Welch, Bruce, and Craig Criddle. 2003. Countering Misinformation Concerning Big Sagebrush. Research Paper RMRS-RP-40. Ogden, UT: US Department of Agriculture, Forest Service. Rocky Mountain Research Station.
RELEVANT TO: GRASSLANDS/SHRUBLANDS
LIVESTOCK GRAZING
SPECIES
DESCRIPTION
This is a review paper of several hundred published scientific papers relating to big sagebrush (Artemisia tridentata) including Wyoming big sagebrush (A.t. ssp. wyomingensis), mountain big sagebrush (A. t. ssp. vaseyana) and basin big sagebrush (A.t. ssp. tridentata). The scientific evidence appears to refute 8 myths (here called "axioms") re: big sagebrush as justification for removing, thinning, controlling, or killing sagebrush.
MAJOR FINDINGS
Scientific evidence is provided for the following eight understandings of big sagebrush:
- Wyoming big sagebrush is not naturally limited to 10 percent or less cover, nor is mountain big sagebrush does often naturally limited to 20 percent or less cover. (pp. 1-4).
Native cover of big sagebrush can vary from 3-51% without livestock grazing, and (as in kipukas), without heavy native ungulate grazing.
Wildlife depending on or associated with big sagebrush have been found to be present at higher numbers or experience higher reproduction success in higher sagebrush cover (e.g., 25-50%).
- As big sagebrush canopy cover increases over 12-15 percent, bare ground does not increase and perennial grass cover does not decrease. (pp. 6-8).
There is no significant relationship between big sagebrush cover and bare ground. In some studies, highest grass cover has been found with highest big sagebrush cover.
- Removing, controlling, or killing big sagebrush does not consistently result in any increase in perennial grass production, let alone two or three or more-fold increases (pp. 8-11).
"Differences in perennial grass production in big sagebrush stands has less to do with shrub cover than it has with soils, moisture (wet or dry years) and especially razing history differences [references cited]." (p.13)
- Big sagebrush is not unpalatable (pp. 11-15).
"A host of organisms feed directly on big sagebrush, including large and small mammals, birds, insects, fungi, parasitic vascular plants, and lichens, which find support on the boles and larger branches of big sagebrush. All parts of big sagebrush are consumed -- leaves and stems, pollen, achenes or seeds, root tissues, and so forth." (p. 11).
Biodiversity is high on big sagebrush -- e.g., 31 fungus species, 52 aphid species, 18 beetle species, 13 species of grasshopper and shield-back katydids; 32 midge species induce galls. Many of these species are eaten by yet other species. About 16 species of paintbrushes (Castilleja), are hemi-parasitic on big sagebrush, as are as many as seven species of owl-clovers. Mule deer, pronghorn, elk, and bighorn sheep variously consume big sagebrush.
- Biodiversity has not been shown to increase with the removal, controlling, thinning, or killing of big sagebrush (pp. 15-16).
Welch and Criddle ask a number of questions about existing and desired studies purporting to examine biodiversity in relation to removing, controlling, thinning, or killing of big sagebrush (p. 15).
- Mountain big sagebrush does not appear to have evolved in an environment with a mean fire interval of 20-30 years, nor is it "well on its way to return" within 5-10 years. (pp. 16-19).
Re-establishment after fire has found to often take far more than 5-10 years (pp. 16-18).
Ten biological and ecological characteristics of mountain big sagebrush are given that do not support the idea that mountain big sagebrush evolved in an environment of frequent fires of 20-30 years, including (1) a life expectancy of 70+ years; (2) highly flammable bard; (3) highly flammable essential oils; (4) a low growth form susceptible to crown fires; (5) non-sprouting; (6) late fall or early winter seed dispersal, long after fire season has ended; (7) lack of a strong seed bank in the soil; (8) seeds lack anatomical fire resistance structures or adaptations; (9) seeds must lie on the soil, exposing them to higher temperatures; and (10) seeds lack adaptations for long distance dispersal (p. 18).
Mountain big sagebrush may have fire intervals of 50 or more years (pp. 18-19).
- Big sagebrush has not been shown to be an agent ofallelopathy (pp. 19-20).
For instance, one study found big sagebrush litter extracts inhibited germination of four particular species, but these are the same species most abundant directly under or very near big sagebrush shrubs. ( p. 20).
Soil nitrogen levels under big sagebrush have been found by five studies to be higher under big sagebrush plants than in the interspaces, indicating big sagebrush is not inhibiting cyanobacteria (p.20)
- Big sagebrush is not a dominating, suppressive plant species (pp. 21-22).
"There are four scientific articles that show when grazing is eliminated or reduced, grass cover increases in spite of high or increasing big sagebrush canopy." (p. 21)
Another found that big sagebrush can draw water from deep, moist soil layers, and at night redistribute water into the drier upper layers of the soil (p. 22); and some studies indicate big sagebrush is a soil builder through nitrogen fixation, animal activity, canopy-capture of wind-distributed solids, and bringing minerals from deeper in the soil, and depositing them as litter (p.22).
This document seems to indicate:
- Much of what has been attributed to big sagebrush ecology has been confused with effects of livestock grazing.
- Shortened fire intervals may cause replacement of big sagebrush by other species, e.g., rabbitbrush (Chrysothamnus spp.).
- Reduction of big sagebrush cover may mean reduction of populations of species that depend on big sagebrush and reduction of biodiversity in the area.
QUESTIONS RAISED FOR THE THREE FORESTS
1. Do the Three Forests have any on-ground evidence that any of Welch and Criddle's conclusions are inaccurate?
RELEVANCE TO FOREST MANAGEMENT
- Maintenance of large areas free of livestock grazing allows for (a) distinguishing between myths and natural regulation; and (b) supporting biodiversity that may be significantly reduced by livestock grazing.
- Any proposed prescribed burning planned in big sagebrush should be preceded with evidence that native big sagebrush and its related native biodiversity will not be diminished.