Deck 17b- Vegetation impacting on coastal recession Flashcards
What is a succession?
Succession refers to how a group of plants changes over time. One community of plants is replaced by another as succession develops. The process is especially important on coasts as it stabilises the coastal features.
What are pioneer species?
Pioneer species are the first plants to colonise an area. They are highly adapted and specialised plants that are able to survive tough conditions.
What is climax vegetation?
A community of plants, animals which, through the process of ecological succession in the development of vegetation in an area over time, have reached a steady state.
What is a psammosere?
An ecological succession that began life on newly exposed coastal sand
What conditions are required for the formation of a sand dune?
-a large supply of sand
-a large flat beach
-time for the sand to dry, so an extensive tidal range is needed
-an onshore wind (wind blowing from the sea to the land) for sand to be transported to the back of the beach
-an obstacle for the dune to form against, e.g. pebble or driftwood
What are the stages of a sand dune succession?
Embryo dune, fore dune, yellow dune, grey dune, dune slack, mature dune
What are the characteristics of an embryo dune?
Initial stage of the formation of a sand dune and is therefore very mobile. Scattered pioneer vegetation found in sand that is of a yellow colour, has a high pH of 8.0 and a low humus content (<1%)
What plants characterise the embryo dunes?
Sand couch and lyme grass
What are the characteristics of a fore dune?
Dunes can grow up to 20metres and have been somewhat stabilised by the colonisation of marram grass that acts to bind the sand together whilst building up the height of the dune by trapping more sand. Soil is yellow, has a pH of 7.5 and a low humus content (<1%).
Which plants characterise the fore dunes?
Marram grass and sea holly
What are the characteristics of a yellow dune?
The sand dune is taller and has become more stable and fixed due to larger concentration of vegetation present. Soil is still yellow in colour, has a neutral pH of 7.0 and a higher humus content (2.5%) due to decay of vegetation.
Which plants characterise the yellow dunes?
Marram grass and sand sedge
What the the characteristics of a grey dune?
Grey dunes can take up to 125-150 years to form and are part of the fixed dune system. The soil colour is grey due to the increase humus content (5%) and has become slightly acidic (pH 6.5)
Which plants characterise the grey dunes?
Scrub-like plants such as heater and gorse
What are the characteristics of a dune slack?
Dune slacks started as a hollow that has been eroded by a blowout event (due to high winds often from storm events). Continued erosion leads to the wet sand at the water table being exposed which cannot be transported and a marshy area forms
Which plants characterise a dune slack?
Creeping willow and common sallows
What are the characteristics of a mature dune?
A mature dune has reached the climax vegetation i.e. a deciduous woodland in the UK. The soil is of a brown colour which is acidic (pH 6.0) and has a high humus content (>40%). It can take over 250 years to reach this stage.
State an example of a local beach that has a sand dune succession
Druridge Bay, Bamburgh, South Shields
How can human activity damage sand dunes?
-Visitor pressure e.g. trampling
-Removal of land of mineral extraction
-Coastal defences interrupting sediment supply
-Pollution from agriculture
-Change of land use e.g. agriculture or urbanisation
-Drinking water abstraction
What strategies have been implemented to sustainably manage the sand dunes at South Shields?
-Sand trap fencing in 2011 helped to raise levels by 1m
-Planting of over 265,000 dune grasses and wild flowers
-Visitor control measures e.g. cordoning off areas recently replanted
-Future plans for planting over 30,000 additional dune grasses including marram grass
What are estuaries?
Estuaries are where the river meets the sea. This enables brackish where there is a mix between fresh water and saline water.
Why is there lots of deposition in estuaries?
High rates of deposition due to very low energy environment and mixture of fresh and saltwater allows for flocculation to occur.
What is flocculation?
Flocculation is the process of clumping small particles in a liquid into larger particles called flocs. In an estuary this refers to the clumping of small clay particles which allows them to be deposited due to their heavier weight.
What landforms forms in an estuary due to high rates of deposition?
Mud flats followed by salt marshes
What is a mud flat?
Mudflats are the landform which results from deposition at the edges of an estuary or on the landward side of a spit. They develop on sheltered shorelines that are not exposed to powerful waves and are composed of silt and clay. Mudflats are known as ‘inter-tidal’ areas because they are only exposed at low tide as they are submerged at high tide
State an example of a mud flat.
Morecambe Bay, Cumbria. It is the largest expanse of inter-tidal mudflats and sand in the UK covering a total area of 310km2.
What is a salt marsh?
Saltmarshes are areas of flat, silty sediments that accumulate around estuaries or lagoons
What pioneer species colonise the mud flat areas and how do they change the environment?
Halophytes and include species like eelgrass. They slow the current and lead to further deposition.
Other pioneer species include Spartina grass which has long roots (up to 2m which secure the deposited material) as well as a mat of surface roots to hold the mud in place.
What species characterise the lower marsh?
As more mud is trapped, decaying plants help build up a soil so that plants such as cord grass, sea lavender and sea aster can grow
How doe the species on the lower marsh change the environment?
These form a dense mat of vegetation up to 15cm high. Dead organic matter also helps to build up the surface, which grows in height between 1-25mm/year. This builds up the height of the saltmarsh through a positive feedback loop.
What species are found on the mid/high marsh?
Red fescue, marsh samphire, sea thrift and sea lavender
How do hollows and creeks form on a sand dune?
As mud levels rise, complex creek systems develop that channel the tides and these deepen as the marsh becomes higher. They are formed because of erosion by tidal currents.
Hollows may form where seawater becomes trapped and evaporates, leaving salt-pans in which the salinity is too great for plants to survive.
What is the climax vegetation along a halosere succession?
Native woodland including trees such as willow, bramble, birch and dog rose
