Coastal Dune Ecology
For many, a trip to the beach means a hike through the dunes, but what exactly are sand dunes?
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Consider the following four part distinction:
- Beach
- Fore Dunes
- Back Dunes
- New Eco-System
The first part of the coastal dune ecology, the beach, sits directly in front of the dune system. A self-sustaining beach, i.e., one not subject to erosion problems, typically has a noticable wet and dry section. The wet portion of the beach changes thoughout the day with the ebb flow of the tide. The dry beach area stays dry from the normal ebb and flow of the tide. As sand accumulates on the dry section, a combination of wind and weather start the dune construction process by blowing the sand further inland.
Somewhere along the way, natural or human placed objects begin to serve as sand stumbling blocks, collecting the blowing sand around them. Over time, the mound of sand begins to grow and the first portion of the coastal dune system, the fore dunes begin forming. One of the distinguishing physical characteristics of the fore dunes is their comparatively less dense amount of plant life such as beach grass. There's a good reason for this. During storms, wave action often reaches the first line of coastal defense, the coastal fore dunes, washing away some of their stabilizing plants.
The back dunes are commonly composed of larger dunes with higher density vegetative cover. Often in a well developed coastal dune system, a last line of back dunes called the ridge can be distinguished. The ridge sets a quasi-boundary between the primarily sandy coastal dune ecosystem and another ecosystem.
All coastal dune ecosystems also support a set of living species. Since most life requires basic commodities such as shelter, food and water, it stands to reason that species density in any one area would be dependent on their availability. Small birds, reptiles, crustaceans, and other coastal species commonly call the coastal dunes their home. As the dune system moves from the fore dunes toward the back dunes, with their increased vegetation, the ecosystem becomes more complex, supporting a larger amount of species.
The transition following the back dunes to the next eco-system could take one of many forms, and be either gradual or sudden. For example, a coastal dune system could transistion into a marsh or lagoon, or even in the case of barrier islands, the other side of the ocean. Dunes located in mountainous regions commonly transition to the cliff rocks. Dunes that transition to land also come in many forms.
© 2003. Patricia A. Michaels.