The always fascinating Sociological Images has an article about wild mustangs that reminds me of some on-going debates between environmental archaeologists and environmental policy makers. Early conservation in the U.S. was all about protecting so-called "virgin" landscapes, or, alternatively, restoring non-virgin (promiscuous?) landscapes by keeping exotic plants/animals out, or reintroducing plants/animals that had gone extinct.
There is nothing inherently wrong with excluding exotics, or reintroducing native species. But these decisions are too often made through a baseline perspective on landscapes. That is, a perspective that assumes all landscapes have a single "natural" baseline state. In this view, human activity disrupts the "natural", and it must be restored by returning the plants and animals to the original baseline.
We now know that the landscape of North America wasn't "virgin" at the time of European contact. (Loewen's line in Lies my Teacher Told Me is something like "it wasn't virgin, it was recently widowed.") Declaring any time period after the initial peopling of the Americas to be the environmental baseline would be arbitrary. Such thinking also ignores the human/environment dialectic, even though people are part of the ecosystem and we play our own part in creating and maintaining it.
Baseline views of landscapes are also misleading and fail to meet our environmental policy needs. Asking what the "baseline" environment should be is like asking which molecules of water are in a river. One could flash-freeze a river and measure each individual water molecule, but the dynamic and flow of the moving water is far more important for understanding how the river functions. So, when conservationists or wildlife managers make policy decisions that lead to some animals or plants being introduced or removed from particular landscapes, sometimes they're making the best decision for the health of the ecosystem, and sometimes they are not. But often their stated purpose is, to extend the metaphor, to restore the exact molecules of water that once flowed in the river, rather than to ensure that the river's overall dynamics are healthy.
Which brings us back to the feral mustangs of the West. There are plenty of arguments for getting rid of the mustangs from a "baseline" landscape perspective. After all, they are exotic animals, introduced originally by the Spanish. There are also arguments for keeping them. Social/cultural factors are influencing our policy decisions. Unlike many exotic species, such as zebra mussels or emerald ash borers, mustangs are charasmatic megafauna: easy to love, and to build a PR campaign around. The mustangs are a tourist attraction, and a symbol of the West. Their relationships with humans, symbolic or physical, are critical to understanding our current policies toward the species.
From an historical ecology perspective, the arguments surrounding wild mustangs are complex. The horse is an exotic animal, but at the same time it is native. Horses were part of the North American landscape during the Pleistocene, and were only extinct in the West for some 10,000 years, a blink of the eye, evolutionarily speaking. The Western grasslands coevolved with ruminant species, many of which are now extinct, but their Old World cousins, in the form of domestic horses and cattle, are filling in the ecological niches those ruminants once filled. Horses became a critical part of the cultural landscape, as well, fulfilling many different social, ritual, and economic roles for many different cultural groups.
The question is not whether exotic species belong on the Western plains, or to what "baseline" environment we should restore our "wild" places. The questions are: are the grasslands healthy? What constitutes health? What policies (for fire, hunting, provisioning of mustangs, reintroduction of wolves, etc.) will ensure a healthy, dynamic, resilient ecosystem, despite, and because of, the constant changes that have occurred in North American environments over the last 500 years?