Soil Erosion Rates Rose More Than 100-Fold In The US Following Colonization Via Deforestation & Industrial Agriculture, Research Finds (+American Indian Forest Management Practices Explained)
Soil erosion rates increased more than a 100-fold in the southeastern US after European colonization via the large-scale deforestation and industrial agriculture that accompanied it, according to new research from the University of Vermont.
Previous to European colonization, the region had seen rates of hill-slope erosion of around an inch every 2500-years — after colonization these rates skyrocketed to an inch every 25-years (with a peak in the late-1800s/early-1900s).
“That’s more than a hundred-fold increase,” noted study leader Paul Bierman, a geologist at the University of Vermont.
“Our study shows exactly how huge an effect European colonization and agriculture had on the landscape of North America,” stated geologist Dylan Rood, of Imperial College, London. “Humans (colonizers) scraped off the soil more than 100 times faster than other natural processes!”
All along the southern Piedmont from Virginia to Alabama — the land between the Appalachian Mountains and the coastal plain — clay-soils had over millennia been building up. With colonization though — as much soil was eroded and lost during only a couple decades as would have been lost over thousands of years before colonization. This occurred largely as a result of widespread deforestation, and cotton and tobacco farming/production.
Here’s the explanation of the methodology used by the researchers:
The scientist collected twenty-four sediment samples from these rivers. From quartz in the sediment, Bierman and his team at the University of Vermont’s Cosmogenic Nuclide Laboratory extracted a rare form of the element beryllium, an isotope called beryllium-10. Formed by cosmic rays, the isotope builds up in the top few feet of the soil. The slower the rate of erosion, the longer soil is exposed at Earth’s surface, the more beryllium-10 it accumulates. Using an accelerator mass spectrometer at the Lawrence Livermore National Laboratory, the geologists measured how much beryllium-10 was in their samples — giving them a kind of clock to measure erosion over long time spans.
These modern river sediments revealed rates of soil loss over tens of thousands of years. This allowed the team to compare these background rates to post-settlement rates of both upland erosion and downriver sediment yield that have been well documented since the early 1900s across this Piedmont region.
While the scientists concluded that upland erosion was accelerated by a hundred-fold, the amount of sediment at the outlets of these rivers was increased only about 5 to 10 times above pre-settlement levels, meaning that the rivers were only transporting about 6% of the eroded soil. This shows that most of the material eroded over the last two centuries still remains as “legacy sediment,” the scientists write, piled up at the base of hillslopes and along valley bottoms.
The researchers behind this work several times made note of pre-colonization as being “pre-human” activity — which is a very strange comment to make since that region has been inhabited by people for at least 16,000 years, and it seems very likely that occupation goes back longer than that.
Genetic studies suggest that part of the population ancestral to modern American Indians split off genetically from the population(s) ancestral to modern Europeans over 25,000 years ago (see: New Branch Added to European Family Tree) — so, people could very well have been in the region for quite some time.
(Author’s note: As always with genetic “science” though, it’s worth remembering that (this coming from a researcher in the field): “Genetic studies operate on numerous assumptions and suffer from methodological limitations such as selection bias and confounding. Phenomenon like genetic drift, foundation and bottleneck effects cause large errors, particularly in haplogroup studies. No matter how accurate the methodology, conclusions derived from such studies are compiled on the basis of how the author envisages their data fits with established archaeological or linguistic theories.”)
And, for that matter, intensive agriculture has been a repeated and important component of the various cultures/civilizations that have lived in that area, for many millennia. (See: Eastern Agricultural Complex) Something worth noting here is that various different agricultural-complexes have existed there and disappeared over this time — all without causing the same degree of rapid soil erosion that we’ve seen in recent times.
Why? Were the land-use practices in use then superior (as far as soil erosion goes)? Were the population-numbers low enough that environmental-problems tended to be more minimal?
It should be noted here that there is absolutely no doubt (this is very well documented) that most of the eastern and southeastern American Indian tribes of earlier times practiced extensive forest management — the forests of the time were heavily manipulated to favor species valuable to human use, such as: American Chestnut trees, Hickory nut trees, butternut trees, fuel-wood trees, berries, etc. And also to create the sorts of biologically-productive lands that supported large bison/buffalo — and moose, bear, salmon, turkey, deer, etc — populations.
While there were a number of different methods used to accomplish said results, perhaps the most important was the regular and deliberate setting of fires at certain times of the year. In addition to allowing for the support of desirable species, and the elimination of undesirable ones, said practices also went a long way towards reducing resident-populations of common pests, such as: ticks, chiggers, fleas, tree-nut larvae, etc.
On the subject of the American Chestnut (Castanea dentata) forests (which could grow to be more than 80-feet tall) that once covered the region — one European explorer at the time commented that the forests were so filled with food that one could seemingly survive quite readily while performing next to no work at all. (Not during the winter months obviously.)
Surely modern industrial-agriculture isn’t the only way to go about things?
The new findings are detailed in a study published in the February issue of the journal Geology.
Image Credit: American Chestnut Society; UVM