Juncus roemerianus Scheele, the black needlerush, dominates much of an irregularly flooded salt marsh at the Cedar Island National Wildhfe Refuge, North Carolina, USA. We examined its dynamics of growth, senescence, and decomposition along a 1.6 km transect into the marsh over salinity and hydroperiod gradients passing successively through 3 distinct vegetational zones. Little difference was noted among zones in any of the dynamic aspects examined. Aerial, annual net primary production of J. roernerianus averaged 812 g dry mass m-2. This rate is comparable to that of J. roemerianusin other North Carolina marshes. Measured parameters for production estimates were production-to-biomass ratio, frequency of replacement of growing leaves (number of times per year in which leaf cohorts grow to maximum height), and standing crop of growing leaves. Only the latter parameter revealed statistically significant change with distance into the marsh with the most inner zone having the least biomass of leaves. Senescence of leaves progressed similarly along the transect, as did decomposition. A lack of dominance by J. roemerianus in the inner zone may be a consequence of competitive advantages of other species in an environment of lower salinity and shorter hydroperiod. On average, Juncus roemerianus leaves grow for 259 d and senesce for 312 d. The rate of decomposition of standing dead leaves is slow (-0.25 F-'). Thus it would not be uncommon for a leaf to remain standing for several years. Given this longevity and persistence, biomass removal by physical processes such as storms and fire may be important.