Ecological drought: Where not just humanity but ecosystems suffer
By Paul Hormick
When droughts strike, our concerns have almost always been limited to those of human society, how a dry growing season might diminish that autumn’s crop yield or how long-term drought might affect water supplies for drinking water and irrigation. But as climate change has exacerbated droughts, making them hotter, last longer, and extend over larger areas of land, there is a growing awareness that, besides human society, ecosystems worldwide are placed in increased vulnerability in a hotter and dryer world.
To this end, a team led by ecologist and paleoecologist Shelley D. Crausbay and biologist Aaron R. Ramirez has defined a new type of drought, ecological drought. In a paper published in the December, 2017 issue of the American Meteorological Society journal, the scientists explain that this more severe type of drought increases the vulnerability of ecosystems, with greater implications for human populations, which rely on the resources and services these ecosystems provide.
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As the authors point out, a framework that excludes the effects that drought may have on a biome will often lead policy and decision makers into an “either/or” mindset, pitting the water uses of humans against the needs of ecosystems. Residents of the US state of California are familiar with this conflict, when drought brings about debates over the agricultural demands for water versus the needs to maintain water levels sufficient in the Sacramento River Delta to maintain the population of the delta smelt, a small endangered fish that lives in the freshwater/saltwater intermixing zone of the delta. Crausbay points out that the smelt could be an indicator species for the health of the entire waterway. By disregarding the fish, the entire ecosystem, and the people who rely on that ecosystem, could suffer.
The authors offer insights into how humans can enhance the ability of an ecosystem to withstand the stress of drought through adaptations in resource management. During severe drought, tree mortality is higher in denser forest stands. By adjusting forestry practices, reducing basal areas in these denser stands, tree mortality can be mitigated. In the US state of Montana, they are finding ways to mimic the effects of beavers, which have been extirpated from many areas. Beaver dams slow down the flow of water and let it pool. The resulting wetlands replenish groundwater. “People can imitate the beaver dams by piling rocks in streams. It’s simple; it’s just stacking rocks. This makes the land work like a sponge, holding the water.” Crausbay says.
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