The syntropic or successional approach to agroforestry outlines a way of interacting with ecosystems which marks a step in the right direction: the ecological (not social/cultural) indigenisation of humans and agriculture. If we put aside cultural factors, what is the biological and ecological role of humans within the ecosystems they are part of?
The uniqueness of Syntropic agriculture lies in this ecological perspective, as opposed to the utilitarian and culturally anthropocentric one which is typical of modern agriculture. That such an approach should strike us as revolutionary gives us a measure of our deep separation not only from our ecosystemic role, but also from the integrated relationship that indigenous cultures have with the land.
The four parts of ecological succession . . .
1. Colonisation
In the wild, a degraded soil gets quickly colonised by a diverse series of plants, animals and microorganisms. Initially, microbes are the only life forms, and they start to make the minerals contained in rocks soluble; they also increase the availability of oxygen and CO2, thus preparing the ground for plants.
The first plants are herbaceous (i.e., without woody tissues), these include ephemeral, annuals, biennials and finally perennials. They are able to adapt to extreme conditions, such as low fertility and water availability. As pioneers, these plants fulfil their role by accumulating minerals from deep down the soil profile; they partner with bacteria including nitrogen-fixing ones; they add organic matter to the soil both by root exudates and with their tissue when they die for the winter or at the end of their life cycle. This phase can be named “colonisation”, and (in syntropic jargon) it represents the “placenta” of the ecosystem.
2. Accumulation
With their work, herbaceous plants prepare the soil for the arrival of more complex species, such as pioneer shrubs and trees. These usually arrive into the system via the wind. Shrubs and trees carry on accumulating and cycling minerals and organic matter on the surface of the soil, adding in the lignin contained in their tissues — a compound that decomposes a lot more slowly than cellulose and induces humification (the creation of humus, or stable organic matter).
The resulting organic material creates an ideal food and habitat for fungi; these, in turn, respond by intensifying their mycorrhizal network through which plants communicate and trade nutrients.
Shrubs and trees are also more effective at improving soil, because of their deeper roots and their ability to provide shade during the hotter months, thus creating less extreme conditions for plants in the undergrowth. As a result, herbaceous pioneers start to be less abundant and are replaced by more demanding plants, more similar to our common vegetables and thus rich in carbohydrates and proteins.
This is the accumulation phase.
What is being accumulated is natural capital, measured in terms of biodiversity, the complexity that characterises the relationships among the living organisms present in the system, and the forms in which energy is being stored (fertility, organic matter). Such an accumulation corresponds to an increasing level of organisation, which can be technically defined as syntropy (or negentropy) — the inverse of entropy, the quantity that measures the level of disorder characteristic of non-living systems.
The accumulation phase marks the arrival of the first fruiting plants; these represent a source of complex sugars that enriches the food dynamics within the ecosystem, and also attract larger animals into the system, birds and mammals in particular. Medium and large size animals (wild bore, deer, etc.) fertilise the soil with their droppings and create ecological niches with their disturbance action, thus allowing the system to further increase in complexity. Mammals and birds also bring the seeds of more demanding plants, such as fruit and nut trees, which indicate the approach to the abundance phase.
3. Abundance
The abundance or climax phase is characterised by plants which populate all the layers or strata of three-dimensional space (low, medium, high, emergent), as well as having a diverse range of life-cycles (ephemeral, annual, perennial).
Above all, we see an increase in diversity, complexity and the accumulation of energy in the form of organic compounds: humus, protein, carbohydrates, sugars, fats, etc — both above and below ground. Typical of this phase are fruit, nut and timber trees, productive climbers, starch-rich roots and a diverse fauna including mammals, reptiles, birds, insects that feed on vegetables and predate on one another.
Thus, the stability of the ecosystem has increased alongside three main factors: biodiversity (of microbes, plants, animals); complexity in the interaction between all the elements (trees communicating via mycorrhizal networks, food chains above and below ground, etc.); and finally soil fertility. The latter is the common thread throughout the entire ecological succession, because it is in the soil that all the efforts of the initial phases focus; and it is in the soil that minerals, organic matter, water and the main core of biodiversity are developed over time.
4. Dynamical equilibrium and patch dynamics
This is clearly a simplified view of one of the most important and defining processes that take place on earth. In fact, each phase has within itself a level of colonisation, accumulation and climax. Some species act as turning points within this internal dynamics. Brambles (Rubus fruticosus) are such an example. These establish themselves as a pioneer shrub, towards the end of the colonising phase; they spread fast by letting the tip of their arching branches root into the soil. With their flowers, brambles attract pollinating insects, and with their fruits they entice birds that introduce the seeds of more demanding species with their droppings. The shrub and trees thus imported germinate among the brambles, protected from herbivores by their vicious thorns. Thanks to this characteristic behaviour, brambles colonise gaps within woodland and field edges, thus marking a turning point between herbaceous and tree species, as well as between tough and delicate ones.
This process can take place also in a mature ecosystem, whenever a gap is created by the disturbance caused by an animal or a geological or climatic event. In such gaps the soil gets disturbed and the level of light is typical of an earlier ecological phase compared to the surrounding areas. When this happens, the neighbouring patches and the existing soil act as an inoculant of biodiversity and fertility, thus stimulating a repopulation of the gap which is faster and adds additional complexity to the entire ecosystem. This process (called secondary succession) repeats itself at random intervals, thus creating a patch dynamics that makes the ecosystem resilient and characterised by a dynamical equilibrium, maintained by an alternation of disturbance and consequent accumulation of natural capital.
A mechanism, in particular, is worth highlighting within this process. Whenever a plant gets damaged, pruned or eaten, it directs carbohydrates from its aerial to its underground parts. This stimualates and influences the microbiological action in the root zone, and where mycorrhizal networks are well established, a biochemical signal (which some believe is mediated by the plant hormone gibberellic acid) is sent to the surrounding plants. This combined microbiological and biochemical/hormonal stimulation has a triggering effect on the surrounding plants, which experienced more nutrient availability, and are stimulated to grow more vigorously, photosynthesise more and set more flowers and fruits. Thus, when the canopy of a plant is pruned, not only light is introduced to the lower layers, but a “growth pulse” is propagated into the system, and felt by the neighbouring plants.
When the first westerners colonised North America, they reported that after clearing a forested area, for a few years they were blessed with the best soil and growing conditions they had and would ever experience. What they were doing was creating a gap in a well-established ecosystem. In the gap, soil is at its peak fertility, the extra light creates the perfect conditions for vegetable and fruit production, and the pulse generated by the felling and the pruning enhances this effect. If one were to plant young trees alongside vegetables in such a gap (like indigenous Amazonian tribes used to do) this would gradually recreate forest conditions in that same patch. Then a new patch can be cleared, thus effectively growing light-, water- and fertility-demanding crops within a forest, without affecting the stability of the latter. This eye-opening realisation lays the basis for a way of growing vegetables that is in harmony with natural processes.
This article is a reformatted version of the original by Dario Cortese
If you want to read and watch and learn more, it is hard to go past Adam Shand’s extensive: Syntropic Agroforestry Resources (in English)