Community and Landscape Patterns of Forb Pannes: On Two Maine Salt Marshes

Mixed forb pannes of Maine are maintained by waterlogging and are replaced by turf-grass species when drained, elevated, or warmed. These drivers, in particular waterlogging and temperature rise, counteract each other and are representative of in-field abiotic influences such as sea level rise (SLR) and climate warming. Researchers in Maine have studied forb panne landscape distribution, plant communities, and nutrients on salt marshes; however, no one has addressed how forb pannes change over time or mechanisms for this change. My objectives were to 1) remap and statistically compare spatial characteristics and changes undergone in mixed forb pannes of the Little River Salt Marsh in Wells, ME to those previously, mapped using GPS and GIS technology, (2) discover small-scale heterogeneity in abiotic and plant community assembly within-pannes to better understand in-field species interactions coupled with plant interactions with edaphic variables, and (3) elucidate any edaphic, species and community patterns between pannes to determine if they are related to broader geospatial variables previously investigated. At the non-tidally restricted Little River Marsh in Wells, 5% of the marsh was covered in forb pannes in 2005 compared to 4% in 2017, showing slight panne loss over time. However, spatial analysis of panne change between years showed these changes were regional and the southern region of the marsh near the river mouth had higher counts and expansion of forb panne area compared to the 2005 mapping effort. Within-panne edaphic analysis showed temperature and NQ3- quantities to be higher in interior habitats, whereas NH4+amounts were higher in edge habitats. Salinity, N03- and NH4+ were all positive functions of panne area and distance to river, and N03- and NH4+ were both inverse functions of distance to urban edge. Edge habitats had higher abundances of Spartina patens, a less water tolerant matrix grass, whereas interior forb panne areas had higher abundances of Spartina alternijlora, a more water tolerant species. Whereas my hypotheses predicted increased SLR to be the main driver of forb pannes in Maine salt marshes, these two studies suggest forb pannes to be dynamic parts of the marsh, associated with regional differences in marsh inundation time. These results indicate that while rising temperatures may play a role in panne loss in some regions of the Little River Marsh, other regions may experience longer localized tidal inundation associated with expansion of forb panne areas. In the Scarborough Marsh, a suburban marsh of Scarborough, ME, a higher percentage (10%) of the marsh surface was occupied by forb pannes. Whereas no baseline coverage exists for forb pannes on salt marshes in Scarborough, ME, this comparatively high percentage of forb panne cover could indicate a longer tidal inundation period of the marsh and vulnerability of the marsh to increased SLR due to its tidal restriction