Holt, E.A., 2007, Community gradients of Arctic macrolichens in relation to succession, grazing and the environment: Corvallis, Oregon, Oregon State University, Ph.D. dissertation, 120 p.
The purpose of this dissertation was to define macrolichen community gradients in relation to succession, grazing, and the environment. First, species scores indicating when macrolichen species appeared following disturbance were derived from the literature. Weighted averaging of these data with a community matrix created a successional score for each sample unit of interest. These scores are surrogates for community age for subsequent analyses. I then described lichen community structure and its relation to the environment in the Bering Land Bridge National Preserve (BELA) in northwestern Alaska. Two primary gradients in lichen community composition were related to habitat rockiness and a substrate-topographic gradient. Next, I sought impacts of grazing by reindeer and caribou on lichen communities. I found lightly grazed areas had taller lichens, greater total lichen cover and minor but significant changes in community structure than heavily grazed sites. Lichen species richness, however, did not differ by grazing status. To create a generalized recovery model, I used plots in burned areas and found total lichen and bryophyte cover varied with time since fire (range 4-49 yrs since fire), while vascular plant cover showed no trend. I then compared these patterns to BELA, an area of unknown disturbance history. Low lichen cover in BELA may not necessarily reflect disturbance but rather site or climatic differences. Last, I found that all 17 GIS variables separated lichen communities to some degree. Separation of lichen communities by variable ranged from strong (Alaska Subsections, soil and surficial geology variables) to weak (Watersheds and Reindeer Ownership). The quality of the underlying relationships, how finely the groups are divided and the average patch size of each variable also contribute to differences in how clearly lichen communities were separated. This work will serve as a baseline for future comparisons to understand implications of climate and land use change on lichen communities. My grazing results may inform managers of the implications of heavy grazing and underscore protection and monitoring of prolific and diverse sites. In addition, this work contributes a new method to age tundra communities and a list of GIS variable successful at separating lichen communities.
Theses and Dissertations