North American prairies are frequently managed by prescribed burning. Burn season can have a major effect on vegetation response to burning. Most related research on fire in tallgrass prairie focuses on dormant season burns (i.e. primarily in winter and spring). This study (conducted in a tallgrass prairie on the Oklahoma State University Research Range, central USA) evaluated response of grazed, high-seral tallgrass prairie vegetation to follow-up herbicide management after growing season (i.e. late-summer) burns.
Vegetation was dominated by four grasses: big bluestem Andropogon gerardii, switchgrass Panicum virgatum, indiangrass Sorghusrrum nutans and little bluestem Schizuchyrium scoparium. Two experiments were conducted in one pasture:
Experiment 1 – cattle grazed season-long at moderate stocking rate (approx. 2.5 AUM/ha) in 1987, and in 1988 up to burning on 9 September. Dates of herbicide application were: 2,4-D -11/5/89; Atrazine 27/3/89;
Experiment 2 – also grazed season-long at 2.5 AUM/ha, in 1989 up to burning on 8 September 1989. Dates of herbicide application were: 2,4-D -10/5/90; Atrazine 5/3/90.
Burns were applied to 10 x 20 m plots (5 to 7 replicates) in a randomized design. After burning, plots were divided into three subplots for herbicide treatments (no herbicide, atrazine at 1.12 kg active ingredient (a.i.)/ha, or butoxyethyl ester of 2,4-D at 0.84 kg a.i./ha). Herbicide was applied using a compressed air bicycle sprayer. Cattle were excluded after treatment application.
Production, fuel load and moisture was estimated by weighing fresh and oven-dried clipped vegetation from five (0.5 x 0.5 m) quadrats per plot: Experiment 1 clipped 19/7/89 and 22/7/90; Experiment 2, clipped 22/7/90 and 25/7/91.
In the year subsequent to burning, dry matter yields of little bluestem, other perennial grasses (excluding tallgrasses), total perennial grasses, and total herbage were all significantly reduced by burns. Reduced production of little bluestem and perennial grasses (excluding tallgrasses) to late-summer burning does not always occur e.g. in an earlier study near this study area, it had no effect on little bluestem. Both tallgrasses and annual grass standing crop were similar between burned and unburned plots. Forb standing crop (rather variable) averaged about twice that on burned plots than unburned plots.
Herbicide was generally detrimental to forbs: 2,4-D significantly reduced standing crop compared to atrazine and controls. Tallgrass and total perennial grass standing crops were greatest on 2,4-D plots.
Late-summer burning (without herbicide) did not reduce herb production or alter community composition greatly for more than one year subsequent to burning; thus it might provide an alternative to dormant season burning in some situations for scrub control and improvement of high-seral tallgrass prairie wildlife habitat.
Note: If using or referring to this published study, please read and quote the original paper, this can be viewed at: https://www.uair.arizona.edu/holdings/journal/issue?r=http://jrm.library.arizona.edu/Volume46/Number6/