Demography of the narrow endemic mint Dicerandra thinicola: Patterns, drivers, and management recommendations based on 18 years of data from its largest wild population1 Authors: Eric S. Menges, Suzanne M. Kennedy, Stacy A. Smith, and Stephanie M. Koontz Source: The Journal of the Torrey Botanical Society, 146(3) : 155-165 Published By: Torrey Botanical Society URL: https://doi.org/10.3159/TORREY-D-19-00003.1 BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Complete website, and all posted and associated content indicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/terms-of-use. Usage of BioOne Complete content is strictly limited to personal, educational, and non-commercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder. BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. Downloaded From: https://bioone.org/journals/The-Journal-of-the-Torrey-Botanical-Society on 01 Oct 2019 Terms of Use: https://bioone.org/terms-of-use Access provided by Torrey Botanical Society Journal of the Torrey Botanical Society 146(3): 155–165, 2019. Demography of the narrow endemic mint Dicerandra thinicola: Patterns, drivers, and management recommendations based on 18 years of data from its largest wild population1 Eric S. Menges,2,5 Suzanne M. Kennedy,3 Stacy A. Smith,4 and Stephanie M. Koontz2 2 Archbold Biological Station, 123 Main Drive, Venus, FL 33960 3 Florivista, Inc., Cocoa Beach, FL 4 Department of Agronomy, University of Florida, Gainesville, FL Abstract. The mint genus Dicerandra is the rarest of any plants in the southeastern USA, and the narrow endemic D. thinicola H.A. Mill. is restricted to one wild population on public land and a few unprotected populations on private lands. From 2001 to 2017, we studied ~9,000 plants and 90,000 annual transitions in permanent plots in Florida scrub and roadsides to assess the health of this population and potential drivers of demographic change. Plant numbers have fluctuated widely, largely due to variably large pulses of winter seedling recruitment, but the overall trend has been upward, especially along sandy roadsides, in scrub gaps, and in chopped/burned scrub. Across the data set, annual survival (mean 67%) varied among habitats (being highest along roadsides) and among years (with decreased survival in some recent years). Nearly half of surviving vegetative plants advanced from vegetative to reproductive each year and most plants, once flowering, continued to flower each year. Growth in number of branches was consistently positive; only one-quarter of plants had reduced size each year. Relative growth rate was higher along roadsides than in other habitats. Reproductive output was lowest in scrub gaps and varied among years. Seedling recruitment was concentrated in winter months, varied widely among years, and was lower in the scrub matrix than in scrub gaps or roadsides. About half of seedlings died before their second year, the maximum observed life span was 13 yr, and fewer than 6% of plants survived 10 yr. Flowering began as early as age 2 (rarely as seedlings) and by age 4–7, 90% of surviving plants were reproductive. Land management (roller chopping and fire) in 2007 had profound effects on the population. Chopping killed 91% of plants and chopping followed by burning killed 100%. However, recruitment in these treated plots was 2.5–5.5 times higher in the 6 yr after treatments than in the 8 yr before treatments; no such differences were seen in untreated plots. Posttreatment plants grew faster and flowered earlier than other plants. Consequently, after several years, plant numbers in the treated areas had increased 4–8 times, whereas plant numbers in untreated areas changed little. This state-endangered plant is short-lived and depends heavily on disturbance (ideally fire) for recruitment and population growth. It is threatened not only by its narrow distribution but by insufficiently aggressive land management. Key words: Fire, Florida scrub, plant demography, population dynamics, prescribed burn, roller chopping, seedling dynamics The mint genus Dicerandra is the rarest of any are narrowly endemic, allopatric, perennial spe- in the southeastern USA (Estill and Cruzan 2001). cies. A few of these species have received Currently, 10 taxa are recognized as occurring in considerable study. On the Lake Wales Ridge, D. Florida (http://florida.plantatlas.usf.edu/) and most frutescens Shinners has received over 30 yr of intensive demographic study (Menges 2008). Fire strongly affects D. frutescens populations, with 1 We thank the City of Titusville Water Resources and Fire departments for their cooperation in allowing access most vital rates (survival, growth, fecundity, and keeping us informed of routine management. Thanks recruitment) and population growth being greatest to the US Fish and Wildlife Service, Brevard County, the in the first 2 decades after fire (Menges et al. 2006; Florida Forest Service, and The Nature Conservancy for Evans et al. 2008, 2010). Dicerandra frutescens is their interest in protecting and managing this species. Zack Prusack of The Nature Conservancy, Rudy Khan of protected at two sites. Two closely related Titusville Water Resources, Ron Weiss of the Florida congeners also endemic to the Lake Wales Ridge, Forest Service, and CalLee Davenport along with staff D. christmanii Huck & Judd and D. modesta from the Brevard County Environmentally Endangered Lands Program were instrumental in working with 5 multiple agencies to accomplish the land management Author for correspondence: emenges@archbold- that has occurred. We thank our funders, including the station.orggene. National Science Foundation (DEB 1347843) and the doi: 10.3159/TORREY-D-19-00003.1 Florida Division of Plant Industry. We thank Stephanie ÓCopyright 2019 by The Torrey Botanical Society Power and many Archbold research assistants and Received for publication December 26, 2018, and in interns for their diligent fieldwork. This manuscript revised form February 28, 2019; first published was improved by comments from Cheryl Peterson. September 6, 2019. 155 Downloaded From: https://bioone.org/journals/The-Journal-of-the-Torrey-Botanical-Society on 01 Oct 2019 Terms of Use: https://bioone.org/terms-of-use Access provided by Torrey Botanical Society 156 JOURNAL OF THE TORREY BOTANICAL SOCIETY [VOL. 146 (Huck) Huck, are protected at a single site. Other Adjacent to the Titusville Wellfield is the sole rare Dicerandra perennial species (D. cornutissima publicly owned conservation site, the Dicerandra Huck, D. immaculata Lakela, D. thinicola) are Scrub Sanctuary, managed by Brevard County’s endemic to other small ridges along the east coast Environmentally Endangered Lands Program. of Florida or in the Ocala area. During 2002, a survey of its namesake conserva- Levels of genetic variation differ among Dicer- tion-acquired land, Dicerandra Scrub Sanctuary, andra species (McDonald and Hamrick 1996, found two adult D. thinicola on the 44-acre Menges et al. 2001, Oliveira et al. 2007) and are sanctuary. An introduction of seeds from the unrelated to current and past landscape patterns or Wellfield to the Sanctuary was made in 2002–03 population sizes (Menges et al. 2010). Different (Menges and Kennedy 2007) and plants from genotypes of D. immaculata var. savannarum had subsequent generations persist where introduced. differential success in experimental introductions As for other perennial members of the genus (e.g., (Peterson et al. 2013). Dicerandra species are D. frutescens, D. christmanii; Menges 2007), D. either tetraploid or hexaploid (Huck and Chambers thinicola occurs in Florida scrub on yellow sands. 1997). Dicerandra thinicola sites are dominated by oaks Dicerandra species share similar ecological and other shrubs (e.g., Q. myrtifolia, C. floridana, traits. They grow in Florida scrub on yellow sands Q. geminata, Q. chapmanii Sarg., Serenoa repens, (Menges et al. 2007; termed oak-hickory scrub or Ximenia americana L.) that resprout and grow yellow sand scrub; Menges 2007), often in areas rapidly after fires and other disturbances. dominated by myrtle oak (Quercus myrtifolia The ecology or management of wild populations Willd.), sand live oak (Quercus geminata Small), of D. thinicola have not yet been investigated. scrub hickory (Carya floridana Sarg.), and pal- Although we hypothesize that this species parallels mettos (Serenoa repens (W.Bartram) Small, Sabal other Dicerandra species in its dependence on fire etonia Swingle ex Nash). Florida scrub is fire and gaps for healthy populations, this hypothesis maintained, with oak-hickory scrub being charac- has not yet been tested. On the basis of 16 yr of terized by intense fires occurring every 5–12 yr demographic data, our goals are to describe the life (Menges 2007). Studied Dicerandra species are history and demography of this plant species, gap specialists (Menges 1992, Menges et al. 1999, assess the trends in the Titusville Wellfield III Peterson et al. 2013, Richardson et al. 2013). population, evaluate fire and weather as potential