Will Plants Move Fast Enough to Keep Up With Contemporary Climate
Researchers James Clark and Gabriel Katul Take Different Approaches to Speculate on the Future p.5
The laboratory for this and similar work is a 150-foot tower in Duke Forest that Katul uses to study the interaction of atmospheric processes with the environment. He and his collaborators festooned all altitudes of the tower with 102 hanging laundry baskets that served as traps for windblown seeds. “We concluded that by setting up seed traps on the tower, we would be able to better resolve the properties of seed dispersal than with traps located on the ground, which is what is typically done,” he says.
The tower also was rigged with wind speed measuring anemometers, and another anemometer was attached to a mobile van with a telescoping arm that could travel to other parts of the study area. Those aided Princeton’s Horn, who had developed a device to selectively release tagged seeds whenever wind speeds were high. “The idea was that if we really wanted to see how far seeds can go under strong winds, we’d like to drop seeds in those winds,” Katul recalls.
A technician collected and processed almost 5,000 seeds overall from five different species—loblolly pine, poplar, sweetgum, American hornbeam and white ash—collected during the autumn of the year 2000. By having a good idea of where the seeds were released, and knowing where they were trapped on the tower, the researchers found that the degree of wind turbulence in tree canopies plays a key role in seed dispersal.
Seeds caught in the calmer regions lower in a canopy tended to travel shorter distances. Conversely, long-distance travelers tend to get caught in stronger turbulences “that rapidly increase with increasing height,” the Nature paper said.
Adding biology to the physics, the paper also noted that while lighter seeds tend to be the furthest uplifted and dispersed, those also may be “less likely to germinate and survive seedling competition, making long-distance colonization more difficult.”
In an another study published in June 2005 in the Proceedings of the National Academy of Sciences, Nathan and Katul draw from the same tower experiments to suggest that seeds within tree canopies get the best wind boosts when there are fewer leaves.
“This may account for the tendency of many temperate tree species to restrict seed release to either early spring on late fall,” they wrote.
In a March 2005 paper in the research journal Diversity and Distributions, Nathan, Katul, Avissar, Horn and others proposed that biophysically based computer models could be made reliable enough to track the movement of seeds and other biological objects just like a camera traced the quirky pirouettes of an airborne feather at the beginning of the movie Forrest Gump.
Such models “can effectively incorporate key elements of aerial transport processes at scales ranging from a few centimeters and fractions of seconds, to hundreds of kilometers and decades,” the authors wrote.
Monte Basgall is a senior writer with Duke’s Office of News and Communications and specializes in science coverage.
photo captions:1. Jim Clark with a collecting basket at the Duke Forest FACE site. 2. Research tower in Duke Forest. 3. Gaby Katul