A forest garden is a designed agronomic system based on trees, shrubs and perennial plants. These are mixed in such a way as to mimic the structure of a natural forest the most stable and sustainable type of ecosystem in many temperate climates. The primary aims for the system are: (1) to be biologically sustainable, able to cope with disturbances such as climate change; (2) to be productive, yielding a number (often large) of different products; and (3) to require low maintenance.
The crops which are produced will often include fruits, nuts, edible leaves, spices, medicinal plant products, poles, fibers for tying, basketry materials, honey, fuelwood, fodder, mulches, game, sap products.
Forest gardens (often called home gardens) have been used for millennia in tropical regions, where they still often form a major part of the food producing systems which people rely on, even if they work elsewhere for much of the time, They may also provide useful sources of extra income. Their use is intimately linked with prevailing socio-economic conditions. They are usually small in area, often 0.1 1 hectares (0.25-2.5 acres).
In temperate regions, forest gardens are a more recent innovation, many inspired by Robert Hart's efforts in Shropshire (UK) over the last 30 years. A major limiting factor for temperate forest gardens is the amount of sunlight available to the lower layers of the garden: in tropical regions, the strong light conditions allow even understory layers to receive substantial light, whereas in temperate regions this is not usually the case. To compensate for this, understory layers in temperate forest gardens must be chosen very carefully there are plenty of plant crops which tolerate shady conditions, but many are not well known. Many of the more common shrub or perennial crops need bright conditions, and it may be necessary to design in open clearings or glades for such species.
Temperate forest gardens are also usually small in area, from tiny back garden areas up to a hectare (2.5 acres) in size. While food production and land use remain the concern of a majority of landowners and businesses, their use is likely to be limited to 'alternative' and organic gardeners and land users.
The key features which contribute to the stability and self-sustaining nature of a forest garden are:
- the very diverse number of species used often several hundred in established tropical forest gardens.
- the careful inclusion of plants which increase fertility, such as nitrogen fixers, e.g., Alders (Alnus spp.),
- Broom (Cytisus scoparius), Elaeagnus spp., and shrub lupins (Lupinus arboreus).
- the use of dynamic accumulators deep rooting plants which can tap mineral sources deep in the subsoil and raise them into the topsoil layer where they become available to other plants, e.g. Coltsfoot (Petasites spp.), Comfreys (Symphytum spp.), Liquorice (Glycyrrhiza spp.), and Sorrel (Rumex spp).
- the use of plants specially chosen for their ability to attract predators of common pests, e.g. umbellifers like tansy.
- the use, where possible, of pest and disease resistant varieties of fruits, nuts etc.
- the increasing role of tree cover and leaf litter that improve nutrient cycling and drought resistance.
The garden is organized in seven 'layers'. Within these, the positioning of species depends on many variables, including their requirements for shelter, light, moisture, good/bad companions, mineral requirements, pollination, pest-protection, etc.
- Canopy trees the highest layer of trees. This may include large trees, e.g., Chestnuts [Castanea spp], Persimmons [Diospyros virginiana] and honey locusts [Gleditsia triacanthos]), or may only contain small trees and large shrubs, e.g., Strawberry trees [Arbutus spp], Siberian pea trees [Caragana arborescens], Cornelian cherries [Cornus mas], Azeroles and other hawthorn family fruits [Crataegus spp], Quinces [Cydonia oblonga], Apples [Malus spp], Medlars [Mespilus germanica], Mulberries (Morus spp], Plums [Prunus domestica], Pears [Pyrus communis], highbush cranberries [Viburnum trilobum]).
- Small trees and large shrubs, mostly planted between and below the canopy trees. Includes some of the above species on dwarfing rootstocks, and others such as various bamboos, Serviceberries (Amelanchier spp.), Plum yews (Cephalotaxus spp.), Chinkapins (Castanea pumila), Elaeagnus spp, and Japanese peppers (Zanthoxylum spp.) Others may be trees which are coppiced to keep them shrubby, like medicinal Eucalyptus spp, beech (Fagus sylvatica) and limes (Tilia spp.) with edible leaves.
- Shrubs, mostly quite shade tolerant. Includes common species like currants (Ribes spp.) and berries (Rubus spp.), plus others like chokeberries (Aronia spp.), barberries (Berberis spp.), Chinese dogwood (Cornus kousa chinensis), Oregon grape (Mahonia spp.), New Zealand flax (Phormium tenax) and Japanese bitter oranges (Poncirus trifoliata).
- Herbaceous perennials, several of which may be herbs, can also contribute to the ground cover layer by self-seeding or spreading. These include Bellflowers with edible leaves (Campanula spp.), Comfreys (Symphytum spp.), Balm (Melissa officinalis), Mints (Mentha spp.), Sage (Salvia officinalis), and Tansy (Tanacetum vulgare).
- Ground covers, mostly creeping carpeting plants which form a living mulch for the 'forest floor'. Some are herbaceous perennials (see above), others include wild gingers (Asarum spp.), cornels (Cornus canadensis), Gaultheria spp., and carpeting brambles (e.g., Rubus calycinoides and R. tricolor).
- Climbers and vines. These are generally late additions to the garden, since they obviously need sturdy trees to climb up. They may include hardy kiwis (Actinidia spp.), and grapes (Vitis spp.).
- The final 'layer' is the root zone, below ground. Any garden design should take account of different rooting habits and requirements of different species. In addition, there may be some species with roots/rhizomes of use such as liquorice (Glycyrrhiza spp.) and the barberries (Berberis spp.) whose roots furnish a good dye and medicinal products. Various beneficial fungi can also be introduced into this layer, including mycorrhizal species and others intended for cropping.
A forest garden can be a long-term biologically sustainable system for growing food and other products for a household which, once established, needs little work to maintain. However, getting started requires large numbers of plants and substantial work.
Martin Crawford is Director of the Agroforestry Research Trust (46 Hunters Moon, Dartington, Totnes, TQ9 6JT, UK) and Editor of Agroforestry News, from which this article was reprinted by permission.