Publication Date

Spring 2020

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Environmental Studies

Advisor

William Russell

Subject Areas

Environmental studies

Abstract

Restoration of late seral features in second-growth Sequoia sempervirens forests is an important management concern, as so little of the original old-growth remains. The abundance of herbaceous species provides a metric for assessing recovery in these forests where associated understory plants are adapted to closed canopy conditions. Data were collected using a stratified random sampling design across three treatments: mechanically thinned second-growth, un-thinned second-growth, and old-growth reference stands. Pairwise PerMANOVA indicated greater abundance and diversity of native herbs in old-growth and un-thinned second-growth compared to thinned stands, as well as higher measures of canopy cover, basal area, and dominance of S. sempervirens. Thinned plots exhibited lower stand density than un-thinned stands but also higher abundance of non-native herbs. Non-metric multidimensional scaling suggested that un-thinned sites were more similar to old-growth than thinned sites in regard to understory composition and abundance, and indicator species analysis returned a suite of indicator species shared between un-thinned plots and old-growth plots while thinned plots shared one indicator with old-growth. In addition, both old-growth and un-thinned second growth sites were dominated by residual species, while thinned plots were dominated by invader species. These results suggest that while mechanical thinning of second-growth S. sempervirens stands may provide temporary effects to stand structure and composition, these treatments do not support the recovery of late seral understory species.

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