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Wildlife, Animals, and Plants |
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FIRE CASE STUDIES
CASE NAME:Malheur National Wildlife Refuge prescribed burns REFERENCES:Young, R. P. 1986 [253] FIRE CASE STUDY AUTHORSHIP:Zouhar, Kris. 2001. SEASON/SEVERITY CLASSIFICATION:winter and early-spring/low to moderate STUDY LOCATION:The study was conducted at the Malheur National Wildlife Refuge in southeast Oregon. PREFIRE VEGETATIVE COMMUNITY:The study area is a mesic herbaceous community dominated by creeping wildrye (Elymus triticoides). Associated vegetation includes Douglas sedge (Carex douglasii), Baltic rush (Juncus balticus var. montanus), Sandberg bluegrass (Poa secunda), and a diverse mixture of other graminoids and forbs. Populations of Canada thistle (Cirsium arvense), ranging from scattered shoots to dense patches, occur throughout the study area. Canada thistle was the dominant or codominant species on each of the study sites. TARGET SPECIES PHENOLOGICAL STATE:Prescribed burns were conducted in winter and early spring while vegetation was dormant. SITE DESCRIPTION:Elevation ranges from 4,100 to 4,200 feet (1,250-1,280 m) and annual precipitation averages 10 to 12 inches (250-300 mm) at the refuge. Soils are derived from lake sediments and alluvium. The landscape consists of extensive wet meadows and mesic herbaceous uplands that have been managed for native hay production and/or grazing since before the turn of the century. FIRE DESCRIPTION:Both the winter (10 December) and spring (7 April) burns were conducted when weather was cool (36 to 43 degrees Fahrenheit (2-6 °C)) with moderate to high relative humidity (38-53%) and steady, light winds (2.4 to 7.2 mi/hr (4-12 km/h)). Fuels were abundant (averaging 473-644g/m2) and continuous and produced uniform, steadily advancing fires. Fire intensities of the winter and spring burns were 1,004 kW/m and 4,465 kW/m, respectively. Both burns consumed virtually all aboveground plant residues, leaving only white ash. FIRE EFFECTS ON TARGET SPECIES:Newly emerged rosettes of Canada thistle were noted on 5 April after the 10 December burn. Height and development over the remainder of the season was not discernibly different between winter and spring burns. Growth on burned plots was not different from controls until 21 June, when control plants were significantly taller (p<0.05). Bud formation in burn treatments was delayed by 1-2 weeks, and most flowerheads were aborted, resulting in the production of few functional flowers (>10%) on the burns, compared with >45% functional flowers on control. Shoots on control sites were still significantly taller than those on burn sites on 8 August. Total shoot density was more than 2 times greater on burn plots compared with control. Number of reproductive shoots was similar between burned and control plots, therefore the difference was attributed to the greater number of vegetative shoots on the burn plots. Total aboveground herbage production was greater on burned plots and was attributed to increased production by the associated vegetation in the burned areas. Burning altered the population structure of Canada thistle to a higher density of smaller shoots. FIRE MANAGEMENT IMPLICATIONS:Prescribed burning during the dormant season did not decrease biomass of Canada thistle and, therefore, may not be effective in eliminating it where it has become established in these plant communities. Fire did, however, reduce the relative abundance of Canada thistle within these communities, as well as the potential for spreading by seed. Canada thistle may be slowed or contained by prescribed burning under these conditions. The treatment warrants further study as a potential control measure.
Related categories for SPECIES: Cirsium arvense | Canada Thistle |
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