Ecological Succession Chapter 5, Section 3

Ecosystems are constantly changing…The same forest area can look very different at different times

Ecological Succession Definition: a gradual process of change and replacement of the types of species in a community The sequence of changes is somewhat predictable May take place over hundreds or thousands of years

Two types of ecological succession Primary succession: occurs on a surface where no ecosystem existed before (no soil) Secondary succession: occurs on a surface where an ecosystem has previously existed but has been disturbed (soil is present)

Primary Succession On new islands created by volcanic eruptions On sand dunes

Primary Succession Where glaciers have retreated

Primary Succession Paved areas that are abandoned

Primary Succession Begins with pioneer species (defined as the first species to colonize a disturbed area), like lichens, that can grow directly on rock; begin the breakdown of the rock to form soil

Primary Succession Once rocks begin to weather and crack, soil forms and small plants can take root

Primary Succession Larger plants continue to move in until the bare ground is covered with life

Secondary Succession Definition: type of ecological succession that occurs on a site where an ecosystem previously existed (soil is present) Due to a disturbance to the ecosystem – something upsets the natural balance May be natural or man-made (anthropogenic) disturbances Think of examples of each….

Examples of natural disturbances tornadoes, floods, trees falling, fire, hurricanes, disease

Examples of man-made (anthropogenic) disturbances deforestation, pollution, urbanization, harvesting

‘General Ecology’, D.T. Krohne

Stages of Secondary Succession in Woodlands Early: plants typically small with short lifecycles (annuals, grasses), rapid seed dispersal, environmental stabilizers (pioneer species) Middle: plants typically longer lived, slower seed dispersal, and usually larger Late: plants and animal species are those associated with older, more mature ecosystem: larger, slower dispersal, better competitors, slower growth Climax community: final stage of succession that will last as long as there is no disturbance

We can see changes in the animal communities over time, too

Each stage of succession brings about changes in the ecosystem that enable or prevent certain species from moving in – better soil, less light, more competition as ecosystem matures Some changes may help other species – called facilitation (example: dogwood trees grow well under the shade of larger trees) Some changes may hinder other species – called inhibition (example: black walnut produces a chemical that keeps other plants from growing near it)

But it’s not so simple: Stages of succession vary, depending on local conditions Amount of rain, temperature, terrain, latitude, altitude, soil type, human impact

Succession in two forests: What causes the difference in these climax communities? For example, eastern U.S. - climax species are oak, hickory, maple Succession in the boreal forest (for example in Canada) – climax species are fir, spruce, hemlock

Even in one location, the climax community depends on many factors Current way of thinking: instead of one stable, final climax community, there are patches that are constantly changing within an ecosystem (called patch dynamics)

Identify the “patches” around SPHS- even though we are in the “deciduous forest” of Alabama, it is not that simple….

Fig 10.7 Diagram of bog succession. Ecological Succession can occur in aquatic ecosystems, too Fig 10.7 Diagram of bog succession. Fig 10.7 Diagram of bog succession. Open water (a) is transformed through formation of a floating mat of sedge and deposition of sediments (b) into wetland forest (c). © 2003 John Wiley and Sons Publishers

“Change is certain. Peace is followed by disturbance….” Percy Bysshe Shelley