In just the first 15 years of the 21st century, droughts have ravaged nearly every region of the globe. As the driest inhabited continent on Earth, Australia is particularly vulnerable. The Millennium Drought struck the southeast corner of the country, where most of the Australian population is concentrated, from 2001 to 2009—the worst recorded drought there in a century. The drought period ended in 2010, when La Niña ushered in one of the wettest periods on record. In a country of extremes, such variation is not unusual. Climate models depict a future with increasing rainfall variability and even more frequent and severe droughts, but the response of vegetation to climate is complex and largely understudied. Here Ma et al. present their findings on how plant life copes with the unique environment.
The response to extreme climate events can fluctuate across ecosystems or even within ecosystems across seasons. Drought nearly always negatively affects ecosystems, but the magnitude varies considerably. For example, in grasslands carpeting the central United States, sensitivity to drought has been found to differ by twofold or more within a single biome. The authors sought to fill in some of the gaps in our understanding in southeastern Australia and to provide insight into plants’ sensitivity, or resilience, to drought.
The researchers looked at roughly 15 years of data collected by the NASA Land Processes Distributed Active Archive Center on land cover types, including cropland, pasture, woodland, hummock grassland, open and closed forests, and shrublands. They compared the Moderate Resolution Imaging Spectroradiometer (MODIS) enhanced vegetation index, which is used to infer vegetation condition, with rain and temperature data as well as indices of drought severity. They also looked at the start, peak, end, and length of growing seasons to evaluate the effect of drought on the plants’ life cycles, or phenology as denoted by scientists.
The study revealed that Australia’s drought and wet cycles in the early 21st century drastically altered vegetation activity. During the dry years, shrubland, grassland, and wheat cropland all saw declines. The drought also shortened growing seasons in acacia shrubland, hummock grassland, and wheat cropland sites—even completely eliminating the growing season in the most severe years. But when La Niña brought relief, the country experienced a jump in vegetation productivity, with shrublands experiencing the biggest boost. The researchers found that the wet sclerophyll forest, mallee woodland, and pasture lands were relatively resilient to the drought.
The declines in vegetation productivity were greatest in croplands, indicating that future droughts will likely have the largest impacts on agricultural systems. The study also found that semiarid ecosystems were most vulnerable. Although the sensitivity of some ecosystems is a concern for a future where drought events become ever more frequent, the authors note that the study also revealed an encouraging flexibility: In the most severe drought years, some vegetation was completely dormant, but when more favorable conditions arrived, even the most afflicted regions bounced back. (Journal of Geophysical Research: Biogeosciences, doi:10.1002/2015JG003144, 2015)
—Kate Wheeling, Freelance Writer
Citation: Wheeling, K. (2016), How plant life survives on Earth’s driest inhabited continent, Eos, 97, doi:10.1029/2016EO046221. Published on 18 February 2016.