Following a 20 year policy of fire suppression, areas of tall grass brush prairie savanna (dominated by big bluestem Andropogon gerardii and other perennial bunchgrasses)at Crex Meadows Wildlife Area (Wisconsin, northern USA) had become overgrown with trees. In the late 1940’s controlled burning was introduced to the tree-invaded areas growth back to prairie. This study investigated changes in herbage yields (i.e. potential forage for grazing animals) following spring burning.
Six areas of at least 10 ha each were selected: four to be burned, adjacent to which were two controls (unburned for 25 years). Burns were undertaken in March-April: stand 1 in 1959; stand 2 in 1957 and 1959; stand 3 in 1956, 1957 and 1958; and stand 4 in 1952, 1954, 1956, 1957 and 1958.
Above-ground vegetation samples (grasses, forbs, and shrubs, separated into living and dead material) were taken by hand clipping at ground level within quadrats, dried and weighed to give a measure of herbage yield, at the end of August (end of main growing season).
Spring burning initially removed 91% of accumulated litter and 78% of dead standing vegetation. Herbage production in the first season after burning was estimated at 2,110 lb/acre, compared to 772 lb/acre on the unburned areas. Dead material comprised about 90% of the total herbage in the unburned areas.
Burned areas also had high productivity of grasses and forbs in the second year subsequent to burning compared to controls (grasses: year 1 - 1,341 lb/acre, year 2 - 1,198 lb/acre, control - 312 lb/acre; forbs: year 1 - 577 lb/acre, year 2 - 237 lb/acre, control - 45 lb/acre). Shrub production was a little higher than control in the first season (577 vs. 415) but declined by the end of the second growing season (237 lb/acre).
Burning up to once every other year, kept litter at low levels and maintained high herbage yields (potential forage for grazing animals), but grasses and forbs appeared to take between four to six years to recover to a preburn state. Based on these observations, the authors recommend burning once every four to six years.