In the USA, prairie threeawn Aristida oligantha is a widespread warm-season annual, often deemed weedy and invasive. In Kansas, grasslands previously heavily grazed by livestock then subsequently lightly grazed, are frequently dominated by threeawn, which has little grazing value. Its dominance presents problems in abandoned field restoration attempts. Native hay meadows have also been invaded. In this study, efficacy of burning to control prairie threeawn on infested grasslands was investigated. Also, native grasses were seeded on an autumn-burned abandoned field site.
Studies were conducted at three localities:
Kobbeman (19 km southwest of Lincoln)
1) autumn burning (1 November 1971), spring burning (26 April 1972), and no burning (control) on 1.83 x 6.10 m (6 x 20 ft) plots (4 replicates, randomized block design);
2) a hay meadow (57 ha) burned mid-November 1972;
3) plots (as 1 above) treated on 30 November 1973 and 12 November 1974: burning, mowing and raking, no burning.
Deweese (5 km northeast of Leonardville)
Autumn burning (10 November 1972, repeated 1 November 1973) and no burning of eight plots each (randomised design); 16 adjacent plots burned 1 November 1973, and eight unburned.
On 20 April 1974, four burned and four unburned plots in the two sets of plots were drill-seeded with native grasses: big bluestem Andropogon gerardi, little bluestem A.scoparius, indiangrass Sorghastrum nutans and switchgrass Panicum virgatum. Seedlings were counted 18 June 1974.
Stover (11 km southeast of Bridgeport)
In an abandoned field (dominated by threeawn and tall dropseed Sporobolis asper) treatments were: burning 13 December 1974, 9 January 1975, 12 February 1975, 5 March 1975, and no burning on 4.57 x 4.57 m (15 x 15 ft) plots (3 replicates, randomized block). Threeawn seedlings were counted 4 August 1975.
Various measures of vegetation response were made, including composition by weight of total herbage (threeawn, other grasses, and forbs), basal cover, seedling counts and density estimates.
Prairie threeawn was effectively controlled by autumn burning, with seedling numbers much reduced the subsequent year. Burning later than early December was ineffective. Mowing and raking (i.e. removing mulch) improved control.
On areas where remnant desirable native grasses persisted, reducing threeawn by autumn burning benefitted their growth.
Seeding native grasses in spring after November burning resulted in satisfactory establishment. Seedling numbers of all four sown species were greater on burned than on unburned plots. Establishment, regardless of species, was better on plots burned in one year than on those burned in two consecutive years. However, in the winter after seeding, stands were considerably reduced by winter (frost/ice) heaving.