Burning of northern mixed prairie during drought.

Standing crop of current year's growth and response of key management species were evaluated following burning in mid-May (before emergence of warm-season grasses) and mid-June (after emergence of warm-season grasses). The study was conducted during 2 dry years in a mesic Mixed Prairie in South Dakota. Cool-season precipitation was 33% below average in both years of the study, while warm-season precipitation was only slightly below average both years. Standing crop of current year's growth was increased by burning on overflow range sites, but not on silty range sites. Big bluestem (A ndropogon gerardi) standing crop was greatest with mid-May burning. Kentucky bluegrass (Poa pratensis) standing crop and leaf length were reduced with burning on both dates. Leaf length, basal area and number of inflorescences of native cool-season grasses were also reduced. Mid-May burning in drought years may be recommended for the reduction of Kentucky bluegrass. However, reductions in production of native coolseason vegetation can be expected on silty range sites. In contrast, mid-June burning in dry years is not recommended. Burning has been widely recommended on the subhumid and humid grasslands of the Great Plains and the Midwestern prairie peninsula for manipulating botanical composition, increasing herbage production, and providing more nutritious forage for livestock. The True Prairie in the Flint Hills of eastern Kansas (McMurphy and Anderson 1965, Anderson et al. 1970) and the humid grasslands of the Midwest (Curtis and Partch 1948, Ehrenreich 1959, Kucera and Ehrenreich 1962, and Ehrenreich and Aikman 1963) can be effectively managed with fire. In the Northern Great Plains, fires have resulted in varying vegetation responses. In the semiarid Mixed Prairie of the Northern Great Plains, fire has resulted in critical reductions in litter (Dix 1960) and decreased herbage yields (Gartner et al. 1978), although effects appear to be dependent on season of the burn and on precipitation. In the mesic (dry subhumid) Mixed Prairie (Kirsch and Kruse 1972) and the True Prairie (Kaiser et al. 1979), fire may benefit the warm-season tall grasses and result in a reduction of undesirable cool-season species. Before fire can be judiciously prescribed as a management tool in the mesic Mixed Prairie, data must be available for burning under a variety of environmental conditions. Series of dry years are common in the Northern Great Plains (Schumacher 1974) and this may limit the application of prescribed burning in these areas during extended drought periods. Studies reviewed by Daubenmire (1968) as well as studies in the Kansas Flint Hills (Anderson et al. 1970, Owensby and Smith 1979) indicate that spring burning reduces Kentucky bluegrass Authors were assistant professor, Department of Animal and Range Sciences, South Dakota State University, Brookings 57007, and manager, Samuel H. Ordway Memorial Prairie, Leola, S. Dak. 57456. Currently, Engle is associate professor, Agronomy Department, Oklahoma State University, Stillwater 74078 and Bultsma is area grasslands management agent, North Dakota Cooperative Extension Service, Pulver Hall, Dickenson 58601. This article is published as Journal No. 1950 of the South Dakota Agricultural Experiment Station, Brookings. The Nature Conservancy provided the study area and a portion of the funding for this study. Manuscript accepted Janu_y 13, 1984. (Poa pratensis). ' Smitfi and Owensby (1972) concluded that actively growing Kentucky bluegrass is more susceptible to injury than the warm-season native grasses that are dormant or just beginning to grow when spring burned. In this study, burning was timed during the latter part of the active growth stage of Kentucky bluegrass, both before and after the emergence of warm-season native grasses. Comparisons were made for 2 burning dates on 2 range sites during a period of below-average precipitation in the prairie pothole region of the mesic Mixed Prairie. Methods and Materials The study was conducted on the Samuel H. Ordway Memorial Prairie in north-central South Dakota. The study area is part of the prairie pothole region of the northern Mixed Prairie (Kuchler 1964). Average annual precipitation from 1940 to 1970 at Leola, S. Dak. , about 10 km east of the study area, was 50.2 cm. Soils of the study area are Williams loams (silty range site) and Bowbells loams (overflow range site). The Williams soils are fineloamy, mixed Typic Argiborolls. The Bowbells soils are fineloamy, mixed Pachic Argiborolls. Silty range sites in excellent range condition are dominated by western wheatgrass (Agropyron smithii), needleandthread (Stipa comata), and green needlegrass (Stipa viridula). Overflow range sites in excellent condition are dominated by big bluestem (Andropogon gerardi). Both range sites become progressively dominated by Kentucky bluegrass as range condition declines. At the time the study was initiated, Kentucky bluegrass was a major component on both the silty and overflow range sites, partly in response to repeated midsummer haying. Treatment plots (25 X 50 m) were established in 1980 on native range neither grazed nor hayed for 3 years. A randomized block design with 3 replications was used in the experiment. Treatments consisted of 2 1980 burning dates and a control nested within 2 range sites (silty and overflow). The early burning date, applied before emergence of warm-season grasses, and the late burning date, applied after warm-season grasses had emerged to a height of 5 to 10 cm, were in mid-May and mid-June, respectively. In a normal year these growth stages would be expected to occur earlier in the season, but were later in 1980 because of late frosts and below normal precipitation. Plots were burned with a headfire after a base control line was established with a backfire. Weather conditions during the burns were monitored and appear in Table 1. 'Common and scientific names after Beetle (1970). Table 1. Weather conditions for May and June 1980 burning treatments at Ordway Prairie. Wind speed Air temperature Relative humidity Burn dates (km/h) (? C) (%) May 13-16 3-13 4-19 23-45 June 16 0-24 20-23 42-66 398 JOURNAL OF RANGE MANAGEMENT 37(5), September 1984 This content downloaded from 157.55. 39.94 on Sat, 19 Nov 2016 04:22:30 UTC All use subject to http://about.jstor. org/terms Table 2. Least squares means of leaf length, number of inflorescences and basal area of dominant species at Ordway Prairie, as estimated on August 8-11, 1980.