Course:Stacking functions and the 7-Layered Garden
From PermaWiki
Date: January 21st
Contents |
The Forest Garden
A forest garden is a guild, or community of plants that densely occupy and support each other, while maximizing biodiversity and production within a sustainable context and providing for both human and non-human animal use. Taking advantage of multiple stories or layers, the forest garden utilizes as much space as possible while limiting competition from undesired plants. Variations on the forest garden dictate different numbers of layers, but the standard is seven; the canopy, low fruit, bush and shrub, herbaceous, rhizosphere, surface and vertical layers. The symbiosis of a forest garden replicates the natural conditions that make woodlands successful, but with varieties of plants that humans find useful and productive.
While not ideal for most popular annuals, the forest garden is a compact, efficient way to grow many fruits and vegetables and allow them to support each other. Most plants in the forest garden are perennials, which grow steadily in stable ground, over annuals, which thrive explosively in disturbed ground.
Plants are chosen either because they directly benefit humans or because they support the ecosystem of the forest garden, such as providing shelter for wildlife or plants that fix nitrogen or release minerals bound to the soil. By maximizing diversity, you reduce the dangers from pests that specialize in a specific plant type, naturally promote crop rotation, and provide more variety in your yield.
The top layer of the standard Forest garden is the canopy, consisting of apple, walnut, heartnut, plum, or other tall, wide, long-living and productive trees at wide spacings. This layer provides cover for the plants in the lower layers, shelter for birds and squirrels, as well as conventional food and fruit yields. Large trees have deep roots, bringing hidden water and nutrients to the surface where it's companion plants can take advantage of them during transpiration and as leaf mulch. Trees that take coppicing well are a good choice, as this allows for more flexibility in management. Try to pick varieties that thrive in local conditions, since pest and nutrient management is very difficult on the canopy layer without causing adverse conditions for the plants in lower layers.
The second layer consists of low fruit trees - dwarf peaches and apricots, and asian pear are good choices. This layer performs many functions similar to the canopy layer, but with more variety and easier harvesting.
Choices for the bush and shrub layer include bush cherries, elderberries, blackberies, sea buckthorn, gooseberries and boysenberries. Bushes and shrubs have developed wide branches on small trunks to take advantage of light that filters through the canopy, often with thorns and pointed branches to discourage squirrels and birds that may steal fruit.
The herbaceous layer should be filled with shade-tolerant producers, such as sorrel, dandelion, rhubarb, bee balm, chive, horseradish and chard. Wide leaves allow them to gather sun from shady conditions, and most of these plants will be healthier and more productive under canopy than in full sun.
On the surface, red and white clover make an ideal ground cover and fix nitrogen into the soil. Strawberries and thyme are good choices, as well. Comfrey can form a natural weed barrier, providing a useful herb and bringing many nutrients up into a natural mulch every fall.
Root crops include lots of alliums that like living in close quarter - garlic, onion, shallots, as well as hardy root biennials, like turnip, rutabaga and parsnip.
The vertical layer consists of vining plants, including grapes, hops and kiwis. These plants make use of normally underutilized spaces, climbing the trunks of trees to seek light, rain and open air. Find wild grapes from your area, which will be hard and productive locally - specific varieties of grapes perform best in a narrow band of regional conditions. In an urban setting, vines minimize pollution by limiting and filtering airflow, and can take advantage of the many non-plant vertical surfaces present (buildings, fences, staircases)
Yields and Functions
In Permaculture, the useful outputs of a system that can be measured conventionally are called yields and functions. Yields are the "products" of a system, the items you can take away and are generally things that get consumed by some other process. Fruits and nuts, wood for a fire, fish from a pond, or salt from the ocean are considered yields. Functions are a wider view of the useful actions a system performs - one function of a system might be to produce a yield. Another might be soil remediation, shelter, or noise reduction.
Stacking Functions
Critical functions in an ecosystem are best met by redundancy - by multiple systems that can produce that same function. A homestead with a water supply that comes from a spring would be best serves with additional catchment systems including swales and roof rainwater systems to ensure the vital resource doesn't become unavailable unexpectedly.
Coaxing multiple functions from each element in a system is just as important. An effective element in a system not only provides a primary yield, but also performs valuable functions. Identifying and promoting these elements with multiple uses is called "stacking" functions, because the uses to which the element can be used are said to "stack" upon each other, increasing it's utility.
As an example, look at the southern brick wall of a house. It serves it's primary functions, to provide support for the roof and shelter from the wind,but let's examine what other functions the wall can serve. It's thermal mass acts as a heat sink, taking heat from the strong southern sun and storing it, releasing it slowly through a long winter night. In the spring and summer, it blocks that same sunlight, radiating it back towards the ground, warming annuals that need it for vitality. It can act as a trellis for vines to grow on, letting them rise above the weeds and vegetables that might block their sun, or hold a downspout for a rainwater catchment system. The solid surface is difficult for animals to climb and could protect eggs in a nest or maturing hams under the eaves. It's earthy nature provides a considerable amount of fire resistance, water resistance, can hold up if a tree were to fall on it, and can act as an anchor for heavy raised beds or a house addition. Brick is one of the few conventional building resources that can be reused when it's dismantled, so today's wall could be tomorrow's roasting pit, paving stone or compost bin. By examining elements in a system with curiosity and an inventive nature, we can begin to truly appreciate all of the resources at our disposal.
Niche guide
| Layer / Function | Roots | Ground covers | Herbs and veggies | Shrubs | Low trees | Tall trees | Vines | Water plants |
|---|---|---|---|---|---|---|---|---|
| Edibles | Potato Garlic Rutabaga Canna | Strawberries Sweet potato Chickweed | Violets Rhubarb Lettuce Alexanders | Burdock Kale Raspberries Blueberries | Gooseberry Pawpaw Peach Persimmon | Fig Mulberry Cherry Linden | Maple Passion fruit Kiwi Akebia | Lotus |
| Medicinals | Garlic Echinacea Dandelion Licorice | Spilanthes Wild ginger Mints Oregon grape | Yarrow Dock Mullein | Rose Wormwood Rosemary Raspberries | Magnolia Chaste tree Lilac Albizia | Magnolia Gingko Chestnut | Wisteria Hops Jasmine | Bacopa |
| Fiber plants | Dock | Most grasses | Nettles Jute Hemp | Blackberry Bamboo | Willow Hazel Maple | Cedar Willow | Akebia Hops | Cattail |
| Nitrogen fixers / detoxifiers | Comfrey Licorice Astragalus Peanuts | Pumpkins Clover Alpine pennycress | Fava Nettles Squash | Oleaster Ceanothus Lupine | Acacia Locust Alder Golden rain | Catalpa | Kudzu Pole beans | |
| Mulches | Comfrey Sunchoke Potato | Ajuga ivy | Burdock Nettles Yarrow | Bamboo | Plum Apple Pear | Maple Empress | Blackberry Kudzu | Duckweed Azolla |
| Habitat | Wood sorrel Cattail Foamflower | Waterleaf Lingonberry | Indian plum Serviceberry Snowberry | Rowan | Oak Mulberry | Honeysuckle Clematis | Water lily | |
| Insectaries | Horseradish Daikon | Ajuga Nasturtium White clover Field peas | Yarrow Dill Marigolds Zinnias | Hydrangeas | Lilac | Linden | Honeysuckle | Water hyacinth |
From food not laws by H.C. Flores (2006)
- Remember that the categorization into layers is really only to help us plan the forest garden. Nature doesn't fit into neat categories; many plants could fit into several layers.
- Similarly, any plant has many functions, and part of this exercise is to make use of each function.
- You can find other functions that are not in this table; most plants are very beautiful, so don't leave out the "ornamentals" (though no plant is strictly ormnamental, they all affect the whole system, either by attracting insects, creating shade or providing habitat). Bamboo can serve as construction material for trellises and such. Onions, beets, berries can be used to make dyes. Some shrubs and trees are effective windbreaks.
Practice
- List some ways that the layers of a forest garden provide for one another. What yields and functions do the different layers provide for the ecosystem?
- Describe some of the dozens of yields and functions of an oak tree.
- Detail the many functions and yields of a freshwater pond.
Additional readings
- Click here for a list of further readings.
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