Biological Factors

Dune plants are found all over the world, from the frosty regions of Canada and Patagonia, to the tropical areas of the Caribbean, Africa, and the South East, and the dry regions of Australia, Peru, and California. They are subjected to very different climatic conditions, they share few species, and life forms vary. Raunkaier developed an ecologically valuable system of plant classification, based on the position of the vegetative perennating buds or the persistent stem apices in relation to the ground level

O Stabilized

Slacks

Beach

Incipient dunes Foredune Active dunes Humid slacks Wet slacks Sheltered zones Stabilized dunes

Topographic profile

(b) Intensity of abiotic and biotic factors

Inundation (freshwater) Inundation (seawater) Salt spray Wind

Sand movement Biotic interactions

Figure 2 (a) Beach and dune topographic profile showing each of the habitats. (b) Intensity, indicated by the width of the line, of some of the abiotic factors mentioned along with the areas where they affect the dune system. Reproduced with permission from Moreno-Casasola P and Vazquez G (2006) Las comunidades de las dunas. In: Moreno-Casasola P (ed.) Entornos veracruzanos: La costa de La Mancha. Xalapa, Mexico: Instituto de EcologĂ­a AC.

during the unfavorable season of the year, which can be either the cold winter or the dry summer. There is a strong correlation between the climate of an area and the life forms of the plants present. This system allows comparisons to be made between particular areas or regions. The biological spectrum found in a dune system is an expression of the number of species in each life-form class as a percentage of all the species present. A comparison of the biological spectrum of a dune system in Braunton Burrows (North Devon, Great Britain) and one in La Mancha (Veracruz, Gulf of Mexico) was made. Braunton Burrows is dominated by hemicryptophytic plants (perennating buds are at the surface of the sand) and therophytes (annuals that survive the unfavorable season as seeds); La Mancha is dominated by phanerophytic types (these grow continually, forming stems that often have naked buds projecting into the air, such as in Hippophae rhamnoides or Chamaecrista chamaecristoides).

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