Old-Growth Grasslands: A Forgotten Habitat
Updated: Apr 21, 2020
Old-growth grasslands. It’s quite possible you’ve never even heard the term. For years, conservation efforts have focused on forests and aquatic ecosystems with little regard to saving grassland habitats. This is extremely unfortunate because old-growth grasslands are one of the most threatened habitats on the planet. In fact, the Great Plains are considered the most endangered ecosystem in North America¹ with tallgrass prairie declining by 82 – 99% since 1830² and with less than half of all the temperate grasslands on Earth remaining intact.³ This is of great significance since 40.5% of the Earth’s terrestrial surface, excluding Greenland and Antarctica, is grassland.⁴
What are old-growth grasslands?
Grasslands can be defined as habitats made up predominantly of continuous grasses, forbs, and shrubs with little to no tree growth. Old-growth grasslands are ancient grassland ecosystems that contain endemic species, have unique combinations of plant and animal species, and support many species of flora. They take centuries to develop and are sustained by a combination of wildfires and heavy grazing of ungulates or through specific growing conditions, such as poor soil, that don’t support trees.⁵ Old-growth grasslands are unique and fascinating ecosystems that deserve to be protected.
What are the threats to grassland ecosystems?
Grasslands worldwide are being degraded and lost. What is causing this?
One threat to old-growth grasslands is actually reforestation. While trying to restore landscapes and habitats, grasslands can be overlooked and even believed to be anthropomorphic, or created by humans, not natural. A 2014 study from the United States focused on three ecosystems that some biologists have felt are human artifacts not worthy of significant protection — the southern Appalachian grass balds, the East Carpathian poloninas, and the Oregon Coast Range balds. The study concluded that these ecosystems have been grasslands since the last glaciation and that grazing herbivores combined with occasional fires may have stopped the growth of forests in these areas. They point to evidence that the grasslands in these areas predate European settlement.⁶ This study points to just a few examples of many where people have incorrectly assumed that grasslands are not natural ecosystems. This is dangerous as through the best of intentions we may mismanage these areas and turn them into unnatural forests, instead of protecting them as the grasslands they are.
Reforestation is also a concern for the grasslands and savannahs of Africa. A South African study from 2016 explored the mesic subtropical grasslands of South Africa. This is just one area of many that has been proposed to be an area that could be reforested to recover what is looked at as a degraded ecosystem. The study found that much of the area was old-growth grassland and even claimed that they could differentiate between old-growth grasslands and anthropogenic grasslands created by humans by looking at the species diversity and species richness.⁷ This adds to the sentiment that reforestation is not always a benefit and it is crucial that we are careful and direct important reforestation efforts at appropriate areas.
Agriculture is another threat to old-growth grasslands all over the world and has been responsible for replacing 41% of the world’s temperate grasslands.⁸
The Great Plains of North America that were once covered in grazing bison, pronghorns, and elk are now grazed by cattle, sheep, and goats. What impact has this change in grazers had on the ecosystems? In some ways, livestock grazing has helped preserve grasslands as cattle can help to reduce the ability for forest to encroach on old-growth forest such as has been seen in some areas of Brazil where the absence of cattle has led to exactly this.⁹ As well, areas that are being used for livestock keep a lot of the properties of the grassland while preventing that area from being developed for other uses.
There is another side of the coin, however. Overgrazing has degraded grassland ecosystems all over the world. In China, overgrazing has been found to be a principal factor in the desertification of their grassland ecosystems¹⁰ and a 2013 review concluded that reducing overgrazing and allowing grasslands to recover would greatly increase the world’s grasslands’ ability to sequester carbon and reduce the overall anthropogenic carbon footprint.¹¹ Animal agriculture also fragments grassland ecosystems not allowing wildlife to move throughout the landscape in a way they once would have. This changes the dynamics of an ecosystem as predators are more easily able to prey on nests of grassland birds and more easily capture grassland mammals. While cattle can replace the once numerous plains bison in some ways, animal agriculture is clearly not a replacement for this natural balance that used to exist without agriculture and fences.
A good example is the pronghorn found in the grasslands of North America. The pronghorn is a grassland species that has been greatly impacted by fences and changes to the landscape due to agriculture. Fences have interrupted their natural migrations and hindered their ability to escape predators.¹² Pronghorns rely on their keen eyesight and impressive speed to escape predators on the grassland ecosystem they have evolved with. Fragmenting this habitat drastically changes the properties of the landscape in a way that is too quick for a species such as the Pronghorn to adapt to. A 2006 University of Calgary study found that, in Alberta, cultivated and fenced agricultural land had considerably lower densities of pronghorns than native prairies.¹³ This impact is not limited to pronghorns either, pronghorns are an example of an indicator species for this North American prairie. If the pronghorns are disappearing from an area, there is a problem with the habitat and other species are probably being impacted as well.
Another impact of agriculture on grasslands is the destruction of nests and nesting habitat for grassland birds. In North America, native, new-world sparrows are currently on one of the steepest declines of North American birds. Large declines of nesting success has been linked to early cutting of hay before the birds have had a chance to fledge, as was found in a 1997 in Saskatchewan.¹⁴ It is not just that birds avoid degraded grassland habitat, the success of birds that are forced into these habitats are also at risk through agricultural practises.
Restoring old-growth grasslands that have been destroyed by agriculture can take centuries¹⁵ so it is crucial that we protect the grasslands we have left from agricultural development as restoration is not easy. We also need to take the areas that we are unable or unwilling to convert back to natural grassland and make them more friendly to grassland species. This can be accomplished through initiatives like changing fences to be more friendly to pronghorns or waiting until after grassland birds have had a chance to fledge before cutting hay.
It is well known that foreign, invasive plants have faster growth rates than native grassland plants and outcompete them due to their earlier and faster growth.¹⁶ This is a large threat to old-growth grasslands.
Many invasive plants found in grasslands were introduced by humans for pastures, lawns, and as ornamental plants and often their ability to spread was enhanced through the degradation and desertification of old-growth grasslands.
One method of controlling invasive plants in grassland environments is through controlled burns. A 2000 study looking at plants invasive to North America and how they could be controlled by burns found that many invasive plants could be completely removed this way.¹⁷ This makes prescribed burns possibly a very useful tool for grasslands as native species thrive in these conditions since they have adapted to these burns. Often burns are one of the main sources in the creation and proliferation of this type of habitat.
One important factor to point out is that while trying to deal with invasive species, sometimes we can do more harm than good. As a study out of Montana found, herbicides and other controls to destroy invasive plants, can destroy the very plants that we are trying to protect.¹⁸ Often species are negatively impacted by invasives but rarely are they completely extirpated so caution should definitely be observed before drastic methods of control.
Why save old-growth grasslands?
Grasslands all over the world are disappearing. So what? Why does it matter?
One large benefit of grasslands is their ability to store carbon to help minimize climate change. Compared to forests, grasslands are superior carbon sinks.¹⁹ For every piece of old-growth grassland that we replace with forest, we are reducing the amount of carbon pulled from the atmosphere and contributing to climate change.
As well, many species of both flora and fauna rely on this habitat and many of them are threatened or endangered. In the United States, 55 grassland species are threatened or endangered with another 728 species as candidates to become so and in Canada, one third of the species considered endangered are found on grasslands.²⁰ A recent 2019 report found that since the 1970s, North America has lost 3 billion birds or 30% of the total number of birds. Of these, the hardest hit were grassland birds declining by a staggering 53%.²¹ Habitat degradation is a huge factor in this decline. If we continue to allow grassland habitats to degrade and disappear, many species will be impacted. Animals we used to see will be seen no more, bird songs we used to hear will go silent, and plants that used to sway in the wind will be lost.
Why save old-growth grasslands? It is our responsibility as stewards of this Earth to do our best to ensure that nature stays intact and healthy and when we are trying to conserve nature it is essential that grasslands are not forgotten.
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