Grasslands around the world are under threat from trees, according to a new study from Kansas State University.
Streams, as well as tall grasslands surrounding them, are being studied by biologists, concerned that prairies could turn into forests or become covered in shrubs.
Tall grass is becoming less common in areas around the world, with shrubs and trees replacing the prairies. Such changes can affect the movement of water through the regional ecosystem, changing soil chemistry. This can have a dramatic, potentially negative, effect on the local environment.
"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," Walter Dodds, distinguished professor of biology at Kansas State University, said.
The Konza Prairie Biological Station, where the research was carried out, stretches over 8,600 acres in northeast Kansas.
Dodds has 20 years of experience studying the area. Along with Allison Veach, doctoral student in biology, the two studied 25 years of aerial photos of the station. The pair were looking for patterns in the growth of trees and shrubs within 100 feet of streams. They wanted to know specifically how grazing by animals affected the growth of plant life, as well as the time between large fires, known as the burn interval. They compared these effects to historical growth patterns of woody vegetation in the regions.
When the burn interval was low -- just a year or two -- growth of trees and shrubberies were kept in check. However, these fires do not appear to reduce the development of such organisms enough to preserve a healthy environment for grasslands, according to the study.
"Although we can reduce woody expansion by burning more frequently, we can't prevent it from occurring over time. Woody plant encroachment may not be prevented by fire alone," Veach said.
This research underscores the importance of controlled burns to keep growth of woody vegetation in check, assisting tall grasses to grow. However, the study also reveals that such actions are not enough to ensure the long-term survival of tall grass in prairies.
Dodds and Veach believe the recent growth of trees in grasslands could be due to increased carbon dioxide in the air. Grasses are more efficient than trees at utilizing the gas in respiration. As concentrations rise in the atmosphere, it is possible that shrubs and trees are able to use the atmospheric component to feed their growth.
Investigation of tall prairie grasses, and how they are affected by the growth of trees around streams, was profiled in the journal Plos One.
