Abstract:
I evaluated the response of the federally listed endangered plant species
Bradshaw's desert parsley (Lomatium bradshawii) to livestock grazing and small
mammal depredation at Oak Creek, Linn County, Oregon, 1997-1998. I established six
study blocks (three each in wooded and herbaceous pastures) with plots in each block
randomly assigned to one of four intensities of livestock grazing based on biomass
remaining after grazing (no grazing [1,746 kg/ha], high biomass [969 kg/ha], moderate
biomass [670 kg/ha], and light biomass [318 kg/ha]). Small mammals were live-trapped
in each of the study blocks pre and post application of the livestock grazing treatments. I
mapped and measured 2,807 Bradshaw's desert parsley plants (n 1,366 in the wooded
and n = 1,441 in the herbaceous pastures) over the two year period to determine changes
in schizocarp production, morphological structure (conical surface area and height),
population composition (plant stage), survival, emergence of new plants, and effects of
small mammal herbivory pre and post application of livestock grazing. Grazing
reductions in standing crop biomass appeared to have a positive effect on emergence of
new Bradshaw's desert parsley plants, while having no detectible effect on total plant
density or survival. Differences in total plant density, survival, schizocarp production,
morphological structure, and population composition were related to pasture type.
residual standing crop biomass may reduce small mammal use of an area, and thus may
serve to reduce the impacts of small mammal herbivory. I found differences in small
mammal depredation of Bradshaw's desert parsley between pastures and among livestock
grazing treatments. Standing crop biomass and peak vole abundance were significant
covariates in plant depredation rates. Livestock grazing initially appears to have increased
Bradshaw' s desert parsley plant emergence and density of several plant stages, but did not
enhance survival at the Oak Creek site. I examined only the initial response of Bradshaw' s
desert parsley to livestock grazing; long-term impacts of this management practice are
unknown. Direct comparisons between livestock grazing and other forms of vegetation
management, such as mowing and prescribed burning, currently do not exist for
Bradshaw's desert parsley and warrant further investigation.
