Ecological Succession (5)

Ecological Succession

A bare patch of ground

The same area 2

years later

ECOLOGICAL SUCCESSION

No plant competition

Soil mobile and liable to

erosion

More extreme surface

microclimate

Drier environment

Ecological succession

Progressive replacement of one community by another through natural processes over time until the development of a stable community (climax) is reachedInvolves a directional, orderly and non-seasonal processIt involves colonization, establishment and extinction which act on the plant species involvedInvolves the formation of seres or seral communities, which eventually advance to the formation of climax communityXerophytic habitat is converted into a mesophytic oneAs succession progresses, species diversity increases

Causes of succession

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.

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

Pioneer species can tolerate harsh

physical conditions better than other plant

species

Grow best where there is little

competition for space and resources

Lichen structure

a) algal part (Chlorophyta or Cyanophyta)b) fungus part (Ascomycota or Basidiomycota)

Adaptation of moss to

unfavorable environment:

low thermal conductivity,high porosity,high water holding capacity, andcapacity to maintain nitrogen-fixing symbioses with Cyanobacteria

Composites as early colonizers

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

a) Volcanic rock b) Transition from pond to land

Xerarch succession

Trend of succession in Lithosere

Pioneer Community

Seral CommunitiesClimax

Community

1 2 3 4 5 6

Crustose lichens stage

e.gRhizocarpus,

Rinodina,Lacanora

Foliose lichens stage

e.gParmellia,Dermato carpon

Moss stagee.g

Polytrichum,Tarula,

Grimmia

Herbs stagee.g

Eleusine,Aristida

Shrub stagee.g

Rhus,Phytocarpus

Forest stagee.g

Mesophytic trees

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

Pioneer Community

1

Crustose lichens stage

e.gRhizocarpus,

Rinodina,Lacanora


Rhizocarpon

Rinodina

Lecanora

Seralcommunity

2

Foliose lichens stage

e.gParmellia,Dermato-

carpon

Parmellia

Dermatocarpon

Seralcommunity

3

Moss stagee.g

Polytrichum,Tortula,Grimmia


Polytrichum

Tortula

Grimmia

Seralcommunity

4

Herbs stagee.g

Eleusine,Aristida

Eleusine

Aristida

Seral community

5

Shrub stagee.g

Rhus,Physocarpus


Climax Community

6

Forest stagee.g

Mesophytic trees

Rhus

Physocarpus

Secondary succession

Series of community changes which take place on a previously colonized but disturbed or damaged habitatExamples include areas which have been cleared of existing vegetation such as after tree-felling in a woodland, and destructive events such as firesOther examples of disturbances: severe storms or droughts, landslides, overgrazing, disease outbreak, floodingBegins 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).

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.

Differences between primary and

secondary succession

Hydrarch succession

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

a

b

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

Retrogression: Dense marsh that was completely washed away by a flash flood occurring down the canyon.

Attribute Early Stages of Succession Late Stages of Succession

Plant Biomass Small Large

Plant Longevity Short Long

Seed Dispersal Characteristics

of Dominant PlantsWell dispersed Poorly dispersed

Plant Morphology and

PhysiologySimple Complex

Photosynthetic Efficiency of

Dominant Plants at Low LightLow High

Rate of Soil Nutrient Resource

Consumption by PlantsFast Slow

Comparison of plant, community, and ecosystem

characteristics between early and late stages of succession

Role of Decomposers in

Cycling Nutrients to PlantsMinor Great

Biogeochemical Cycling Open and Rapid Closed and Slow

Community Site

Characteristics Extreme Moderate (Mesic)

Ecosystem Stability Low High

Plant Species Diversity Low High

Life-History Type r K

Seed Longevity Long Short

Comparison of plant, community, and ecosystem

characteristics between early and late stages of succession

Plant Leaf Canopy Structure Multilayered Monolayer

Site of Nutrient Storage Litter and SoilLiving Biomass and

Litter

Species diversity- variety of species within a regionIncludes both species richness (# of species) and species evenness (how close in numbers each species in an environment are) in a community.

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.

Species # found Pi ln(Pi) Pi ln(Pi)

1 84 0.3281 -1.1144 -.03656

2 4 0.0156 -4.1589 -0.0650

3 91 0.3555 -1.0343 -0.3677

4 34 0.1328 -2.0188 -0.2681

5 43 0.1680 -1.7840 -0.2997

Total 256 1.0000 -1.3661


1 40

2 40

3 40

4 40

5 40

Total

Community #1


1 1

2 1

3 196

4 1

5 1

Total

Community #2

Documents

Ecological Succession (5)