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Ecological Succession

Succession is a sequence of changes that occur in plant and animal communities of an ecosystem.

There are two main types of succession: Primary Succession and Secondary Succession.

Primary Succession

Follows events such as a lava flow, severe erosion, glacier recession, or exposure of rock and sand through mining
Soil must be made through biological weathering
Pioneer species such as lichens and mosses break down rock into soil
Meadows form as grass and wild flower seeds take root in soil
Shrubs and bushes form clusters in the meadow
In mature fields, spruce or red cedar trees grow individually
Tree seedlings begin the process of changing the field to a woods
The climax community of mixed hardwood trees or evergreens is achieved depending on the climate

Example of Primary Succession in New Jersey Following Mining

Animals		Insects Rodents Birds	Rabbits Eastern kingbirds Raptors	Eastern bluebirds Deer Rufous-sided towhees	Black-throated green warblers Broad-winged hawks Bears
Bare Rock	Pioneer Species	Meadow	Shrubs and Bushes	Early Trees in Mature Fields	Climax Forest
Plants	Lichens Mosses	Weeds, Wildflowers, Grasses	Wild rose Blueberry Willow Aspen	Red Cedar Spruce Pine	Oak Maple Beech Hemlock

	Thousands of years ago, the Wisconsin Glacier covered northern New Jersey. In its path, the glacier ground rock into sand, gravel and boulders. When the glacier melted and receded, the exposed rock surfaces were gradually worn down by exposure to wind and water. Biological weathering by lichens and mosses further degraded the rocks into soil. Mosses and lichens are examples of pioneer species. In primary succession, pioneer species are the first to establish life on barren rock and sand surfaces.
	Lichens, the gray-green leathery patches on the rock, are actually two organisms, a fungus and an alga. The alga and the fungus work together to survive and in the process break down the minerals in the rock through biological weathering. The relationship between the two organisms is an example of mutualism because both derive a benefit from the relationship.
	Ten thousand years after the glacier melted, humans made economic use of the glacial till by quarrying rock for building materials. The top ridge shown in the picture is secondary succession with vegetation replacing existing vegetation in a narrow dark organic soil layer at the surface. The lower ridge shows the grass stage of primary succession along the area exposed by quarrying operations. Here, there was no organic soil, only sand and rock.
	As succession continues, shrub plants and seedling trees are added to the vegetation. The soil is very poor quality along this ridge. It will be many years before enough organic matter is added to the soil for it to support larger trees.

Secondary Succession

Follows events such as logging, farming, or a forest fire
Soil is already present to support plant growth
First, grasses, wild flowers, and weeds take root forming a meadow
Second, shrubs and bushes grow throughout the meadow
In old fields, red cedar trees grow individually
Tree seedlings begin the process of changing the field into a woods
The climax community of mixed hardwood trees or evergreens is achieved depending on the climate

	Secondary succession begins after a disturbance when there is still an organic layer of soil. In the picture a road has been cut through a forest. The edges of the roadway support wildflowers and grasses after a single season.
	Succession may also take place in aquatic ecosystems. Thousands of years ago a glacier created a shallow swale pond in New Jersey. Light penetrates the water allowing aquatic plant life to grow in dense patches across the bottom of the pond. The plants are the vertical green spikes in the picture below the leaf layer on the surface. Over time, the pond could fill in with soil and become a marsh before changing over to a swamp. The story isn't over for this pond!
	The view from a rock outcrop in Jenny Jump State Park, NJ, shows many stages of succession at one time. Mosses and lichens grow on the exposed outcrop of gneiss rock. Grasses and other herbaceous plants have set roots into thin soil atop this ridge. Cedar trees that need sunlight for growth have established themselves further down on the next ledge where soil is deeper and somewhat richer. In the distance a mature forest of oak, hickory, beech and maple has grown up in the past century. The flat green strip is a valley currently in use for agriculture. When it is abandoned, it too will slowly yield to the forces of nature and gradually change into a new ecosystem.

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