Many experienced permaculturists and foresters, at first, dismiss successional agroforestry. They usually think that this approach is simply another take on Agroforestry Systems (AFS) or of the Permaculture Food Forest with a stronger “chopping and dropping” element in system’s maintenance. Ernst Gotsch’s insights and classifications, however, are much deeper. In this article I discuss some basic differences between the classic Permaculture Food Forest and the AFS developed within the successional agroforestry principles.
Already concerned with the devastating effects of soil tilling and the cultivation of annuals, Russel Smith wrote Tree Crops: a permanent agriculture in 1929. Smith’s work bears great influence over regenerative agriculture farmers and environmentalists. David Holmgren and Bill Mollison, co-creators of Permaculture, for example, wrote Permaculture 1 in great part inspired by Smith’s book. Robert Hart’s book Forest Gardening: Cultivating an Edible Landscape, was also influenced by Smith’s work. Hart’s book, in turn, became one of the foundations for the Food Forest concept in Mollison’s Permaculture: a designer’s manual (1989).
Hart pioneered the implementation of food-forests in the temperate climate, and according to him a forest has 7 layers:
- The canopy,
- a low tree layer,
- a shrub layer,
- a herbaceous layer,
- a ground cover,
- a rhizosphere or underground dimension of plants grown for their roots and tubers,
- a vertical layer (of climbers and vines).
Following this principle, Hart designed an edible landscape based on an already existing apple and pear orchard Shropshire, England. The majority of the other plants were replaced by edible, medicinal and nitrogen-fixing species (Hart, R. 1991). Hart eventually developed a diet that was 90% vegan and sourced almost in its entirety from fruits, nuts and vegetable from his property’s Forest Garden.
The illustration above demonstrates how it is possible to replace all layers (or strata) of a forest with edible species to create a Forest Garden (a.k.a. Food Forest). For example, we could have from the bottom up: tubers (sweet-potato, ginger, turmeric, cassava, etc.); ground covers (pineapple, lettuce, tomato, basil, etc.); shrubs and small trees (coffee, cacao beans, pawpaws, etc.), large fruit trees (avocado, mango, jack-fruit, etc.), the highest or emergent trees (palm trees such as Brazil or Pupunha Nut, etc.) and the climbers (passionfruit, choko, loofah, etc.) (Mollison, 1988).
Ernst Gotsch, a Swiss geneticist botanist who became a Brazilian citizen, with over 30 years of experience designing, implementing and maintaining successional agroforestry systems, created his own classification. According to Gotsch, a successional agroforestry is constituted of 4 layers or strata:
- Low strata species. Plants which demand less light to grow and produce, and that occupy up to 80% of the forest layer niche;
- Medium strata species. Plants that may occupy up to 60% of the niche and, in the right percentage, can withstand shade from taller trees;
- High strata species. These trees may occupy up to 40% of the niche area. In this percentage the light permeates through them and hits medium and low strata species;
- Emergent species, in turn, occupy about 20% of the niche and can take full sun.
In Gotsch’s classification, however, it is important not to confound the different strata (that are related to the amount of sunlight demanded by each species in its specific layer) with cycles (that are related to the life span and harvest cycles of each species). Gotsch has also created a new classification system that deals specifically with life cycles. These are: Placentas I and II, Secondary I, II and III, and climax (see table below). Whereas Hart’s 7 layers classification deals with the forest structure, Gotsch’s strata system deals with a fractal-like classification that is contextual to the amount of sunlight a plant demands in each life cycle. Gotsch’s strata system, thus, allows a deeper understanding of plant consortiums and their life cycles within the ecological succession. And here it is worth noting that ‘plant consortiums’ in successional agroforestry are not quite like the permaculture concept of guilds, but this topic falls out of this article’s scope.
In other words, each life cycle may contain all 4 strata. For example, within the Placenta 1 cycle we might have a consortium in which Nira garlic is low strata, rocket medium, lettuce high and corn is the emergent. Within Placenta 2 we could plant sweet potato as low, taro as medium (depending on which variety), cassava as high strata, and okra as emergent. This way it is possible to design each strata within each cycle. And because this approach deals with varied spatial (strata) and temporal (life cycles) dimensions, it optimises the production up to 400%.
The processes by which nature establish its ecosystems, that in turn give support to life in the planet are called ecological succession. And it is the understanding of the structural layers of a forest and of ecological succession (with its life cycles) that allow us to design, implement (all at once) and speed up a system with all the necessary species to reach climax. Ecological succession creates the ideal conditions for the establishment of biodiversity. Biodiversity, in turn, creates the biomass, soil cover, and sufficient nutrients so that the system can become more complex as it evolves. Primary ecological succession takes place for the first time in completely barren areas (e.g. after earthquakes, volcanic eruptions, glacial eras, etc.). It might take millions of years until Primary ecological succession can support a more complex system such as a Climax forest. Secondary ecological succession happens when a forested area is degraded either by human action (e.g. slash and burn agriculture, deforestation for logging or the agri-business, etc.) or by natural events (e.g. a bushfire, landslides, severe storms, etc.) and then it is left alone to recover. In this case the area is not completely barren and when there is still enough biodiversity left this forest might evolve to a Secondary (or Second Growth) Forest.
There are few classifications for the different stages of ecological succession stages. In the most commonly used we find:
- Pioneer stage. Plants in this stage have rapid growth, thrive in full sun, and are short lived;
- Secondary stage. In this stage plants grow more slowly, need some shade to thrive and have a medium life cycle; and
- Climax. In this stage plants have a long life cycle, but can only evolve after a primary forest has already been established.
In another common classification in Brazil we find:
- Capoeirinha (initial stage of regeneration);
- Capoeira (intermediate stage of regeneration);
- Capoeirão (advanced stage of regeneration); and
- Secondary (or Second Growth) Forest.
Ernst Gotsch (1997) coined yet another classification system according to the species’ function and their life cycles. Gostsch uses this system to design consortiums of species and develop his AFS to regenerate areas that have been degraded by (negative) human interventions. In Gotsch’s system these stages are:
- Placenta I (with plants living up to 6 months);
- Placenta II (plants living up to 2 years);
- Secundária (Secondary) I (with plants living up to 10 years);
- Secundária II (plants living up to 25 years);
- Secundária III (plants living up to 80 years); and
- Climax (with plants living more than 80 years).
Regardless of which kind of theoretical classification is used to understand a place or system or of which practical approach (Permaculture or successional agroforestry) is taken to establish Agroforestry Systems, the understanding of ecological succession, of the structural layers, and of each species’ role within its life cycles is crucial to the farmer’s/designer’s success. In a Syntropic system, however, different trees (e.g. pioneer, medium strata, nitrogen-fixing, windbreak, biomass, timber, and climax trees) are planted with a subsistence of market garden (with ground covers, vegetables, tubers and annuals) so that the farmer can start offsetting the costs of implementation as soon as possible. This strategy, together with (specific strata and life cycle-related) pruning and mulching, allows us to speed up the natural processes of ecological succession, producing quality food, fibres, timber and fuels while also regenerating degraded lands.
Upcoming Agroforestry Courses
Forestry in Practice – With nearly 30 years of experience and literally thousands of farm plans under his belt, Darren J. Doherty comes to the Northern Rivers (NSW, Australia) to teach the course “Forestry in Practice“. The course equips farmers to holistically integrate trees in their landscapes and enterprises. Darren, who also works closely with livestock producers, has been an adamant promoter of tree integration for all farm enterprises. The course will run on the 9th and 10th of February, 2019, at the Holos Regenerative Design learning site in Brunswick Heads, Northern New South Wales.