REMOVAL OF AN EXOTIC INVASIVE, CAREX KOBOMUGI (ASIATIC SAND SEDGE), FROM NEW JERSEY’S COASTAL DUNES: IMPLICATIONS FOR DUNE STABILITY

Asiatic sand sedge, Carex kobomugi, was probably introduced to North America about a century ago when shipwrecks released plants used to pack Oriental porcelain. Shorter than American beach grass (Ammophila breviligulata), C. kobomugi’s dense foliage and disease- and trampling-resistance led to its being deliberately introduced into dune systems for many years. However, New Jersey’s coastal parks recently initiated an aggressive management strategy aimed at its eradication. The case for eradication is based on 1) concerns about the ecological impact of C. kobomugi 2) the assertion that it holds dunes less well than native species, and so its spread threatens dune stability. C. kobomugi is expanding rapidly in our study sites. As native plant abundance and species diversity are often lower within C. kobomugi beds than outside them, there is reason for concern at an ecological level. However a literature survey failed to find any studies showing C. kobomugi to hold dunes less well than native species. Indeed, walking on C. kobomugi dunes, it seems that the sand there is better consolidated than in dunes stabilized by native species. The major argument for why C. kobomugi is a poor dune-stabilizer appears to be that, due to its diminutive stature, it catches/holds less sand. There are several flaws in this logic: 1) 50-80% of sand transport occurs by saltation < 1mm above the dune surface. As even C. kobomugi stems extend at least 10cm above dune surface, differences in height between it and native species would have little impact on their relative particle retention 2) A. breviligulata’s more flexible blades bend in response to wind, further reducing differences between the two, 3) C. kobomugi can reach densities > 400 plants /m², each with at least 5-10 blades, whereas A. breviligulata rarely exceeds 200 stems/m². As dense foliage should increase wind resistance, C. kobomugi beds probably accumulate at least as much sand as do beds of native species, 4) Both C. kobomugi and A. breviligulata have deep, extensive root systems, so sand caught by both is likely to be retained, resulting in dune accretion. Thus, while removal or control of C. kobomugi may be necessary for ecological reasons, removal should not be predicated on arguments about dune stability. Indeed, its eradication may actually result in reduced, rather than improved, dune stability.