school energy&environment

The ecological succession

The history of an ecosystem from birth to maturity is called ecological succession. The ecological succession is essentially an uninterrupted sequence of changes in the biotic and abiotic components of an area, which leads to a stable ecosystem (the one that is defined as the “climax”), in which components are balanced, i.e. no one prevails over the others, making then disappear. The sequence of communities that replace each other with time within the ecosystem is called “sere” and the different transition stages are called “seral stages”. It is the populations themselves that sometimes alter the environment in which they live and cause themselves to disappear in favour of other species of organisms. Examples of this type of evolutionary process can be easily found in nature, where the formation of any new environment (due to a fire in a wood, to the detour of a river, a deserted farmland, etc.) initially causes the so-called “pioneer” organisms to spread, i.e. organisms that can grow despite the harsh conditions of the area (few nutrients). The living activity of these first organisms alters the environment, creating new conditions that are favourable to other, more demanding, organisms. The latter develop, often causing the pioneer organisms to disappear.
To understand it better
For instance, moss, lichens and grass are often pioneer species on solidified lava or rocky substrata. These organisms can actually break up the rocky substrata to take the minerals they need to survive. In addition, once dead, they provide that organic matter that decomposes into the “soil”, that will be used by the vegetal species that will settle there at a later stage to feed on and grow. An example of an ecological succession is what happens on sandy dunes: the first vegetal species that settle there are very adaptable and can use the very few nutrients available. These first pioneer species fix the sand through their root apparatuses, making the dunes more stable and, once dead, enrich the soil with organic matter. This creates a richer environment, which is fitter to sustain the life of the more demanding organisms that slowly replace the pioneer ones, the composition of the species becomes more and more diversified and more and more complex natural feeding and competition processes develop.