How does saltation affect the sand dune ecosystem?

Introduction:

A sand dune system is an example of an ecosystem, meaning it has abiotic and biotic factors that interact with each other through energy flows and nutrient cycles to produce a dynamic and fairly stable system. Within this system we can identify habitats with their own specific set of conditions and organisms, in the sand dune ecosystem these are called seral stages (the seral stages are embryo, fore, yellow and grey dunes). The conditions in the dunes change as the seral stage progresses away from the sea.

The Formation of Sand Dunes

Sand dunes form by a process known as saltation, which is the discontinuous movement, transition, or development; advancement by leaps. Sand can only be moved by strong, steady winds. The air must be moving at least 15 miles per hour to be able to pick up sand grains, by a coastline this is easily present. All a sand dune then needs to form is an obstacle like a bush, rock, or in some cases an abandoned car where wind can deposit sand. Wind acts just like water in a stream and splits to flow around obstacles.

As you can see by the diagram above as one granule of sand moves it hits the ground causing more to move with it, once these hit an obstacle it forms a steep bank up against it, with a long “tail” stretching out behind where it is more sheltered from the wind.

Sand Dune Succession

The communities of animals and plants within the sand dune ecosystem change over time; this is referred to as succession.

Embryo Dune:

This dune is the first seral stage and is the most volatile of all the seral stages. This is the place where the sand dune ecosystem starts with the pioneer species of plants and animals, which are referred to as the pioneer community. An embryo dune is formed on a beach where ideally there is a lot of sand exposed at low tide. The edaphic factors are high salinity which means that only halophytes will grow, the ph is alkaline due to the calcium carbonate of the broken down sea shells, the soil drains quickly as it does not have very good water retention, the soil is aerobic, it leaches away the minerals which results in its low mineral content, it is unstable and very low in humous (humous holds the soil together, acts as a fertilizer and aids in water retention). The climatic factors of these embryo dunes are the high wind speed and the tide. All these abiotic factors result in the plants that grow in the embryo dunes being highly specialized. The way in which the plants will change the physical properties of the embryo dune is that the dune will grow through the positive feedback as the sand will pile up against the plant, the soil will stabilize and the plants will contribute some marginal humous and decrease the salinity slightly as the sea spray does not get to them as much. The adaptations of the plants to be able to grow in these conditions are a waxy cuticle to minimize water loss, this also results in a slightly reflective surface for the same reason, the leaves roll when dry closing over the stomata, there are no stomata on the waxy cuticle side, the stomata are in the ridges with hairs on the inside to help trap water. The root system is extensive to help gain water from the soil, and also the root system is adapted so that the salinity of the soil does not draw water out of the roots. The main plants that grow in this dune are couch and Lyme grasses, as these plants are the most adapted to the harsher conditions. Within this pioneer community there is not much competition as the plants that grow here are so specified. The next stage after the embryo dune is the Fore Dune.

Fore Dune:

The physical characteristics of the fore dune are different from that of the embryo dune in slight ways. There is less salinity, more humous as the plant cover increases due to the increasing stability of the soil, slightly more nutrients and it is partially stable the fore dune is also slightly higher than the embryo dune so does not suffer from the sea spray as much but still is effected by the high wind speed and the heat the soil still suffers from leaching though so there is still little mineral content. The species of plants ...