Severity is recognized as an important attribute of disturbance in man
y plant communities. However, the effects of disturbances of different
severity on patterns of regeneration in oligohaline marsh vegetation
have not been experimentally examined. In these communities, a critica
l difference in the effects of disturbance severity may be whether the
vegetation dies as a result of the disturbance or is merely damaged a
nd hence capable of resprouting. We described the regeneration of vege
tation in two Louisiana marsh community types, one dominated by Sagitt
aria lancifolia L. and the other by Spartina parens (Ait.) Muhl., foll
owing three levels of disturbance: no disturbance, a nonlethal disturb
ance, and a lethal disturbance. In the nonlethal disturbance, abovegro
und vegetation was clipped to simulate common disturbances such as fir
e and herbivory that remove aboveground vegetation but leave rhizomes
intact. In the lethal disturbance vegetation was killed using herbicid
e to simulate disturbances causing plant mortality such as wrack depos
ition, sedimentation, scouring, and flooding following fire or herbivo
ry. Regeneration was assessed over a 2-year period by measuring plant
species richness, relative abundance, relative dominance, cover, and f
inal biomass. To elucidate mechanisms for observed responses of vegeta
tion, the species composition of the seed bank, light penetration, wat
er level, salinity, and soil redox potential were evaluated. Despite d
ifferences in the structure of undisturbed vegetation in the two commu
nity types, they exhibited the same overall pattern of regeneration. F
ollowing nonlethal disturbance, the dominant species resprouted and qu
ickly reestablished the structure of the vegetation. In contrast, reco
lonization following lethal disturbance occurred primarily via seedlin
g recruitment, which resulted in marked shifts in community structure
that persisted throughout the study. While the two communities respond
ed similarly overall to disturbance, the response of individual specie
s was not uniform; abundance, dominance, biomass, or cover increased f
or some species but decreased for others in response to disturbance. S
eed bank species occurred in the vegetation following lethal disturban
ce in the Spartina community and in both disturbed and undisturbed plo
ts in the Sagittaria community, indicating that the seed bank is a sou
rce of propagules for regeneration and maintenance of oligohaline mars
hes. Of the environmental variables measured, light level was most clo
sely related to the effect of disturbance severity on community struct
ure. Our results suggest that lethal and nonlethal disturbances have d
ifferential effects on regeneration of vegetation that can create patt
ern in oligohaline marshes communities.