Pressures from grazers hastens ecosystem collapse from drought.
The researchers found that these tipping points can happen much sooner than current models predict because of the added pressures placed on drought-weakened plants by grazing animals and fungal pathogens.
The researchers performed a series of experiments before, during and after the drought to test how pressures from heavy grazing by crabs — the main natural enemy of plants in the protected marshes — affected resilience to and recovery from the drought.
"In test plots where crabs were excluded, we found that vegetation loss was significantly lower and many plants could survive the drought," said Qiang He, a postdoctoral researcher in Silliman’s lab.
"But in control plots, grazing by crabs decimated the drought-stressed plants, resulting in nearly complete vegetation loss," said He, who has studied the Chinese marshes for more than 10 years since he was a student at Beijing Normal University.
"Plants in forests and grasslands can also be decimated by natural enemies, such as insects and fungal pathogens, during droughts."
"The problem is that most of the plant-tolerance models we currently use to predict these outcomes are based on laboratory studies or plant physiological studies, so they often don’t factor in the compounding effects of simultaneous stressors like drought and pressure from natural enemies.
The result has been that ecosystems are dying well before our models predict they will.
"Pressures from grazers hastens ecosystem collapse from drought: Experiments show grazing pressures compound drought stress, delay recovery."
"Pressures from grazers hastens ecosystem collapse from drought: Experiments show grazing pressures compound drought stress, delay recovery."