Graduate Thesis Or Dissertation
 

Contrasting Epiphytic and Ground Layer Macrolichen Communities along the Coast-to-inland Climatic Gradient in Oregon

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  • Cyanolichens, lichens with a cyanobacterial photobiont, benefit our ecosystems by the fixation of atmospheric nitrogen into a usable form for other organisms. They are highly sensitive to air pollution and require liquid water for photosynthesis. Many cyanolichen species frequently occur on the ground in the Pacific Northwest, however, most macrolichen community studies in this region focus only on epiphytes above half a meter in height. Less is known about lichen communities at ground level, particularly those in western Oregon. To help broaden our understanding of cyanolichen ecology, the ground layer was incorporated into this study. We tested several hypotheses regarding how cyanolichens in the epiphyte and ground layers respond to both regional climate and site-level variables. We also examined how lichen diversity varied along this gradient in each sampling layer. Both epiphytic and ground-dwelling lichen communities were sampled in 38 plots along a climate gradient in Oregon. This gradient incorporated five climatic regions: the Pacific Coast, Coast Range, Willamette Valley, Cascade Range, and central Oregon. We drew many plots from the vast network of the Forest Service’s Forest Inventory and Analysis (FIA) program, and combined community data from multiple sources to cover as wide a study area as possible. Lichen communities were analyzed using non-metric multidimensional scaling (NMS) and correlated with an array of climate variables. The community weighted averages of lichens containing cyanobacteria were calculated to compare lichen community composition to photobiont frequency. Split-plot ANOVAs were used to test for the significance of region, layer, and the interaction of region x layer in lichen community composition. Paired t-tests tested for significant differences in cyanolichen frequency between epiphyte and ground layers in each climatic region. We found that the ground macrolichen communities do not differ as strongly from one climatic region to the next in the wetter, western half of Oregon, as do the epiphytic communities. There is, however, a strong difference between the ground communities in western and central Oregon. There are proportionally about as many cyanolichens in the epiphyte layer as in the ground layer on the immediate coast, Coast Range, Willamette Valley, and Cascade Range. There are proportionally more cyanolichens in the ground layer than the epiphyte layer in central Oregon. The most prominent variables related to higher proportions of cyanolichens were lower elevation, less annual snowfall, warmer winter temperatures, higher annual precipitation, and a higher basal area of hardwood trees. On average, 76% of total plot diversity was captured by sampling epiphytes, and 39% by sampling the ground layer. Plots contained on average 18 species unique to the epiphyte layer and 7 unique to the ground layer. Lichen diversity was higher in the epiphyte layer than the ground layer in the wetter climatic regions in western Oregon, but higher in the ground layer in central Oregon. Total plot macrolichen diversity can be estimated fairly well from epiphytic lichen diversity. We propose our sampling protocol as a standardized method for the ground layer that can be used across studies and is directly comparable and complimentary to FIA sampling methodology. Both microclimate and substrate availability at ground level likely play key roles in the composition of these lichen communities and the abundance of cyanolichens at a site. Direct measurements of moisture sources and understory composition will help determine the mechanisms driving the observed patterns.
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  • Glauser A. 2018. Contrasting epiphytic and ground layer macrolichen communities along the coast-to-inland climatic gradient in Oregon. Oregon State University, Corvallis, OR. Master's Thesis.
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