Ecological Succession When a location is destroyed by volcanoes, fire or other catastrophe, living organisms re-colonize in a predictable pattern beginning with the simplest, lowest trophic level organisms and evolving to more complex organisms as the ecosystem rebuilds.

Beavers When beavers return to a depleted area, the ecosystem changes. Water is retained on the landscape because beavers build dams and dig grooves in the pond bottoms to deepen them. Aquatic plants appear along with edge grasses, shrubs and saplings. With water comes insects, amphibians, birds, etc. The ecosystem is succeeding from an arid, prairie like ecosystem to a temperature and aquatic based system. Here again, as with the wolves of Yellowstone, animals have reshaped the ecosystem.

Types of Succession Primary Secondary When a catastrophic event occurs, much of an existing ecosystem can be wiped out.

Mount St Helens 1980 The eruption of Mount St Helens gave biologists a once-in-a-lifetime chance to observe succession. The old growth forest was destroyed in minutes leaving bare rock.

Mount St Helens - after the eruption                                                                                                                                                  Mt St Helens Recovery

Mount St Helens – 30 years after the eruption                                 http://ngm.nationalgeographic.com/2010/05/mount-st-helens/cook-photography#/04-ash-sediment-714.jpg Thirty years later, evergreens and aspen return, as do the large herbivores like elk.

Primary Succession – Glacial Melt As the glacier retreats, bare soil is left behind. The predictable process of primary succession begins and stabilizes in this case as a mature boreal forest (taiga).

Primary Succession Lichen and mosses are often the first organisms to inhabit the ecosystem after a catastrophic event. They are then followed by more complex plants like grasses and annuals, and the heterotrophs that depend on them.

Pioneer Species: Gold Cobblestone Lichen Lichens are composed off fungi living in a close relationship with algae or cyanobacteria. Together, the pair is able to attach to bare rock and begin colonizing the area. The algae or cyanobacteria produce food using the sun’s energy. Flame Lichen

The Yellowstone Fire “Twenty years ago, in the summer of 1988, Yellowstone caught fire. The fires, which began in June, continued to burn until November, when winter snows extinguished the last blazes. Over the course of that summer and fall, more than 25,000 firefighters were brought in from around the country. In the end, the flames scorched about 1.2 million acres across the greater Yellowstone area, leaving the impression that the world's first national park had been destroyed.” http://www.npr.org/templates/story/story.php?storyId=94126845

Yellowstone – 20 years later

Secondary Succession Secondary succession differs from primary succession. Secondary succession starts with soils in place compared to bare rock as the starting point for primary succession. Because soil is present, the recovery process is much faster (10’s of years versus 100’s or thousands).

Lake succession lake turned peat bog 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. Not all lakes are subject to succession, of course. If a lake has a steep, rocky shore, there is no way for the shore to creep into the lake, short of dynamite. You can tell where a lake is disappearing by the plant-life: wherever you see grasses, rushes, reeds and sedges along wet, indistinct and muddy shorelines, you know that the lake is being taken over, ever so slowly. lake turned peat bog

a New England Example of secondary succession Presettlement 1700 Height of Clearing 1830 Hardwood Forest 1930

What if all the humans were gone?