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PARENT SESSION
Oral Session # 92: Biogeography IV: Dispersal.
Presiding: J Choo
Friday, August 8. 8:30 AM to 12:00 PM, SITCC Meeting Room 104.

A mechanistic model for wind-dispersed seeds in heterogeneous environments: Design and validation.

Nuttle, Tim1, 2, Haefner, James2, 1 Friedrich Schiller University, Jena, Germany2 Utah State University, Logan, Utah, USA

ABSTRACT- Seed dispersal is an important determinant of local and regional community composition. We present a mechanistic model of seed dispersal by wind that incorporates heterogeneous vegetation structure within the model landscape. Such vegetation heterogeneity is important because it affects the horizontal wind profile, which is one of the primary determinants of seed dispersal distance. The model was developed for hardwood bottomland forests in the Mississippi Alluvial Valley, but is applicable to any forest community for which the requisite data are available. The model moves seeds in 3-dimensional space from the parent tree until it reaches the ground, by combining local wind speed and seed terminal fall velocity. The model differs from other mechanistic seed dispersal models in that vegetation, and thus wind speed, may vary along the trajectory of each seed. The model was validated using source populations of trees in forests and seed trap data in adjacent reforestation sites of two distinct vegetation structures (younger, open reforestation sites and older, closed reforestation sites). The model was replicatively and predictively valid for all species and vegetation types, even though patterns of seed density differed greatly between the two vegetation types. The model's sensitivity to vegetation structure, and its ability to accurately predict seed arrival when this structure is incorporated, demonstrates its utility for modeling seed dispersal in heterogeneous environments, and its potential utility for incorporating mechanistic seed dispersal in a forest simulation model.

Key words: wind profile, micrometeorological wind dispersal, seed traps, reforestation