• Abstract and Figures
• Public Full-text

ABSTRACT WALKER, ANDREW SCOTT. Soil Seedbank of Rare Plant Communities Associated with Diabase Soils in Durham and Granville Counties, North Carolina. (Under the direction of Dr. Jon M. Stucky) In Northeastern Durham County and Southwestern Granville County, North Carolina, there are a cluster of unique, species-rich plant communities associated with diabase soils. These communities are characterized by an abundance of shade-intolerant forbs with prairie affinities, including the federally endangered smooth coneflower, Echinacea laevigata. Monitoring reports of E. laevigata indicate that, while most populations declined between 1988 and 2002, the population at Picture Creek Diabase Barren increased dramatically, presumably in response to a prescribed fire and canopy clearing associated with a power line right of way. This suggested the possibility that E. laevigata and other rare plants form a persistent soil seed bank which can contribute to population increases. Presence of a soil seed bank could have conservation value and facilitate restoration of other “prairie remnants” in the area. We tested the soil seed bank at Picture Creek and two other nearby locations which have similar floras and were reported to have had similar numbers of E. laevigata in 1988. We also tested the litter layer at Picture Creek. No rare plants were found in the soil seed bank, but a few were recovered from the leaf litter. Soil Seedbank of Rare Plant Communities Associated with Diabase Soils in Durham and Granville Counties, North Carolina by Andrew S. Walker A thesis submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the degree of Master of Science Botany Raleigh, North Carolina 2009 APPROVED BY: _______________________________ ______________________________ Dr. James Mickle Dr. Robert Beckmann ________________________________ Dr. Jon Stucky Committee Chair . ii DEDICATION To my father, Gabriel Walker Jr. iii BIOGRAPHY Andrew Walker was born and raised in Portland, Maine. He earned a degree in English from the University of Chicago, after which spent the next decade in Seattle and Chicago working at a variety of jobs. During this time, he developed a strong interest in botany, which led him to graduate school at NCSU. Andrew now works in the conservation department at the North Carolina Botanical Garden. iv ACKNOWLEDGMENTS It was a great pleasure working with Dr. John Stucky, and I thank him for his patience and support. Special thanks are due to Sue Vitello, whose encouragement has meant a great deal to me. I am also grateful for my fellow students and good friends Laura Gadd and Wade Wall. Without their help I couldn’t have completed this project v TABLE OF CONTENTS LIST OF TABLES . vi LIST OF FIGURES . vii 1 Introduction . 1 2 Methods . .5 3 Results . 9 4 Discussion . 10 Bibliography . 13 APPENDICES . .16 Appendix A: Rare plants found on study sites . .17 Appendix B: Soil seed bank results . 19 Appendix C: Litter layer results . .21 vi LIST OF TABLES Table 1 Echinacea laevigata population changes at study sites . .5 vii LIST OF FIGURES Figure 1 Smooth coneflower in the power line right-of-way . .2 at Picture Creek Diabase Barrens Figure 2 Woody encroachment at Picture Creek between 1955 and 2003 . .4 1 Introduction In Durham and Granville counties, North Carolina, a locally unique plant community is found on diabase soils belonging to the Iredell and Picture Soil Series. These sites contain some of the highest concentrations of rare plants in the North Carolina piedmont (Oakley et al 1995). The community type has been described as a Xeric Hardpan Forest Community (Prairie Barren Subtype) (Schafale 2004), and is characterized by the presence of many shade-intolerant species with prairie affinities. Some consider these remnant “Piedmont Prairies” (Barden2002), which were historically more extensive. All of these areas have been altered from their natural state by logging, fire suppression and other disturbances. Today the prairie forbs are generally restricted to artificial clearings along roadsides, railroad tracks, and in power line rights-of-way (ROWs). One of the best remaining examples of this community is Picture Creek Diabase Barrens in Butner, NC, which has the largest known population of the federally endangered smooth coneflower, Echinacea laevigata (C.L. Boynton & Beadle) S.F. Blake (Figure 1). In addition to the smooth coneflower, at least 16 other species (Appendix A) recognized as rare are found at this site (1994 NC NHP site report). The vast majority of the rare plants occur in a large (60 meter wide) power line ROW, and in an area of open woodland which experienced a prescribed burn in April 1994 (Murdock 1995). The remainder of this site has a fairly closed canopy. Aerial photographs taken in 1955, 1972, and 1997 clearly demonstrate an increase in forest cover during this time (Figure 2). The power line ROW at Picture Creek Diabase Barrens was installed in the mid 1980’s (Barnett-Lawrence 1993). A 1988 survey of the smooth coneflower at this site 2 estimated that there were a total of 200 flowering stems and 2000 rosettes (Gaddy 1991). In 2001 the population of smooth coneflower in the power line ROW was estimated at over 10,000 flowering stems and over 100,000 rosettes (Lundsford 2002). In the nearby woodland opening, which was burned in 1994, a single 1000 m2 vegetation plot sampled in 2001 tallied nearly 9000 rosettes and 1009 flowering stems (Lundsford 2002). Figure 1: Smooth coneflower in the power line right-of-way at Picture Creek Diabase Barrens. Picture taken June 2006. 3 Although not documented, we assume that some of the other rare species which today thrive alongside Echinacea laevigata at Picture Creek Diabase Barrens also increased as a result of the prescribed burn and the canopy opening associated with the power line ROW installation. The dramatic increase in the number of smooth coneflower plants suggested that there may have been some recruitment from a persistent soil seed bank. Confirming that smooth coneflower and possibly other rare forbs persist in the seed bank could have important restoration potential. “Prairie remnants”, already few in number and isolated from each other, persist mainly along roadsides where they are vulnerable to herbicide spraying, untimely mowing, and destruction caused by road widening and development. Recruitment from a soil seed bank could help restore and expand these species-rich plant communities. Also, research on smooth coneflower has shown that there is genetic variability between geographically close populations (Peters 2004), and recruitment of new individuals in situ from a soil seed bank would be an excellent and an inexpensive way to retain the genetics of small, isolated plant populations. Our objectives in this seed bank study were to ascertain if smooth coneflower and other rare prairie forbs form a persistent soil seed bank. Previous studies of prairie communities have found that the seed bank was dominated by ruderal species and was not strongly correlated with the above-ground vegetation (Johnson 1986, Rabinowitz 1981, Abrams 1996, Laughlin 2003). However, the communities tested in those studies were dominated by grasses and had a relatively low density of prairie forbs. In comparison, the communities included in this study are dense with perennial forbs. Some of our target species (Ruellia humulis(Nuttall), Symphyotrichum leave (Linnaeus), and congeners of others (Echinacea pallid(Nuttall), Silphium spp., Parthenium integrifolium 4 (Linnaeus)) were recovered in small numbers from the seed bank of a tallgrass prairie in Illinois (Johnson 1986). Given the density of prairie forbs at Picture Creek Diabase Barrens, this offered some encouragement that some of the state listed prairie forbs listed in Appendix A, including smooth coneflower, may be present in the soil seed bank at these remnant sites. Woody encroachment at Picture Creek between 1955 and 2003 Figure 2: 1955 aerial is on the left, 2003 on the right. Circles indicate areas where rare plants are found today. Diagonal lines drawn on 1955 photo approximate location of the power line ROW established in mid 1980's. The north-south road which bisects the circle in the 1955 photo still exists, but is overgrown and no longer visible in the 2003 photo. 5 Methods Site selection According to the 1990 monitoring report, the Picture Creek Diabase Barren, Eno River Diabase Sill (ERDS), and the Knap of Reeds Diabase Levee and Slopes(KORLS) natural areas had comparable populations of smooth coneflower (Table 1). In addition to the smooth coneflower, many other rare plants occur at these sites (Appendix A). At the time of this study, the smooth coneflower populations at Eno River Diabase Sill and Knap of Reeds sites were declining, and both sites were becoming overgrown with woody vegetation. Table 1: Echinacea laevigata population changes at study sites. 1990 numbers from Gaddy 1990, Picture Creek 2002 numbers from Lundquist 2002. The 2004 estimates for Knap of Reeds and the Eno River Diabase Sill populations are ours. 1990 2004 Rosettes/Flowering Rosettes/Flowering site stems stems Eno River Diabase Sill 1500/125 <500/25 Knap of Reeds Diabase Slopes 1000/200 <500/30 Picture Creek Diabase Barrens 2000/100 >100,000/10,000 Site descriptions Picture Creek Diabase Barren(36°09’50.78”N, 78°44’19.43”W) has a thriving prairie community in a large power line ROW, with a remarkable density of smooth coneflower (Figure 1), and large populations of Solidago ptarmicoides (Nuttall) Nesom, Symphyotrichum depauperatum (Fernald) Nesom, and Silphium terebinthinaceum Jacquin. These rare plants 6 are most dense in a 200m X 60m section of the ROW. Smooth coneflower and other rare forbs are also numerous in a nearby open woodland which was burned in 1994. The surrounding closed woods maintain a fairly diverse herb layer. The total size of the property is 550 acres, and is owned by North Carolina Department of Agriculture.

Load more

  30

Copy Link