The American Tallgrass prairie used to be one of the largest continuous ecosystems – and also one of the most diverse ones. Originally it covered 170 million acres, spanning from Indiana to Kansas and from Canada to Texas. The complexity of this unique ecosystem is said to be surpassed only by the Brazilian rainforest.
It is hard to imagine that this sort of natural diversity can be lost only within a few generations’ time. However, it is exactly what happened with the prairie.
Loss of the Tallgrass Prairie in the United States
Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) has defined five key drivers of biodiversity loss; the top 1 position belongs to changes in land and sea use – and there is no better witness to that fact than the prairie, now one of the rarest and most endangered ecosystems in the world.
To put it plainly, the tallgrass prairie ecosystem has practically been plowed to its near-death, mostly within only a generation. Most has been transformed into farmland or pasture, and a significant chunk has been a target of urban development.
While we may argue that conquering and developing the prairie has been an inevitable move, when we calculate how much of the original ecosystem has actually survived, the numbers are anguishing. The estimates vary, but they roughly agree that only between one and four percent of the original prairie cover has lasted into present times.
The situation is even worse locally. For example, Iowa, which has historically been 75 to 80 percent prairie landscape, now holds less than 0.1 percent of the original land cover in the form of small pockets dispersed across the state.
That is why when we’re talking about the original tallgrass prairie, we’re actually discussing prairie remnants – mere fragments of the authentic, pre-settlement prairie landscape.
It is not the tallgrass that made the prairie such an attractive target for agriculture development; it’s what’s underneath it. By taking a look at it, we’re able to comprehend both its history and the reasons for its downfall.
Precious Prairie Soil
The prairies formed in the middle of the North American continent about 10,000 years ago. The retreating glaciers left behind the glacial till which served as a base on which the ecosystem was built.
Wind-carried loess and organic matter started to accumulate and the vegetation started to take root, creating deep, rich topsoil. Herbivores such as elk, deer, rabbits, and most of all, bison and prairie dogs, helped build up the level of nitrogen further with their feces.
Still, some mammals have had a more prominent role than others.
With their elaborate network of tunnels, prairie dogs aerated the soil, further upping its productivity. On the surface, the most numerous large prairie herbivore, the American Bison, kept the woody plants from even beginning to take over the space with their grazing habits, and had continuously fertilized the ground as a by-product. Thus, the prairie dog and the bison were – and still are – the keystone prairie species.
The biodiversity of the ecosystem was astounding – it was home to hundreds of wildflowers, grasses, and other plant taxons, and animals such as bison, elk, wolf, black bear, and hundreds of species of birds.
Human diversity was also a feature of the prairie – a large group of people known as the Plains Indians inhabited the Great Plains territory. Their agriculture, hunting, gathering, and even the use of controlled burning have been relatively in tune with the prairie’s natural dynamics. All until the beginning of the 19th century. (Related: Using LiDAR to Show How Native American Depopulation Impacted Forests in the United States)
From the 1800s onwards, the first European settlers took notice of this wide, “empty” space, and after suppressing the Native American tribes, began to colonize it and use it as a resource. Bison and prairie dogs were nearly hunted to extinction.
Domesticated cattle took over the grazing, and the land was increasingly cultivated for agricultural purposes with much more effective and invasive methods – specifically, the use of the plow. The development of motorized mechanization made this process even quicker and more intense.
Of course, such systematic destruction of the original ecosystem on a huge piece of land has had consequences that remain relevant and active today.
With the keystone species eliminated and the original plant cover gone or exposed to different, more intensive grazing patterns of domesticated cattle, the prairie soil was left exposed and with no mechanism to renew itself.
While most of the prairie was still pasture land up until World War I, during the war, large amounts of it were plowed and then over-cultivated due to the increased demand for wheat. Poor land management that followed had first led to serious soil degradation, and then erosion.
Perhaps there is no more foreboding symbol of these consequences than the Great Dust Bowl.
In the early 1930s, the region was struck by a severe drought that lasted for nearly a decade. The exposed soil, with no native plant root structures to keep it down, was swept away by high spring winds, forming clouds of wind-eroded soil.
The so-called “Black blizzards” were able to block out the sun. The dirt got into everything – people’s eyes, clothes, houses, and increased the social crisis propelled by the drought. In fact, the Dust Bowl or “The Dirty Thirties” phenomenon was one of the key causes that triggered the Great Depression.
Estimates are that between 1934 and 1935 – the drought’s harshest period – the Great Plains lost 1.2 billion tons of soil were lost across 100 million acres (156,000 square miles).
In the 21st century, there is heightened awareness about the importance of topsoil preservation and erosion prevention. However, the intensive agricultural practices are still focused on yields; although the topic is more often discussed, it seems that soil preservation is still not among the top priorities of agricultural production, ironically endangering the production itself.
While in most places the historic erosion levels are a matter of speculation, with estimates based on calculations rather than direct measurements, the Midwest is different. The intensity of erosion has created escarpments at the borders of fields and prairie remnants, meaning that soil scientists have a realistic insight into the historical rates of erosion.
Using high-resolution topographic surveys run across erosional escarpments at the boundaries of 20 prairies and the neighboring agricultural fields, a fresh study published in the AGU’s Earth’s Future journal has estimated that the median reduction in soil thickness over the past 150 years ranges from 0.04 to 0.69 m. That translates to median erosion rates of 1.9 mm per year ( 0.2–4.3 mm/year).
The median historical erosion rate was estimated to be 1.8 ± 1.2 mm per year – nearly double the rate considered tolerable by the USDA, surpassing all the earlier national soil erosion assessments.
The science is clear – the current erosion rates are underestimated and unsustainable.
There are positive developments, however. Techniques that conserve the soil are migrating from the realm of “alternative,” regenerative agriculture and making their way into large-scale commercial agriculture. But is the pace of the movement enough?
Among the applicable techniques to help reduce future soil erosion while still dedicating the land to agriculture, the most realistic farming techniques are cover crops and no-till farming.
Cover crops are specially chosen plant cultures planted in agricultural fields off-season, thereby not allowing the soil to remain bare during prolonged periods; thus, it becomes less prone to erosion by wind and water. The common cover crops usually have additional soil-enriching benefits such as nitrogen fixation to enrich the soil.
Unfortunately, although it has many benefits in the long run, planting cover crops is not overly popular due to the lack of short-term payoff.
Bruno Basso, a sustainable agriculture researcher at Michigan State University in East Lansing says that cover crops are used in just about 5 percent of possible cases. “It costs $40 to $50 per acre to plant a cover crop… The costs of cover crops are not supported” he says. Despite the fact that some government grants are available for this purpose, Basso stresses that there is a need for additional incentives.
Although the issue is often overlooked, it has been known for quite a while that mainstream soil tilling techniques are one of the major contributors to soil degradation and erosion.
But there is an alternative. The no-till farming is a technique that allows farmers to plant and grow crops without having to resort to tilling. In ideal cases, the no-till farmers have an established field that doesn’t require breaking the topsoil structure and remains productive without disturbance and losses.
The participation of no-till farming in commercial production has risen sharply. USDA estimates that at least 51 percent of corn, cotton, soybean, and wheat farmers use no-till and strip-till at some point in their production cycle. However, the percentage of those who go full-no-till is much smaller.
Also, there is a lingering concern about the inevitable link between no-till farming and heavy herbicide use; in fact, modern, high-yield no-till farming was not possible before the invention of broad-spectrum herbicides such as glyphosate. Many no-till farmers rely on the combination of herbicides and herbicide-resistant GMO crops to make their practice viable.
Besides conservation of prairie remnants and soil-friendly agricultural practices, prairie restoration is also one of the ways to help the tallgrass prairie come back
Despite being one of the ecosystems suffering what we could call extreme destruction, the tallgrass prairie was also an object of historic pioneering land restoration efforts.
In 1934, the University of Wisconsin-Madison Arboretum initiated the restoration of the 25-ha Curtis Prairie. The idea and the actualization of the idea to convert an abandoned ex-agricultural field back into the original prairie landscape are attributed to three people: Aldo Leopold, who likely initiated the idea, the ecologist John Thomson who oversaw the early sowing of native plant species, and John Curtis, who later did the pioneering research in the field of plant community ecology and the ecosystem restoration process. Due to his groundbreaking work, the Curtis Prairie got its name in 1962 to honor the dedicated scientist.
Since the time of the Curtis Prairie, many initiatives – government, scientific, civilian, and even private or commercial – dedicated to Tallgrass prairie restoration have sprung up.
The method and level of restoration vary – a restoration project can include utilizing the abandoned land, roadsides, and other disturbed or unused land pieces, working on enhancing the degraded existing prairie, incorporating native vegetation into agriculture by creating prairie strips, and more.
Prairie restoration projects have advanced from a couple of dozen of hectares in the early days to thousands of hectares after the 1990s. The record-holder is the Midewin National Tallgrass Prairie, a multi-community reconstruction and remnant restoration project on 7,689 hectares, initiated in 1996 near Joliet, Illinois.
The remaining issue to be solved is the severe fragmentation of the ecosystem, with its small remnants spread wide apart. There is an ambition to connect these sections by creating state and interstate native vegetation networks. By preserving the existing quality remnants, restoring degraded habitats, and reconstructing new prairies from scratch, we have already headed in that direction.
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