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
Long-distance dispersal of tree seeds by wind: the role of vertical wind updrafts.
NATHAN, RAN1,2, HORN, HENRY1, LEVIN, SIMON1, PACALA, STEVE1, KATUL, GABRIEL3, AVISSAR, RONI4, WALKO, ROBERT4, THOMAS, SUVI4, 1 2 3 4
ABSTRACT- While most wind-dispersed tree seeds are dispersed short distances, the long-distance dispersal of very few seeds is disproportionately important for large-scale processes of colonization, spatial spread, metapopulation dynamics and gene flow. We argue that vertical wind updrafts that are strong and long enough to lift relatively heavy seeds above the forest canopy provide the key mechanism for long-distance dispersal of tree seeds by wind. We use models to simulate seed uplifting and long-distance dispersal, and collect empirical data on trees, seeds and winds to test them. Seed traps placed at 13 levels along a 45-m tower in Duke hardwood forest, trapped >9,000 seeds of five wind-dispersed species in two months during fall 2000, including 63 seeds (0.7%) in traps 34-42 m above the top of the canopy (31 m). Seeds of Liriodendron tulipifera were the most abundant overall (73%), but were under-represented above the canopy (40%). Seeds of Liquidambar styraciflua were less common overall (25%), but relatively more common above the canopy (46%). Seeds of Pinus taeda, Fraxinus americana and Carpinus caroliniana were rare overall (0.7, 0.4 and 0.2%, respectively); no seeds of Fraxinus or Carpinus were trapped above the canopy, but Pinus seeds were disproportionately frequent there (14%). This large inter-specific variation is explained by our models as due to differences in tree distribution, tree height and canopy structure, seed aerodynamics and wind conditions during seed release.
KEY WORDS: seed dispersal by wind, long-distance dispersal, vertical wind updrafts, seed aerodynamics