AgriLife Research study shows population changes cause woodlands encroachment
Woody plant encroachment is one of the biggest challenges facing rangelands worldwide, but it consistently has been under-measured and poorly understood, according to Dr. Matthew Berg, a Texas A&M AgriLife Research postdoctoral research associate in the Texas A&M University Department of Ecosystem Science and Management. He is trying to change both the understanding and measurement with his latest study, which was published in the July issue of Rangeland Ecology and Management.
Berg used time-series aerial imagery and historical census data to quantify changes in population, land ownership patterns and woody cover between 1937 and 2012 in three different settings in Central Texas: a semi-urban watershed almost entirely within the city limits of Lampasas, rural watersheds in Lampasas County and a portion of Burnet County, and the adjoining rural watersheds in Mills County.
Joining Berg in this study were Dr. Bradford Wilcox, AgriLife Research and Texas A&M Department of Ecosystem Science and Management; Dr. Michael Sorice, Virginia Tech; and Dr. Jay Angerer, Dr. Edward Rhodes and Dr. William Fox, all with AgriLife Research.
The research was funded by grants from the U.S. Department of Agriculture – National Institute of Food and Agriculture and the National Science Foundation, and a Tom Slick Graduate Research Fellowship from the Texas A&M College of Agriculture and Life Sciences.
Berg said most past research focused on environmental and ecological connections. This study documents for the first time the relationship between human demographics and the conversion of grassland to woody plant cover, shrubs and woodlands.
In this effort, the scientists were able to document the changes in grassland along with population, and for some, the results might be surprising.
“What we found was unexpected,” Berg said. “What makes these relationships remarkable is the strength of the correlations for all three settings, despite large differences in both the direction and timing of changes.”
Typically, it is thought that when people move into an area, they clear off the land to build their homes and eventually to build cities. But the reality is, unless they are in the agriculture business, the widespread clearing does not occur, the scientists found.
“Where people moved, woody plants followed,” he said. “Only when the size of farms increased did the amount of woody plant cover decrease.”