Wetland Mitigation Plants Are Rocking Enviromentalists' Worlds

June 28, 2009 - PRLog -- No chemicals, no chainsaws, no blowtorches — just an adequate fence, an occasional shelter, and the appropriate livestock, which, depending upon the habitat size and invasive plant species may be goats, sheep, or cattle
At first glance this may not read like a recipe for bog turtle conservation. Yet, in the marshes, fens, and wet meadows of northwestern New Jersey, it has shown remarkable promise. The federally-threatened bog turtle (Clemmys muhlenbergii) is a tiny species, small enough to wade in the puddle of a cow’s hoof print. A single turtle can bring as much as $1200 in the illegal pet trade. Although New Jersey still harbors a significant concentration of bog turtles, a suite of native and exotic plants is rapidly degrading the mucky fens and wet meadows where the turtles thrive. Once established, these plants can rapidly replace the native herbaceous communities that the turtle depends on for its survival with dense, shaded monocultures. Without intervention, New Jersey will likely lose 40 percent of its bog turtle populations in the next twenty years.

Most traditional vegetation management techniques employ herbicides, which are generally effective but not without negative effects. For example, using broadcast herbicide applications (such as glyphosate-based Rodeo) in bog turtle habitats kills desirable, non-target species. While glyphosate is EPA-approved for wetland use and considered safe for wildlife, its effects on ecosystems is unknown. Bog turtle habitats are rich in amphibian and insect species, many of which are rare. Spraying these species with a biocide that is labeled with the following precautionary statements: “Harmful if inhaled. Avoid breathing vapors or spray mist. Wash thoroughly with soap and water after handling,” may well have a deleterious effect on some of these species. Even biological control (such as using beetles to control purple loosestrife, Lythrum salicari) can take years, during which time the bog turtles may be extirpated.

Given these and other drawbacks of traditional techniques, coupled with the conservation urgency of the situation, my coworkers and I resolved to explore a new innovative approach to the problem — prescribed grazing.

Using Livestock to Control Invasive Species: The Empirical Evidence
The New Jersey Division of Fish and Wildlife’s Endangered and Nongame Species Program (ENSP) first began experimenting with prescribed grazing to control succession and the invasion of exotic plants in bog turtle habitats in 1999. The idea first evolved from field observations and anecdotal evidence and later from research presented in the scientific literature. While conducting bog turtle surveys in northwestern New Jersey and southwestern New York, I was struck by the contrast between grazed wetland pastures and adjacent areas. In the wetland pastures, cows had pruned purple loosestrife and/or phragmites to knee-height, effectively eliminating it’s canopy-closing ability and reducing its productivity. Neighboring non-grazed areas characteristically were choked with purple loosestrife. Moreover, the cows — simply by doing what cows do — had broken up the plants’ dense rhizomes and had improved the burrowing quality of the soil for the bog turtle. The same was true in areas where goats had been given seasonal access to wetland pastures. In fact, in a survey of bog turtle habitat in over 200 emergent wetlands in the shale bedrock regions of Sussex County, New Jersey and Orange County, New York, I found that the majority of the wetlands composed of native floristic communities were actively grazed. The non-grazed wetlands, most of which were grazed several decades ago, were now densely colonized, primarily by purple loosestrife.

None of this should come as a surprise to those who graze livestock or to those who manage plants and wildlife. Controlling unwanted vegetation with livestock has been widely practiced in North America and Europe for some time. Livestock have been used to manage utility line rights-of-way, curtail the invasions of exotic species, control brush, and even create firebreaks.

Even the unintentional control of exotic/invasive plants by livestock in wetlands is well documented. In New York, for example, researchers have correlated grazing with high fen species richness. In Great Britain, scientists have shown that grazing maintains species diversity and prevents invasion of the tall-growing herb, Epilobium hirtellum. Even more specific to the case at hand, Dennis Herman, a renowned bog turtle expert from the North Carolina State Museum, witnessed a 64 percent decline in bog turtle captures at a North Carolina site after grazing had been stopped.

This association between grazers and turtles also makes sense from a historical perspective. David Lee and Arnold Norden have theorized that the interplay between beaver and wild herbivores (such as bison and elk, and even the now-extinct mastodon) created and maintained open fen habitats long before humans entered the picture. During the course of colonial settlement, bison and elk were extirpated and domestic livestock, including cattle, sheep, and horses, filled the niche of these herbivores. Today, as farming communities give way to suburbia, livestock no longer help to impede the encroachment of invasive vegetation in bog turtle habitats. The result, in conservation terms, has been disastrous.

Prescribed Grazing in Wetlands
The above evidence notwithstanding, grazing in wetlands often has been disparaged because it is associated with degraded water quality from manure and soil compaction. Yet, our experience with bog turtles dispels the belief that all grazing is deleterious to wetlands. The key is density. By using low densities of livestock and minimizing the use of feed subsidies, which can lead to eutrophication, livestock can become a conservation tool for the threatened bog turtle — without harming sensitive wetland ecosystems.

This was the rationale for the experimental prescribed grazing project initiated by the ENSP. To test the idea that prescribed grazing could help restore and maintain bog turtle habitat, we set up four sites: two phragmites control projects using goats and goats/sheep, one reed canary grass (Phalaris arundinacea) control project using cattle, and one purple loosestrife/woody vegetation control project using cattle. We chose livestock for each site based on habitat size and plant community structure. To avoid over-grazing and excessive trampling, we used cattle on sites larger than one-acre and goats and sheep on the smaller sites. Goats and sheep also were paired with sites that were densely colonized by phragmites, shrubs, and briars. Unlike cows that tend to avoid thicket-like habitats, goats seem to have no problem penetrating deep into the core of dense patches of vegetation for forage and refuge. At present, the prescribed grazing project is still young. Nevertheless, we can report some extremely encouraging preliminary results.

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