Environment and development in coastal regions and in small islands

Coastal management sourcebooks 1
Case 8

When vegetation has been removed from behind the beach

E N V I R O N M E N T A L
B A C K G R O U N D

Roots and stems trap sand  and soil

Turtle grass

Beaches and dunes are accumulations of loose particles of sediment. There is no ‘cementing’ material to hold the particles together, unlike in the case with rocks. Waves, currents and wind are the main processes acting on the loose sediments. These factors make beaches one of the most dynamic and fast-changing systems in nature.

On the dry part of the beach, above the high water mark, and on the coastal sand dunes where they exist, vegetation stabilizes the sand or other sediment. The roots of plants and trees help to hold the sediment – especially sand – in place. The deeper and more extensive the root system, the greater the degree of stability.

Offshore, seagrass beds play a similar role. The roots of turtle grass and manatee grass for example stabilize and hold the sandy offshore sediments in place, keeping the water clear and clean.

However, conditions on the beach and in the dunes are harsh for plants. Coastal plants must adapt to high temperatures, dryness, few nutrients and occasional inundation by salt water. Not all can survive in such conditions.

The dry beach area above the high water mark is part of the salt spray zone and is generally colonized by grasses like seashore dropseed (Sporobolus virginicus) and trailing vines like beach morning-glory (Ipomoea pes-caprae). This vine is also known as goat-foot and has pink-purple flowers. Other plants that may be found on the back beach include beach bean (Canavalia maritima) and sea purslane (Sesuvium portulacastrum). Many have fleshy stems or leaves which allow them to store rainwater. High storm waves often destroy these plants, so they are considered temporary.

Inland from the salt spray zone, there is often a belt of trees known as the coastal woodland. These trees may be stunted and wind-blown. Consisting of a few species able to tolerate the harsh conditions, this coastal woodland includes: sea grape (Coccoloba uvifera), seaside mahoe (Thespesia populnea), manchineel (Hippomane mancinella) and West Indian almond (Terminalia catappa).

Coastal woodland trees are very deep-rooting. During storms, their roots may be exposed as the waves erode the sand, but they also provide a focal point around which sand accretes after the storm. These trees provide lands adjacent to beaches with a much greater degree of resistance to winter swells and hurricane wave attack. Furthermore, they provide shade and add aesthetic value to the beach, as well as local fruits like sea grapes.

Manchineel trees are often feared in the Caribbean for their poisonous fruits and the painful rashes their sap causes. However, manchineel trees should not be cut down. Public awareness-building campaigns, such as the posting of notices and signs, should be promoted as a means of assuring the safety of beach users, especially tourists who may not be familiar with these trees.

Photograph 26. Warning notice on a manchineel  tree, Mustique, 1993. MANCHINEEL TREE POISONOUS  DO NOT TOUCH  DO NOT STAND UNDER IF RAINING  DO NOT EAT THE APPLES These trees provide the beach with stability and should not be destroyed, despite their  poisonous nature. Public awareness-building campaigns can help tourists and other visitors  to the beach to learn to live with them.

 

Coconut palm

The coconut palm (Cocos nucifera), while not a native tree (it was actually introduced from the Indo-Pacific region), is very common in the islands. Tourists in particular associate the coconut palm with the Caribbean. While it is a useful tree, since it provides milk, ‘meat’, oil and other products, it is very shallow-rooted and easily undermined by high waves. It is fine to plant coconuts for shade or fruit, but do be aware that, from a beach conservation viewpoint, it is best to vary the planting effort with other trees, such as sea grape and West Indian almond.

Photograph 27. Undermined palm trees, Levera,  Grenada, 1986. Palm trees are very  shallow-rooting, as can be seen here, and are  easily undermined by wave action.

At some beaches, there are sand dunes between the back beach and the coastal woodland. The dunes are often colonized with the same grasses and vines as the back beach zone although there may also be other shrubs such as sea lavender (Tournefortia gnaphalodes). Since vegetation on the dunes helps to encourage deposition of wind-blown sand, every effort should be made to preserve the plants. See also Case 7 for more information about dunes. Figure 25 shows a typical cross-section through a Caribbean beach/dune/coastal woodland zone.

Figure 25. Cross-section showing typical vegetation zones in a  coastal dune area. The frontal zone, which comprises the back  beach and seaward dune slope, is covered with grasses and vines. In the back beach zone, there are more shrubs and herbaceous plants. This eventually gives way to the coastal woodland (adapted from  Craig, 1984).

Besides giving the beach stability and promoting accretion, coastal shrubs and trees provide shade and privacy for beach users and beachfront property owners alike.

The vegetation is affected in many different ways by human activities that include: cutting and clearing for construction purposes; cutting of vegetation for barbecues and fires; replacing of native with with foreign species; walking on unmarked routes; and driving vehicles over dunes and on beaches.

Preserve all coastal vegetation.

Help care for the coast by planting native trees and shrubs like those described in this section. Preserving the natural vegetation may help to slow down beach erosion. If you prefer to plant palm trees for the ‘tropical atmosphere,’ vary them with deep-rooting species. Whether you are a home owner or community group desirous of taking care of the beach, remember that, in order to be successful, any tree-planting project should make provision for the following factors:

• The plants need to be a reasonable size.

• The plants will need fertilizer, especially nitrogen fertilizer.

• Spreading a layer of mulch (dead leaves, seagrass) around the plant will minimize wind and water erosion and help the soil retain moisture.

• At the early stages of the project, regular watering may be necessary.

• Fences around the plants will be needed if animals graze freely in the area.

Obtain advice from local horticulturists about what species are most appropariate to plant and where.

Obtain advice from local horticulturists.

Sea grape

Local horticulturists will know what works and does not work on your island. For instance, some people say they do not like planting sea grape because it grows as a bushy shrub and obscures their view. Sea grape will grow as a shrub when it is near the back beach or the seaward face of the primary dune. However, farther back in the coastal woodland, it will grow as a mature tree reaching up to 8 m (26 ft) high. (See the cross-section in Figure 25.) 

Similarly, the casuarina tree, or Australian pine (Casuarina equisetifolia), is sometimes favoured for coastal planting, since it grows very fast. However, it casts dense shade and produces a thick carpet of pine needles. Both of these factors may help to reduce the number of low-growing plants nearby. A lack of ground cover under these trees may lead to greater erosion of the beach or dune.

Construct walkways from buildings to the beach.

	Case 7	Case 9

start		Introduction	Activities	Publications	search
		Wise practices	Regions	Themes