Grasslands being overtaken by trees

 Water resources for America's grasslands are limited, and a new study suggests those grasslands are increasingly under threat as adjacent woodlands encroach upon them and soak up precious groundwater.
"This is an important issue regionally, because as trees expand into these grassland areas, people who are using grassland for cattle production have less grass for animals, too," said Walter Dodds, the study's lead author and a distinguished professor of biology at Kansas State University.
Dodds has been studying watersheds for more than two decades, and is interested in the transition from grasslands to forest, as it can have a profound effect on the hydrology and biogeochemistry of prairie streams that run through them.
To better understand the dynamics of this interplay between field, stream and forest, Dodds and his research colleagues analyzed 25 years worth aerial photographs of the Konza grasslands in Kansas. They plotted factors like burn intervals, the presence of bison and other grazers, as well as the historical presence of woody plants. They found that burn intervals had most obvious effect on the encroachment of trees and shrubs.
Burning every one to two years, researchers found, kept woodlands at bay. But longer periods without burning allowed for increased encroachment.
"Although we can reduce woody expansion by burning more frequently, we can't prevent it from occurring over time," said Researcher Allison Veach. "Woody plant encroachment may not be prevented by fire alone."
"It's clear from this research that if you don't burn at all, these grassland streams basically are going to switch to forests and will not be grassland streams anymore," Dodds added.
The study was published this week in the journal PLOS ONE.