Identifying vegetation’s influence on multi-scale fluvial processes based on plant trait adaptations

Abstract:

Riparian vegetation-geomorphic interactions are critical to the physical and biological function of riparian ecosystems, yet we lack a mechanistic understanding of these interactions and predictive ability at the reach to watershed scale. Plant functional groups, or groupings of species that have similar traits, either in terms of a plant’s life history strategy (e.g., drought tolerance) or morphology (e.g., growth form), may provide an expression of vegetation-geomorphic interactions. We are developing an approach that 1) identifies where along a river corridor plant functional groups exist and 2) links the traits that define functional groups and their impact on fluvial processes. The Green and Yampa Rivers in Dinosaur National Monument have wide variations in hydrology, hydraulics, and channel morphology, as well as a large dataset of species presence. For these rivers, we build a predictive model of the probable presence of plant functional groups based on site-specific aspects of the flow regime (e.g., inundation probability and duration), hydraulic characteristics (e.g., velocity), and substrate size. Functional group traits are collected from the literature and measured in the field. We found that life-history traits more strongly predicted functional group presence than did morphological traits. However, some life-history traits, important for determining the likelihood of a plant existing along an environmental gradient, are directly related to the morphological properties of the plant, important for the plant’s impact on fluvial processes. For example, stem density (i.e., dry mass divided by volume of stem) is positively correlated to drought tolerance and is also related to the modulus of elasticity. Growth form, which is related to the plant’s susceptibility to biomass-removing fluvial disturbances, is also related to frontal area. Using this approach, we can identify how plant community composition and distribution shifts with a change to the flow regime (e.g., as a result of dams or climate change) and as such, how the strength of the plant-geomorphic linkage may shift lateral to the stream and along the riparian corridor.