Hydrosere
- A Wetland Example of Succession in Action. A hydrosere is simply a succession which starts in water. A wetland, which is a transitional area between open freshwater and dry land, provides a good example of this and is an excellent place to see several stages of a hydrosere at the same time. In time, an area of open freshwater such as a lake, will naturally dry out, ultimately becoming woodland. During this process, a range of different habitats such as swamp and marsh will succeed each other. This succession from open water to climax woodland is likely to take at least two hundred years (probably much longer). Some intermediate stages will last a shorter time than others. For instance, swamp may change to marsh within a decade or less. How long it takes will depend largely on the amount of siltation occurring. Discover wetlands here before you begin.
Scroll sideways to follow the succession. Scroll down under each successional stage for information and images of species likely to be present in a British hydrosere. You can also hold your mouse pointer over images for information. |
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Open Freshwater |
Submerged Plants |
Swamp |
Marsh |
Climax Woodland |
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| Deep
freshwater will not support rooted, submerged plants because there is not enough light for
photosynthesis in the depths. There will be micro-organisms and plankton floating in the water.
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Over
time, sediments will be transported into the lake (or pond) by streams or rainwater
draining into it from the land. Large amounts of sediment can be deposited in this way. Images here. The water depth will gradually decrease, allowing rooted, submerged plants, such as starwort and pondweed to grow. Waterlilies, which are rooted, but with floating leaves may also become established. Fringed Water-lily
Floating plants, such as duckweed, may also be present. With the added plant life will also have come a great variety of invertebrates and fish. The large numbers of different species present give rise to complex foodwebs. The vegetation traps and holds more and more of the incoming sediment, so that the water becomes shallower. Decomposing dead plant and animal matter provides food for detritivores and increases the nutrients in the water. This promotes plant growth. |
By
this stage, the water may be too shallow to support fully submerged plants. Instead,
emergent plants,such as Yellow Iris, Branched Bur-reed and reedmace, grow partly in and
partly out of the water. Yellow Iris
(Yellow Flag)
Branched Bur-reed
Greater
Reedmace
These plants tend to have tall, flexible spear-shaped leaves. This allows the plants to cope with large fluctuations in water level, always retaining some portion of the leaves above the water for effective photosynthesis. The water in swamp areas teems with invertebrate life. It also provides an ideal place for frogs to spawn. Frog Spawn
The leaf bases of the swamp plants are extremely effective at retaining incoming silt, particularly in the winter when the leaves have died back (below). Rotting plant material progressively builds up, which also raises the ground level.
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Swamp
plants which are adapted to grow in partially submerged conditions, will gradually die out
as the marsh floor progressively rises above the water level. Some plants such as Yellow Iris, which grow equally well in swamp or marsh conditions, will continue to grow, while marsh plants such as Water Mint, scent the air with minty aromas when crushed. Water Mint
These damp areas provide a wonderful transition habitat for young amphibians such as frogs and toads newly emerged from the water. At this point they are very small and extremely vulnerable to drying out. The lush wet vegetation provides an ideal hiding place. Common Frog
However, their presence will also attract predators such as Grass Snakes. A Marsh is a good place to spy Grass Snakes (which are not poisonous!) basking in the sun. Tree seedlings, such as willow, which favour wet soil conditions, will become well-established and begin to grow up. Willow has a very high transpiration rate, transferring large quantities of water from the sediment into the atmosphere. Together with the silt-trapping effect of the marsh plants, this greatly increases the rate at which the marsh dries out. |
The
soil is still wet, but no longer completely waterlogged and anaerobic. By now, the willow has grown up and dominates the ground. Willows will support a diverse range of invertebrates (more than 450 different species). This means that there is plenty of food for insectivorous birds such as Marsh Tits. (For a list and information on birds surveyed in a wet woodland area, click here) Alder, another tree which flourishes in wet conditions may also be present. Many of the marsh plants will have been shaded out by the trees. They are replaced by a variety of woodland floor plants including sedges, rushes, ferns and small flowering herbs which are adapted to low light levels and which flourish in wet conditions. Star Sedge
Golden Saxifrage
A variety of fungi which grow well in wet soils will also become established. In the more boggy patches of the woodland, the bright orange fruiting bodies of the fungus, Mitrula palludosa might be spotted protruding from the soil like miniature lollipops. Fruiting Bodies of
In drier areas, increasingly aerobic decomposition will accelerate nutrient recycling, elevating the humus and nutrient content of the soil. Tree transpiration will continue to dry out the soil to the point where climax tree species such as Oak, Beech or Ash can become established. |
Climax
tree species include Oak, Ash and Beech. They are slow-growing, but because they are also
tall and long-lived, in time, they will come to dominate an area. The particular climax tree species which eventually dominates the woodland will depend on soil type and other environmental conditions. In many parts of Britain, the climax community is likely to be a mixed Oak wood. The number of species making up the woodland community is very dependent on the structure of the wood and on how much light gets through to the woodland floor. Where the ground is not too heavily shaded, herbs such as Wood Anemone and Wild Garlic will flourish. Wood
Anemone
A ground cover of flowering plants and grasses will ensure that a variety of woodland butterflies are present. Speckled Wood
A different range of fungi will inhabit the climax woodland. Rotting wood provides microhabitats for many different fungi and invertebrates. The living trees are also hosts for a variety of mycorrhizal fungi, such as the Fly Agaric, which is associated with birch. Fly Agaric
Many mammals will inhabit the woodland from Dormice (in southern counties of Britain) to squirrel, fox and badger. Dormouse
The number of different species present in a climax oak woodland community will run to many thousands.
Continue to Primary Succession
Find out about plant zonation in wetlands here. Explore plant adaptations to life in and out of water here Find out about woodlands and their management here. |
