Andrew Williams Replies

Williams’s master’s thesis (1996a), which I found to be conspicuously weak on both data summary and analysis in this regard. Williams’s main argument in support of grazing seems to be the presence of rare species in prairie pastures. This does indicate the conservation value of prairie pastures. But it is not necessarily an indication of the dependence of those rare species upon grazing. Additional evidence is needed to determine whether they are present because of the grazing or in spite of it. This distinction is something Williams has failed to address, leaving rne with the impression that he is not adequately distinguishing between correlation and cause and effect in his thinking on the subject. For example, the endangered plant prairie bushclover (Lespedeza leptostachya), is found in prairie pastures. However, it is also found on sites that have not been grazed for many decades, and it has demonstrated an ability to increase dramatically on these ungrazed sites. It is my experience that many of the other rare species listed by Williams in his article as evidence of the benefits of grazing also seem capable of doing just fine without it. I also believe Williams is mistaken in his assessment of optimum regal fritillary butterfly (Speyeria idalia) habitat when he states that "grazed prairie habitat is, almost without exception, the only habitat in which the regal fritillary is now found in Wisconsin. " However, of the five largest populations in the state, I believe only one is on an actively-grazed site. Even the plant at the heart of Williams’s argument, O. molle, has yet to be documented as being dependent upon grazing, even though it is probably the best example of a rare prairie species in Wisconsin that is likely benefitting from, or may even be dependent upon, grazing. Unfortunately, neither Williams’s article, nor his M.S. thesis on which it is based, provide any summarized data relating the occurrence or density of O. molle to site history. I also find Williams’s grazing article wanting in that he does not address well the issue of species that decline or disappear because of grazing--an issue he does recognize in his thesis. For example, members of the genus Silphium seem to be a preferred food of domestic livestock, and thus disappear with grazing (see Curtis, 1959, page 426). A quick summary of Williams’s thesis data reveals that of the 70 species found with O. molle 50 percent of the time or more, 33 percent are non-native, 20 percent are weedy or ubiquitous natives, and 13 percent are invading woody species. Only 26 percent are characteristic prairie species. Of this latter group, less than a third--that is, five species--can be considered conservative prairie species, and none are rare. Granted, lightly-grazed sites fare better than the heavily-grazed ones, but it is my experience that invasion by non-native and woody species, and loss of natives, occurs even on the best prairie pastures. In summary, I believe Williams is premature in advocating the routine use of grazing in prairie management, especially on the least-disturbed, highest-quality sites. Before grazing is employed beyond the experimental stage, I believe research is needed in three areas: (1) a good literature review starting with chapters 14 and 23 in Curtis (1959) and Dix’s Ph.D. thesis (1955) on the effects of grazing on the vegetation of xeric prairies in Wisconsin; (2) quantitative comparisons of species compositions from sites with various grazing histories; and (3) for rare species-(i) documentation of how they fare when grazing is stopped, or reduced, and fire is reintroduced, and (ii) an attempt to correlate species occurrence and density with specific factors in site history, including grazing, followed by manipulative experiments to establish cause and effect.