Ecological Succession
The composition of all ecosystems keeps on changing with change in their environment. These changes finally lead to the climax community.
Climax community: It is the community which is in equilibrium with its environment. Gradual and fairly predictable change in the species’ composition of a given area is called ecological succession.
Sere(s): It is the sequence of communities that successively change in a given environment. The transitional communities are called seral stages or seral communities.
Succession happens in areas where no life forms ever existed as in bare rocks, cool lava, etc. (primary succession), or in areas which have lost all life forms due to destruction and floods (secondary succession).
Primary succession takes hundreds to thousands of years as developing soil on bare rocks is a slow process. Secondary succession is faster than primary succession since the nature does not have to start from scratch.
During succession, any disturbances (natural/man-made) can convert a particular seral stage to an earlier one.
Hydrarch succession: It takes place in wet areas and converts hydric conditions to mesic.
Xerarch succession: It takes place in dry areas and converts xeric conditions to mesic. Xerosere is a plant succession which is limited by water availability.
Pioneer species: These are the species that first invade a bare area. On land, these could be lichens that secrete enzymes to dissolve the rock surfaces for soil formation while in water, pioneer species could be phytoplanktons.
The ultimate result of all successions is a climax community, a mesic.
Hydrarch succession/Stages in Hydrosere
a. Phytoplankton stage
$\displaystyle \small \bullet$ Phytoplanktons are pioneer community in the Hydrosere.
$\displaystyle \small \bullet$ Algal spores are brought into water in initial stages of succession.
$\displaystyle \small \bullet$ They germinate, multiply and fix light energy.
$\displaystyle \small \bullet$ Various zooplanktons also appear.
$\displaystyle \small \bullet$ Death of planktons add nutrients to the soil and water.
b. Rooted submerged stage
$\displaystyle \small \bullet$ Addition of nutrients to the soil and water by death of planktons form a soft muddy bottom.
$\displaystyle \small \bullet$ The water depth reduces and promotes growth of rooted submerged hydrophytes.
$\displaystyle \small \bullet$ Ex: Hydrilla, Vallisneria
c. Rooted floating stage
$\displaystyle \small \bullet$ Depth of water reduces by addition of more nutrients to soil by death and decomposition of rooted plants.
$\displaystyle \small \bullet$ Rooted floating hydrophytes appear and cover complete water surface.
$\displaystyle \small \bullet$ Light penetration into water is inhibited and results in disappearance of submerged plants.
$\displaystyle \small \bullet$ Ex: Nymphaea, Trapa, Pistia
d. Reed-swamp stage
$\displaystyle \small \bullet$ The water level is much reduced and level of soil and silt increases.
$\displaystyle \small \bullet$ Soil become more fertile and rooted floating plants are replaced by plants which can survive both in aquatic and terrestrial conditions.
$\displaystyle \small \bullet$ Plants in this stage form very dense vegetation preventing light penetration to the lower portion.
$\displaystyle \small \bullet$ Ex: Typha, Polygonum
e. Sedge meadow stage
$\displaystyle \small \bullet$ Water level reduces and marshy soil is formed
$\displaystyle \small \bullet$ Grasses and cyperous plants start growing forming a mat-like vegetation over the top of soil
$\displaystyle \small \bullet$ They remove large amount of water and reduce moisture
$\displaystyle \small \bullet$ The soil is exposed to air and leads to formation of terrestrial soil.
$\displaystyle \small \bullet$ Ex: Cyperus
f. Woodland stage
$\displaystyle \small \bullet$ Shrubs and medium trees will appear.
$\displaystyle \small \bullet$ Shrubs and herbs predominates the area
$\displaystyle \small \bullet$ Shedding of leaves results in accumulation of humus
$\displaystyle \small \bullet$ Ex: Acacia, Terminalia
g. Forest stage
$\displaystyle \small \bullet$ Forest stage is climax community in hydrarch succession.
$\displaystyle \small \bullet$ Shrubs are invaded by large trees and their canopy cover the entire area.
$\displaystyle \small \bullet$ The climate of the region determines the type of forest
$\displaystyle \small \bullet$ Forest stage is the most stable stage in the hydrarch succession.
Xerarch succession/ Stages of Xerosere
a. Crustose Lichen Stage
$\displaystyle \small \bullet$ On bare rock the crustose lichens adhere and absorb moisture from atmosphere.
$\displaystyle \small \bullet$ They produce acids which corrode the rock and help in the formation of soil.
$\displaystyle \small \bullet$ When these lichens die their thalli decomposes into humus, which promotes growth of foliose and fruticose type of lichens.
b. Foliose and Fruticose Lichen Stage
$\displaystyle \small \bullet$ They can absorb and retain more water and accumulate more dust particles.
$\displaystyle \small \bullet$ They build substratum and improve soil moisture contents.
c. Moss stage
$\displaystyle \small \bullet$ Rhizoids of mosses penetrate into soil and crevices of rocks leads to weathering of rocks.
$\displaystyle \small \bullet$ After death they add nutrients to the soil.
d. Herb Stage
$\displaystyle \small \bullet$ Herbaceous weeds mostly annuals, invade the rock.
$\displaystyle \small \bullet$ Their roots penetrate deep down and increase the weathering process.
$\displaystyle \small \bullet$ Shading of soil decreases the evaporation.
$\displaystyle \small \bullet$ Many perennial herbs and shrubs and grasses starts to inhibit.
e. Shrub stage
$\displaystyle \small \bullet$ Dense scrub growth shades the soil and enhances the moisture content of the soil.
$\displaystyle \small \bullet$ The environment becomes mesic or moderately moist.
f. Tree stage
$\displaystyle \small \bullet$ Tree species are colonised.
$\displaystyle \small \bullet$ The kind of tree species inhabiting the area depends upon nature of soil.
$\displaystyle \small \bullet$ Mosses and ferns grow and population grows abundantly.
g. Forest Stage
$\displaystyle \small \bullet$ The stable forest type depends upon climatic conditions.
Nutrient Cycling
$\displaystyle \small \bullet$ The amount of nutrients present in the soil at a given time is known as the standing state.
$\displaystyle \small \bullet$ Nutrients are never lost from the ecosystem. They are only recycled from one state to another.
$\displaystyle \small \bullet$ The movement of nutrients through the various components of the ecosystem is called nutrient cycling or biogeochemical cycles.
$\displaystyle \small \bullet$ Types of nutrient cycling
Gaseous: Reservoir for these types of cycles exist in the atmosphere.
Sedimentary: Reservoir for these types of cycles exist in the earth’s crust.
Carbon Cycle
$\displaystyle \small \bullet$ About 49% of the dry weight of living organisms is made up of carbon.
$\displaystyle \small \bullet$ The ocean reserves and fossil fuels regulate the amount of $\displaystyle \small CO_{2}$ in the atmosphere.
$\displaystyle \small \bullet$ Plants absorb $\displaystyle \small CO_{2}$ from the atmosphere for photosynthesis, of which a certain amount is released back through respiratory activities.
$\displaystyle \small \bullet$ A major amount of $\displaystyle \small CO_{2}$ is contributed by the decomposers who contribute to the $\displaystyle \small CO_{2}$ pool by processing dead and decaying matter.
$\displaystyle \small \bullet$ The amount of $\displaystyle \small CO_{2}$ in the atmosphere has been increased considerably by human activities such as burning of fossil fuels, deforestation.
Phosphorus Cycle
$\displaystyle \small \bullet$ Phosphorus is an important constituent of cell membranes, nucleic acids, and cellular energy transfer systems.
$\displaystyle \small \bullet$ Rocks contain phosphorus in the form of phosphate.
$\displaystyle \small \bullet$ When rocks are weathered, some of the phosphate gets dissolved in the soil solution and is absorbed by plants.
$\displaystyle \small \bullet$ The consumers get their phosphorus from the plants.
$\displaystyle \small \bullet$ Phosphorus returns back to the soil by the action of phosphate-solubilising bacteria on dead organisms.
Ecosystem Services
$\displaystyle \small \bullet$ The products of ecosystem processes are called ecosystem services.
$\displaystyle \small \bullet$ It includes:
$\displaystyle \small \circ$ The healthy forest ecosystem, purify air and water
$\displaystyle \small \circ$ Mitigates floods and droughts
$\displaystyle \small \circ$ Cycle nutrients
$\displaystyle \small \circ$ Generate fertile soil
$\displaystyle \small \circ$ Provide wildlife habitat
$\displaystyle \small \circ$ Maintain biodiversity etc.
$\displaystyle \small \bullet$ Robert Constanza and his colleagues put an average price tag of US ＄33 trillion a year on these fundamental ecosystems services which are taken granted because they are free although its value is twice the total global gross national product (GNP).
$\displaystyle \small \bullet$ Out of total cost the soil formation constitutes for about 50 percent.
$\displaystyle \small \bullet$ Contribution for recreation and nutrient cycling is less than 10 percent
$\displaystyle \small \bullet$ The cost of climate regulation and habitat for wildlife are about 6 percent each.
The composition of all ecosystems keeps on changing with change in their environment. These changes finally lead to the climax community.
Climax community: It is the community which is in equilibrium with its environment. Gradual and fairly predictable change in the species’ composition of a given area is called ecological succession.
Sere(s): It is the sequence of communities that successively change in a given environment. The transitional communities are called seral stages or seral communities.
Succession happens in areas where no life forms ever existed as in bare rocks, cool lava, etc. (primary succession), or in areas which have lost all life forms due to destruction and floods (secondary succession).
Primary succession takes hundreds to thousands of years as developing soil on bare rocks is a slow process. Secondary succession is faster than primary succession since the nature does not have to start from scratch.
During succession, any disturbances (natural/man-made) can convert a particular seral stage to an earlier one.
Hydrarch succession: It takes place in wet areas and converts hydric conditions to mesic.
Xerarch succession: It takes place in dry areas and converts xeric conditions to mesic. Xerosere is a plant succession which is limited by water availability.
Pioneer species: These are the species that first invade a bare area. On land, these could be lichens that secrete enzymes to dissolve the rock surfaces for soil formation while in water, pioneer species could be phytoplanktons.
The ultimate result of all successions is a climax community, a mesic.
Hydrarch succession/Stages in Hydrosere
a. Phytoplankton stage
$\displaystyle \small \bullet$ Phytoplanktons are pioneer community in the Hydrosere.
$\displaystyle \small \bullet$ Algal spores are brought into water in initial stages of succession.
$\displaystyle \small \bullet$ They germinate, multiply and fix light energy.
$\displaystyle \small \bullet$ Various zooplanktons also appear.
$\displaystyle \small \bullet$ Death of planktons add nutrients to the soil and water.
b. Rooted submerged stage
$\displaystyle \small \bullet$ Addition of nutrients to the soil and water by death of planktons form a soft muddy bottom.
$\displaystyle \small \bullet$ The water depth reduces and promotes growth of rooted submerged hydrophytes.
$\displaystyle \small \bullet$ Ex: Hydrilla, Vallisneria
c. Rooted floating stage
$\displaystyle \small \bullet$ Depth of water reduces by addition of more nutrients to soil by death and decomposition of rooted plants.
$\displaystyle \small \bullet$ Rooted floating hydrophytes appear and cover complete water surface.
$\displaystyle \small \bullet$ Light penetration into water is inhibited and results in disappearance of submerged plants.
$\displaystyle \small \bullet$ Ex: Nymphaea, Trapa, Pistia
d. Reed-swamp stage
$\displaystyle \small \bullet$ The water level is much reduced and level of soil and silt increases.
$\displaystyle \small \bullet$ Soil become more fertile and rooted floating plants are replaced by plants which can survive both in aquatic and terrestrial conditions.
$\displaystyle \small \bullet$ Plants in this stage form very dense vegetation preventing light penetration to the lower portion.
$\displaystyle \small \bullet$ Ex: Typha, Polygonum
e. Sedge meadow stage
$\displaystyle \small \bullet$ Water level reduces and marshy soil is formed
$\displaystyle \small \bullet$ Grasses and cyperous plants start growing forming a mat-like vegetation over the top of soil
$\displaystyle \small \bullet$ They remove large amount of water and reduce moisture
$\displaystyle \small \bullet$ The soil is exposed to air and leads to formation of terrestrial soil.
$\displaystyle \small \bullet$ Ex: Cyperus
f. Woodland stage
$\displaystyle \small \bullet$ Shrubs and medium trees will appear.
$\displaystyle \small \bullet$ Shrubs and herbs predominates the area
$\displaystyle \small \bullet$ Shedding of leaves results in accumulation of humus
$\displaystyle \small \bullet$ Ex: Acacia, Terminalia
g. Forest stage
$\displaystyle \small \bullet$ Forest stage is climax community in hydrarch succession.
$\displaystyle \small \bullet$ Shrubs are invaded by large trees and their canopy cover the entire area.
$\displaystyle \small \bullet$ The climate of the region determines the type of forest
$\displaystyle \small \bullet$ Forest stage is the most stable stage in the hydrarch succession.
Xerarch succession/ Stages of Xerosere
a. Crustose Lichen Stage
$\displaystyle \small \bullet$ On bare rock the crustose lichens adhere and absorb moisture from atmosphere.
$\displaystyle \small \bullet$ They produce acids which corrode the rock and help in the formation of soil.
$\displaystyle \small \bullet$ When these lichens die their thalli decomposes into humus, which promotes growth of foliose and fruticose type of lichens.
b. Foliose and Fruticose Lichen Stage
$\displaystyle \small \bullet$ They can absorb and retain more water and accumulate more dust particles.
$\displaystyle \small \bullet$ They build substratum and improve soil moisture contents.
c. Moss stage
$\displaystyle \small \bullet$ Rhizoids of mosses penetrate into soil and crevices of rocks leads to weathering of rocks.
$\displaystyle \small \bullet$ After death they add nutrients to the soil.
d. Herb Stage
$\displaystyle \small \bullet$ Herbaceous weeds mostly annuals, invade the rock.
$\displaystyle \small \bullet$ Their roots penetrate deep down and increase the weathering process.
$\displaystyle \small \bullet$ Shading of soil decreases the evaporation.
$\displaystyle \small \bullet$ Many perennial herbs and shrubs and grasses starts to inhibit.
e. Shrub stage
$\displaystyle \small \bullet$ Dense scrub growth shades the soil and enhances the moisture content of the soil.
$\displaystyle \small \bullet$ The environment becomes mesic or moderately moist.
f. Tree stage
$\displaystyle \small \bullet$ Tree species are colonised.
$\displaystyle \small \bullet$ The kind of tree species inhabiting the area depends upon nature of soil.
$\displaystyle \small \bullet$ Mosses and ferns grow and population grows abundantly.
g. Forest Stage
$\displaystyle \small \bullet$ The stable forest type depends upon climatic conditions.
Nutrient Cycling
$\displaystyle \small \bullet$ The amount of nutrients present in the soil at a given time is known as the standing state.
$\displaystyle \small \bullet$ Nutrients are never lost from the ecosystem. They are only recycled from one state to another.
$\displaystyle \small \bullet$ The movement of nutrients through the various components of the ecosystem is called nutrient cycling or biogeochemical cycles.
$\displaystyle \small \bullet$ Types of nutrient cycling
Gaseous: Reservoir for these types of cycles exist in the atmosphere.
Sedimentary: Reservoir for these types of cycles exist in the earth’s crust.
Carbon Cycle
$\displaystyle \small \bullet$ About 49% of the dry weight of living organisms is made up of carbon.
$\displaystyle \small \bullet$ The ocean reserves and fossil fuels regulate the amount of $\displaystyle \small CO_{2}$ in the atmosphere.
$\displaystyle \small \bullet$ Plants absorb $\displaystyle \small CO_{2}$ from the atmosphere for photosynthesis, of which a certain amount is released back through respiratory activities.
$\displaystyle \small \bullet$ A major amount of $\displaystyle \small CO_{2}$ is contributed by the decomposers who contribute to the $\displaystyle \small CO_{2}$ pool by processing dead and decaying matter.
$\displaystyle \small \bullet$ The amount of $\displaystyle \small CO_{2}$ in the atmosphere has been increased considerably by human activities such as burning of fossil fuels, deforestation.
Phosphorus Cycle
$\displaystyle \small \bullet$ Phosphorus is an important constituent of cell membranes, nucleic acids, and cellular energy transfer systems.
$\displaystyle \small \bullet$ Rocks contain phosphorus in the form of phosphate.
$\displaystyle \small \bullet$ When rocks are weathered, some of the phosphate gets dissolved in the soil solution and is absorbed by plants.
$\displaystyle \small \bullet$ The consumers get their phosphorus from the plants.
$\displaystyle \small \bullet$ Phosphorus returns back to the soil by the action of phosphate-solubilising bacteria on dead organisms.
Ecosystem Services
$\displaystyle \small \bullet$ The products of ecosystem processes are called ecosystem services.
$\displaystyle \small \bullet$ It includes:
$\displaystyle \small \circ$ The healthy forest ecosystem, purify air and water
$\displaystyle \small \circ$ Mitigates floods and droughts
$\displaystyle \small \circ$ Cycle nutrients
$\displaystyle \small \circ$ Generate fertile soil
$\displaystyle \small \circ$ Provide wildlife habitat
$\displaystyle \small \circ$ Maintain biodiversity etc.
$\displaystyle \small \bullet$ Robert Constanza and his colleagues put an average price tag of US ＄33 trillion a year on these fundamental ecosystems services which are taken granted because they are free although its value is twice the total global gross national product (GNP).
$\displaystyle \small \bullet$ Out of total cost the soil formation constitutes for about 50 percent.
$\displaystyle \small \bullet$ Contribution for recreation and nutrient cycling is less than 10 percent
$\displaystyle \small \bullet$ The cost of climate regulation and habitat for wildlife are about 6 percent each.
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