• Tidal salt marshes occur wherever the accumulation of sediments is equal to or greater than the rate of land subsidence and where there is adequate protection from waves and storms.
• Distributed along coastlines in middle and high latitudes along intertidal shores throughout the world.  Mangrove swamps replace them along coastlines in tropical and subtropical regions.

• Alaska, northern Canada, Greenland, Iceland, Russia, and northern Scandinavia.
• They are generally more brackish rather than saline.
• Dominated by various halophytes species of sedges (Carex), grasses (Puccinellia phryganodes), shrubs (Suaeda), and Salicornia.

• Marshes along the the west coast of Europe from the Iberian Peninsula to Scandinavia, including Great Britain.
• Dominated by Puccinellia maritina, Juncus gerardi, Salicornia, Spartina anglica and Spartina townsendii.
• In 1860 the introduction of Spartina alterniflora (cordgrass) dominated the salt water marshes, it's a very aggressive plant.
• Spartina alterniflora and Spartina maritima learned how to double their chromosomes allowing them now to reproduce sexually producing Spartina townsendii, from here Spartina alterniflora developed as a hybrid.
• Spartina townsendii is very aggressive and is spread by clones.

• Arid, rocky-to-sandy, high-salinity coasts of the Mediterranean Sea.
• Dominated by low shrubby vegetation, Arthrocnemum, Limonium, Juncus, and Salicornia.

• Along the eastern coasts of the U.S. and Canada and along the Gulf Coast of the U.S.
• Dominated by Spartina and Juncus.
• This group is subdivided into three small groups.                                                                                                            1.  Bay of Fundy - Puccinellia americana dominated the lower marsh and Juncus balticus the highest level                2.  New England - from Maine to New Jersey it's dominated by Spartina alterniflora in the low marsh and Spartina     patens with Distichlis spicata in the high marsh.                                                                                                         3.  Coastal Plain - From New Jersey along the southeastern coast to Texan along the Gulf of Mexico. Dominated by Spartina alterniflora, S. patens, Juncus, and Distichlis spicata.

• Salt marshes are far less developed along the western coasts of the U.S. and Canada.
• Mediterranean-type climate gives rise to Spartina foliosa, Salicornia and Suaeda.

• Most salt marshes are found in tropical regions.
• High rainfall and geographic isolation gives rise to Sporobolus, Sarcocornia, and Suaeda.

• Along the coasts of China, Jampan, Russia, and Korea.
• Dominated by Triglochin, Limonium, Salicornia, and Zoysia due to moderate percipitation.

• Too far south and too cold for mangroves
• Dominated by Spartina, Limonium, Distichlis, Juncus, Heterostachys, and Allenrolfea.

• Mangroves generally dominate the coastlines.
• Salicornia and Limonium also dominate in non high-salinity flats.

1. 1.  sediment accretion on the marsh, which causes it to expand outward and grown uuward in the intertidal zone.
2. 2.  coastal submergence caused by rising sea level and marsh surface subsidence.

• Sediments compact by own weight and sink
• Sea level rise is constantly changing.
• Example:  Gulf of Mexico and the Mississippi Delta have the general tendency of having rapid marsh submergence due to compaction that lowers it by 1.6cm/yr.  Normally this is balanced by new sediment but with dams the sediment does not come in and there is a net loss of ~.78cm/yr.
• Example:  North Atlantic Marshes have a more stable dynamic equilibrium and some of the oldest marshes are 3,000-4,000 years old.
• Example:  Subarctic North America, Canada, Alaska.  It's expanding due to land level rising caused by ice sheets compacting down coast, since the last ice age, the ice has melted an the land has been rising.  As the mud flats appear, they are colonized by salt marshes.
• Example:  Global warming will cause a very rapid change in sea levels usually tend to rise.

Productivity:
Defined as the net plant production in salt marshes
George and Howard Odum studied Georgia's productivity in salt marshes (Spartina).

1. 1.  Annually  up to 80 metric tons per hectar of plant material is produced.  Such as sugar cane.
2. 2.  Productivity is dependent with the amount of tidal exchange.  These marsh systems receive a "tidal energy subsidy", TES, that might produce salinity as they go in and out delivering nutrients, oxygen, remove carbon monoxide, and hydrogen sulfite.
3. 3.  High production marshes are somewhat unique to the east coast.

The Mediterranean produces ~ 100g/m²/yr and it does not have many high tides