Plant extinctions could cut ecosystem productivity in half
A meta-analysis of 44 experiments in natural habitats shows that plant extinctions reduce ecosystem productivity by up to 50%.
The fate of life on earth is tied inextricably to plants: they absorb CO2, produce oxygen and food, and provide myriad ecosystem services. Now a study, published November 8 in Proceedings of the National Academy of Sciences U.S.A., indicates that the extinction of plant species diminishes the total amount of biomass in natural habitats by as much as 50%. The take-home message: diversity matters greatly if we are to maintain critical benefits from nature, the researchers say.
Scientists investigating the effects of declining diversity on ecosystems are generally divided into two camps. One group holds that it's the loss of highly productive dominant species that is important in biomass loss; the other contends that dwindling numbers of species in unique and complementary niches are to blame. Following up on previous work, ecologist Bradley Cardinale of the University of California Santa Barbara and his colleagues analyzed 44 experiments that manipulated species numbers in plant communities to simulate extinctions. The experiments encompassed the global gamut of habitats, from tundra to tropical rain forest. Each included an average of 15 species and lasted on average 2.5 years.
For each experiment, Cardinale's team compared the amount of biomass produced in the most diverse plant assemblage (i.e., the "natural" community) with the least diverse one (typically a monoculture). The analysis showed that, reduced to a minimum of species, natural communities forfeited on average about 50% of their productivity. Strikingly, the effect increased over time. "Because research generally is funded for short time periods, it's difficult to assess how long it takes to reach the maximum impact of diversity loss, but clearly we've underestimated the effects," Cardinale says.
Perhaps more important, the analysis revealed that losing dominant, highly productive species accounted for just 34% of the biomass loss. The remainder was attributable to the departure of suites of complementary species. "Whether that's because the species facilitate each other's growth or because each occupies an irreplaceable niche isn't clear," Cardinale says. But, he warns, "as large areas around the world are being converted to monocultures, it behooves us to understand we may be compromising nature's capacity to provide ecological services critical to humanity."
