ecological succession
whats ecological succession
a natural progression in species composition & community structure over time
through ecological succession, ecosystems undergo a series of transformation
whats a notable example of ecological succession
ecological succession occurred after the eruption of Mount St. Helens
volcanic eruption devastated a vast area, leaving behind a barren landscape of ash & debris
in the following years, nature began to reclaim
the soil was now volcanic soil, which is nutrient rich
allowed pioneer species to return & coniferous forests reclaimed the land
what’re some factors that affect ecological succession (ecological succession occurs as a response to these factors)
natural disturbances
human activities
changes in environmental conditions
natural disturbance as a factor that initiates ecological succession
disrupt existing vegetation & community composition, providing opportunities for new communities to populate an area
ex - after a forest fire, pioneer species that’re adapted to open, sunlit areas will be the first to grow. as time progresses, other specie that’re better suited to the new environmental conditions will replace the pioneers, resulting in a change in the community composition
human activities as a factor that initiates ecological succession
human activities disturb natural ecosystems, and initiate a series of changes in species composition
ex: if a forest is cleared for agriculture, the lack of trees allows sunlight to reach forest floor, allowing the growth of grasses
eventually, shrubs & trees may colonise the area, leading to a different community structure compared to the original forest
changes in environmental conditions as a factor that initiates ecological succession
environmental changes (both natural & human-induced) can drive succession
these changes can include changes in temperature, precipitation patterns or soil fertility, or introduction of new species
as environment undergoes changes, different species may become better adapted to new conditions & outcompete or replace previous inhabitants
whats primary succession
the process of ecological succession that occurs in a newly formed or exposed area with no pre-existing soil
the first plants that grow are pioneer species
they can survive with limited nutrients
break down rock or organic matter to construct a rudimentary soil layer
so they’re important for soil formation, which allows for the support of more advanced plant species
then herbaceous plants form
they hv deep root systems which enhance nutrient availability & stabilise the soil
provide habitats for small animals
presence of herbaceous plants = environment is favourable for shrubs & small trees
these plants hv deeper root systems & compete for light & resources
enrich the soil through their leaf filter, promote the accumulation of organic matter & provide shelter for a range of organisms
construction of forest canopy = shade & shelter, increases accessibility of light & moisture, and limits the growth of understory plants
then successional climax
eventually, the ecosystem reaches a state of relative stability, known as successional climax
stage is characterised by a mature & diverse community of plants & animals that’re well adapted to the prevailing environmental conditions
what is secondary succession
process of ecological change that occurs in an area that’s been colonised by living organisms, but has experienced a disturbance that disrupts the existing community & returns it to any previous stage of development
basically occurs in an environment that was previously an ecosystem, but underwent a disruption
what’re the stages of secondary succession
0-2 years - after a disturbance, pioneer species quickly colonise the area. they are generally fast growing & have high dispersal abilities, enabling them to rapidly occupy the space
3-4 years - other species that were present before the disruption, begin to colonise the area. eventually, the diversity of plant species increases, leading to a complex community
5-150 years - development in community = interaction between different plant species, which compete for resources
competition leads to changes in species composition (some species become dominant, others become less abundant or locally extinct)
150+ years - reaches a successional climax, where community is relatively stable & there’s a balance between species composition & environmental conditions
climax community depends on the specific ecosystem
what is cyclic succession
a type of ecological succession where the community undergoes repeated cycles of change in response to periodic natural events
at each stage, the community will hv its own characteristic plant & animal population composition
the stages occur in a predictable sequence & eventually returns to the original starting point
one example is coastal chaparral ecosystems
these ecosystems are characterised by dense strands of shrubs & small trees, that’re adapted to periodic fires
after a fire, the first plants to grow in the burned area are annual grasses
these plants grow rapidly & produce seeds, which’re dispersed by the wind
seeds germinate in the following season & area is covered in a growth of grasses
eventually, these grasses are replaced by shrubs & small trees
these plants are even more fire-resistant than the grasses, & can survive if the area is burned again
but if the area is burned too frequently, then the shrubs & trees will die
whats arrested succession
a disruption in the normal progression of ecological succession
occurs when development of a community is halted or slowed down due to external factors, such as recurrent disturbances, changes in environmental conditions
can also occur when the environmental conditions become unfavourable for the survival & growth of certain species
can be due to soil degradation, or pollution or invasive species
in which stage of ecological succession can arrested succession occur
in the early stages of succession
can result in the establishment of a community that remains at an early stage of succession, meaning it doesn’t develop & reach climax community
ex: frequent fires in grasslands prevent growth of woody plants
whats an example of arrested succession
overgrazing by farm livestock in grasslands
overgrazing by livestock removes the vegetation cover & reduces the number of plant species that’re present
this leads to a shift in the composition of the plant community
selective feeding habits of the livestock also means that certain plants will dominate, as they aren’t consumed
so the grassland may be experience arrested succession - cannot progress into the next stage
the arrested succession reduces the biodiversity & the ecosystem’s resilience
reduced plant cover also contributes to soil erosion & degradation of grassland ecosystem