Salt marshes develop rapidly on North Beach, although marsh development 

 is not as predictable as dune development. In as little as 10 years, salt 

 marshes have become visible on aerial photos in areas that had been washovers. 

 Only with shallow deposits at the outer edges of washovers do salt-marsh 

 species recover from burial. These recovering species often do cot survive 

 unless overwash activity is reduced in the area. Although rhizome outgrowth 

 into shallow bay water has increase^ marsh area along some sections of Old 

 North Beach, most new salt marshes develop on washovers. la some sections 

 of Old North Beach, cores and _-e.ich.es reveal layers of salt-marsh peat over- 

 lain by washover deposits, which have been recolomzed by marsh vegetation. 

 Marshes on North Beach tend to survive in place for longer periods of time 

 than dunes, because of their bayward position and protection afforded by the 

 dune line. 



Shrub communities have also developed rapidly on North Beach. At belts A, 

 D, and I, t>hrub communities have developed in less than 40 years. Three pitch 

 pines at belt 1 are 5 meters tall and lu centimeters in diameter, but these 

 trees may have been planted by homeowners. At belt D a felled juniper that 

 had not been buried by overwash was aged at 32 years, although the belt was 

 overwashed 40 years ago. The development of shrub communities is dependent on 

 protection from salt spray and seed availability. Belts closer to the glacial 

 headlands in Orleans undoubtedly have greater access to seed supplies of 

 Myrica, Junivevue , Salix, Rhus, and R\buo, which are common at belts A and D. 

 Shrub communities are not a good indicator of the age of a site over 25 years, 

 unless dating of individual trees or shrubs is undertaken. 



Supratidal grassland communities are present in many areas on Old North 

 Beach and appear to be associated with older washovers. All the species in 

 this zone are at least marginally salt tolerant. The grassland community on 

 North Beach may be equivalent to the narrow ecotone in Nauset Spit-Eastham 

 between dune and salt-marsh communities and may only exist as a broad area on 

 North Beach because the tidal range is very low in upper Pleasant Bay. 



In general, classical ecological succession does not appear to occur on 

 North Beach. The entire spit system is migrating rapidly landward by overwash 

 processes and inlet dynamics. Few areas on the spit are older than 110 years. 

 With the exception of members of the stable dune communities, all the species 

 dominant on North Beach can grow in bare sandy substrate. The particular 

 species colonizing an area is dependent on environmental factors operating ou 

 undeveloped soil, such as the level of cidal flooding, soil salinity, 60il 

 moisture, exposure to salt spray, degree of substrate stability, and propagule 

 availability. 



V. DISCUSSION 



1. Migratlonal Processes . 



Many barrier beaches along the east coast of the United States are under- 

 going landward retreat in response to sea level rise. Landward displacement 

 can be divided into two separate phenomena: migration of the barrier landform 

 as a whole and migration of physiographic features (e.g., sand dunes) on the 

 barrier surface. The barrier width can be defined as the continuous unit 

 extending from the berm to the bay shoreline or first major waterway. In 

 order for landward barrier migration to occur, material must be eroded along 



213 



