Ecological succession.docx

Ecological succession - Progressive replacement of one community by another through natural processes over time until the development of a stable community (climax) is reached

Involves a directional, orderly and non-seasonal process

It involves colonization, establishment and extinction which act on the plant species involved

Involves the formation of seres or seral communities, which eventually advance to the formation of climax community

Xerophytic habitat is converted into a mesophytic one

As succession progresses, species diversity increases

Causes of succession

1. Autogenic factors

those which are due to the presence or growth of the plants themselves, eg., light capture by leaves, water and nutrient uptake, detritus production, nitrogen fixation, amount of moisture in soil, etc.

Many species change the environment in which they live in ways that make it less unfavorable for themselves and more favorable for others.

2. Allogenic factors

Factors external to the plants, such as climatic factors, periodic fires, floods

Stages of succession

Pioneer stage - starts when hardy individuals of a species invade or colonize the area; pioneer species such as lichens and moss are able to tolerate harsh conditions

Seral stages - the intermediate stages of succession

Climax community- one that has reached the stable stage; when extensive and well-defined, it is called a biome; usually exhibits a large species diversity and stability

Prepared by:Aleine Leilanie B. Oro Ecological Succession

Lichen structurealgal part (Chlorophyta or Cyanophyta)fungus part (Ascomycota or Basidiomycota)

Primary succession

occurs in an area that previously was devoid of life;

may start from bare rocks or in areas in which the soil is incapable of sustaining life as a result of lava flows, newly formed sand dunes, or rocks left from a retreating glacier;

The rate of succession is slow because of the arduous process involved in soil formation


Trend of succession in Lithosere

Pioneer Community

Seral Communities Climax Community

1 2 3 4 5 6

Crustose lichens stagee.g

Rhizocarpus,Rinodina,Lacanora

Foliose lichens stagee.g

Parmellia,Dermato carpon

Moss stagee.g

Polytrichum,

Tarula,Grimmia

Herbs stagee.g

Eleusine,Aristida

Shrub stagee.g

Rhus,Phytocar

pus

Forest stagee.g

Mesophytic trees

------------General trend of succession ------------->


Adaptation of moss to unfavorable environment: low thermal conductivity,high porosity,high water holding capacity, andcapacity to maintain nitrogen-fixing symbioses with Cyanobacteria

a) Volcanic rock b) Transition from pond to land

Xerarch succession


Trend of succession in LithosereRhizocarpon

Rinodina

Lecanora

ParmelliaDermatocarpon

Trend of

succession in Lithos

ere

Polytrichum

Tortula

Grimmia

Eleusine

Aristida

Trend of succession in Lithosere

Rhus

Physocarpus

Secondary succession

Series of community changes which take place on a previously colonized but disturbed or damaged habitat

Examples include areas which have been cleared of existing vegetation such as after tree-felling in a woodland, and destructive events such as fires

Other examples of disturbances: severe storms or droughts, landslides, overgrazing, disease outbreak, flooding

Begins in an area that already has soil

The disturbance leaves seeds, spores, or the subterranean portions of plants present

Secondary succession

The reestablishment of a community in which most, but not all organisms have been destroyed.

Lodgepole pines (a) will replace meadows in the absence of fire.

Prescribe fires (b) burned trees in the meadow (c).

Differences between primary and secondary succession

Secondary succession is usually much quicker than primary succession for the following reasons:

There is already an existing seed bank of suitable plants in the soil.

Root systems undisturbed in the soil, stumps and other plant parts from previously existing plants can rapidly regenerate.

The fertility and structure of the soil has also already been substantially modified by previous organisms to make it more suitable for growth and colonization.

Hydrosere/ hydrarch

Death and decay of rooted submerged plants and rooted floating plants add organic matter to substratum; a layer of soil builds up, making the pond shallower; reed swamp stage follows


(partially submerged plants); this is followed by the sedge meadow stage of grass, then by woodland (shrubs and trees)


Hydrarch succession

1. Submersed aquatic plants in the deeper water. 2.Emergent cattails and bulrushes rooted in the mud of shallow water. 3. Willow thickets along the banks of distant shoreline. 4. Conifer forest in drier, well drained soil above the willow thickets.


a)Douglas firs and hemlocks in an old-growth forest b) the same area a year after eruption of Mt Saint Helens

ab

Comparison of plant, community, and ecosystem characteristics between early and late stages of succession


Grasses and sedges encroaching on the pond

In time, depending on local geological and climatological conditions, the pond may gradually turn into a meadow

A subalpine meadow in the Sierra Nevada under invasion by lodgepole pines (Pinus contorta).

Lodgepole pine forest


Species diversity

The Shannon-Wiener Diversity Index, H, is calculated using the following equation:

H = - Pi(lnPi) where Pi is the proportion of each species in the sample.

Community #1

Community #2

Ecological succession.docx

Documents

Transcript of Ecological succession.docx