Have you ever thought about how volcanic areas like Hawaii are teeming with life? Or how long does it take for a forest to recover after a big fire? Or what would happen if we stopped taking care of the crops? Like living things, ecological communities also grow, change and develop. These changes are due to a natural process called ecological succession. If you want to learn more about it, keep reading, because then, in Green Ecologist, we are going to talk to you about the ecological succession, its definition, stages and examples.
What is ecological succession
The ecological succession is a natural process in which a sequence of changes in the ecological community that are observable in time and space. It is due to colonizations and local extinctions of species.
During ecological succession, the level of complexity of ecosystems evolves. The first stages represent communities with simple food chains and little biodiversity, but that eventually disappear transforming into complex ecosystems where there are more interactions and a greater richness and diversity of living beings.
The ecosystem formed at the end of the succession is called the climax or climax community. This stage represents the maturity of the community, that is, when it remains stable and well developed for many years. In relation to these two concepts, climax and maturity, some controversy has arisen since there are immature communities (in primary stages) in climax, that is, without changes, such as the vegetation of the dunes or the deserts.
Depending on the starting point of the ecological community, ecologists differentiate two types of ecological succession:
- Primary succession.
- Secondary succession.
Primary succession
The primary succession is one that develops in a virgin biotype, that is, an area lacking a pre-existing community, as occurs in the dunes, new volcanic islands, retreat of glaciers, etc. It is rare.
The process begins with the formation of the soil, understood as the biologically active layer of the earth's surface that contains roots, microorganisms, invertebrate communities and nutrients. Normally, primary succession occurs in areas where the bedrock is exposed to the surface, but cannot be directly colonized. First it undergoes the action of erosion and weathering, a set of physical and chemical processes that fragment, degrade and dissolve the rock. In this way begins the colonization of the soil by lichens and mosses, as they can grow in shallow substrates and little amount of organic matter. The biological action of these organisms contributes to the degradation of the rock and the release of nutrients, they also provide organic matter when they die. Thus, the arrival of other species is favored, such as annual plants, herbs that have a year of life, and later the perennial annuals that last longer. If the community continues to evolve, the seeds of shrub species could germinate forming thickets and finally trees would grow giving rise to forests.
The same happens with animals, then, the first to settle will be insects and other invertebrates and small reptiles that can hide between rocks and feed on invertebrates. Small birds could also arrive whose diet is based on seeds, or even invertebrates and reptiles. As the plant community becomes more complex, small mammals appear, such as rodents and other birds. Finally, large mammals and other predators would reach the community, as the ecosystem will provide them with enough food and a den.
Secondary succession
The secondary sequence appears when there has been a regressive succession in the ecosystem. This means that it has destroyed the ecosystem that existed and, therefore, the ecological succession process must be started. This ecosystem has been eliminated by fires, floods, diseases, logging, crops, etc.
The secondary succession It occurs in places whose characteristics depend on the previous communities or the situation prior to the disturbance. The residues or legacies are those organisms, sometimes alive, that come from the previous community. The greater the amount of waste, the greater the speed of succession or recovery.
The presence and abundance of residues buffer the difference between the conditions before and after the disturbance. They work like source of new species, increase the heterogeneity of the environment and also decrease the loss of soil and nutrients.
Mechanisms of ecological succession
Ecologists have studied for a long time how ecological succession occurs and they have found a series of mechanisms that favor the succession of species in communities.
One of these mechanisms is facilitation, whereby species with high colonization capacity favor the arrival and survival of species that appear in the later stages of succession. It is especially important in primary succession. If stress increases in the physical environment, facilitation increases. Although, if the environmental conditions become extreme, it is necessary the competition Faced with facilitation, that is, species become selfish and fight for available resources to survive.
Ecological succession occurs thanks to pioneer species, those that reach the inhospitable places first. They have a great capacity for colonization, but a low capacity to compete when resources are scarce. Some pioneer species are the lichens and mosses mentioned before.
In addition, pioneer plant species have tissues with high concentrations of nitrogen and phosphorus, making them the preferred food of herbivores. In this way the ecological succession is accelerated, as these plants will suffer a high mortality and will be replaced by plants of later stages.
Some examples of ecological succession
These are some clear examples of ecological succession.
The dunes of Lake Michigan
After the end of the last ice age, the glaciers that covered the Great Lakes gradually retreated, revealing large dunes. These dunes are large formations of sand that accumulate on the shores of lakes.
Over the years, plant species have been succeeding. First, drought-tolerant species were established that also allowed the dunes to be fixed, preventing the wind from eroding and transporting them. After a score of years, grasses appeared, shrubs such as the sands cherry tree and trees such as willows and poplars, which continued to stabilize the substrate. After another 50 or 100 years, the pine forests began to grow rapidly, finally being replaced by oak groves, and could be maintained for millennia.
Currently, this sequence of plants can be observed, since the lakes have a lower level and the process continues over time.
The clogging of a lake
An oligotrophic lake (with little amount of nutrients) begins to receive nutrients and sediment by the streams and rivers that flow into it. Thanks to the increase in nutrients, the algae begin to proliferate. If the nutrients increase, floating aquatic plants appear and others that begin to take root. The death and decomposition of the organisms cause remains to accumulate at the bottom of the lake and the peat is created, at the same time that it loses depth. In this way the lake begins to transform into a swamp. The soil becomes acidic and typical plants from the banks such as reeds begin to proliferate. Terrestrial animals such as earthworms and some insects can appear. Trees that tolerate high humidity, such as alders or birches, grow on the bogs formed. Over time they will be replaced by other trees that will form a more mature forest. The fauna of the place also evolves, amphibians disappearing due to the lack of humidity and birds and typical mammals of the forests appear. In the case of a lot of peat, a lot of moss would grow that would acidify the soils so much that the trees would die.
This process has originated the current bogs of the planet after the glaciations and could happen within thousands of years in lakes such as Geneva or Leman, the largest lake in Western Europe and located in the Alps, and in Lake Constance, which borders with Germany, Switzerland and Austria.
If you want to read more articles similar to Ecological succession: definition, stages and examples, we recommend that you enter our Ecosystems category.
