Trait-based inference of environmental constraints on lichen epiphyte communities at multiple spatial scales

Ecological systems respond to processes that operate at a variety of spatial scales. Epiphytic lichens are a useful group for studying community response to cross-scale environmental variation because tree and forest architecture organize epiphyte communities into discrete hierarchical scales and because lichens' limited homeostatic ability makes them potentially sensitive environmental indicators. Examining variation in the functional traits of organisms can elucidate the role of the environment in structuring communities because these traits provide a direct link between organismal fitness and environmental filters. For lichens, such trait-based approaches are not yet fully developed.;This dissertation examines how lichen traits can provide insight into environmental constraints on communities across multiple spatial scales. The primary goals of this research were to 1) evaluate the extent to which larger-scale processes influence lichen epiphyte communities at smaller scales and 2) assess the utility of functional versus morphological trait-based approaches for understanding community assembly in lichen epiphytes. I utilized a national forest inventory (U.S. Forest Service) and conducted two field-based surveys in temperate deciduous forests across North Carolina (U.S.A.) to assess environmental factors affecting lichen assemblages at three focal scales: forest patches, tree trunks, and individual branches within tree canopies. To evaluate trait-based approaches, I quantified the response of functional and morphological traits to environmental variation at different scales and assessed whether observed relationships were consistent with hypothesized environmental constraints.;Results highlighted a previously underappreciated role for larger-scale processes in determining the composition of lichen epiphyte assemblages at multiple scales, but also revealed high community variability at small scales, which was not well accounted for by linear environmental models. This suggests a potentially important role for stochasticity in lichen community formation. Analyses also indicated that future development of trait-based approaches to lichen community studies should focus on quantifiable and functionally interpretable traits rather than the categorical characters used for species identification. This research demonstrates that traits are a useful, but not powerful, tool for understanding processes shaping lichen assemblages.