Minimal net loss of vegetation via interior pond dynamics in an extensive unditched salt marsh

Ponds in salt marshes are often interpreted as a symptom of degradation, yet ponds can also be part of a cyclical process of pool formation, expansion, tidal breaching and vegetation recovery. Pond dynamics may be altered by accelerated sea level rise, with consequences for the long-term stability of ecosystems. We test the prediction that ponds are in dynamic equilibrium across one the largest expanses of unditched salt marsh in the Northeast USA by (1) examining change in pond and marsh area between 1970 and present and (2) by tracking individual pool dynamics across an 87-year time series. We found that net pond area has remained unchanged since 1970 because the amount of marsh conversion to ponds is equivalent to the amount pond recovery to marsh. The ratio of tidally-connected ponds is increasing relative to non-tidal ponds which suggests that some rates of change may be decoupling, which may be related to a decline in the rate of pond formation. A nuanced understanding of marsh pools needs to be incorporated into marsh condition assessments and establishment of restoration priorities so that ponds are not interpreted as evidence of degradation when they are exhibiting a recovery cycle. Unditched marshes around the world are a rare resource that remains essential for advancing scientific understanding and serving as reference sites for restoration of marshes altered by past management.