Ecological Succession (5)
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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
Trend of succession in Lithosere
Rhizocarpon
Rinodina
Lecanora
Seralcommunity
2
Foliose lichens stage
e.gParmellia,Dermato-
carpon
Parmellia
Dermatocarpon
Seralcommunity
3
Moss stagee.g
Polytrichum,Tortula,Grimmia
Trend of succession in Lithosere
Polytrichum
Tortula
Grimmia
Seralcommunity
4
Herbs stagee.g
Eleusine,Aristida
Eleusine
Aristida
Seral community
5
Shrub stagee.g
Rhus,Physocarpus
Trend of succession in Lithosere
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
Species # found Pi ln(Pi) Pi ln(Pi)
1 40
2 40
3 40
4 40
5 40
Total
Community #1
Species # found Pi ln(Pi) Pi ln(Pi)
1 1
2 1
3 196
4 1
5 1
Total
Community #2