Structure and organization of a northern New England salt marsh plant community

1 Northern New England marshes are characterized by mid-elevation areas of sparse vegetation, but high species diversity, which are not found in the well-studied marshes further south. These forb pannes occur in habitats that are more waterlogged and anoxic than adjacent clonal turf-dominated areas. 2 When the clonal turfs were transplanted into forb pannes, they showed reduced growth with and without neighbours present, suggesting that they are physically limited from invading the forb pannes. Conversely, when forb panne species were transplanted into surrounding turf areas, they flourished when neighbours were removed, but were suppressed when neighbours were present, suggesting that interspecific plant competition restricts the forbs to panne habitats. 3 Recovery of disturbance-generated bare patches was extremely slow, taking twice as long as in southern New England marshes. Secondary succession in northern New England marshes was driven by competitive interactions rather than by facilitative processes typical in southern New England marshes. 4 Differences in the structure and dynamics between northern and southern New England marsh systems may be due to differences in climate and human impacts. Waterlogged pannes are probably more common in northern marshes because they are generally larger and less ditched and drained. Reduced solar radiation and summer heating in northern New England reduces the potential for high soil salinities seen in southern marshes. This lack of the need for amelioration by neighbours probably explains the absence of facilitation.