Georgian Court University

Spread rate and changes in species diversity associated with the introduced Asian sand sedge, Carex kobomugi, in New Jersey coastal dune communities

 Wootton, L.S. Georgian Court University, Department of Biology 

Keywords: Asiatic sand sedge, Carex kobomugi, invasive, non-indigenous, spread rate, coastal dunes, impact on species diversity, management implications. 

Citation: Wootton LS.  2003.  Spread rate and changes in species diversity associated with the introduced Asiatic sand sedge, Carex kobomugi, in New Jersey coastal dune communities.  5-page Extended Abstract.  Coastal Zone 2003 Conference Proceedings.

Introduction

Carex kobomugi, Asiatic sand sedge, was probably introduced to North America via discharge of ballast material containing either seeds or culms into local waters. It was first collected in the US in 1929 from sand dunes near Seaside Park, NJ (Small 1954). By the 1980s, a combination of accidental and deliberate introductions resulted in the species’ spread from Falmouth MA to Duck NC (Shisler et al. 1987).  Deliberate plantings of this species for dune stabilization were made from the late 1960s through the mid-1980s (Shisler et al. 1987).  Planting of C. kobomugi was initially promoted because it is resistant to a number of diseases and pests that impede growth of American beach grass and is more tolerant of trampling than beach grass (Shisler et al. 1987).  Moreover, although its growth is more vigorous on actively accreting dunes, C. kobomugi prospers on stable dunes, back dunes and blowout areas where American beach grass and other native species grow poorly (Shisler et al. 1987). C. kobomugi’s naturally spiky flowers and rhizomes also formed a natural way to deter traffic from leaving established trails. However, propagation of C. kobomugi from both seed and vegetative culms proved difficult. In addition, changes in political climate in the late 1980s led to avoidance of non-native species in land management after that time. Consequently, planting C. kobomugi dunes in New Jersey had ceased by the late 1980s or early 1990s.

Initially populations of C. kobomugi that had become established either naturally or by deliberate planting were allowed to remain on the dunes. However, in the 1990s the species was declared an “invasive exotic” and was placed on New Jersey’s “top ten most unwanted species” list (Bennett-Chase 2001).  Consequently management practices changed from introduction to elimination.  However, little is actually known about the degree of invasiveness of the species.  Few quantitative surveys of C. kobomugi’s extent or impact on species diversity have been published.  The most extensive existing data bases come from a survey commissioned by NJDEP in the mid 1980s (Shisler et al. 1987) intended to investigate the feasibility of the species for introduction as a dune stabilizer and from a Master’s thesis conducted soon after (Pronio 1989).  To help fill this data gap our team set out to locate and re-map the stands mapped in 1985 (Shisler et al. 1987) in order to determine the rate of spread of this species. We also collected information on new stands formed since the 1985 study, again mapping size, species composition, plant densities and position of each stand.  Finally, we set out to assess the species composition of plants within the C. kobomugi stand and in the adjacent areas to determine the impact C. kobomugi’s spread on other dune species.

Materials and Methods

The size and position of all C. kobomugi stands at Island Beach State Park (IBSP) and Sandy Hook Unit (SHU) of Gateway National Recreational Area were mapped in the summer of 2002.  Areas covered by stands of Carex kobomugi were mapped using the same methods used in an earlier study of this plant in the same areas (Shisler et al. 1987).  Specifically: Length of each stand was measured along the longshore axis.  Widths across each stand were then measured at 5-meter intervals (2-meter intervals for small stands) along the length of the stand. A portable GPS unit was used to pinpoint the location of the center and extreme edges of the stand. The data so collected was used to calculate the area covered by each stand and these areas were compared to those reported by Shisler et al. (1987) to determine the rates of change in stand area since that time. 

Again following Shisler et al. (1987), circular, 1 m² plots were randomly selected within each stand and the position marked with a center pole.  Enough plots were surveyed to sample approximately 1-5% of the stand area. Species composition was determined by counting and identifying all plants within the 1m² plot.  Similar plots were established in areas of dune 5m outside the Carex kobomugi stand. These plots were positioned seaward, landward and at both ends of the stand.  Position of all diversity plots (in and out of stand) was documented with GPS.  Species composition and number of plants within each plot was assessed in the same way as those within the Carex kobomugi stand.  

Results

We found 66,053m² (16.3 acres) of Carex kobomugi at SHU and 90,032m² (22.2 acres) at IBSP.  Relative to a 1985 NJDEP survey in IBSP (Shisler 1987), and a 1987 study by a Rutgers graduate student (Pronio 1989), our results show a doubling in number of beds at IBSP a 20-fold increase in bed number at SHU.  Total area occupied by the species at IBSP increased by about 300% since 1985. Affected area at SHU increased by 780% over the same period, largely as a result of the addition of new beds rather than expansion of older ones (Tables 1 and 2).   Mean spread rate between 1985 to 2002 was approximately 100m²/bed/year at SHU and 250 m²/bed/year at IBSP.  Plotting all available data for this species in New Jersey, expansion rates of C. kobomugi can be seen to be approximately exponential (Figure 1). 

Comparing stem densities in beds present in Shisler’s 1985 study (Shisler et al. 1987) with those in the same beds in 2002, an increase of about 55% in stem density was observed (Table 3).  While fewer than 50% of quadrats in most beds studied contained only C. kobomugi, abundances of many species, including American beach grass (Ammophila breviligulata), cheatgrass (Bromus tectorum), seaside goldenrod (Solidago sempervirens), seaside spurge (Euphorbia polygonifolia) and little bluestem (Schizachyrium scoparium), were reduced by 50 to 75% within C. kobomugi beds (Table 4).  None the less there were several species whose abundances within C. kobomugi beds matched those in surrounding areas.  These included wormwood (Artemisia biennis) and Gray’s umbrella sedge (Cyperus grayi).  Species diversity as calculated using the Shannon-Wiener diversity index (Table 5) was lower inside C. kobomugi stands than outside those beds at SHU. However there was no statistical difference in diversities inside versus outside C. kobomugi stands at IBSP.

Figure 1.  Extent of C. kobomugi beds in New Jersey’s Coastal Parks over time

Table 1.   Comparison of documented size of beds of Carex kobomugi at IBSP

* Slight underestimate due to non-inclusion of beds around the Governor’s mansion.

** Calculated for beds present in both studies, omitting beds treated with Roundup® since 1999.   Variance estimate is 1SD.

Table 2.  Comparison of documented size of beds of Carex kobomugi at Sandy Hook

* Value is an underestimate. Area of smallest of three beds described was not reported.

** Calculated only for the two beds measured in both studies

Table 3.   Comparison of stem densities in beds documented in both the 1985 NJDEP study (Shisler et al. 1987) and the current study

Table 4.   Comparison of stem densities of native species within and outside Carex kobomugi beds.

* For each comparison, means denoted with the same letter are statistically similar.  Means denoted with different letters are statistically different at the p < 0.05 level.

Table 5.   Comparison of species diversity within versus outside Carex kobomugi beds as calculated using the Shannon Wiener Diversity Index for meter square quadrats.

For each comparison, means denoted with the same letter are statistically similar.  Means denoted with different letters are statistically different at the p < 0.05 level.

Discussion

This study has confirmed the Park manager’s qualitative perceptions of the rapid spread of Carex kobomugi within New Jersey’s Coastal Parks. Indeed, we have demonstrated that the species is currently expanding exponentially in both parks studied. Moreover we have shown that this spread is significantly impacting abundances of a number of native plants within the dune community. We conclude that classification of C. kobomugi as an invasive alien plant within New Jersey’s coastal dune systems is appropriate. 

Removal of this species using targeted spraying of Roundup® is already underway at IBSP (see McGough et al., this issue, for details). However, the presence of numerous small bed fragments, and the stronger impact on species diversity at SHU, as well as the presence of species of particular concern such as sea beach amaranth and wormwood at that park make the spread of C. kobomugi in this park a particularly serious problem. Stringent regulations against chemical use within federal parks make chemical treatment of C. kobomugi logistically difficult at SHU. We are, therefore, working with managers at that park to find viable alternatives that use physical rather than chemical removal techniques. In both parks, care must be taken to develop management strategies that maintain dune stability. C. kobomugi is an effective dune stabilizer, so its removal, if not carefully implemented, could result in increased risk for dune erosion, and thus for flooding of the natural and human communities behind the dunes.

ACKNOWLEDGEMENTS

This study was supported by the National Sea Grant College Program of the U.S. Department of Commerce’s National Oceanic and Atmospheric Administration under NOAA grant #A/S-1 SGEP-1. The views expressed herein do not necessarily reflect the views of any of those organizations. NJSG-03-513.  Thanks also to Dr. Michael Gross for plant identifications and to my fabulous student interns and volunteers whose hard work made this project possible: Katy Bevaart, Audrey McGough, Jason Ondreika, Purvi and Sheetal Patel, Courtney Rella and Anna Shipman.

Literature Cited

Bennett-Chase D. 2001. Japanese sedge. http://www.savebarnegatbay.org/herbarium/japanesesedge.shtml

McGough A, Bevaart K, Ondreika J, Patel P, Wootton L.  (This issue)  Effectiveness of low-impact management strategies for eradication of Carex kobomugi (Asian sand sedge) from dune communities within New Jersey’s coastal parks. 

Pronio, MA.  1989. Distribution, community ecology and local spread of Carex kobomugi (Japanese sedge) at Island Beach State Park, New Jersey.  Masters Thesis.  Rutgers University.

Small JA. 1954.  Carex kobomugi at Island Beach, New Jersey.  Ecology 35:289-91.

Shisler JK, Wargo RN, Jordan RA.  1987.  Evaluation of Japanese sedge, Carex kobomugi, for use in coastal dune planting and stabilization.  New Jersey Agriculture Experiment Station Publication number P-40502-03-87

Stalter R. 1980.  Carex kobomugi Owhi at Sandy Hook, New Jersey.  Bulletin of the Torrey Botanical Club 107:431-2.