Sand Dunes [Date] Today I will: - Look at a transect across sand dunes to see what the differences are. Geography Biosphere X Y Geography Biosphere Pioneer Stages: The first plants to colonize an area are called the pioneer community. They add humus, nutrients and water and therefore improve the soil. Geography Biosphere Succession Stages: The improved soil begins to attract larger species. The number of species and height of plants increase. Geography Biosphere Climax Vegetation: This is the final stage in succession when the ultimate vegetation has developed. The type of vegetation is mainly dependant on the climate. Geography Biosphere What is Climax Vegetation? [8marks] Climax vegetation is the final stage in the development of the natural vegetation in any given region . Plant communities will change as environmental conditions change . Hardy pioneer species will colonize an area first . As they die out they add humus to the soil, allowing other plants to grow and survive – this is known as succession  . When this happens, the composition of the plant community is relatively stable and in equilibrium with the existing environmental surroundings (normally the soil or climate) . When climax vegetation has been reached plants are well established and trees such as pine and birch can be found . Biomass is also at its maximum . Equilibrium: In balance or the same as. Biomass is biological material derived from living, or recently living organisms. Geography Biosphere Read pages 165 to “Introducing Soils” on page 168 and answer the following questions. 1. What are the three necessary requirements for the development of a sand dune system? 2. Why is it so difficult for plants to grow on sand dunes? 3. How has marram grass adapted to the difficult conditions on the Yellow Dune? 4. Define the following terms: [a] Xerophytic [d] Rhyzomes [b] Colonising [e] Hydrophytic [c] Saltation [f] Psammosere Geography Biosphere This is a cross section view of the dunes. On your piece of A3 paper draw out the cross section neatly. You should notice that there is a change in relief and the vegetation Geography Embryo and Fore Dunes: the environment Biosphere On-shore winds High water mark Poor water retention Sand builds up against pioneer plants Seaweed deposits humus Transient dunes Sand alkaline Geography Biosphere The Strandline Sandwort Sea rocket Strandline - Sea Sandwort; Sea Rocket; These are all salt-tolerant (halophitic) species. They are low in height and have waxy leaves to withstand the wind and retain moisture. Some can even withstand periodic immersion in sea water. The presence of these plants leads to the further deposition of sand by trapping the sand. The high pH figures can be attributed to a high concentration of shell fragments. (CaCO3). Geography Biosphere Embryo Dunes Lyme grass Sea couch Embryo Dune - Sea/Sand Couch; Lyme Grass: These dune pioneer species grow side roots and underground stems which bind the sand together. These grassy plants too, can tolerate occasional immersion in sea water and a low humus content. Some species found on the strandline are also found on the embryo dunes (Sea Rocket). Geography Biosphere Fore Dunes Sea Bindweed Sea Holly Fore Dunes - Sea Bindweed; Sea Holly; A slightly higher humus content (from decayed plants), and lower salt content (further from the sea) allows these species to further stabilise the dune and allow the colonisation of Marram Grass which becomes a key plant in the build up of the dune. Geography Biosphere Yellow Dunes Above the level of high tides Reduced wind speeds ‘Soil’ slightly less alkaline and more water retentive Some humus forming Surface continually blown away and replenished with fresh sand Geography Biosphere Yellow Dunes Marram Grass Yellow Dune – Marram Grass: Both the humus content and the acidity of the soil have increased at this location. Marram can align itself with the prevailing wind to reduce moisture loss; it can also survive being buried by the shifting sand of the dune. In fact, as sand deposition increases the Marram responds by more rapid growth (up to a staggering 1 metre a year). It is better able to survive the dry conditions of the dune than other plants. This allows it to become the dominant species on the Yellow Dune. It also has long roots which help to bind deposited sand and anchor it into the dunes as well as access water supplies some distance below. Geography Biosphere Dune Slacks Occur in low lying hollows between dune ridges Soil acidic Relief intersects the water table Water table high – especially in winter Geography Biosphere Grey Dunes and Slacks Sand Sedge Sand Fescue Grey Dunes and Slacks - Sand Sedge; Sand Fescue; As a result of an increase in organic content (humus), greater shelter and a damper soil a wider range of plants can thrive here. Marram dies back (contributing humus) to be replaced by other grasses, sand fescue and sand sedge. As a result of leaching and the build up of humus the soil is considerably more acidic again supporting a wider plant community. In the wetter slacks, close to the water table, several water-loving (hydrophytic) species may survive. Geography Biosphere Climax Vegetation Birch Pine Climax Vegetation – Birch, Pine: Eventually trees such as birch, pine or spruce could establish a foothold. Here the ecosystem has reached a dynamic equilibrium.