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Spring 2016 Seed Dispersal: A Tale of Two Species W. John Hayden University of Richmond, [email protected]
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Recommended Citation Hayden, W. John. "Seed Dispersal: A Tale of Two Species." Sempervirens, Spring 2016, 6-7.
This Article is brought to you for free and open access by the Biology at UR Scholarship Repository. It has been accepted for inclusion in Biology Faculty Publications by an authorized administrator of UR Scholarship Repository. For more information, please contact [email protected]. 6 Sempervirens, Spring 2016
+FTTF4PSSFMMTBOE3PCFSU8BSSFO conducted their study in the Bent SeeD DISPeRSAl Creek Experimental Forest located within the Pisgah National Forest in North Carolina. They measured A Tale of Two Species abundance of Goodyera pubescens By W. John Hayden evergreen, perennial plants that live and Hexastylis arifolia (Arrowleaf Botany Chair among the leaf litter of deciduous Heartleaf) in a series of forest plots forests; each has tough, leathery that had been clear-cut at various rchids have minute, dustlike leaves, and each produces only a UJNFTTJODF"TQSFEJDUFE Oseeds. In this respect, Goodyera few new leaves per plant each year. the researchers found a robust pubescens (Downy Rattlesnake It should not be surprising that correspondence between heartleaf Plantain), the 2016 VNPS Wildflower both species are frequently found abundance and average age of of the Year, is a typical orchid. together. nearby trees—the older the forest, Like all other orchids, Goodyera In undisturbed forests, over seeds contain little more than a few long periods of time, differences in embryonic cells enclosed in a thin average distance of seed dispersal seed coat. There are two advantages may not make much difference in to small seed size in orchids: minute terms of plant distribution. Sure, for seeds can be produced in prodigious a given year’s seed output, an orchid quantities, and they can disperse over will easily outdistance a heartleaf. great distances by wind. But over the course of centuries, or In contrast, consider species millennia, the small yearly increments of Hexastylis (heartleaf). Though by of heartleaf dispersal add up. One can no means huge, at just a few mm in imagine that, given time, each should size, its seeds are much larger than be able to colonize the full extent of dust. Further, each heartleaf seed undisturbed forest habitats that suit bears an aril, a ridge of fleshy cells their requirements. along one side. Dispersal in Hexa- But eastern North America is stylis occurs with the assistance of no longer the forest primeval. Very ants, which, attracted to the fleshy little virgin forest remains. Most of aril, actively forage for its seeds and our forests are secondary, patchy carry them off some distance before bits of habitat, at various stages of consuming the aril and leaving the regeneration since the preceding remainder of the seed to its destiny. forest was destroyed. If clear-cutting Distances traveled with ant assis- temporarily renders the former tance are not great. Studies indicate forest floor uninhabitable for plants that effective rates of dispersal from like Goodyera and Hexastylis, parent plants in ant-dispersed species seed dispersal ability should are frequently less than one meter per have a measurable impact on the year. Of course, sporadic rare events distribution and abundance of these may disperse heartleaf seeds across plants in our present-day patchy distances much greater than that pro- secondary forests. One might predict vided by assistance from ants. that wind-borne orchid seeds should In terms of dispersal strategy, access suitable habitat in regenerating therefore, Goodyera and Hexastylis secondary forest much more quickly are pretty much at opposite ends of than ant-dependent heartleaf. Two the spectrum. Otherwise, however, researchers recently set out to test their ecological characteristics this very prediction (Sorrells and Goodyera pubescens seedpods. (Photos by are quite similar. Both are small, Warren 2011). W. John Hayden) Sempervirens, Spring 2016 7
trees plus everything liv- ing on, among, and be- Flora Fund Drive low the trees. And when forests are destroyed by Surpasses Goal clear-cutting, full recov- resounding “Thank you!” to ery of the whole commu- A you, members of the Virginia nity may well lag behind Native Plant Society, for once again tree regeneration. Rapid knocking it out of the park for the dispersers, like Downy Flora of Virginia Project. The friends Rattlesnake Plantain, of the Flora Project surpassed our may be able to keep up goal of $30,000 in our fall funding with frequent harvest appeal, and the lion’s share of those cycles of hardwood donors are VNPS members. forests. But slowly dis- With only two weeks to go in the persed plants, exempli- funding drive we notified our friends fied by the ant-dispersed of a very good development. We Goodyera pubescens, Downy Rattlesnake Plantain, is the heartleaf, are likely to were awarded a challenge grant by Society’s 2016 Wildfower of the Year. have difficulty tracking Richmond’s Mary Morton Par sons the more likely that heartleaf would through time and space the patchy Foundation, which also supported be found. In their study, no heartleaf bits of forest habitat that we have the print Flora of Virginia. They’ll was found in any forest younger carved from the once vast eastern match donations to the Project until than 34 years, but it was always deciduous forest. Downy Rattlesnake December or until they have matched found in plots with trees 60 years Plantain and Arrowleaf Heartleaf $40,000 in gifts. This was definitely old or older. In contrast, Downy may be broadly similar species but a motivator in the second half of Rattlesnake Plantain was found their seeds are different, and therein the drive, and about one-third of in young and old forests alike— lies the tale. the donations we received will be abundance was not tightly linked to matched by that grant. the age of the forest stand. Work Cited To receive our electronic news- Though Sorrells and Warren 4PSSFMMT + BOE358BSSFO** letter, Flora scope, sign up on our focused on Goodyera pubescens and Ant-dispersed herb colonization lags website, floraofvirginia.org, or our Hexastylis arifolia, their results can behind forest re-establishment. Jour- Facebook page. —Bland Crowder, be viewed more broadly. The good nal of the Torrey Botanical Society executive director, Flora of news is that species with efficient 138: 77–84. Virginia Project long-distance dispersal should be able to colonize patchy secondary forests with relative ease. But the bad news is that there are a great number of plants, like heartleaf, with ant-dis- persed seeds. In the eastern deciduous forests of North America, depending on forest type and location, an esti- Sempervirens (*44/ JTUIFRVBSUFSMZOFXTMFUUFSPGUIF7JSHJOJB/BUJWF1MBOU mated 30 to 70 percent of herbaceous 4PDJFUZ #MBOEZ&YQFSJNFOUBM'BSN #MBOEZ'BSN-BOF 6OJU #PZDF 7B forest plants depend on this relatively 837-1600, [email protected]. slow mode of dispersal. Nancy Vehrs, President The tale told by these two species Nancy Sorrells, Editor Karen York, Office Manager is a cautionary one. Forest trees may Original material in Sempervirens may be reprinted if credit is given to the Virginia Native well regenerate and cover the scars Plant Society, to Sempervirens, and to the author of the material, if named. Readers are of clear-cutting in just a few decades. invited to send letters, news items, and queries for consideration. E-mail items to Nancy But in ecological terms a forest is Sorrells at [email protected]. more than its trees. A forest is the Next submission deadline: March 15, 2016