Plant community responses to fire exclusion, species invasions, and restoration in California woodlands and grasslands
Graduation Date
2014
Document Type
Thesis
Program
Other
Program
Thesis (M.S.)--Humboldt State University, Natural Resources: Forest, Watershed, and Wildland Sciences, 2014
Committee Chair Name
J. Morgan Varner
Committee Chair Affiliation
HSU Faculty or Staff
Keywords
Bald Hills, Oak woodlands, Conifer encroachment, Invasive grasses, Humboldt State University -- Theses -- Natural Resources, Flammability, Fuel moisture, Prescribed fire
Abstract
Quercus garryana woodlands and coastal grasslands in the Pacific Northwest are fire-dependent communities, threatened by encroachment from the native conifer Pseudotsuga menziesii in the absence of fire. In the Bald Hills of Redwood National Park in California, prescribed fire and conifer removal are used to restore and maintain woodlands. Understory vegetation was compared in four categories: encroached woodlands; formerly encroached woodlands treated with conifer removal; formerly encroached woodlands treated with conifer removal and prescribed fire; and never encroached and burned woodlands. At the site level no difference was found in mean native species richness (p = 0.155). When sites were combined by treatment category, the two categories that included fire had the greatest number of unique native species. Encroached woodlands had significantly lower richness (p 0.001), and lower Shannon Diversity (p 0.01), compared to the three other categories. The two categories that included fire also had a significantly greater number of mean non-native species compared to encroached woodlands (p 0.001). These results suggest prescribed fire and conifer removal have benefits to understory plant communities and the maintenance of this ecosystem; however, the abundance of exotic species and their adaption to fire in the Bald Hills complicates the restoration of native flora. Fuel moisture content of four native and four non-native grass species were sampled in a coastal grassland during the 2012 fire season. Differences in mean moisture content were compared between native and non-native groups using a linear mixed effects model with species as a random effect nested in group. No significant difference was found between natives and non-native groups (p = 0.337). Differences in moisture content among species, across dates, and for the species × date interaction were compared with a two-way analysis of variance. Across all dates, moisture content of the eight grasses differed significantly (p 0.001). Harding grass, Phalaris aquatica, an aggressive non-native, had the highest mean moisture content for all months and differed significantly from all species for all dates (p 0.05). The non-native dogtail, Cynosurus echinatus, had the lowest moisture content in August (21%), and fell well below the moisture of extinction before most species studied. Our results suggest that some non-native species have the capacity to alter fire behavior by either increasing or decreasing fire intensity and rate of spread. These findings reveal another way non-native species complicate restoration in this fire-dependent ecosystem.
Recommended Citation
Livingston, Amy C., "Plant community responses to fire exclusion, species invasions, and restoration in California woodlands and grasslands" (2014). Cal Poly Humboldt theses and projects. 2128.
https://digitalcommons.humboldt.edu/etd/2128
https://scholarworks.calstate.edu/concern/theses/b2773x920