A study was conducted during 1954-1956 to determine effects of burning and clipping on plant growth and plant communities of Hayden Prairie, a mesic upland protected grassland in Iowa, northwest USA. As well as guiding best practice for native species conservation, some grasses non-native to the prairie (Kentucky bluegrass Poa pratensis, timothy Phleum pratense and redtop Agrostis alba) were also present although scattered and of low vigour. However, their presence posed an invasion threat if native vegetation lost vigour e.g. through inappropriate management.
Prior to becoming a conservation area in 1945, the prairie was mown for hay and cattle-grazed. It was then left to recover (from overgrazing) until March 1954. Dominant species (all native bunchgrasses) were prairie dropseed Sporobolus heterolepis, little bluestem Andropogon scoparius and big bluestem A.gerardi.
Areas of 0.4 to 4 ha were burned about 1 March 1954, 1955 and 1956. Treatments (3 replications each) were: burned year 1 only, year 2 only, year 3 only, years 1 and 2, years 1 and 3, years 2 and 3, all years, and unburned (control).
Vegetation was clipped to 2.5-5 cm height within randomly located l m² plots in each area. A set of plots was clipped at: 4-week intervals during 1955 and 1956; 4-week intervals during 1956; the end of the 1955 and 1956 growing seasons; and the end of the 1956 growing season only.
Measurements of yield and flower/seed stalk development were made on main grasses and forbs periodically through the 1955 and 1956 growing seasons.
Early March burning had no observed adverse effect on native vegetation but reduced Kentucky bluegrass growth. On burned areas, plants initiated above-ground growth 2-3 weeks earlier, and produced more and taller flower stalks than on unburned areas, probably due to higher early spring (April) soil temperatures as litter had been burnt off. There was no significant difference in total yields due to burning.
Repeated clipping (i.e. 4 times per growing season) reduced yields much more than clipping only at the end of the growing season. In 1956, a 79% reduction in yield was obtained from 2 consecutive years (42% after 1 year) of frequent clipping compared to a 16% reduction from 2 years of clipping at the end of the season. There was little synergistic effect of clipping and burning in terms of further reduction in yields. The author concludes that mowing should best be undertaken at the end of the growing season after seed set.