Permaculture Designers Manual
CHAPTER 10 –
THE HUMID TROPICS IN PERMACULTURE
Section 10.11 –
Pioneering in the Humid Tropics in Permaculture
If we are going to pioneer in the tropics, the only ethical conditions in which we would contemplate such a process are to rehabilitate:
1. Grasslands developed by burning/grazing sequences and monsoon grasslands.
2. Semi-forested clearings and old monoculture plantations of, e.g. sugarcane, banana, pine, eucalypt, pineapple. (We will suppose some “weed” invasion by Lantana, tobacco bush, vines or shrubs.)
3. Logged and burnt forest with reject logs, branches, stumps and weedy re-growth.
These are some typical conditions. The end results we would envisage would range from:
- Terrace culture and water absorption systems;
- Extensive aquaculture or substantial dams;
- Polycultural forests;
- Managed forestry or rehabilitative forestry for perpetual yields;
Or, more probably, we would plan for all of these in appropriate combinations for site.
(Figure 10.43) and (Figure 10.44)
The management or deforested grassland areas are the main problem of the wet dry tropics: soil erosion, rank grasses in the wet and inflammable or low nutrition reed in drought result from burning and over-grazing.
Once deforested, the pastures are open to summer winds and the nutrient cycle of trees/grass/ browsing is broken.
Fire, often out of control, only accelerates the process. Although there are very few trees which can survive in tropical grasslands, it is essential to reestablish tree legumes.
Some vigorous grassland cover crop legumes (Desmodium, Suratro) will help reduce the grasses and eventually lay down mulch.
Under trees, a short stemmed Desmodium will defeat the grasses, but it is then essential to be able to supply dry-season water, as the legume also competes with the young trees for moisture.
Some fast-growing leguminous trees (Albizzia, Acacia, Inga, and Leucaena) will quickly establish, and can be grown in the shelter of banna grass or elephant grass (Pennisetum).
If these grow vigorously, they also provide green mulch.
Heavy cattle browsing are a major cause or pasture deterioration and soil loss.
Their extensive grazing is probably the most common destructive use or tropical lands.
The first step is therefore to relieve the land of the weight of too many cattle.
No nation, nor the globe, can support destructive grazing agriculture on the agribusiness/cowboy/pyromaniac model so general in tropical countries and wherever “cheap” beef is produced.
The long term cost makes such systems uneconomic in any terms.
A positive approach is to re-establish either a multi-species system ecology (trees and a variety of browsers), or to intensify cattle rearing.
Cliff Adam, Chief Research Officer at Grand Anse, Mahe, in the Seychelles has grown Pennisetum atropurpureum (7 parts) plus Leucaena leucocephala the low-mimosa type available in Australia (1 part) and may add the Bocking strain of comfrey.
This “pasture“, cut and fed to cows, supports seven milk cows to the acre.
All manure and washings from stable/dairy are returned to the irrigated field.
Imported artificial manures have been reduced to one-tenth and he hopes to further reduce this import by building soil.
Meanwhile, in the same climate in Australia, one cow per square mile is enough to lay waste to the land.
A friend who bought a degraded cattle property north of the Daintree River (Queensland, Australia) gathers a load of coconut from the beaches and (travelling the ridges or old fields just before the wet season) throws dozens of coconuts at intervals into the stream-lines and gullies.
About 4% take root and grow into sheltered and pioneering palms. Not far south of there, another innovator rolls down the monsoon grasses as they begin to die off in the dry season and broadcasts tall-stalk rye and field legumes (Fava, Dolichos, Vigna) into the thick resulting mulch.
Enough moisture persists over the dry winter season to grow these crops; after harvest, the monsoon grasses re-grow for next year’s rye crop.
This clever use of seasons and growth is possible for the establishment of many species, some of which be come permanent and grass-defeating pioneers for later evolutions.
Consolidation of the area for regenerative forestry, however, proceeds more surely as a scattered set or pioneer tree and herbaceous nuclei; that is, the steady establishment of CLUMPED pioneer trees in open grassland.
This is a “natural” process which duplicates the seeding or grasslands by fruit pigeons and fruit eating birds. (Figure 10.45)
In steep moist valleys, there is good reason to plant patches of bamboo and rattan palm for a later “wild” harvest, large nut trees of heavy water demand (macadamia, coconut, pecan), wind sensitive large fruits (Avocado) and a selection of high value timber trees (rosewood, teak, cedar, tropical conifers, balsa, mahogany).
On more gentle and accessible slopes, a mixture of productive tree and palm crop can be planted in the shelter of pioneers and on ridges a protective windbreak of hardy palms, Casuarinas and wind-fast legumes.
Excellent nuclei clumps in grassland are built up from a close planted (1-2m spacing) mixture of Acacia mearnsii, A melanoxylon, Inga, Gliricidia, Nicotiana, Casuarinas, Vigna, Tagates, Comfrey, a box or two of nasturtium (box, soil and all), a few handfuls of fertilizer and a visit to slash grass and tall weeds occasionally.
Any stones, logs, cardboard or old carpets help if laid in the clump.
Natural aids are stumps (plant in these) and large rocks, keep them central to the clump. Plant around boxes, logs, log piles (pocket soil and plant in the logs) even around old buildings and rock walls. It is within and around these pioneer nuclei that we can commence re-forestation of productive tree crop, using our nuclei as mulch sources.
A GENERAL NOTE ON THE LEGUMES
Most legumes and other genera of plants such as alder and Casuarinas have mycelia root associates which fix atmospheric nitrogen.
As these organisms, and the roots to which they attach, are in a constant process of death and replacement over a growing season, much of the nitrogen is also released for use by other plant species.
Clover and tree legumes perform the same benefit for pastures. Such trees as the rain tree (Samanea saman) can preserve green grass below even in dry seasons
The amount of nitrogen fixed has usually been underestimated, at 75-100kg of nitrogen/ha/year, but efficient legumes such as lucerne (alfalfa) may provide 250-500kg of nitrogen/ha/year, and tree legumes such as Albizzia as much in quite poor sandy soils [Iseky, D, 1982, Economic Botany 36(1)].
Every part of such legumes as Leucaena, Acacia, Albizzia, Gliricidia and Tephrosia may contain high nitrogen levels; one can actually smell the ammonia from the trees in rain or when the roots are crushed.
Thus, cut green material from such trees (green mulch) lightly turned into crop, water mulched or even as interplant, supplies much of the nitrogen for crops.
It is necessary to make sure the trees are inoculated as seed with the correct root, associates in the nursery or in the field.
Most agricultural departments can supply a list of strains of inoculants or the inoculums themselves. Many firms supply inoculums for legume and other species or soil from nodulating trees can be washed in around newly planted trees or mixed with potting soils
The nitrogen is distributed around root zones as per Figure 10.46.
Some shrubs and trees lay down about a 9-year supply and if cut or ring barked, the slow decay of the roots gives up nitrogen for 6 years or so.
Nitrogen, if supplied artificially, quickly leaches in warm rains, so legumes, with their slow nitrogen release, are of critical importance in any tropical crop situation.
The management of leguminous tree crop must be carefully assessed for local conditions.
Some considerations are:
With shrubs and small trees, 0.5m apart is the best for foliage production and a trimming height of from 0.5-1.5m is recommended.
Only in frost-free tropics can we trim all year (4-5 cuts). Wherever cold is a seasonal problem, two months of growth must be allowed to harden the plant before winter or it will weaken as the shoots are cold-killed. Trees in drought can be part-trimmed.
There is some danger that young (coppice) shoots will have higher levels of metabolic poisons than 2-3 year old shoots and if stock does not thrive, this factor should be assessed.
Trees can be more widely spaced for root nitrogen, seed production (e.g. for poultry and bees) and for on crop shelter, as flowering and seed production is better at 2-20m spacing (depending on tree size). A full canopy may be needed to reduce or eliminate frost.
Although many trees will coppice for 4-30 years, any sign of loss or vigor should indicate the need to replant. Replant for small shrubs may be necessary every 2-3 years, while some shrubs and ground covers are annuals or become annuals in cold-season areas.
To assess total nitrogen yield, we must assess soil nitrogen from mycelia (say 200kg/ha/year) and leaf and slash nitrogen/ha. In such crops as Tephrosia, yielding 135t/ha in 4 cuts, leaf nitrogen should be about 20-30 kg/t, or 1,000-1,500kg/ha/year, which is some factors higher than the root nitrogen yield.
This is the whole rationale for avenue cropping and legume mulch. Phosphate and potash levels in green mulch are also satisfactory for crop production.
PIONEERING IN SECONDARY FOREST GROWTH AND LANTANA
Lantana is analogous to the rampancy of gorse and blackberry in cooler areas and the essential process remains the same:
- Roll down, crush or cut out contour strips;
- Plant advanced vigorous mixes of Acacia, Eucalyptus, vines such as chayote, ground legumes and local pioneer species.
- Manure each plant and mark small plants so they can be easily seen;
- Slash every few weeks in the wet season until the trees are above the Lantana canopy and free any new natural tree seedling that comes up;
- Do final slash at or about 18 months and then cut or roll adjacent strips to extend the system;
- Use early pioneers (e.g. Acacia) as mulch for selected high-value species as previously planned.
The shading out of Lantana takes from 2-6 years and only remnant and weak shoots remain under productive forest.
In all extensive hill areas of gorse or Lantana, benches or roads cut on contour every 250-1000m is a great aid to the regenerative forest processes and subsequent harvesting or slashing of new plantations.
These can be kept mowed and cleared and eventually stabilize as trees grow.
Road borders can be of dense, evergreen, wide-crowned trees for track shading and stability.
Such deep shade also keeps fences clear of grasses and weed crops.
PIONEERING ON DIFFICULT TERRAIN
On man-made and natural landslide or volcanic areas of the tropics, it is first necessary to pocket the area with soil-mulch mixtures. (nut husks from coconut and macadamia are excellent to establish any pioneer species)
Thereafter, species such as Inga edulis, Leucaena leucocephala, various Acacias (A. mearnsii), Scalesia pedunculata, Prosopis pallida, and like legumes (Dolichos, Desmodium) will prepare the area for palms, cacti, figs and the more useful fruit trees, by providing shelter and mulch for subsequent plantings.
It is better to plant small assemblies than to space out a lot of species on their own.
A heavy spiked roller crushes new lava; crushed lava is both accessible and easily rotted to soils. Soil pockets can be provided with trace elements (boron, manganese, zinc, copper, molybdenum) if not analyzed as present in any specific location.
Near the sea and on islands, the night air condenses on the sea-facing side of the stones, which have a richer moss-algae-lichen flora than the inland side and pockets of vegetation act in a similar manner to condense sea vapors for their use.
Thus, islands and sea coasts will have dry and wet sides suited to different plant species.
In such conditions, a ragged or spiky forest canopy, where palms and tall pines or fruit trees lift above the general canopy layer, will ensure more condensation from sea air than will a level and relatively closed canopy.
The saturated winds that sweep off tropic seas carry a heavy moisture load which is available as dew on grasslands, but is much more effectively trapped on the myriad leaf surfaces of an uneven canopy of trees, hence, the forested slopes of sea-facing mountains in tropic trade wind areas.
Even small garden tree patches “rain” softly on clear nights when a sea-wind is blowing and let down drips in a steady stream to swell dried out leaves and to channel down leaf mid-ribs to the fibrous trunks of palms and tree ferns.
Once plants are cleared, the effective precipitation falls, rivers cease to flow and the land becomes truly dry.
Wherever overgrazing, plus fire or cut and burn forestry, has ruined native forests, in particular towards the wet dry tropics, closed grassland species of fire-prone and tough grasslands develop, closing out the tree seedbed and preventing good management practices.
Further burning or cultivation may result in a depauperate grassland of low stock carrying capacity over the dry period and patches of bare and eroded soils, low in nutrient states and at times acidic (pH 4.0-4.5) may develop.
Blady grass (Imperata cylindrica) and other tropical forage grasses are stubborn, tough and almost impenetrable barriers to gardeners and stock, although they provide good mulch.
Given rains of 60-150cm, a set of rough pioneer legumes are available for the rehabilitation of exhausted sites (including mine spoils and road embankments).
Providing enough seed can be obtained, direct seeding in scratch holes or chiseled strips will result in the fast establishment of some or all of the species listed below, to which can be added Leucaena and Albizzia species.
Tropical grasses, scythed or mown 5-8 times annually, make good mulch for trees and gardens.
When using legumes, leaf-drop and nodulation will re-establish soil fertility.
The canopies of Acacia auriculiformis or A. mangium will shade out and kill the grasses, so that fire intensity is reduced or eventually eliminated.
Using these pioneer legumes as nurse crop, firewood, pulp timber, mulch and honey sources, and high-value timber such as rosewood, mahogany and ebony can be introduced in lines or clearings in the first crop and the gradation made to either high-value forestry or to sensible strip cultivation on a sustainable basis.
If Leucaena, Samanea, Prosopis and Inga are planted, a long-term forage system will evolve, providing replanting or rest periods are given for seedlings to re-establish.
The only thing preventing or delaying savannah forestry is a lack of tree nurseries and seed sources of appropriate species and this too presents an opportunity for a pioneering enterprise in the humid tropics.
A very good selection of potential species can be found in the National Academy of Sciences publication referenced at the end of this chapter.
Species such as Pterocarpus indicus or P. erinaceus can be first seed-planted in a nursery stand, then coppiced for 2m quickset planting in bore-holes in the field.
Some species can be set out at 10cm diameter, and make good timber trees. (Figure 10.47)
PIONEER AND GRASS-EXCLUDING SPECIES, FIREWOODS
Acacia auriculiformis is an important pioneer for exhausted savannah and tropical soils, where over a very wide range of soils and sites it can defeat blady grass (Imperata cylindrica), restore fertility, provide firewood and act as a tree nurse crop.
It reduces fire and provides good paper pulp. It coppices and self-seeds and is widely used in tropics as a shade and street tree. A. mangium has similar characteristics but is straight-stemmed and therefore better suited to forestry operations.
Sesbania grandiflora is a fast tropical pioneer, can be coppiced and is a good forage tree, an excellent green manure in rice and re-invigorates worn-out land.
It has exceptional nodulation, grows to 10m and provides good firewood. It also has wide soil tolerance and is extensively used for eroded hill sites.
Young leaves, pods, and flowers are used for human food (36% crude protein). Seeds are 40% protein.
Used as a light shade crop or vine support. It is frost and wind tender, with a life of about 20 years.
All of the food from this tree should be cooked. It is exceptionally fast growing.
Calliandra collothyrsus is a stick wood coppicing species which defeats grasses and provides abundant firewood.
Repairs exhausted soils and restores fertility.
Dalbergia sissoo is salt and frost tolerant, fast and defeats grasses.
It tolerates a wide range of soil types and can be quickset from large cuttings (India).
Enterolobium cyclocarpum is a durable timber tree with large pods, defeats grasses (Central America)
Mimosa scabrella of Brazil is a subtropical pioneer; it provides good humus and a living fence
Samanea saman (rain tree) is a very last-growing large tree of the tropics and subtropics, with sugary pods. Grass grows well below it plus the wood is valuable and durable.