Environment and Natural Resources. “When we’re working on solving these other problems we should make sure the solutions don’t negatively impact biodiversity.”
“These extinctions may well rank as one of the top five drivers of global change,” said Brad Cardinale, a University of Michgan ecologist and co-author on the study.
“Some people have assumed that biodiversity effects are relatively minor compared to other environmental stressors,” said biologist David Hooper of Western Washington University, the lead author of the new paper. “Our new results show that future loss of species has the potential to reduce plant production just as much as global warming and pollution.”
Global synthesis
In their study, Hooper and colleagues used combined data from a large number of published studies to compare how various global environmental stressors affect two processes important in all ecosystems: plant growth and the decomposition of dead plants by bacteria and fungi. The new study, funded by the National Science Foundation and the National Center for Ecological Analysis and Synthesis, involved the construction of a database drawn from 192 peer-reviewed publications about experiments that manipulated species richness and examined the impact on ecosystem processes.
This global synthesis found that in areas where local species loss this century falls within the lower range of projections (loss of 1 to 20 percent of plant species), very few impacts on plant growth will result, and changes in species richness will rank low relative to the impacts projected for other environmental changes.
In ecosystems where species losses fall within intermediate projections (21 to 40 percent of species), however, species loss is expected to reduce plant growth by 5 to 10 percent, an effect that is comparable to the expected impacts of climate warming and increased ultraviolet radiation due to stratospheric ozone loss.
At higher levels of extinction (41 to 60 percent of species), the impacts of species loss ranked with those of many other major drivers of environmental change, such as ozone pollution, acid deposition on forests and nutrient pollution.
“Within the range of expected species losses, we saw average declines in plant growth that were as large as changes seen in experiments simulating several other major environmental changes caused by humans,” Hooper said.
“I was surprised, and most of the people in the study were surprised, to see species loss rank up there with all these other changes,” UVM’s Adair said.
Policy points
The strength of the observed biodiversity effects suggests that policymakers searching for solutions to other pressing environmental problems should be aware of potential adverse effects on biodiversity, as well, the researchers said.
“For example, one of the things we can do about climate change is to use biofuels,” say Adair, “but some biofuels incentives result in rainforest destruction -- palm oil plantations and soybeans instead of rainforests -- so you’re losing diversity.” Instead, Adair points towards several international projects that seek to decrease greenhouse gas loads and also preserve biodiversity.
Still to be determined is how diversity loss and other large-scale environmental changes will interact to alter ecosystems. “The biggest challenge looking forward,” said J. Emmett Duffy of the Virginia Institute of Marine Science, a co-author of the paper, “is to predict the combined impacts of these environmental challenges to natural ecosystems and to society.”
This story is adapted from materials prepared by Jim Erickson at the University of Michigan.