Maschinski, Joyce. 2001. Impacts of ungulate herbivores on a rare willow at the southern edge of its range. Biological Conservation 101(1):119-130.
RELEVANT TO: |
SPECIES -- PLANTS |
AQUATIC/RIPARIAN |
|
WILDLIFE |
|
LIVESTOCK GRAZING |
DESCRIPTION
This article reports on four years of cattle and/or wild ungulate herbivory for different lengths of time (i.e., 30 days wild ungulate and cattle herbivory in 1995; 10 days cattle herbivory in 1996; 10 days wild ungulate herbivory during 1997 and 1999) on the rare Arizona willow (Salix arizonica) in its native habitat; and three years of either (a) year-round exposure to wild ungulates; or (b) 10 day's exposure to cattle herbivory in an arboretum meadow with abundant herbaceous forage.
MAJOR FINDINGS
- Native habitat exposure
- Significantly reduced plant height and total branch length
- Mortality of 25-3%
- Arboretum exposure
- Significant decline in branch length and biomass
- Reduction or elimination of reproduction
- Increased mortality
- Lack of compensation for tissue lost in the first year of exposure
- "...[O]nce S. arizonica is browsed, a single year of rest will not be enough to replace lost tissue."
- Year-round exposure maintained plants in a stunted, non-reproductive condition.
- "...[I]t may be necessary to protect large sections of drainage from both wild and domestic herbivores to restore healthy, naturally reproducing S. arizonica populations in Arizona.
- Subsidized wild ungulate populations are not in equilibrium with the natural vegetation that is available.
QUESTIONS RAISED FOR THE THREE FORESTS
- What has been learned in Utah about ungulate herbivory and reproduction and growth of Arizona willow since Fishlake and Dixie NF (as part of the USFS) entered into the Arizona Willow Conservation Agreement with the National Park Service and the Fish and Wildlife Service in 1995?
- What is the population trend of Arizona willow in (1) livestock-grazed, (2) livestock-free and (3) ungulate-free sites in Utah?
RELEVANCE TO FOREST MANAGEMENT
- Current Forest livestock grazing/browsing standards (e.g., browse of 40% of branch tips of riparian or upland shrubs) cannot be assumed to allow for growth, reproduction, maintenance, or recovery of Arizona willow ( or other sensitive plants) on these three Forests' lands.
- Arizona willow may not be able to be sustained or re-establish on the Three Forests if it is not protected from ungulate herbivory.