1 Ecological Succession Change over time 1

2 Pioneer Organisms Pioneer organisms are the first organisms to reoccupy an area which has been disturbed by a disruption. Typical pioneers in a succession include grasses in a plowed field or lichens on rocks. 2

3 Pioneer Organisms: What is it? Why does it matter to the ecosystem? What is it?

4 Primary Succession Occurs in areas where no ecosystem or biological activity has existed previously (bare rock, no soil) The creation of an uninhabited area due to an event (e.g. volcano eruption) 4

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6 Secondary Succession A pattern of change in areas where biological activity or an ecosystem has previously existed (e.g. after a fire, landslide, logging). Large disturbance of an area that leaves some of the original species 6

7 Secondary Succession As succession proceeds, groups of organisms are replaces so that the dominant species changes over time 7

8 Climax Community The final stage of succession The species composition of the climax community remains the same because all the species present successfully reproduce themselves and invading species fail to gain a foothold. 8

What’s the change? These photos are from the same field taken two years apart 9

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ECOLOGICAL SUCCESSION: AN EXAMPLE

Deep freshwater will not support rooted, submerged plants because there is not enough light for photosynthesis. There will be microorganisms and plankton floating in the water.

Over time, sediments will be transported into the lake (or pond) by streams or rainwater draining into it from the land. The water depth will gradually decrease, allowing rooted, submerged plants, such as starwort and pondweed to grow.

By this stage, the water may be too shallow to support fully submerged plants. Instead, emergent plants, like marsh grasses, emerge and take root.

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.

The soil is still wet, but no longer completely waterlogged and anaerobic. By now, the willow dominates the ground. 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.

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.