Sustainable and profitable control of invasive species by browsing goats on small farms

The invasion of fallow cropland, pasture and woodland by native and non-native weeds is a common problem throughout the southern USA, Puerto Rico and the U.S. Virgin Islands (USVI). In Florida alone, 29% of non-cultivated plants are classified as non-native (Langland and Stocker, 2001). Native mesquite (Prosopis glandulosa), cedar (Juniperus spp.), and greenbrier (Smilax spp.) are examples of widespread southeastern USA invasive plants resulting from overgrazing by cattle and its disruption the natural balance in plant communities (Welch and Hyden, 1996; Racher and Britton, 1997; Taylor and Fuhlendorf, 2003). Kudzu (Pueraria lobata), coral vine (Antigonon leptopus) cogongrass (Imperata cylindrica), Japanese climbing fern (Lygopodium japonicum), and leucaena (Leucaena leucocephala) are well-documented examples of non-natives that have become widespread invasive species in the region (Miller, 1988; Engle et al., 1994; Langland and Stocker, 2001; Terrill et al., 2003). Most of the non-native species have proved very difficult to eradicate once established. For example, current guidelines for kudzu control warn that repeat applications of herbicide may be necessary for 5 to 10 years after initial treatment (Demers and Long, 2002).

For this reason, it is not hard to understand why both public and private landowners are often overwhelmed by the logistics and cost of controlling these invasives. Dade County Florida Parks and Recreation Department has spent $2.3 million for the removal of invasive plants from 500 acres of upland area since 1993 (Langland, 2003). In one year alone, the State of Florida budgeted $12 million for control of wetland species alone (Langland, 2003). The environmental repercussions of widely applied and indiscriminate chemical and mechanical control are poorly understood, however. This is particularly true in natural areas where special care is needed to minimize damage to non-target vegetation, soil and fauna that depend on them (Langland and Stocker, 2001).

Non-chemical methods exist for controlling invasive weeds. Non-grass weedy invaders can sometimes be suppressed using grass-fueled fires (Briggs et al, 2002) but this rarely results in 100% eradication and is sometimes a socially or environmentally unacceptable means of brush management. Other methods commonly used include grubbing, root-plowing, removal by hand, chaining, and herbicides (Taylor, 1992; Hart, 2001), all of which have environmental and economic downsides. Biological control of regrowth following mechanical or chemical brush control has proven more effective than single-control approaches (Magee, 1957; Green and Newell, 1982). The use of small ruminants for biological control may be more socially acceptable (Ball, 2004) and their forage predilections (Huston, 1978) and specialized digestive tracts (Huston et al., 1986; Hofman, 1989) make them better brush control tools than other larger ruminants. In addition, goat and sheep feed preferences are determined by a complex mixture of genetics, learned behavior, and feed availability (Malechek and Provenza, 1983) that can be manipulated to produce specific modifications in plant communities.

The use of intensive, short duration goat/sheep browsing (ISDGB) may be an efficacious, remunerative, and ecologically mild form of manipulating vegetation (Muir et al., 1997; Briggs et al., 2002). The use of small ruminants for brush control is not completely unknown in the southern USA (Bull, 2000) and has been supported by SARE grants (LS01-119) in the past. The commercial application of this practice, namely contracting herds specifically to suppress invasive vegetation (Ball, 2004), is not, however, widespread in the southeastern USA or its Caribbean territories but has been successful elsewhere (Green and Newell, 1982). At the same time, market demand for goat and sheep meat is strong (www.vdacs.virginia.gov/livestock/goatprice.html), indirectly encouraging over-stocking on ecologically sensitive rangelands where most small ruminants have traditionally been raised (Malechek and Leinweber, 1972) and in the eastern United States where most producers have limited land areas to utilize. The growing invasive plant problems, in conjunction with a strong small ruminant market, provide a fortuitous opportunity to combine profitable animal husbandry with biological control of weeds. The details for this union of circumstances, however, have not been developed.