Edible Forest Gardens: Part 1: Why?
Written by Trent Rhode
Yields have gone up, but this is mostly thanks to new technologies and increased exploitation of the environment. Even in an era of mass soil erosion and destruction of vital ecosystems, modern industrial agriculture still persists in the idea that nature can be controlled and forced into productivity. This can’t go on much longer. But what can we do?
Approximately 40 per cent of the world's agricultural land is seriously degraded. According to the UN, an area of fertile soil the size of Ukraine is lost every year because of poor farming practices and climate change.
"Policy changes that result in improved conservation of soil and vegetation and restoration of degraded land are fundamental to humanity's future livelihood," said Zafar Adeel, director of the international network on water, environment and health at the UN University in Toronto.
The problem, largely, is our lack of understanding of ecology, and our tendency to separate ecology and farming. However, various permaculture systems around the world have proven that we can create our own natural ecosystems that build and nourish soil, but with a twist: our systems are geared towards producing an abundance of food, fiber and other goods.
By looking at a permaculture system known as “edible forest gardening” it becomes obvious that the best way to reduce and reverse the massive problem of soil erosion and rising costs of inputs inherent in modern agriculture is by mimicking nature and working with natural ecosystems. Forests build organic matter very quickly, not only protecting soil, but actually building it. Furthermore, their biomass production levels are far beyond that of modern agricultural systems, and when such natural ecosystems are mimicked in form and structure, but with species that are edible, the potential for food production is phenomenal.
Soil erosion isn’t the only problem with modern agriculture practices. Soil structural deterioration, and organic matter loss are also major problems. By looking at these three key problems, we can better understand how a forest garden works to build and protect soil.
Erosion is defined as a natural process that involves the movement of soil from one area to another. Since the two natural agents of soil erosion are wind and water, we’ll look at the effect that forest systems have on these two forces.
It is now widely known that trees reduce or eliminate the undesirable impacts of excessive wind.
Windbreaks create a zone of reduced wind speeds that can extend from between 10 and 20 times the height of the trees. The fact that a forest garden system is totally surrounded by trees, and would ideally have clearings no larger than 10 to 20 times the height of sheltering trees, means that the potential for protecting soil within these systems is great.
Besides trees, however, forest systems also contain many other perennial crops, all of which provide permanent cover and protection from erosive wind forces, ensuring that the soil is never bare and exposed to wind. Such alternative crops offset wind erosion risks.
Falling raindrops break the soil up by detaching particles from soil aggregates (bundles of bound soil). If water is not able to penetrate the soil then it will flow over the surface as runoff. So erosivity has two components: impact (also called intensity), the force that breaks up the soil, and runoff, the force that carries soil away.
Whereas rain can easily damage many conventional agriculture crops through erosivity at certain times in the growingseason when soil cover is minimal, a forest system is covered continuously, if not by canopy trees and herbaceous ground covers, than by leaf and plant litter (during the fall).
Erodibility factors influenced in a beneficial way by a forest garden system include: vegetative cover, management practices, and some soil physical properties including soil structure and soil porosity (discussed below).
Probably the most obvious of these factors is vegetative cover, since forest gardens are generally completely covered in permanent vegetation. Additionally, the deep, permanent roots of trees can create channels for improved water infiltration.
Primary management practices in a forest garden system that would decrease the erodibility of the soil include no-till practices and the absence of heavy machinery in such a system. This would lessen compaction and contribute to better soil structure.
Soil structure is influenced by forest ecosystems in a number of ways. First, the diversity of root depths, patterns, shapes and sizes ensure that a larger amount of the soil system is stabilized and held in place by the roots of various understory and canopy plants. Additionally, the roots break up the soil and create stability over long periods of time, maintaining soil structure by adding organic matter to the soil in their continuous growth and death cycles. This in turn encourages the arrangement of smaller particles into larger, bound soil aggregates, which are more resistant to erosion.
Additionally, in an undisturbed soil, leaves and other organic debris accumulate on the surface, where they are broken down by the decomposers. The main by products of the decomposition process are soluble plant nutrients and microbial remains that bind the soil particles together, giving a stable crumb structure.
Soil Organic Matter
In order to gain a better understanding of soil organic matter (SOM) and how an edible forest garden can be of benefit to this aspect of soil health, we can look at some of the ways in which forest systems add and maintain organic matter in the soil.
The decomposers are most active in the upper layer of the soil, i.e. the top 8 cm (3 in.). Therefore, it is important to incorporate organic matter into the surface layers to stimulate decomposition and thereby provide plant nutrients.
Edible forest garden systems do this naturally through the shedding of leaves and through people cutting quickly growing dynamic accumulator “mulch” plants such as comfrey and leaving them on the soil surface to decompose.
Additionally, it is known that forest systems encourage bacteria, fungus and other soil organisms. These organisms themselves create large amounts of organic matter in their life and death cycles, and are important in decomposing other organic matter, making nutrients available to plants. Such organisms also bind up nutrients in their bodies, preventing them from being lost to runoff.
Soil fertility refers to the ability of the soil to supply or provide the required macro and micronutrients for a growing crop, and this includes all of the tree and other plant crops within an edible forest garden. Since soil fertility will have a direct impact on the growth of plants within an agricultural system and the number of plants that can be grown, and since the growth of crops in an agricultural system will influence the amount of organic matter, the soil structure, and soil erosion, this is an important area to explore.
Agroforestry systems are known to cycle nutrients much more efficiently than conventional monoculture systems. It is therefore easy to see why an edible forest garden has greater potential to improve soil fertility than conventional systems, even organic ones.
Woody perennials have deeper root systems than herbaceous plants and thus have a potential to capture and recycle a larger amount of nutrients. Their litter contribution to the soil’s surface is also commonly greater than that of herbaceous plants.
Additionally, it is known that perennial herbaceous plants in particular, which are also a large part of an edible forest garden, generally have deeper roots than annual conventional crops, and thus, they cycle nutrients more efficiently.
Tree roots also reach down below the rooting zone of most crop species and capture nutrients that would otherwise leach away, promote microbial populations that can use potential contaminants, pesticides and excess nutrients as a source of food, and recycle nutrients through root turnover.
Additionally, it is known that tree leaves break down slowly and thus release their nutrients over a period of time.
Mimicking a Forest
In conclusion, since it is an established ecological fact that forest ecosystems, and even mimicries of forest ecosystems, can enhance soil conditions and reverse soil erosion while creating an abundance of (edible) organic matter, it makes sense to start implementing edible forest systems as a form of agriculture.
Agroforestry, and specifically, a bio-mimicry and production based agroforestry system commonly known as edible forest gardening can, like natural forest systems, evolve with and span all levels of ecosystem succession, improving soil conditions along the way while producing an abundance of food.
In Part 2 of this series, we will introduce the how of creating an edible forest garden.