Fast-growing, drought-tolerant trees is slowly spreading to the grasslands of every continent except Antarctica. Considering how eager we are to reduce carbon emissions in the atmosphere, the millions of new tree seedlings sprouting every year seems like a good thing. But in reality, their spread in fragile grasslands and shrublands is upending ecosystems and livelihoods. As these areas become woodland, wildlife disappears, water supplies dwindle and soil health suffers. The risk of catastrophic wildfires has also risen sharply.
in a new research Published on Journal of Applied Ecology, researchers show how woodland expansion can cause economic losses. American ranchers typically rely on treeless pastures for their livestock. Between 1990 and 2019, landowners in the western United States lost nearly $5 billion in forage (plants eaten by cattle or sheep) due to the growth of new trees. The amount of pasture lost over these 30 years is equivalent to 332 million tons, or enough hay bales to circle the Earth 22 times.
“Grasslands are the most dangerous and least protected terrestrial ecosystems,” said Rheinhardt Scholtz, a global change biologist and affiliated researcher at the University of Nebraska-Lincoln. Grasslands on our planet, also known as savannahs, pampas, or plains, are in sharp decline. According to Scholtz, less than 10 percent of the land is intact because most of it has been cultivated for crops or bulldozed for human development. One of the most dire threats to remaining grasslands is tree erosion. “It’s a slow, silent killer,” Scholtz said.
Historically, tree expansion on grasslands has been suppressed by periodic fires that relegated woody vegetation to wet or rocky sites. But the number of trees exploded as European settlers put out the fires and planted thousands of trees to provide a windbreak for their homes and livestock. When trees invade grasslands, they compete with native grasses and wildflowers by stealing most of their sunlight and water.Birds, often used as bellwethers of ecosystem health, are sounding the alarm: North American birds Grassland bird populations down by more than 50 Percentage since 1970, a 2019 study exist science established.
Tree cover has increased by 50 percent in the western half of the U.S. over the past 30 years, with tree cover increasing steadily each year, according to a study of grassland forage loss led by University of Montana researcher Scott Morford .A total of nearly 150,000 kilometers2 Once treeless meadows have become woodlands. “That means we’ve lost an area the size of Iowa,” Morford said, emphasizing that another 200,000 square kilometers2 of treeless pastures — an area larger than Nebraska — are “under immediate threat” because of their proximity to seed sources.
To calculate pasture yield losses due to woodland expansion, Morford and his team used satellite imagery combined with meteorological data, topography, and soil and ground vegetation information to estimate changes in herbaceous biomass (that is, nonwoody plants, such as grasses) over time. Relationship between passage and tree cover. “Our computer model allowed us to turn the tree cover up or down like a knob on a stereo to see how production was affected,” explains Morford.