The ecology of Northern New England salt marsh plant communities

In contrast to the well studied salt marshes of Southern New England, Northern New England salt marsh plant communities are relatively poorly understood. These marshes are characterized by having large amounts of winter ice disturbance and by a unique plant community, called forb pannes. The goals of this study were to describe the plant community patterns and to understand the mechanisms that generate them. Specifically I, (1) describe the overall plant zonation and investigate the latitudinal difference in succession, (2) document the recovery of a Northern New England salt marsh from a severe icing event, (3) examine the role of waterlogging in maintaining forb pannes, and (4) examine the role of Agalinis maritima, an annual hemi-parisictic plant, within the forb pannes. I found that forb pannes are widely distributed across the middle marsh in waterlogged and anoxic habitats adjacent to areas dominated by the typical clonal turfs. Transplant experiments indicated that clonal turfs are physically limited from invading panne habitats and that interspecific plant competition restricts the panne species to the pannes. Recovery from ice disturbance was extremely slow, taking at least twice as long as in southern marshes and that secondary succession in northern marshes appears to be driven by facilitating the reduction of anoxia stress. Experimentally draining natural pannes led to the replacement of typical panne vegetation by the clonal turf Spartina patens. These results demonstrate that the forb panne communities are the consequence of poor drainage and waterlogged soils that limit the success of competitively dominant clonal turfs and permit the persistence and coexistence of panne forbs. In addition, I found that the hemiparasite, Agalinis maritima , plays a role in setting panne size and in the temporal dynamics of succession by slowing the encroachment of the clonal turfs into the forb pannes, suggesting that Agalinis maritima may play an important role in determining forb panne species richness and diversity.; These results provide an initial framework with which to understand the structure and organization of Northern New England salt marsh plant communities. As well as allow us to begin to understand latitudinal difference in marsh plant communities.