Developing salt marsh

Figure 11. Stumps are all that remains of a forest taken over by salt marsh. (Photograph by the author. More about the photograph)

In case you were doubtful that salt marshes can really invade and take over forested areas, I have included Figure 11 to lay these doubts to rest. In this photograph you will see a developing salt marsh with the trunks and roots of the preexisting forest still present up in both the marsh and the new seafloor around it.

Note also that there is an island of salt marsh here. This might be one of the rare examples where a new marsh has resulted from seed germination, but more likely it simply represents an erosion event in which the relatively loose forest soils were stripped away by tidal currents. In a fully developed salt marsh, the roots and rhizomes of the plants make a soil binding matrix that holds sediment in place. This mixture of soil and vegetative tissue is called peat, and it is much more resistant to erosion than forest soil. Fully developed peat forms only after many years of salt marsh growth.

In a developing marsh, the matrix is not fully formed and even modest currents can erode the unbound forest soils. The unvegetated intertidal area around this marsh island and the small cliff on the side of the marsh are consistent with the hypothesis that this island also formed by erosion, but to test the hypothesis you would have to dig into the unvegetated area to see if there is evidence of marsh peat under the surface that is now bare — something I didn’t think to do when I took this photograph.

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