In nature, there is a set of processes that allow natural ecosystems such as forests, estuaries and others to function with great efficiency. In many agricultural systems, these functions have been removed or severely diminished by management, so that constant intervention is necessary to repair the broken balances. Unfortunately, we do this with substances and methods that often affect the development of many organisms, deteriorate the productive base (the soil), the environment in general and can even affect humans, including the toxic substances we apply to kill insects, bacteria, fungi and plants.
This is why it is essential to know which functions of nature can be used in the development of organic agriculture in order to engage in organic farming.
The main functions present in natural systems that need to be enhanced in organic production systems are:
▪ Efficient use of resources.
▪ Biotic regulation and stability.
▪ Soil protection.
▪ Nutrient recycling.
▪ The water cycle.
▪ Environmental stability.
Efficient use of resources
Life is made possible by plants converting solar energy into organic substances in a process called photosynthesis, where CO2 from the air and hydrogen (H) from water combine to form carbohydrates from which other substances are synthesized, and where other minerals in the air and soil also participate.
From the production of organic substances by plants, different and complex food chains are established, through which solar energy captured by plants circulates, and the nutrients necessary for their formation are recycled. In this cycle, the plants are the producers; the organisms that live on the living parts of the plants are called herbivores or phytophagous; and those that feed on the herbivores are called predators, which may also feed on other predators, and there are several levels in this group. Animals that break down dead organic matter (microorganisms, some insects, earthworms, and other small organisms) are called transformers, and their function is to maintain the soil in optimal conditions for plant development and to return the nutrients needed to continue the production of organic substances for the renewal of life.
At the level of organisms transforming soil organic matter, different food chains are also established, because if a large number of organisms feed on dead organic matter (saprophytes), others are predators of these organisms.
Biodiversity is expressed in this cycle in two ways: the one we have described, which shows how different organisms come together to form a life cycle; the second is the biodiversity of organisms that complement each other to enhance biomass production from existing resources.
This second function of biodiversity is found at all trophic levels of living organisms. Thus, we have plants adapted to live in different soil types, water regimes, latitude and altitude, etc. Within the same climatic condition, ecosystems are made up of plant communities: some are tall and have high solar energy requirements; others grow below, using the sun’s rays that the former allow to pass through and diffuse the energy, developing their potential in these conditions. In terms of soil exploration, biodiversity also allows the exploitation of different strata and the use of different nutrients.
The biodiversity of animals also allows them to use the different resources produced and, while creating complex food chains and the production of biomass, biotic regulations of the different populations are established.
The use of biodiversity to optimize existing resources is also used in agricultural systems. Examples include agroforestry, agroforestry systems, silvopastoral systems, polycultures, integration of livestock with agriculture and, to some extent, crop rotations.
Intensive” agriculture bases its production on monoculture and the separation of agriculture, forestry and livestock, which means that the benefits of biodiversity to optimize resource use and system productivity are lost. In order to maintain the productivity of its crops, “intensivist” agriculture uses elements alien to the system, usually toxic to living organisms or agro-ecosystems.
Biotic regulation is another important function that occurs in natural systems. It consists of the regulation of the growth of populations of organisms by other organisms. This regulation is of great importance in controlling any population explosion of organisms that may become pests, whether they are microorganisms, insects, mammals or plants (such as those mistakenly called “weeds”).
The food chains that are established in nature are the key to biotic regulation. However, there are other mechanisms of regulation, such as competition between plants for resources such as light and nutrients, or the secretion of chemicals that can affect the development of other organisms, such as the secretion of antibiotics by actinomycetes, which inhibit the growth of bacteria and fungi; or the case of plants that can inhibit the growth of other plants (allelopathy), soil pathogens or repel insects.
Regulation can also be facilitative, that is, the presence of certain plants or structures can facilitate the presence of an organism or groups of organisms by providing food, shelter, nesting sites or environmental changes. These organisms can be beneficial to agricultural activity, such as predators and parasitoids of lepidopterans and aphids, which need to feed on flowering plants to provide nectar and pollen, as well as shelter, which they find in many wild plants growing on the edges of fields, in groves, borders, and in agricultural fields themselves.
All organisms have a role in the ecosystem, whether known or unknown, more or less important, and the disruption of balances, which can be caused either by changing conditions or by the removal of organisms, can create conditions for the emergence of pests and epidemics.
In all major groups of organisms, there are, from our point of view, potentially harmful species (which are phytophagous and parasitic organisms), usually with a high rate of reproduction and spread; there are also predators, which are animals that feed on other animals and which we call biological regulators or beneficial organisms ; and others that, because of their feeding habits (saprophages, which feed on dead substances), reproductive capacity, or other characteristics that limit their population, are considered neutral or without potential for harm.
The control activities carried out by predators and parasitoids in nature are innumerable and partly unknown. Examples include the following:
▪ Syrphid fly larvae eat 200 to 800 aphids until they develop into pupae.
▪ One ichnoumonid wasp is able to parasitize and destroy 1,000 aphids.
▪ A ladybug larva is capable of devouring 200-600 aphids until it turns into a chrysalis.
▪ A garden spider devours about 2 kg of insects per year.
▪ A blue tit (Parus sp.) of only 11 cm destroys about six and a half million insects and needs at least 24 million to feed its 6 to 12 young.
It should be noted that birds, insects and other phytophagous organisms, which are potential crop pests, also perform beneficial regulation by consuming huge quantities of wild plant seeds or their aerial parts.
The use of pesticides in agriculture, in addition to eliminating pests, also eliminates predatory or parasitic organisms of pests, either directly or through the contamination they accumulate, thus creating conditions more conducive to the growth of phytophagous pests and the emergence of more and more pests.
Biodiversity also exerts biotic regulation through diversity itself. Many pests are specialists in certain plants, so that the homogeneity of crops in a given area or their continuous repetition over time creates conditions conducive to the emergence of pests. Thus, plant mosaics, polycultures, crop rotations and other techniques, by partially simulating nature’s diversity, create the conditions for biological regulation.
Nature, through the biodiversity of plants, always tends to cover the soil if there are minimum conditions for its development. This is a natural reaction to the use of resources for reproduction and competition for survival, which leads to the production of biomass. Plants do not only occupy the soil, they develop and maintain it through the work of their roots, their exudates and the life of the different organisms that live in it, thanks to the contribution of organic matter by the plants themselves. A soil capable of supporting abundant plant production is a mixture of inorganic substances from the original substrate, organic matter produced by the plants and an intense life that transforms the organic matter, making available to the plants a large part of the nutrients they need, joining with them to facilitate the absorption of nutrients, reducing the loss of nutrients in the soil and creating conditions for aeration, penetration and retention of water in the soil.
Therefore, keeping soils uncovered and unprotected is an unnatural act, which we pay for by the erosion that occurs in them, and by the need to provide nutrients to the plant due to the sterilization to which we subject the soil, losing the beneficial functions for plant nutrition performed by all the organisms that live in a living soil.
Biodiversity allows for nutrient recirculation, nutrient supplementation, and fertility recirculation in ecosystems and agro-ecosystems, which greatly reduces nutrient losses from the system and helps bring significant amounts of nutrients from the deep soil layers or atmosphere to the surface and the more active part of the soil.
For example, deep-rooted plants such as trees, shrubs, and some legumes extract nutrients from deep in the soil and deposit them on the surface when their leaves fall; grass species are able to take up potassium that cannot be assimilated by other plants and deposit it in the soil when their aerial parts die; legumes fix nitrogen from the atmosphere and solubilize phosphorus ; Soil microorganisms, by growing and absorbing nutrients, prevent the release and loss of nutrients through leaching, making them available to plants as they die or feed, as well as transforming a group of nutrients so they can be taken up by plants; earthworms make nutrients more available by transforming the soil that flows through their digestive system; mycorrhizal fungi, which associate with plants, not only increase the surface area of the roots, but also allow them to absorb nutrients that are not directly available to the root, such as phosphorus. Figure 8 shows, as an example, the nitrogen cycle in an ecosystem. We can see how animals contribute to the recirculation of nutrients. Similarly, the existence of forests in the hills and uplands, with intense production of organic matter and recirculation of nutrients, can support the fertility of neighboring valleys by transferring nutrients and organic matter from rainwater to the valleys.
Biotic and environmental stability
Biodiversity is a critical component of biotic stability and contributes to environmental stability. As mentioned above, plant diversity prevents the concentration of the same resource or plant species and thus limits the growth and spread of specialized phytophages. In general, these specialized phytophages become pests when a few plant species dominate the system. These diversity-poor systems are not the result of natural selection, but of human pressure, as in the case of agricultural monocultures.
The intrinsic biodiversity of each species is also an important element of subsistence in the face of periodic variations in climate or the natural development of a disease, which may affect some individuals (one of the genetic types, natural or selected), but others will resist and replace the susceptible individuals.
Plant diversity, by providing diverse organic matter to the soil, also allows for a greater diversity of organisms in the soil, thus preventing the proliferation of certain species of potential pathogens specialized in one type of plant or plant residue.
Polyculture practices and crop rotations, among others, aim to simulate nature in this biotic regulation of biodiversity. A clear example is the need to rotate potatoes over long periods of time to avoid certain diseases caused by nematodes, fungi and insects.
In any ecosystem or agro-ecosystem with little degradation, there are many plant species represented by a few individuals. These species can play an essential role in the system as a refuge, food source, attractant or repellent for other organisms that may be essential to the biological balance of the system. For example, polyphytic grasslands (i.e., with many species) have been shown to recover more quickly from drought than those that have been dominated by one or a few species.
In general terms, biodiversity is associated with the biological stability of systems, assuming that every ecosystem is changing and evolving. But this occurs naturally in geological time. Today, the degradation to which we subject ecosystems and agro-ecosystems, directly or indirectly, is outside any period of natural change; hence the risks and dangers we face.
In their evolution from immature to mature or stable systems, such as forests, grasslands, or other so-called climax systems, ecosystems not only transform themselves, but also the substrate and regional mesoclimate, allowing the establishment of communities of species that would never have developed in the original environment. Therefore, excessive destruction of natural ecosystems can have negative effects on the mesoclimate of a region, making it drier, hotter or colder depending on the time of year, and erosive agents such as rain and wind have a greater impact on soil erosion.
Trees, in particular, play a very important role in regulating the environment: by evaporating water, they reduce the ambient temperature, which is also controlled by the rest of the plants covering the soil, and prevent the soil from heating up and diffusing heat into the air, as happens when the soil is not covered. The decrease in air temperature reduces the rate at which the air rises, which, along with evaporation, contributes to the occurrence of precipitation. On the other hand, trees and vegetation also prevent temperatures from dropping excessively.
Under and around the trees, the temperature is lower and moisture, organic matter and nutrients are higher. Trees also reduce wind speed, thereby reducing evapotranspiration caused by drought, when winds carry moisture away from the field. A barrier of trees can protect a crop field from wind for a distance of 10 times its height.
Vegetation and especially trees play an important role in water conservation. Their roots and the macro-porous structure of the soil, which allows for a high organic matter content and abundant life, promote the infiltration of water into the soil, increasing its reserve and preventing it from running off the surface, thus avoiding erosion as it passes. This water runoff can create flooding in low-lying areas due to the large floods that occur in heavily deforested areas. This, together with the ability to create favorable conditions for precipitation, favors the regulation of the climate and avoids the processes of desertification, a widespread phenomenon in our territory.
From a practical point of view, there is a set of essential elements for the beneficial effects on ecosystems to occur, which would allow the preservation of nature and the end of the negative effects that intensive agriculture has on it. It is an agriculture that destroys biodiversity and soils, which, with the use of toxic and polluting substances, not only affects natural life and the destruction of resources (on which humanity depends for its food and other needs), but also threatens human health and existence itself.
Restoration of ecosystem functions is linked to the reconstruction of the landscape of degraded areas. In Table 3, we list the essential elements for restoring functional biodiversity and the main functions they can play. The fundamentals of landscape restoration are:
▪ Reforesting the upper parts of hills and steep slopes with native species or a mixture of native and introduced species, provided they do not negatively impact the system.
▪ Reforest all streams, allowing other native plants and ground-covering grasslands to become established in addition to trees.
▪ Protect runoff areas with trees, shrubs, and volunteer vegetation.
▪ Establish living barriers on slopes used for agriculture to stop erosion and produce natural terraces.
▪ Arborize roadsides and edges and allow natural vegetation to grow.
▪ Facilitate the creation of polyphytic grasslands.
▪ Create some temporary shelters or nests for beneficial animals.
▪ Diversify agriculture by using plants from different families, incorporating local varieties, and encouraging the use of different varieties of the same crop, both in time and space.
▪ Use mulch on permanent crops such as fruit trees and use no-till or minimum-till methods.
▪ Rotate crops using at least four crops.
▪ Integrate livestock into farming.
▪ Use of native breeds.