01 November 2023

The Great Plains is being invaded by trees

The "Great Plains" of the central United States is predominantly a grassland biome, but in relatively recent years, that biome is being encroached upon by woody plants, including trees.  

Trees are good? Right?  They soak up carbon to offset human-induced climate change.  So we should be happy about this change?  Not so fast.  There are deeper implications, including the underlying aquifer:

The standard explanation for the ongoing depletion of underground aquifers is that they are being drained dry by modern farming techniques and the drilling of wells for urban and industrial use.  But vegetation can contribute to this process by the transpiration of water from the soil to the air.  

This problem has been extensively studied, espeially by agricultural extension services at universities in the Great Plains.  Some of that information has been summarized by The Prairie Project and in this 88-page longread.  I encountered the concept in a shorter article by The Cornell Lab, which considers the effect of decreasing grasslands on the survival of various avian species.
The Sandhills occupy roughly 20,000 square miles in north-central Nebraska, a quarter of the state. Formed as shift­ing, growing dunes of wind-driven sand, the hills stabilized as recently as 1,000 years ago and today are capped by mixed-grass prairie. Known by locals and ecologists as “choppy sands,” the low but steep hills are prone to slumping areas called “catsteps” and wind-caused “blowouts” of exposed sand.

When European explorers first surveyed the land, hardly a tree could be found. “You could travel across the entire Sandhills without seeing a tree,” says Dillon Fogarty, researcher and program coordinator for working lands conservation at the University of Nebraska–Lincoln. “They were tucked in on just a few stream banks.”

In those days, the force on the landscape keeping trees in check was fire—some set naturally by lightning, but most by busy humans with an eye toward game and land management. The earliest inhabitants of the Plains, says Fogarty, “actively shaped their environment to create an environment that they could thrive in... 

Settlers unwit­tingly aided the destruction of the prairie by planting more trees—even making an organized effort of it... And that means the trees are on the move. According to 2022 research pub­lished in the Journal of Applied Ecology, tree cover has increased 50% across the rangelands of the western U.S. in the last 30 years. The creeping woodlands threaten open prairie, prairie wildlife species, and the ranching industry. They also increase the chances of uncontrol­lable wildfire.
I would encourage anyone interested in the subject matter to read the links.  The best course for the future is neither simple nor obvious.


  1. I wonder what effect removing large grazers (like buffalo/ bison) had? I would think any young saplings along the edges of areas with trees in particular would be prone to nibbling and even being trampled or having their bark scraped by animals using them to scratch itchy hides. Grass seems like it could rebound more quickly than woody plants from those pressures.

  2. I see something similar in the Eastern Townships (Estrie) of Quebec - farmers die off, no one to take over as a farmer, their no longer hayed fields grow over and become forests. That 're-forestation' also can happen because of the small size of the hay fields and the humongous farm machinery modern farmers now have that requires big, flat fields. If they (the fields that is) are lucky, they are kept open by use as beef cattle pastures.

  3. I will never forget asking my 8th grade history teacher what is to stop the forest from covering the prairie .. As a kid who grew up in the edge of the prairie in the Black Hills of SD … and lived a few years on the CO prairie in a house surrounded by wind break trees .. I knew trees grew in the prairie. My teacher had no solid answer for me … something that I have studied the rest of my life.

    I agree with others — Native peoples and the bison managed the prairies. Before that mega fauna surely played a large part in minimizing tree growth.


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