Using prescribed fire and herbicide to manage rank native warm season grass for northern bobwhite

Abstract

Converting fields of exotic cool season grass to native warm season grass creates habitat for northern bobwhite (Colinus virginianus). If converted stands are left unmanaged they can become rank, or over-vegetated and unsuitable for grassland wildlife. Northern bobwhite populations have been declining across their range for decades, and maximizing the amount of habitat is vital to increasing their abundance. We investigated prescribed burning followed by herbicide application as a management strategy to improve vegetative composition and structure for northern bobwhite in rank native warm season grass stands. Within 4 study areas using a randomized block design, we applied the following treatments: burn-only, burn then application of 27.7% isopropylamine salt of imazapyr (ISI), burn then application of 7.78% imazapyr 62.22% diuron mixture (imazapyr), and burn then 41% glyphosate application. We measured vegetative parameters related to structure and composition and compared these metrics between treatments using repeated measures analysis of variance blocked by sampling area. We compared grass stands to hypothetical optimum conditions for bobwhite using principle components analysis. The ISI treatment produced levels of forbs and native warm season grass beneficial to bobwhite throughout the study, and was initially most similar to optimum conditions. Glyphosate treatment also produced vegetation beneficial to bobwhite. Imazapyr produced beneficial levels of bare ground during the first growing season but none of our treatments produced beneficial levels after 2 growing seasons. Herbicide treatments initially had greater influence on habitat structure than did the burn-only treatment, but all habitat structure variables were similar among treatments after 2 growing seasons. Our results indicate that management of rank grasslands for northern bobwhite occurring at <2-year intervals provides near optimal levels of native warm season grass and forbs and has potential to create habitat structure. On private lands managed for northern bobwhite where landowners do not have access to disking, we recommend prescribed burning followed by either 2.81 L/ha ISI or 5.62 L/ha glyphosate application using a non-ionic surfactant followed by annual or biennial prescribed burning. We do not recommend the use of imazapyr or burn-only treatments when managing rank grasslands for northern bobwhite habitat because they do not create beneficial levels of native warm season grass or forbs. © 2014 The Wildlife Society.