Hydrosere

A hydrosere is a plant succession which occurs in a freshwater lake.

In time, an area of open freshwater such as a lake will naturally dry out, ultimately becoming woodland. During this change, a range of different landtypes such as swamp and marsh will succeed each other.

The succession from open water to climax woodland is likely to take at least two hundred years. Some intermediate stages will last a shorter time than others. For example, swamp may change to marsh within a decade or less. How long it takes will depend largely on the amount of siltation occurring in the area of open water.

Examples of Hydroseres

An example is a small kettle lake called Sweetmere, which is located within Shropshire, UK. Sweetmere is one of many small kettle lakes which formed at the end of the last glacial period when the temperatures began to increase. The ice began to melt and retreat approximately 10,000 years ago.

As the climate slowly began to warm this allowed algae, water lillies and floating aquatic plants to begin to colonise the lake. These, in essence, were the pioneer species. Once these began to die it provided dead organic matter to the lake bed sediment and therefore increased fertillity and depth. As a result this allowed deeper rooted species to develop such as reeds and bullrushes. At this point there is a growing floating raft of thick organic matter within the lake. Because the bulrushes and reeds have relatively deep roots, this encouraged bioconstruction which traps more sediment, allowing sedges wilow and alder to develop. This process decreased the water depth and raised the lakebed thus making it drier.

Drier conditions now meant that a wider range of species could inhabit the area. Birch and alder came into dominance. All species which have grown have occurred because of seed transfer either by animals, birds, wind, or water transfer. Water level is further reduced as a result of further bioconstruction and also due to increasing temperatures there is increased evaporation from the lake.

Underneath the birch canopy; developed terrestrial shrubs and grasses. This then increased the acidity which increased the rates of nutrient exchange. The area has been artificially drained and this allowed the oak and ash community to develop. This is the last seral stage.

The lake is now being managed by cutting down certain species in order to stop the whole lake becoming dried up and dominated by the oak and ash woodland.

Another example of a hydrosere is Loch a' Mhuilin, located on the Isle of Arran, Scotland. This small lake lies behind a ridge of material deposited towards the end of the last Ice Age. The lake exhibits characteristic features of a hydrosere, the succession from a fresh water surface with small pioneer plant species to a sub-climax vegetation of alder and willow. The climax vegetation of oak and thomas beech woodland has not been achieved due to the impact of human activities of clearing grazing land, as well as grazing by red deer and rabbits.

References

cite web
title = Hydrosere - A Wetland Example of Succession in Action.
url=http://www.countrysideinfo.co.uk/successn/hydro.htm
accessdate = 2007-02-14

cite book
last = Palmer
first = Andy
coauthors = Nigel Yates
title = Advanced Geography
publisher = Philip Allan Updates
date = 2005
pages = 379
isbn = 1-84489-205-0