High temperatures, strong winds and stormy seas constantly shape our coastline, creating and destroying sand dunes. These sand dunes act as a buffer zone between sand and sea. Without this buffer zone, the salt air would easily dry out the delicate land plants suited to soil, freshwater and unsalted air.
The sand dune plant community comprises various species, each suited to particular zones of the dune system and serving certain functions within these zones. The plant species found here at Hastings Point are typical of Eastern Australian sandy beaches.
The study of sand dune systems involves the sampling of vegetation using quadrates along a transect from the beach to the dune behind the fore dune. A profile of the dunes will be drawn and factors that influence the sort of plants growing along the transect will be noted.
Succession and Zonation
Two concepts are used to help understand the changes seen in vegetation as you walk from the beach back to the high dunes: succession and zonation. As we move from the beach towards the back or ancient dunes we see a change in the types of species that occur as the dunes have been built over time. The transition in the community structure that occurs over ecological time is known as succession. The species that dominate the newly formed fore dunes are gradually replaced by other species.
A variety of interrelated factors determine the course of succession. Early species are good colonisers with excellent dispersal mechanisms. However, many of these species do not compete well in established communities. The differing tolerances to abiotic factors also determine the course of succession in a particular area.
The end stage of the succession process is identified as the climax community. At this stage, the same species continue to maintain themselves. An example of a climax community would be a mature forest. However, climax communities may not be stable when considered over longer time frames. They may also be subject to disturbance by factors outside the community, such as fire, that could radically alter the community structure.
Succession could take place on a sand island after it is initially formed. The first species to grow would be those which are first to get to the island and can grow in the nutrient poor, salty, bare sand. These plants would then stabilise the sand, increase the organic matter in the sand and provide some shelter from the wind and sun. Rain could add some nutrients and wash out some salt. The modified environment would enable other plants to become established. These may eliminate the original colonisers such as grasses and creepers. This process of gradual replacement of species continues until a climax community is reached.
Zonation refers to the existence of populations of organisms in zones such that a particular set is different from that on either side. Zones in sand dunes usually arise because of abiotic influences such as strong currents, large waves, strong winds, strong sunlight and exposure to salt.