Environmental drivers of plant community composition in subalpine and alpine fens of the San Juan Mountains, Colorado, USA
Date
2015
Authors
Bultema, Betsy L. H., author
Cooper, David J., advisor
Dwire, Kathleen A., committee member
Steingraeber, David A., committee member
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Abstract
Fens are a widely distributed type of wetland worldwide and offer vital habitat for plant and animal species in the Rocky Mountains. Fens support a high biodiversity of flora and fauna given the proportionally small space they occupy on the landscape, often serving as refugia for disjunct plant species at the extremes of their ranges. While some literature exists on subalpine fens in the southern Rocky Mountains of the United States, alpine fens in this region remain understudied. Alpine fens are relatively rare in the southern Rocky Mountains and are concentrated within the San Juan Mountains where topography and climate favor peat development in the alpine. While studies of montane and boreal peatlands have identified water chemistry as a main driver of plant community composition, it is unclear whether the same drivers of plant community composition are important in alpine fens in the San Juan Mountains. The goal of this study was to 1.) Describe and classify the vegetation of subalpine and alpine fens and, 2.) Determine underlying environmental variables influencing plant community composition. To do this, I mapped fens within the BLM Gunnison Management Unit (approximately 243,000 hectares). I then visited, verified, and sampled vegetation and environmental data from 33 subalpine and 32 alpine fens. To classify vegetation data into plant communities, I used hierarchical cluster analysis. I used non-metric multidimensional scaling and comparisons of ranked environmental and vegetation distance matrices to investigate relationships between plant community composition and environmental variables. I compared the influence of environmental variables on subalpine and alpine plant community composition with cumulative r² values from linear regressions with NMS axes and Spearman rank correlations between ranked vegetation and environmental distance matrices. I classified 226 stands of vegetation into 11 plant communities that were correlated with elevation and water chemistry variables. Water chemistry variables, particularly pH, EC, and bicarbonate, were more important in structuring vegetation in subalpine than alpine fens. This was in part due to a lower range in values of alpine water chemistry variables. However, lower variance in water chemistry variables did not correspond to decreased plant community diversity in the alpine. To thoroughly explain alpine fen plant community diversity, future studies should consider measuring additional variables, such as soil temperature and temporal variation in water table. Elevation was a relatively important explanatory variable for plant community composition in alpine fens, suggesting that climatic variables are important influences on community composition. Results of this research indicate that the relative importance of environmental variables differs for alpine and subalpine fen plant communities. Thus, future studies examining mountain fen plant community composition should treat alpine and subalpine fen data separately.
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Rights Access
Subject
ecological gradients
peatlands
water chemistry
fens
alpine
species composition