PARENT SESSION
Symposium #4: Long-distance dispersal.
Sponsored by ESA Plant Population and Theoretical Ecology Sections
Organized by: R. Nathan, M. Cain, S. Levin.
Monday, August 6, 2001. 1:00 PM to 5:00 PM. Lecture Hall

A Large-Eddy / Lagrangian Dispersion model to study long-distance dispersal of tree seeds.

Avissar, Roni¹, Walko, Robert¹, Thomas, Suvi¹, Baidya Roy, Somnath¹, Katul, Gabriel², Nathan, Ran³, Horn, Henry³, Levin, Simon³, ^{1 2 3}

ABSTRACT- One of the key challenges to quantifying long-distance seed dispersal by wind is describing the complex and three-dimensional eddy motion inside and above canopies. The Large-Eddy Simulations (LES) option of the Regional Atmospheric Modeling System (RAMS), a state-of-the-art, three-dimensional, non-hydrostatic atmospheric numerical model was modified to simulate atmospheric turbulence within and above tree canopies. The primary modification included a new coordinate system designed to contour the shape of trees, thereby permitting a more faithful descriptor of the interaction between canopy morphology and the energetic eddies. The model was set up to simulate turbulence within a second-growth 180-year old hardwood stand at Duke Forest having a mean canopy height of 30 m and a maximum leaf area index of 6. The LES was initialized with measured hourly mean wind speed, temperature, and humidity profiles near a 45-m tower in this stand. The simulation duration was 30 minutes for consistency with Reynolds type averaging intervals of canopy flows. The various statistical moments needed to drive seed trajectories were compared with the corresponding moments measured at the tower. A Lagrangian Dispersion Particle Model (LDPM) driven with the turbulent flow simulated with the RAMS-LES was then used to quantify seed dispersal at that site. The combined RAMS-LES and LDPM simulations adequately match the patterns of seed dispersal as quantified by observations conducted near the tower.

KEY WORDS: long-distance dispersal of seeds, simulations of seeds dispersal, turbulence in and above tree canopies