The Legacy of the Past, pt. 1
Cowboy country - Ranching and invasive plants
Invasive plants are one of the biggest threats to biological diversity worldwide and pose increasing problems for land managers (or gardeners) when it comes to sustaining wildlife and our natural legacy, including on the 64 acre campus of the Environmental Learning Center. It’s Wild Out There #25 and #26 will cover a few of these examples in a brief historical context to answer questions like why do so many plants become invasive in Florida and where do they come from?
A hike at the Sebastian River State Park and other pine flatwoods and savannas on the lower southeastern Coastal Plain, to the trained eye, reveals the grazing patterns of cattle like scars in the landscape sometimes from more than a century ago. In areas where cattle have overgrazed the native landscape, plants like wiregrass (Aristida stricta) have become scarce and been replaced with more grazing resistant grasses like bluestem (Andropogon spp.,) which lead to changes in the fire regimes and plant compositions with an often impoverished species richness. Land managers are trying to restore these landscapes that belong to the most biodiverse ecosystems in the world to their historic state with a more modern approach of the use of fire to increase species diversity. However, many plants like wiregrass or also saw palmetto (Serenoa repens,) an endemic to the lower southeastern coastal plain, usually don’t grow back in a human lifetime once they are lost. Even though large browsing and grazing herbivores like cows are nothing new to landscapes of the southeastern coastal plain, including Florida.
Grasslands like pine savannas and prairies in Florida evolved under the evolutionary pressure of megaherbivores of the Miocene until the late Pleistocene epoch (23 million years to ca. 11 thousand years ago,) like mastodons, giant ground sloths, a grazing glyptodont (a giant armadillo-like animal, also known from animated ice-age movies,) and later bison and elk until European colonists eradicated them. As we know from close relatives of some of these extinct animals, like elephants in Africa, they also consumed tree seedlings and saplings for their high carbohydrate contents, as well as uprooted larger trees. This likely decreased the frequency of lightning-caused fire in grasslands due to the reduction of fine-fuels in in the understory but mimicked the filtering effect of fire.
However, the exotic cow (Bos taurus) typically does not consume tree seedlings but is adapted to feed primarily on grasses and forbs and is therefore less suitable for maintaining open grasslands. Unlike cows, the most recent herbivores of the southern grasslands, like bison, were migrating animals which reduces disturbance and allows soil and plants to recover. Many of these landscapes have quickly been overused or overgrazed by cows to the point where native
vegetation has become insufficient to support the ever-growing herds. This made it necessary to introduce new fast growing species for forage with a higher nutritional value than native grasses, that are more resistant to trampling and overgrazing, and easily occupy disturbed soil. In other words, the recipe for a highly invasive species. According to the 2007 paper “The Invasive Legacy of Forage Grass Introductions into Florida,” Overholt and Franck state that during the early years of European colonization in the subtropical and tropical south, cattle herds relied on native vegetation until the first exotic grasses with a higher nutritional value were inadvertently introduced and then quickly spread by humans as cattle fodder in the 16th century. Since then at least six of sixteen listed invasive grasses in Florida were intentionally introduced specifically for cattle forage until 1971, all of which originate from Africa, presumably due to many similarities between both places like their climate and a common geologic history (Florida and Africa used to be joined between 500 and 180 million years ago.) Among the species that the ELC land management has to deal with are cogongrass (Imperata cylindrica), natal grass (Melinis repens), smutgrass (Sporobolus jaquemontii,) and Guinea grass (Urochloa maxima). While some have been rejected as forage grass after their introduction, limpograss (Hemarthria altissima) is still widely used and planted on rangelands for forage, despite it being listed as a category II invasive by the Florida Invasive Species Council. In fact, climate change and introduced cow forage grasses are the two biggest threats to the biological diversity on the landscape and species level on the ELC campus.
The reason for the introduction of these plants was to mitigate the human-caused effects on the environment, like desertification, by “improving” rangeland (from the perspective of a cattle farmer) with plants that are more resistant to the natural, as well as newly created local conditions under an overpopulation of herbivores that most native plants are not adapted to. The ecological damage that invasive plants cause in wild areas is easily comparable to large-scale deforestation and human development. Thus, the idea that nature has to be “improved” by the introduction of new species might, at least to some people, seem like a kind of mindset of the past. However, despite new efforts to control the introduction of potentially invasive species by the United States Department of Agriculture-Animals and Plant Health Inspection Service, as well as the “Assessment on Nonnative Plants in Florida’s Natural Areas” by the University of Florida, this is unfortunately by far not just a legacy of the past. Invasive plants usually do not originate from a place, but from a mindset.
If you would like to learn more about Florida, visit the Environmental Learning Center in Vero Beach and join us on a guided kayak excursion through the beautiful backwaters of the Indian River Lagoon. Call 772-589-5050.