Not all species wait for the right conditions to grow. Some, impatient, settle in uninhabitable places until that moment, and start the process of bringing life into being or regenerating it. These species are called pioneer species.
But to get to know them better, we have to understand the natural process they are a part of: ecological succession.
Ecosystems seek dynamic balance at all times. When habitats change after a fire, deforestation or flood, among others, gradual changes occur in the species that inhabit them.
The sequence of living being communities that replace one another over time in a given habitat is called ecological succession. This is a collaborative process, started by simple, almost invisible forms of life, the true foundations of the ecosystem that will develop.
Ecological succession includes three distinct phases: pioneer community, intermediate community and climax community.
It corresponds to the first species, namely the pioneer species, that settle in an inhospitable environment. We are talking organisms that resist harsh conditions, capable of surviving and thriving in poor soils where organic matter is scarce, and temperatures are extreme.
A classic example of these organisms is lichens, whose combination of fungus and algae enables them to break down rocks and thus create the first layers of soil, paving the way to the establishment and growth of moss and grass.
These species are indispensable to improve the environment they live in with organic matter, thus enabling the development of gradually more complex and diverse communities.
As environmental conditions improve, larger shrubs and plants appear, followed by herbivorous animals and, later, predators. Over time, biodiversity and ecological relationships become more complex, and ecosystem balance is consolidated.
It’s the ecological maturity stage. An ecosystem, now rich in diversity and stability, where energy flows, and life cycles strike a balance.
In addition to its three stages, there are also two types of ecological succession: primary and secondary.
Primary succession – develops in areas never before occupied by living communities, such as solidified lava surfaces, dunes or bare rocks.
Secondary succession – occurs in places where life once existed but which have suffered disturbances such as fires or deforestation.
Secondary succession tends to be more frequent and also to develop faster, as the soil and part of the biota may have survived the disturbance.
As mentioned above, pioneer species start the colonisation of an inhospitable region in primary or secondary succession, where most living beings could never survive. These species stand out for their resistance to abiotic factors and their ability to transform the environment, thus setting the stage for the arrival of new forms of life.
The role of these species goes well beyond “getting there first”. When they settle, they modify the environment, fixing nutrients, creating shadow, retaining moisture and reducing erosion. They thus pave the way for the settlement of more demanding species, which would not survive otherwise in such hostile environments.
Although certain microorganisms can also be acknowledged as pioneer species, the term is often associated with plants. As such, we shall focus mainly on this group of living beings.
Pioneer plants are not necessarily small or fragile. Despite the existence of many species with such morphological characteristics, some shrubs or even trees also perform this function.
What defines them, therefore, is not their size, but rather their ability to adapt and resist inhospitable environments. For them to thrive in such conditions, they share a number of adaptive strategies, including:
– Growth speed, allowing them to benefit from very short windows of opportunity;
– Accelerated and effective reproduction, with abundant seed production;
– Efficient dispersion, often through the action of the wind;
– High tolerance to hostile conditions.
These characteristics are also common to certain invasive species, making them, at the same time, pioneer species in their habitats of origin.
Dune systems – A primary succession
Dunes stand out for both their instability and salinity. Pioneer species face harsh wind conditions and nutrient shortages in this environment. Their main mission – should they choose to accept it – is to stabilise sands and create conditions for plant succession.
European Marram Grass (Ammophila arenaria), with its deep roots and flexible stems, is skilled in establishing primary dunes and creating microhabitats for new species, given its ability to form tufts that will serve as the basis for future species.
The sea cottonweed (Otanthus maritimus), the sea thrift (Armeria maritima) or the Portuguese crowberry (Corema album), on the other hand, stabilise inland sands and pave the way to more biodiversity.
Post-fire areas – A secondary succession
After a fire, the soil is exposed and vulnerable to erosion. Pioneer species, such as the three main Portuguese forest species (pine, cork oak and holm oak), are fundamental for the quick regeneration of the soil and restoration of the ecosystem.
The maritime pine (Pinus pinaster) “uses” heat to facilitate the release of its seeds, which, when they germinate and grow, provide shade for new species. The cork oak (Quercus suber), thanks to its thick cork, resists fire and helps recover degraded soil.
Plants such as rosemary (Lavandula stoechas) and prickly broom (Pterospartum tridentatum) tend to emerge after a fire, given their capacity to withstand soil drought and high temperature, thus quickly occupying the burned and unoccupied land.
Certain herbs, such as underground clover (Trifolium subterraneum), also help cover exposed soil, preventing erosion and improving its fertility.
The ecological value of Pioneer Species
Pioneer species are ecological transformation agents. By stabilising the soil, accumulating organic matter, creating shade and retaining water, they prepare the ground for the succession of life and for species that require more demanding conditions.
Its deep and/or branched roots increase soil cohesion and, when they decompose, improve it with nutrients that dramatically improve its fertility. In addition, they help moderate extreme temperatures and increase environmental humidity, making the habitat more hospitable.
And as they attract insects, birds and mammals, they also promote seed dispersal and pollination, accelerating the natural regeneration process.
In short, pioneer species are the foundations of ecological restoration, the “first to arrive” and those responsible for ensuring the appearance or return of life.
