Perennial Grasses and Their Response to a Wildfire in South-Central Washington

Abstract

Three years of past burning responses of three perennial grasses were evaluated by comparing a burned area with an adjacent control (unburned) area. The average leaf length of Cusick bluegrass and Thurber needlegrass was shortened by burning in all 3 years, but leaf shortening was inconsistent for bluebunch wheatgrass. Burning increased the number of flowering culms per clump for Cusick bluegrass during the second year of postburning and for Thurber needlegrass during the third year. The average number of flowering culms per clump in bluebunch wheatgrass was greater in the burned area for all 3 years of postburning. Culm and spike lengths of bluebunch wheatgrass were increased by burning for the first 2 years. Cusick bluegrass and Thurber needlegrass generally responded to burning with shortened culms and spikes. The basal area of Cusick bluegrass and Thurber needlegrass was reduced by burning. Phytomass production of bluebunch wheatgrass showed an increase during the 3 years of postburning, whereas Cusick bluegrass and Thurber needlegrass showed a reduction in phytomass production. No single measurement provided a way to evaluate overall plant responses. Wildfire is a common event in grasslands which, depending on how, when and where it occurs, may have an important influence on grassland vegetation. Rangemen have often used controlled fire to improve the quantity and quality of livestock forage by eliminating unpalatable but fire sensitive competitive woody species. Recent literature reviews on fire and its effects on western grasslands are presented by Daubenmire (1968), Vogl(l974), and Vallentine (1974). Daubenmire ( 1975) reported that burning of bluebunch wheatgrass (Agropyron spicatum) only moderately reduced canopy coverage and frequency, but dry-matter production was reduced 50% of the unburned area during the first season, with 16 and 17% reduction during the second and third years of postburning respectively. Mueggler and Blaisdell (1958) reported a 56% reduction in herbage production of bluebunch wheatgrass 3 years after burning. Pechanec and Stewart (1944) indicated that bluebunch wheatgrass, Cusick bluegrass (Pea cusickii) and Thurber needlegrass (Stipa thurberiuna) were only slightly damaged during the first year after burning, but yield subsequently increased approximately 50%. Wright and Klemmedson