Terrain Influences on Conifer Seed Dispersal

Advancing low-cost conifer seed dispersal models is essential for predicting ecosystem evolution under future climates and for enhanced agroforestry decision making. Recent research has demonstrated that inverse Gausssian (WALD) models reasonably reproduce terrain's influence on conifer seed dispersal, however such research has primarily focused on dispersal by turbulent flow over two-dimensional forested hills (ridges). This presentation will present analysis of turbulence-resolving large-eddy simulations (LES) investigating the role of isolated two-dimensional (2D) and three-dimensional (3D) hills of varying steepness on seed dispersal characteristics from horizontally-homogeneous forests, where seeds are assumed to disperse like inertial particles by a Lagrangian particle dispersion model (LPDM) driven by LES flow fields. To validate the solutions, the coupled LES-LPDM system is vetted against results in the literature and against physical wind tunnel simulations conducted in collaboration with this project. Flow statistics are dependent on hill slope and shape. For the configurations studied, steeper hills induce flow separation (recirculation) which alters the canopy-top locations where peak wind speeds and turbulence levels occur compared to flow over shallower sloped hills. Flow statistics in the alongwind direction at hill centerline are similar between 2D and 3D hills, yet leakage around the sides of 3D hills impacts seed dispersion. For releases on the windward and leeward sides of cosine hills, seeds are most likely to travel long distances in flows interacting with 2D steep hills and 3D shallow hills, respectively. WALD model predictions driven by LES flow fields produce notably larger downstream dispersal than predicted by the LES-LPDM.