Succession

Ecological succession is the gradual process by which ecosystems change and develop over time. Nothing remains the same and habitats are constantly changing.

Life Span of a Lake

Lakes, like all things, change over time. Even a lake has a life span like people do - there are young lakes, middle-aged lakes and old lakes. Many of the lakes in British Columbia are still quite young because they were formed by the last ice age that carved our northern landscape.

As our lakes age, many of them will slowly shrink. Land naturally takes over at the edge of a lake. It's very slow, but it happens. This is called “lake succession,” and this is how it works.

Each year trees and shrubs along the edge of a lake shed leaves and debris into the water that then settle to the bottom. This debris slowly decays to form new habitat for grasses, rushes and sedges. The grasses take root quickly and stabilize the new ground for dry land species. Some day shrubs and small trees will grow where lily pads once floated.

As the lake becomes smaller and smaller, it may not be able to provide enough oxygen or food for some fish. But this happens so slowly that they have plenty of time to move on to other lakes, if the lake is connected to the rest of the watershed by a stream.

•Primary Succession follows the formation of new land surfaces consisting of rock, lava, volcanic ash, sand, clay, or pavement, NOT SOIL

•Secondary Succession follows the destruction or partial destruction of the vegetation (plant) area by some sort of disturbance, like a fire, windstorm, or flood that leaves the soil intact.

http://www.kscience.co.uk/as/module5/succession/index.htm

Some organisms are able to environments where there is no stable soil. They have to be able to extract nutrients from the air and to attach themselves to the surface. As they grow and produce dead matter, they start to develop soil and weather the surface. Other colonizers then start to grow in the area and the pioneers are rapidly out competed. Lichens are an example of pioneers of bare rock.

Animals are often able to avoid fires or survive them in a number of ways.  The ant nest was in an area that had burned the day before.  The ants quickly dug themselves out and moved their pupae and young to a new nest about 10 feet away . 

In the drought year of 1988, huge fires swept through Yellowstone National Park (above and left).  After years of fire suppression in the park, the forest floor was loaded with potential fuel, and the resulting fire burned hotter than it would have if more frequent, patchy fires had been allowed to take their natural course.  The pictures above were taken in 1999; 11 years after the fires.  The slow regrowth is in part due to the cold temperatures there; average annual temperature in Yellowstone is only about 1° C.  To the left, a pine sapling struggles to regrow after the fire.  In Yellowstone, the fires moved the community away from its climax and set secondary succession into motion.

The good thing about replanting is that we have more trees. The bad thing is that they are all the same type and the same age – not giving much diversity for animals who rely on different kinds of trees.

This old pasture is reverting back to forest. Grasses are gradually being replaced by flowers and weeds. Next will come shrubs and small trees.

Finally, larger trees will sprout up and grow, creating a mature forest or CLIMAX COMMUNITY.

In 1980, Mt. St. Helens in Washington erupted, essentially destroying all life in a large blast zone.  Trees were killed (left) and the ground was covered with ash.

Above:  A nurse log in a temperate rainforest shows many of the stages of succession, with mosses and other plants taking roots.  Tree seedlings will also grow here, and eventually the nurse log may give rise to 2 or 3 full-size trees.