|Taylor, Fred - USDI-BLM|
|Farstvedt, Jerry - OREGON FISH & WILDLIFE|
Submitted to: Journal of Range Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 13, 2003
Publication Date: March 1, 2004
Citation: Ganskopp, D.C., Svejcar, A.J., Taylor, F., Farstvedt, J. Can spring cattle grazing among young bitterbrush stimulate shrub growth? Journal of Range Management. 2004. 57(2):161-168. Interpretive Summary: Bitterbrush is an especially important shrub on western rangelands for elevating the nutritional plane of wintering deer, pronghorn and elk. Many range and wildlife managers were concerned that spring/summer grazing by beef cattle might deplete or damage the growth of this browse. We discovered that lightly stocked cattle grazing among young bitterbrush stands actually stimulated increases in shrub height by 10 to 15 percent and shrub diameter by 20 to 30 percent. Heavier stocking, that actually resulted in consumption and tranpling of the shrubs by cattle, also stimulated growth, and shrubs were 2 to 6 percent taller and 20 to 30 percent wider than plants in ungrazed pastures. Shrub growth was not stimulated as much by cattle grazing during dry years because there was not enough soil moisture left for the shrubs to use during mid to late summer after cattle left. When cattle are grazed later in the growing season after grasses have matured, they will seek out bitterbrush and consume much of the foliage and twigs. These results show that spring cattle grazing can benefit wintering wildlife by actually stimulating growth of this important shrub. Ranchers and range and wildlife managers can use these findings to stimulate browse production on their properties for later consumption by cattle or several species of big game.
Technical Abstract: Due to its palatability and high forage quality, bitterbrush (Purshia tridentata Pursh DC)is a desirable shrub on western U.S. rangelands. This study was conducted to: 1) determine the effects of light and heavy spring cattle grazing on subsequent growth of young shrubs, and 2) explore stocking pressure thresholds for management of young shrubs. On average, 13.6(+4.8) and 62(+ 9.3) percent of the bitterbrush were browsed by cattle in lightly and heavily-grazed paddocks, respectively. Analyses of residual standing crop suggested cattle began browsing bitterbrush in spring months when available herbage declined to about 100 to 150 kg/ha. Browsing by cattle in the heavily-grazed paddocks in both 1998 and 1999 immediately reduced (P<0.01) the maximum diameter of bitterbrush by 4.5 to 9.5 cm, respectively, but shrub height was not affected (P>0.05) by cattle in either year. At the end of the 1997 and 1998 growing seasons, shrubs in the heavily-grazed pastures were about 11 cm wider (P<0.01) than ungrazed controls and equal to shrubs in the lightly-grazed treatment. To stimulate bitterbrush production, we suggest the stand be lightly grazed to a 30 to 40 percent utilization level by cattle when bitterbrush is flowering and accompanying grasses are in their vegetative to late-boot stages of growth.