Influence of hydrology and recreational pack stock grazing on subalpine meadows of the John Muir and Ansel Adams Wilderness Areas, CA

Graduation Date

2010

Document Type

Thesis

Program

Other

Program

Thesis (M.S.)--Humboldt State University, Natural Resources: Planning and Interpretation, 2010

Committee Chair Name

Steven Martin

Committee Chair Affiliation

HSU Faculty or Staff

Keywords

Wilderness, Sierra Nevada, Grazing, Meadow, Multivariate analysis, Humboldt State University -- Theses -- Natural Resources Planning and Interpretation

Abstract

Subalpine meadows of the Sierra Nevada are groundwater-dependant ecosystems, making them highly vulnerable to hydrologic disturbances, including pack stock grazing. This study evaluated the interrelated effects of hydrology and grazing on plant species composition in subalpine meadows of the John Muir and Ansel Adams Wilderness Areas, California. Evidence was found for the primary importance of the hydrologic gradient in structuring subalpine meadow plant communities through vegetation sampling at groundwater monitoring wells and multivariate statistical analyses. Species composition was significantly correlated to water table depth, while species diversity was significantly correlated to water table drawdown. Basal cover of vegetation at monitoring wells was not significantly correlated to water table variables and may correspond more to some other factor. Seven meadows with stream channels previously rated to be in Proper-Functioning-Condition were also compared to seven meadows with channels rated Functional-At-Risk in a downward or unknown trend. Meadows in Proper-Functioning-Condition had significantly greater cover of hydric, deep-rooted graminoids and hydric woody species than meadows rated Functional-At-Risk, but no differences in bare soil levels were detected. Finally, permanent meadow plots in four meadows were sampled for changes in species composition over the last two decades. Plots in two meadows showed significant decreases in cover of obligate wetland species, possibly as a result of hydrologic changes stemming from past grazing pressure. Inconsistent trends across plots within each meadow highlighted the inherent variability of these environments.

https://scholarworks.calstate.edu/concern/theses/12579v58s

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