By Kathleen Wong, UC UC Nature
An international research effort into the effects of drought has quantified just how much prolonged periods of extreme dryness curbs the growth of grasslands and shrublands. Because climate change is increasing the possibility of severe future droughts, extended droughts could threaten the long-term health of ecosystems that cover nearly half the planet.
The research measured the effects of drought on 74 grasslands and shrublands around the world. Among the sites was Younger Lagoon Reserve in Santa Cruz, one of the 42 sites in the UC UC Nature. Michael Loik, a professor of environmental studies at UC Santa Cruz, established the International Drought Experiment plot at the reserve in 2015.
The new study, published in the journal Science, finds that while native grasslands and shrublands could adjust to moderate drought, they are no match for extended and severely dry conditions. Multiple years of drought, the study revealed, compounded the effects a single year of dryness. After four years of extreme drought, the plants lost 77% of their productivity, or ability to generate new organic matter. The bottom line: grassland and shrubland ecosystems lose much of their ability to recover from long periods of dryness.
The experiment was intended to replicate a once-a-century extreme drought. The Great Plains of North America experienced nearly a decade of such unusually dry years in the 1930s. Yet the worst effects of the Dust Bowl occurred only after multiple consecutive drought years, as would be predicted by the new study. Unfortunately, climate change is expected to make such extreme drought conditions more common in the future.
The research has major implications for a large swath of earth’s life support system. Grasslands and shrublands store more than 30 percent of global carbon, support industries such as cattle grazing, and provide habitat for iconic wildlife ranging from North American bison to African antelopes. In combination with a previous International Drought Experiment paper that quantified the effects of a single extremely dry year, this research will help scientists forecast the impacts of droughts on terrestrial ecosystems in the decades to come.
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