Spatially Heterogeneous Vegetated Canopy Boundary Layers

Wind dispersed mosses rely on a combination of canopy structure and favorable atmospheric conditions to eject spores into the atmospheric boundary layer for transport to new habitats. Here spatial heterogeneity within the canopy is considered in terms of its impacts on the vegetated canopy sublayer and its consequences for spore transport. In order to assess the role of heterogeneity within the canopy, a series of wind tunnel experiments were performed at Portland State University using a live moss canopy and two surrogates manufactured from reticulated foam. Instantaneous velocity measurements were obtained from two hot wire probes located above the canopy. The lower probe remained fixed while the second probe performed a vertical transect of the boundary layer. Canopy heterogeneity is quantified with a lacunarity based index and related to two-point correlations as well as the turbulent spectra above each canopy type. The natural moss canopy is more heterogeneous than its manufactured counterparts and introduces turbulence across a broader range of scales. Further comparisons between the boundary layer over each canopy based on two-point correlations will be detailed in presentation.