Seed Size and Dispersal Potential of Acer rubrum ...

1 Seed Size and Dispersal Potential of Acer rubrum (Aceraceae) Samaras Produced by Populationsin Early and Late Successional EnvironmentsAuthor(s): Patricia A. PeroniSource: American Journal of Botany, Vol. 81, No. 11 (Nov., 1994), pp. 1428-1434 Published by: Botanical Society of AmericaStable URL: : 28/09/2010 19:41 Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available JSTOR's Terms and Conditions of Use provides, in part, that unlessyou have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and youmay use content in the JSTOR archive only for your personal, non-commercial contact the publisher regarding any further use of this work.

2 Publisher contact information may be obtained copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printedpage of such is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range ofcontent in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new formsof scholarship. For more information about JSTOR, please contact Society of America is collaborating with JSTOR to digitize, preserve and extend access to AmericanJournal of Journal of Botany 81(11): 1428-1434. 1994. SEED SIZE AND Dispersal Potential OF ACER rubrum (ACERACEAE) SAMARAS PRODUCED BY POPULATIONS IN EARLY AND LATE SUCCESSIONAL ENVIRONMENTS1 PATRICIA A.

3 PERONI2 Department of Botany, Duke University, Durham, North Carolina 27006 In order to determine if red maple Dispersal Potential or seed size change during secondary succession, samaras were collected from five populations located in early successional environments and five populations located in late successional environments. Wing loading ratios ( samara mass-mg/ samara area-cm2), which are inversely proportional to Dispersal ability, were computed for all samaras, and seeds were excised from each samara and weighed. Samaras from the early successional red maples showed slightly but significantly lower wing loading ratios than those from the late successional environments. This result corresponds with the conclusions reached by several theoretical investigations of seed Dispersal evolution that predict that recently founded populations will show greater Dispersal abilities than more established populations.

4 The earlier successional populations had slightly heavier seeds than the later successional populations, which suggests that the changes in community composition and dynamics that occur during this successional sequence do not select for heavier seeds in older red maple populations. Coefficients of variation for wing loading and seed size showed no consistent trends with successional stage, which indicates that variation in these characters does not decrease as succession proceeds. Seed size and the Dispersal structures of plant propa- gules can influence the ability of plant populations to colonize new habitats and to persist at these sites. As succession proceeds at a site, selection on propagule char- acters may change in ways that can result in the evolution of these traits.

5 Although several theoretical treatments offer predictions regarding the Potential evolutionary ef- fects of successional changes on Dispersal structures of fruits (Van Valen, 1971; Levin, Cohen, and Hastings, 1984; Olivieri and Gouyon, 1985), Olivieri and Gouyon's (1985) analysis of propagule polymorphisms in two het- erocarpic species of Carduus represents the only published investigation that compares Dispersal Potential across a successional sequence. Several investigators have studied variation in seed size of herbaceous species in successional habitats (Reinartz, 1984; Aarssen and Turkington, 1985; Hartnett, Hartnett, and Bazzaz, 1987), but similar studies on woody plant species are lacking. The current study represents part of a larger investi- gation into genetic change and persistence of red maple (Acer rubrum L.)

6 During old field succession in North Carolina piedmont forests. The winged fruits of red maple colonize fields soon after abandonment, and these pop- ulations persist throughout the remainder of the succes- sional sequence. The unit of Dispersal is a samara (a single seed attached to a wing), and the mass, area, and shape of these samaras vary greatly within populations (Town- send, 1972). In this study, I compared samaras produced by early 1 Manuscript received 6 July 1993; revision accepted 16 May 1994. The author thanks J. Antonovics, N. L. Christensen, R. K. Peet, and S. Mazer for comments on initial drafts of this manuscript. Support for this study was provided by a Sigma Xi Grant-in-Aid of Research and a Sigma Delta Epsilon Graduate Women in Science Grant-in-Aid.

7 2 Current address: Department of Biology, Davidson College, David- son, NC 28036. and late successional red maple populations in order to evaluate the following questions: 1) Do samaras produced by red maple populations in early and late successional environments differ in dis- persal Potential ? Hypotheses based on the theoretical work of Van Valen (1971), Levin, Cohen, and Hastings (1984), and Olivieri and Gouyon (1985) predict that propagules produced by populations in early successional habitats will show greater Dispersal Potential than those produced by populations at older sites, and that the magnitude of the difference in Dispersal Potential observed between ear- ly and late successional populations will be greatest in those landscapes where the rate at which new sites become available for colonization and the probability of extinc- tion for established populations are both moderate.

8 2) Does the size of seeds produced by red maple pop- ulations vary with the successional maturity of a popu- lation's habitat? Several investigators have extended Abrahamson and Gadgil's (1973) hypotheses regarding life history differences among successional species to life history evolution within species that inhabit successional environments (for a review see Gray, 1987). In the case of seed size, these models predict that phenotypes that produce small seeds will dominate colonizing popula- tions, while populations in more mature habitats will be dominated by phenotypes that produce heavier seeds. MATERIALS AND METHODS Old field succession in piedmont forests-In the North Carolina piedmont, widespread abandonment of agri- cultural land during the late nineteenth and early twentieth centuries initiated secondary forest succession across much of the region.

9 Herbs and grasses dominate fields in the years immediately following the cessation of cultivation (Keever, 1950), but within 3-5 yr after abandonment, pines (primarily Pinus taeda) begin to overtop and shade 1428 November 1994] PERONI-CHANGES IN Dispersal OF RED MAPLE DURING SUCCESSION 1429 this grassy/herbaceous cover. A pine forest with a hard- wood understory develops and eventually forms a closed canopy. As these forests reach 80-100 yr of age, the pines begin to senesce (Peet and Christensen, 1987). Since pine seedlings show poor survival in the low light and high litter environments created by their parents, hardwood species gradually replace the pines. Within 200-300 yr after abandonment, this transition is complete, and a hardwood forest dominated by various oak (Quercus) and hickory (Carya) species occupies the former field.

10 These hardwood forests are relatively stable and self-perpetu- ating, and Oosting (1942) designated them the climax community for the piedmont old field successional se- quence. Oosting (1942) and Peet and Christensen (1987) provide detailed descriptions of old field succession in the North Carolina piedmont. Red maple-General description -Under forest condi- tions red maple is classified as a short to medium-lived understory and subcanopy tree (Fowells, 1965). Although stem turnover may be relatively high (Peet and Christen- sen, 1979), genetic individuals may be extremely long- lived since red maple shows a great capacity to stump sprout (Wilson, 1968). Despite its prodigious sprouting abilities, red maples apparently do not survive cultivation since sprouts are absent from recently abandoned fields in the study area (personal observation).