Tree expansion is threatening crucial tall-grass praries, and researchers are looking at streams in hopes of gaining insight into how to slow down the takeover.
Researchers determined burn intervals can predict how quickly woody vegetation will expand along streams, Kansas State University reported.
The conversion of grasslands into forest ecosystems is a growing problem in the U.S., and it can have a significant effect on stream hydrology and biogeochemistry.
"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, university distinguished professor of biology.
To make their findings the researchers looked at 25 years of aerial photography on the Konza Prairie Biological Station and focused on three observed factors: "burn intervals; grazers, such as bison; and the historical presence of woody vegetation." The analysis revealed burn intervals effectively predicted the rate of woody vegetation expansion in these regions. Burning can help cut back the tree takeover in grassland prairies.
"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 said.
The study found bison do not help cut down tree and shrub expansion along streams because they don't normally spend time near the water.
Another theory suggests increased carbon dioxide in the atmosphere is contributing to the expansion of woody vegetation into grasslands. Grasses are better at conserving water and utilizing carbon dioxide than trees, beating them out in competition, but as atmospheric carbon levels increase the trees have an easier time growing.
"The tall-grass prairie is almost nonexistent on the globe," said Allison Veach, doctoral student in biology. "In order for us to preserve tall-grass prairie, we need to look at woody encroachment because it has been an issue. Things like no fire or differences in climate change may allow woody plant species to competitively take over grasslands."
The findings were published in a recent edition of the journal PLOS ONE.
