To calculate ecosystem water use, the scientists used satellite observations to approximate above-ground net plant productivity at each site. Then they combined these approximations with field data of precipitation and estimates of plant water loss to generate indicators of plant water use efficiency.
The team observed that ecosystem water-use efficiency increased in the driest years and decreased in the wettest years. This suggests that plant water demand fluctuated in accordance with water availability and that there is a cross-community capacity for tolerating low precipitation and responding to high precipitation during periods of warm drought.
However, the team observed that the water-use efficiency data exhibited a trend of "diminishing returns." This suggests plant communities eventually will approach a water-use efficiency threshold that will disrupt plant water use and severely limit plant production when drought is prolonged.
"Prolonged, warm drought makes a difference," Moran said. "To date, it appears there is resilience, but in the more sensitive biomes like grasslands, we are starting to see evidence of decreasing resilience. And as more and more ecosystems increase in aridity, more will reach this threshold."
The authors report that in some Australian grasslands, ecosystem resilience has decreased with the increasing aridity widely reported as a result of the prolonged warm drought over these biomes.
Moran cautioned that her team also saw the limit in some of the study areas in Utah, Arizona and New Mexico.
"We know what the resilience was in the 1980s and 1990s, and we compared it to the early 21st century," she
|Contact: Daniel Stolte|
University of Arizona