Shaking the fake tree: UV seeds the way

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  • Published: Mar 1, 2014
  • Author: David Bradley
  • Channels: UV/Vis Spectroscopy
thumbnail image: Shaking the fake tree: UV seeds the way

Mock seeds

At a conservation corridor experiment in South Carolina, Univ. of Wisconsin-Madison postdoctoral researcher Dirk Baker releases artificial seeds that glow in the dark. Image: Lars Brudvig

US researchers have constructed mock plant seeds, dusted them with fluorescent powder, and then released them at tree canopy height to simulate real seed dispersal on the wind. They could then return after dark with ultraviolet lamps to track where the seeds had landed, offering a neat and novel way to learn about certain aspects of the savanna eco-system.

Field ecologists expend a great deal of effort in tagging and tracking wildlife with radio collars, RFID chips, automatic day and night video cameras and many other technologies. But, tagging the wind and its passage through the corridors of an ecosystem is not so easy. However, a team hoping to study isolated patches of habitat in the longleaf pine plantations of South Carolina have devised an ingenious method for tracking the wind, a kind of airborne proxy. The team made artificial seeds from twisted yarn dusted with fluorescent powder, which they could scatter across the patches of habitat in which they were interested and let the wind carry their mock seeds at its whim just as if the yarn twists were natural tree seeds.

That night, the field crew returned for a black-light treasure hunt, locating more than 80 percent of the fake seeds, which glowed under the ultraviolet light. The paths of these glowing seeds were matched with output from a computer model to produce the first accurate picture of how wind moves seeds through corridors linking two patches of habitat.

Diversity corridors

At first glance, the approach sounds like a school science project, but its simplicity belies its serious purpose as ecologist and first author Ellen Damschen of the University of Wisconsin-Madison explains in the journal Proceedings of the National Academy of Sciences. "Understanding the conservation impact of corridors is at the cutting edge of conservation,” Damschen says. Corridors are designed to improve conditions for uncommon native species living in separated habitats. Small populations in these 'islands' of habitat may be killed by storms or disease. They may lack genetic diversity and be prone to inbreeding. And they may be unable to reach new habitats."

For almost half a century, conservation biologists have discussed building conservation corridors to link isolated patches of protected land. "It makes intuitive sense that these connections could foster genetic and biological diversity," adds Damschen. One large project that will link the famous Yellowstone National Park with Canada's Yukon Territory, is now taking shape. However, it is important to have the scientific evidence available that such corridors will act positively on natural diversity and in overcoming the problem faced by ecosystems isolated by human construction, mining and other activities. "Unfortunately, there has been very little scientific evidence for if and how they work," laments Damschen.

She points out that until now most of the studies that have been carried out have focused only on animals despite the fact that plant life underpins every terrestrial ecosystem acting as the great solar converter for harvesting carbon dioxide from the air and generating the nutrients at the "bottom" of the food chain on which the animals depend.

Long-distance solutions

Wind matters for the movement of seeds and whole organisms, Damschen says. "In many open habitats, more than one-third of plants are wind dispersed, but there are also insects, spiders, pathogens and fungi that move on the wind," she adds. In work supported by the National Science Foundation and the US Forest Service, which began in 2000 with the creation of eight groups of identical patches at the Savannah River Site, a large holding of the US Department of Energy in South Carolina. Each set of patches was built at a different orientation to prevailing winds.

In the latest work, the interdisciplinary team of meteorologists and ecologists has found that corridors increased the movement of wind and of their fluorescent mock seeds. The findings corroborated a computer simulation model developed by Gil Bohrer of The Ohio State University. And, when Damschen and fellow scientists in the Corridor Research Group counted newly dispersed plants they demonstrated that a corridor linking two patches of land does indeed promote the diversity of plants dispersed by the wind especially when said corridor is orientated close to parallel with the prevailing winds.

Both the data and the model reveal that the wind accelerates in certain areas of the patches, and that strong vertical air movement is present. "Uplift is important because the wind tends to be faster higher above the ground," Damschen adds, "And uplift can lead to long-distance dispersal, which is most significant for moving plants around the landscape." These findings confirm the importance of studying such corridors in conservation biology. "We predicted that corridors in line with the dominant wind would move more species, and this is what we found. Wind alignment matters for species diversity in conservation areas," Damschen says.

Much of the US Midwestern ecosystems as with grasslands, prairies and savannas, elsewhere, depend on the wind to loft the seeds of plants like big bluestem and milkweed and other native plants for their persistence and spread.

"In conservation science, it is often assumed that wind-dispersed seeds can go everywhere, but that's not true," Damschen says. "Wind direction and the shape of the habitat control where these seeds go. While this adds another factor to consider in management of natural areas, at least the information is on the table so we can make better decisions about how to achieve management goals," she concludes.

"The next step in our research is to use our model to determine if the size (width and length) of corridors affects their ability to move seeds as we saw here," Damschen told SpectroscopyNOW. "We also are planning to examine how plants respond over the next ten years to corridors and whether we see the same pattern reported here over that time period.  Ultimately, we hope to understand how corridors affect the diversity of plants (and other organisms) over decadal time scales."

Related Links

Proc Natl Acad Sci (USA) 2014, online: "How fragmentation and corridors affect wind dynamics and seed dispersal in open habitats"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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