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Accueil du site → Master → Etats Unis → 2000 → Effects of livestock grazing and small mammal populations on endangered Bradshaw’s desert parsley (Lomatium bradshawii) at Oak Creek, Willamette Valley, Oregon

Oregon State University (2000)

Effects of livestock grazing and small mammal populations on endangered Bradshaw’s desert parsley (Lomatium bradshawii) at Oak Creek, Willamette Valley, Oregon

Drew, Aaron D.

Titre : Effects of livestock grazing and small mammal populations on endangered Bradshaw’s desert parsley (Lomatium bradshawii) at Oak Creek, Willamette Valley, Oregon

Auteur : Drew, Aaron D.

Université de soutenance : Oregon State University

Grade : Master of Science in Wildlife Science 2000

Résumé
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.

Mots-clés : Lomatium — Oregon — Oak Creek —Grazing — Environmental aspects

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