|Agroforestry for the Pacific Technologies - Fact-Sheets of the Agroforestry Information Service - Nrs 1-15 and Agroforestry Species Highlights nrs 1-2 (Winrock, 1992-1995, 58 p.) (Winrock, 1992-1995, 58 p.)|
|Ais technology fact-sheet|
Ais technology fact-sheet
A Regular Publication of AIS, 1010 Holomua Road, Paia, Hawaii, 96770
Agroforestry land-use technologies are nothing new in the Pacific Island region, or the world for that matter. In a loose sense, agroforestry began when Man first turned from a hunting and gathering lifestyle and took up plant culture. Though maybe not purposefully integrated, trees and farm crops have always occurred together in systems where subsistence was the primary farming objective.
Social trends and economic development forces of more recent times have placed a huge amount of importance on short-term product and thus profit maximization. Cash, rather than subsistence crops have understandably been the focus of more advanced societies. Economic rationale tells the farmer to maximize production of the crop that gets him/her the most money at the market. Agroforestry systems were often replaced with crop mono-culture where trees were seen to interfere with crop yield maximization.
Today, many agree that the rapid agricultural conversion that went on during the 'green revolution'. was short-sighted indeed. Intensive mono-cropping systems, though perhaps more profitable for a time, are much more risky and costly in the long run. Risky because crop prices are always changing and pest infestations can destroy entire harvests. Costly because these intensive farming practices degrade most soils rapidly, and thus require expensive chemical and fertilizer inputs to sustain productivity.
The scattered and isolated nature of Pacific Island countries is a mixed blessing. The region has been excluded from most global trade activities and international market pressures. Most countries have not been driven to costly mistakes in attempting to maximize short-term export income. Multi-cropping agroforestry systems remain intact over much of the landscape.
The region is not without its problems. Arable land has never been in abundant supply. Growing population pressures and modern land ownership uncertainties make land scarcities increasingly apparent. The most common traditional agroforestry systems of the swidden variety, are no longer sustainable where a shortage of land forces farmers to reduce fallow periods. Root crops, staples in most cultures, require that the soil be disturbed twice in a single rotation. Shortened fallows do not allow soils to recover. They quickly lose their productive potential and become highly erodible.
Traditional agroforestry systems must be improved so as to increase subsistence and market produce from limited land areas over time. In more modern, more intensive agroforestry systems, trees are not just tolerated or passively allowed to regenerate during fallows. They are planted, arranged, managed, and harvested alongside agricultural crops and/or farm animals in a way that optimizes overall farm productivity in the short and long term. Trees are used to create a more favorable and sustainable environment for crop and/or animal production while providing additional products themselves.
Why are Agroforestry Systems more Productive?
They use limited resources more efficiently.
· SUN: Multi-storied cropping systems absorb sunlight at all levels.
· SOIL NUITRIENTS: Deep tree roots take up soil nutrients and moisture that are out of reach of root crops.
· WATER Trees shelter crops and soil surfaces from drying winds and intense sun. Tree-leaf mulch retains moisture in upper soil layers.
· LAND: Trees serve to continuously sustain rather than periodically rebuild soils. Fallow requirements are reduced, leaving more land in production at any one time.
They provide a more favorable environment for sustained cropping
· SHADE: Filtered shade keeps topsoil cool, increasing beneficial soil microbe activity and reducing soil water loss.
· WIND PROTECTION: Trees protect the soil and crops from damaging, erosive, and drying winds.
· SOIL ANCHORING: Tree roots bind soil, preventing down-slope erosion during rains.
· SOIL BUILDING/MAINTENANCE: Tree leaf litter becomes organic humus that builds good soil structure. The stronger soil is more resistant to erosion and more able to absorb/hold water.
· NUTRIENT CYCLING: Trees draw nutrients from below crop root reach and then release them on the soil surface as leaves fall or branches arc pruned.
· HABITAT DIVERSITY: Trees provide habitats for animals and birds that eat crop pests and insects.
Promising agroforestry system for pacific islands
They provide a more continuous flow of more products over time.
· SHORT-TERM PRODUCTS: Root and grain crops, tree nuts and fruits, fuelwood, posts, animal fodder, medicines, and livestock.
· LONG-TERM PRODUCTS: Valuable construction timber, larger fuelwood, and other wood products such as pulp and veneer.
Why is Agroforestry so Necessary in the Pacific?
· TRADE WINDS: Crops and soils need protection from wind damage, drying, and erosion.
· ROOT-CROP CULTIVATION: Methods expose and disturb soil twice in a rotation.
· INTENSE RAINS: On sloping
terrain, frequent, intense rains wash soil away rapidly if it is disturbed and
SOILS: Soils derived from volcanic rock and ash are commonly acidic and thus more subject to nutrient loss/leaching.
· LAND SCARCITY: Arable land is the most scarce and thus valuable natural resource.
Agroforestry is arguably a more sustainable and optimal way of farming in most resource-limited environments. This seems to be especially true in the Pacific, where growing and developing populations are confined to relatively small and scattered areas.
Successful agroforestry though, requires careful planning and usually more labor. Trees and crops must be arranged and managed properly if overall productivity is to be increased and sustained. Left unmanaged, trees can out-compete crops, and reduce yields.
Pacific Island farmers appreciate the worth and function of trees in agricultural systems. They did not traditionally, however, manipulate and manage the tree component to the degree that most modern agroforestry practices require. They must be convinced that the products and benefits will justify their added time and labor inputs.
The active promotion of agroforestry in the Pacific, through information transfer, demonstration, and on farm research, is without question a worthwhile and timely task.
AIS TECHNOLOGY FACT-SHEET
A Regular Publication of AIS, 1010 Holomua Road, Paia, Hawaii, 96770
Root-crops, primarily taro, sweet potato, and cassava, are important subsistence and market foods in most Pacific Island cultures. Traditional upland root-crop cultivation included lengthy soil restoring fallows between short croppings. After just 2 to 3 years of root-crop production, lands were typically left to rest for 10 to IS years. Farmers have always recognized that the planting and harvesting of root crops disturbs soils more than does the farming of above-ground crops. Root crops must be dug in and dug out.
Unfortunately, modern population pressures and landowner ship uncertainties are creating situations of land scarcity that make long fallows infeasible for most. The soil degradation resulting from shortened fallows is affecting productivity and increasing dependencies on food imports such as rice and flour in many areas.
Hedgerow intercropping (HI), the practice of farming annual crops in the spaces or 'alleys' between rows of multipurpose trees is a promising alternative to the traditional fallow system. Trees planted and managed in hedgerows provide the same products and services as those that were allowed to grow during traditional fallow periods. Trees cycle nutrients from deeper in the soil profile by shedding organic matter on the surface as leafy and woody litter or 'green manure'. Litter rebuilds a soil's structure making it less erodible and more able to absorb and hold water. Hedgerows also yield other products such as fuelwood and fodder. They create a more favorable micro-climate for crops by shielding them from drying winds. Hedges planted on slopes, also anchor soil and form terraces, preventing the loss of precious topsoil by heavy rains and the overland flow of water.
Traditional systems combined trees with crops on the same piece of land in a time sequence. Hedgerow intercropping combines trees with annual crops on the same piece of land at the same time. The tree and crop components are managed so as to be complimentary rather than competitive. The successful HI system maximizes the product per unit of land over time. To accomplish this, competition between the crops in the alleys and the trees in the rows must be minimized. This requires the orderly spatial arrangement and rather intensive management of the tree component. It could be said that traditional systems require a large land input whereas HI systems require more labor input. Where land is more scarce than labor, this agroforestry practice makes good sense.
Hedgerow intercropping does not necessarily eliminate the fallow requirement. Because the tree component of the HI system is kept on the land during crop production, one could say that it performs a 'semi-fallow' function continuously. This means that cropping cycles can be lengthened and fallows shortened without degrading the soil and reducing system productivity over time.
The trees recommended for these systems are chosen for their multipurpose/multiproduct characteristics. They provide soil-improving services, are fast-growing, and produce a number of useful products.
In short, the primary benefit of HI over traditional systems, is a more continuous, more sustainable flow of both tree and food products from one piece of land through time.
SETINGUP AND MANAGING A HEDGEROW INTERCROPPING SYSTEM
I. TREE SPECIES SELECTION
HI trees provide desired products/services while competing as little as possible with neighboring crops. Characteristics of good HI trees are:
Rapid growth and biomass production: More leafy biomass and small branch production means more litter/mulch accumulation, more fodder, and/or more fuelwood.
Smaller, bushy Smaller: Smaller, multistemmed trees normally produce more biomass of a higher leaf: stem ratio than larger, single stemmed species.
Deep-rooting: Take-up nutrients and water out of reach of root-crops.
Easy to destablish: Trees are easy to raise from seed either directly field-planted or in pots. Cuttings develop more rapidly but produce only lateral roots that compete more with neighboring crops.
Repeated crops and/or reability Stems and leaves grow back again and again after pruning or topping.
Nitrogen fixing Nitrogen fixing trees are able to 'fix' atmospheric nitrogen and contribute this to the system in leaf litter fall/break-down.
Free from pests and diseases: Trees should not be hosts to crop-damaging insect or fungus pests.
Easily controlled: Trees that become weedy and will spread into alleys or neighboring fields are not desirable.
Widely adaptable and stress tolerant: Trees should be adapted to a range of soil characteristics and tolerant of environmental adversities such as high winds and periodic drought.
Multipurpose:. To provide an adequate return to land and labor inputs, trees must produce a number of useful products and services.
The multipurpose tree species so far identified as being very promising for Pacific Island use are: Calliandra calothyrsus, Gliricidia sepium, Flemingia macrophylla, and Erythrina subumbrans. All grow rapidly and produce lots of soil enriching 'green manure', good fuelwood, and fodder. Calliandra and Gliricidia can both produce fuelwood-diameter limbs within one year. Flemingia and Erythrina usually produce smaller diameter stems early-on, but more leaf litter than the other two. On very acid soils (<pH 5), Calliandra does the best. Flemingia litter takes longer to break down which can be an advantage in the tropics where some humus build-up is desired. All have done well on both basalt and coral derived upland island soils.
Less tried but also promising are, Albizia saman, Pithecellobium dulce, Paraserianthes falcataria, Cajanus cajan, and some Acacia, Leucaena, and Prosopis spp.
Albizia, Acacia, and Prosopis spp. all have a tendency to become weedy on islands. Leucaena species are also considered weeds in most situations and are attacked by psyllid insects when pruned repeatedly as in HI systems. Paraserianthes falcataria and Cajanus cajan tend to die back after 3 or 4 years of repeated pruning. These species do not coppice very well in general. Paraserianthes is also very susceptible to wind damage.
HEDGEROW TREE SPECIES FOR PACIFIC ISLAND UPLANDS
Wise tree species selections cannot be made without considering planting site characteristics. Species all have unique sets of tolerances and preferences for certain soil types and climates. The following site factors must be examined so that suitable tree species are selected:
· Mean annual
· Mean annual temperature.
· Length and frequency of yearly droughts.
· Yearly/daily minimum and maximum temps.
· Incidence of frost.
· Topography elevation, aspect, and %slope.
· Soil pH, texture, and depth.
II. SPATIAL ARRANGEMENT
Orientation: The ideal tree row would be oriented east to west, perpendicular to prevailing winds, and parallel to slope contour. This orientation provides maximum 'alley' (crop) sun exposure and maximum erosion control. Obviously, this is not always possible. Tree rows should be oriented to provide the most benefit and the least competition given the particular environment. Where there is slope, it is always best to plant along contours.
'Alley' Width: The most important HI system design decision is alley width. Alley width will determine the ratio of tree products/services to crop product and the degree of competition between the root-crops and trees. If alleys are too narrow, root-crop yields will drop off dramatically as tree hedges grow. If alleys are too wide, the soil improving role of trees is reduced and long fallows will still be required. Based on tried systems, a 5 to 6 meter width is recommended.
Within row spacing. The recommended hedge consist of two lines of trees 50 em. apart. Trees within the lines should be at 30 to 50 em. spacings. Close spacings encourage more leaf and smaller branch production. In general, HI systems of 2-row hedges and wider alleys are more productive than those of 1-row hedges and narrower alleys. With 2-row alleys, there is less tree-crop interface (competition).
Root-crop spacing. Root-crops should be planted at traditional spacings. The space between crop plants and any one tree row should be at least 0.5 m.
Diagram adapted from work of nfta associate charles rogers, vanuatu
III MANAGEMENT AND PRODUCT HARVESTS
Hedge Periodic hedge hedge is necessary to prevent trees from shading-out your crop. The amount/frequency of pruning required will depend on the shade tolerance of a particular root crop at a particular stage in development. -Most root-crops are very light demanding but will benefit from some shade during the first couple months of development. Shade also discourages weeds. A good rule is to maintain a hedge height equal to the distance between the hedge and nearest crop row (50cm to lm).
Hedge Height Relative to Distance Between Hedge and Crop Row
Pruning frequency will also depend on the product mix desired. More frequent pruning adds more 'green manure' to the soil. Less frequent pruning will produce more fuelwood-diameter branches.
The timing of prunings is more important in tropical environments where leaf decomposition and organic matter mineralization occur rapidly. Prunings should be timed so that applied litter is releasing nutrients when the root crops are most demanding - during rapid corm development.
Crop Rotation and Fallows:. Continuous cropping may be possible in some very productive HI systems where organic matter and nutrients are continually returned to the soil in large enough quantities.
It is likely though, that some fallow between the normal 3 to 4 year cropping period will be required. Two years seems to be a reasonable period. After a 2-year fallow, during which hedges are left alone, a major fuelwood harvest can be expected. Crop yields are the best indicator of the fallow requirement. Once the hedgerows arc in place, the farmer should experiment with different fallow lengths to find the combination that yields the most while maintaining the site's productivity. Different sites will require different management strategies. In any situation, continued, close observation of crop performance is essential.
PRODUCT AND SERVICES PROVIDED BY TREK HEDGEROWS,
· Nutrient cycling from deeper
The technical guidelines offered here are based largely on information collected by the AIS Information Officer during field visits and personal interviews with project personnel. The following research projects are especially noteworthy and continue to provide useful information on this subject for all those interested:
EC/Pactfic Region Agricultural Program Agroforestry Trials at USP Alafua, Apia, Western Samoa. Stephen Rogers, IRETA Research Fellow.
Plantation Training Center, Integrated Smallholder Cropping/Livestock Triad, Montmartre, Port Vila, Vanuatu. Charles Rogers, Project Manager.
GTZ/Fiji-German Forestry Project, PO Box 14041, Suva, Fiji. Martin Homola, Chief Forestry Advisor, and Wieland Kunzel, Technical Advisor.
AIS Technology Fact Sheet
Many farming activities interfere with-or even prevent the natural processes of nutrient and organic matter cycling. Some harvesting practices remove plant material or organic matter year after year while returning none JO the soil The inevitable result is a rapid decline in soil productivity. In some cases inorganic store-bought fertilizers are then added in larger and larger quantities to sustain crop yields. In other cases, farmers must allow a soil to fallow or 'rest' for several years between relatively brief cropping periods. Both of these methods of soil maintenance are very costly, especially where land and/or cash is in short supply.
Agroforestry strategies that integrate trees with crops provide a variety of products and services depending upon species included, management techniques, etc. They do share one common objective - sustaining the soil organic matter component.
The trees in all agroforestry systems, make continuous organic matter contributions to the soil. Scattered trees in fields, windbreaks, and live-fences all shed leaves and branches. Trees in hedgerow intercropping systems are usually chosen and managed purposefully to maximize their organic matter contribution. Leaf material is frequently pruned and applied to cropping soil as green manure.
Some grasses and annual 'coyer-crops' are seeded and grown seasonally in fields to provide organic matter or 'green manure'. Various Crotolaria and Sesbania species are grown in this way and then plowed into soils between cropping periods.
Organic matter returning organic matter to a soil as it is removed - can do wonders to increase and sustain a soil's productivity. All of the properties of a highly productive soil are dependent upon the presence of organic matter
· Soil fertility Organic matter adds plant nutrients to the soil as it breaks down. It also provides sites for nutrients to bind to, holding them in upper soil layers where plants can use them.
· Soil structure The slimes and microbial gums produced by decomposing organic matter bind soil particles. The result is a stronger, granular, more permeable and workable soil.
· Soil water holding capacity: A soil with good structure is more permeable and porous. Water infiltrates more easily and is held in small soil pores.
· Soil pH: Organic matter additions reduce the pH of excessively alkaline soils. The decomposition process releases hydrogen ions, increasing soil acidity.
Without regular organic matter addition, soils become drained of essential plant nutrients and unable to absorb or retain water. As their structure is weakened, soils are much more susceptible to the forces of wind and water erosion.
All trees, regardless of how they are arranged or managed, can be regularly harvested for organic matter. This plant material can then be applied to the soil surface around crops as mulch - or mixed with the soil in piles or pits to form compost.
Mulching is the spreading of any material - green or dry - on the soil surface.
What are the benefits of mulching?
· Mulch controls weeds: A good
layer of mulch shades the soil and prevents weeds from germinating.
. Mulch conserves soil moisture It creates a barrier against the drying effects of sun and wind.
· Mulch fertilizes soil: As mulch breaks down, it releases essential plant nutrients.
· Mulch builds soil structure: As mulch breaks down it makes the surface soil permeable and increases its water holding capacity.
· Mulch stops soil erosion It protects soil from the erosive forces of wind and water. It shields soil from heavy raindrops and slow-c runoff water that flows over the soil surface.
What materials can you use for mulch?
· Plant materials: Leaves, small
branches, coconut husks and stems, and wood chips all make good mulch. Whenever
possible, cut or crush materials into small pieces. Smaller sized pieces produce
a more effective mulch.
· Animal residuesuch as manure. Do not use fresh/wet manure as this can burn plant roots.
How do you apply mulch?
· Before planting If you want to
apply mulch before planting, spread the plant material about 4 cm thick over
individual rows - or the entire area. Then just clear small areas for
seed/seedlings and plant as usual. Do not cover newly sown seeds with
· After planting: If you want to mulch after planting just take care not to damage seedlings. If the plants or trees are already established, just pile mulch around the bases of trees in 1 m diameters.
Composting is the practice of mixing and piling plant and/or animal material with soil to form partially decayed, smaller particles of organic matter - or humus. Composting practices favor the micro-organisms that work - or break organic matter down into the proteins, starches and sugars of humus. Humus contains chemical and mineral substances in forms that plants can use immediately. Humus is also the form of organic matter that most directly adds to a soil's productive properties.
What are the benefits of composting?
Composting simply speeds the organic matter breakdown process that occurs over time in nature when the same materials pile up in layers on the soil surface as mulch. Composted organic matter can be placed in direct contact with plant roots as a soil amendment or bedding material Compost improves soil properties just as mulch does - just more immediately and extensively. Compost is really just partially decomposed mulch. A soil that contains a lot of compost or organic matter is said to have a "spongy structure". Such soil resists compaction and erosion. It captures and holds water oxygen, and essential plant nutrients.
What materials can you use for compost?
Plant materials: Leaves from trees or grass, animal manures, twigs, sawdust, wood-ash, and kitchen scraps all make good compost ingredients.
Animal residues: Dry or wet manure can be used for composting.
How do you make compost?
Quite simply, you make compost by throwing a lot of organic matter - and some soil - into a big pile or pit.
Many consider composting an art and recommend special composting structures and various material layering techniques. Most recommend gathering all needed materials at once to form a complete pile. These techniques demand lots of time and labor.
You may not have enough material on-hand to build a complete pile at once. You can also create a good compost pile over time, bit by bit Making a good compost is not that tricky but there are some simple steps that will greatly speed the whole process:
· Add an equal ratio of green to dry material: Add dry stems, leaves and soil to your pile in equal measure with green plant material and manure.
· Keep compost moist: Build your compost pile in the shade and keep it covered with large leaves, coconut fronds, or a mat. If it rains often enough you should not have to add any water. It is best to check the pile every few days to make sure it stays moist. It should not be too wet - just moist.
· Keep compost aired - provideoxygen Turn/mixyour pile once a week. The microbes that work the compost need oxygen.
A Compost Pile
All of the above will speed the process of organic matter decomposition by favoring the activity of the microorganisms responsible. A compost made and maintained like this will be ready for use about 6 weeks after the last ingredients are added.
How do you use the compost?
You can use the finished compost as a potting mix, a bedding mix, or a soil amendment. If your soil is really poor, you may want to raise demanding food crops such as vegetables, in beds or pots of only compost This is a common practice on atolls where soil is often completely lacking in organic matter. You can also add compost to existing soil or dig it into the soil surroundinga plant.
You can also just dig holes next to fruit trees and periodically throw organic matter into them. This works where soils are well drained. If too wet, these pits may lack the oxygen required by the composting microbes.
AlS Technology Fact Sheet
Atoll soils form from coral reefs that grew on the tops of subsiding volcanoes during various periods - throughout the Pacific. Most of these soils are quite young in geologic terms and thus still similar in property to this coral parent material. Coralline soils are extremely nutrient deficient and highly alkaline. They are especially lacking in iron potassium, and nitrogen. The so-called "soils" of atolls is really not soil at all since it is not made up of the usual components of soil: mineral sand, silt, and clay Organic matter is all that really does distinguish most atoll soil from crushed coral.
Atoll farmers have always practiced mulching and composting to some degree. Most consider regular organic additions integral to any agricultural activity. Organic matter management - more on atolls than anywhere - is crucial to sustained food production Organic matter holds nutrient ions, retains precious soil moisture, and buffers soil pH. In all soils, it builds and maintains good soil structure and provides essential plant nutrients. In atoll soil, it must also take the place of the missing clay component in providing nutrient caution exchange sites that are crucial to nutrient cycling processes.
Atoll farmers and gardeners typically make compost by piling-up rotting coconut shells/stems, household rubbish, and any green material they can find. Most simply pile this material next to a target crop or tree as a mulch. The mulch then breaks down into compost over time. Many actually make compost first and then purposefully place it into garden trenches, holes, and taro pits as bedding material.
Although composing has always been part of the farming/gardening routine on atolls, one key ingredient is in very scarce supply - Fresh/green organic matter. As a result, mulch and compost are often spread too thinly to yield significant benefits. Compost formation is slowed drastically in piles with too high a dry green (carbon: nitrogen) ratio of organic material.
Nitrogen-fixing trees are gaining recognition as promising atoll agroforest/garden additions and renewable sources of soil-building organic matter. Anyone who knows a bit about the unique characteristics of these trees should not find this surprising.
Why Nitrogen Fixing Trees?
Nitrogen-fixing trees are able to "fix" or take-up atmospheric nitrogen (N2) that is not available to other trees. They do this through a symbiotic relationship with certain bacteria - Rhizobia and Frankia - that form nodules in their roots. When the leaves and branches of these trees drop off or are harvested, this nitrogen becomes available to other plants or animals in the ecosystem.
Most nitrogen fixing trees are "pioneers" - They establish easily on poor or degraded sites. These tenacious trees also grow rapidly, and produce large amounts of nitrogen-rich green foliage in some rather harsh environments.
Good mulch/compost producing nitrogen fixing trees for atolls also have the following characteristics:
A high leaf nitrogen concentration
A tolerance to excessive soil alkalinity A tolerance to excessive soil salinity
A relatively high leaf tannin content:
Many nitrogen fixing trees - such as Acacza spp. - contain tannins that slow the decomposition process. This is desireable in very humid, warm environments where the rapid break-down of organic matter prevents the build-up of a protective mulch or humus layer.
· Repeated and vigorous resprouting/regrowth after pruning: Many nitrogen fixing trees can be pruned or lopped as often as four times a year.
· Multi-purpose/multi-product: In addition to compost/fertilizer, many nitrogen fixing trees produce human-food, firewood/charcoal, pig or goat fodder, and timber or poles for construction.
· Establishing and Integrating Nitrogen Fixing Trees
Because land-area is so scarce on atolls, it is especially important that selected trees be easily integrated into existing systems. Depending on local needs and preferences, a variety of tree planting and maintenance shames are possible:
· Living fences and hedges protect crops from roaming animals and human foot-traffic. Trees are arranged densely or planted as fence posts.
Living fences and hedges
Windbreaks are single or multiple rows of trees planted on windward field boundaries. Windbreaks slow wind, reducing physical damage to crops and fruit trees. Placed on the windward side of atolls, they can also prevent salt-spray from reaching the interior and reduce coastal erosion
· Hedgerows are dense single or multi-row plantings of trees within fields or among fruit tree plantations. Trees are arranged to minimize competition with the associated crop and pruned regularly to add compost or 'green manure' to the farming or garden system.
Shade and support are attained quickly from fast growing nitrogen fixing trees. Shade provides protection from the hot, drying sun. Living, soilenriching support is quickly established for vine crops such as beans, potatoes. yams. and Pepper.
Shade and support
Home garden plantings of nitrogen fixing trees provide soil organic matter/ fertility while yielding edible fruits. leaves and flowers.
If a nitrogen fixing tree is being introduced to a site for the first time, seed or soil inoculation may be required. Seed inoculation is the process of coating seeds with the nitrogen fixing bacteria prior to planting. The inoculant is just a material that contains the bacteria. inoculation is required when the proper bacteria is not already living in the soil where the tree will be planted. Most nitrogen fixing bacteria tolerate adverse environmental conditions such as soil alkalinity, to the same degree as the host tree. Inoculant for various nitrogen fixing tree species can be obtained from the NifTAL Center, 1000 Holomua Road, Paia, HI USA 96779.
Problems/Limitations with Nitrogen Fixing Trees
Weediness is a potential problem with nitrogen fixing trees, especially on small atolls with few native species. These trees, because of their nitrogen fixing capability, establish easily, grow rapidly, and tend produce large quantities of seed. Genetic improvement research has produced several varieties of many species such as Leucaena leucocephala. These improved varieties have less tendency to become weedy and are more compatible with crops. They are thus safer for introduction. All species introductions should be made with considerable caution.
Nitrogen Fixing Trees
On atolls, competition for precious groundwater is another possible problem where nitrogen fixing trees are planted into fields or fruit-tree plantations. Proper spacings and management techniques - such as periodic pruning - should reduce this problem.
Promising Nitrogen Fixing Trees for Atolls
The following nitrogen fixing trees are those that are proving themselves in harsh atoll conditions as good, renewable sources of nitrogen-rich mulch/compost material. All of these trees are tolerant to high soil pH. Those that are especially tolerant to soil salinity are noted for this. Each brief profile includes a list of outstanding characteristics and primary uses. All are easily propagated by seed and recommended seed-treatments are listed.
· Low to medium sized tree 8 to
20 m in height
· Thornless, heavily branched, short, crooked stem
· Open, spreading crown
· Tolerates droughts of 4 to 6 months
· Tolerates poor drainage/water logging
· Used for fuelwood, construction
· Boil seed for 30 seconds-let soak overnight or scarify
· Moderate to large deciduous
· Reaches 30 m in height with enough rain
· Straight bole when grown in dense forests
· Spreading and low branching in the open
· Produces an abundance of seed, unless coppiced frequently
· Tolerates droughts up to 8 months
· Highly tolerant of salt-spray
· Shallow roots - subject to wind-throw
· Leaves and young twigs make good livestock fodder Wood good for construction and fuel
· Soak seed in cool water 24 hrs or scarify
· Multi-stemmed shrub to 6
· Tolerates droughts to 6 months
· Used for fuelwood, fodder (fresh), honey
· Does not tolerate water logging
· No treatment necessary
· Soak seed in cool water 24 hrs or scarify
· Tall tree to 30 m
· Conifer-like appearance
· Thrives in sea-spray zones
· Tolerates droughts to 8 months
· Not tolerant to brush fires
· Relatively short-lived - 40-50 years
· Used for fuelwood, charcoal. windbreaks No seed treatment necessary
· Small, branching tree to 10
· Tolerates droughts to 8 months
· Tolerates saline soils
· Coppices and re-sprouts vigorously
· Used for fodder. nurse tree. Iive-fencing, windbreaks
· Leafless sticks root easily
· No seed treatment necessary
· Medium, thorny tree to 15
· Broad-spreading with irregular branches
· Coppices vigorously
· Shallow roots - subject to wind-throw
· Used for fuelwood, honey, fodder, edible pods
· Highly tolerant of soil salinity
· Tolerant to drought No seed treatment necessary - or scarify
· Medium tree to 12 m
· Tolerates droughts to 7 months
· Highly tolerant of soil salinity
· Tolerates poor drainage/water logging
· Susceptible to wind damage
· Used for fodder, edible flowers
· Scarify or soak seed in cool water 24 hrs
· Small, shrubby tree to 6
· Tolerates droughts to 8 months
· Tolerates periodic flooding and waterlogging
· Regenerates rapidly after pruning
· Used for fodder. firewood, edible flowers/leaves. windbreaks
· Scarify or soak seed in cool water 24 hrs
Cronquist A 1954. "Galegeae", in Flore du Congo Belge et do Ruanda-Urundi, Vol 5,p.77, Brussels.
Little E.L.Jr. 1982, Common Fuelwood Crops. Morgantown, West Virginia: Bower Communications Group.
Little E.L. Jr. and F.H. Wadsworth. 1964. Common Trees of Puerto Rico And the Virgin Islands. Ag. Hand. No. 249. USDA Forest Service, Washington D.C.
Verdcourt B. A manual of New Guinea legumes. Division of Botany, Papua New Guinea.
AIS Technology Fact Sheet
Windbreaks are single or multiple rows of trees planted to protect an area from prevailing winds. Windbreaks are planted along the windward boundaries of fields to provide a more favorable environment for crop growth. Windbreaks are also established to protect and improve the environments around homes, gardens, and villages.
Windbreaks are especially important on Pacific Islands where stiff trade winds blow throughout the year and tropical storms occur frequently. Salty maritime winds affect the most interior areas of exposed smaller islands.
Why slow the wind?
Wind can be very destructive, especially when combined with high temperatures, drought conditions, or salty sea air.
Wind damages crops: Strong winds break stems, strip leaves, and tear fruit from crop plants.
Wind sucks moistiure from plants: When wind blows against crop plants, it dries the air immediately surrounding them. When this boundary air is dry, more moisture is pulled from the plant through transpiration. This is why plants wilt in high winds.
Wind sucks moisture from the soil: Wind dries the soil surface, pulling moisture from soil pores. Wind removes fertile topsoil: Even moderate winds can remove tons of topsoil annually from fields that are exposed during cultivation and harvesting. The topsoil is the most organic and fertile soil layer.
· Wind carries salt: Along coastal zones and on small islands wind can and deposit tons of salt per hectare annually. In soil, salt draws moisture away from plants. Deposited on some plants, salt burns leaves and kills plant tissue.
· Wind affects the health/performance of livestock: Animals exposed to cold or hot winds can become stressed and much less productive.
Wind affects human environments: Strong winds can disrupt or damage human households. Wind borne dust may be a human health hazard.
Because they slow the wind, windbreaks conserve plant and soil moisture, prevent crop damage, prevent soil erosion, and reduce salt-spray. They also enhance animal welfare/performance and create a more habitable environment for humans.
Windbreaks made up of well-chosen multi-purpose tree species may also provide a variety of household and marketable products including fodder, fuelwood, timber, poles, fruit, mulch/compost, spices and medicine..
There are a few important windbreak design considerations:
Orientation: Correct windbreak orientation is crucial. You should obviously plant your windbreak on the windward side of the land-area or field you want to protect. You must also plant your windbreak in lines that are perpendicular to the prevailing wind direction. This may not be so obvious. If the wind direction changes from season to season you need to decide when it is most important to provide protection. This might be when the crop is most susceptible to wind damage, when the soil is exposed, or during the most windy season. In most Pacific locations, trade winds blow from a fairly constant direction so orientation should not be difficult or risky.
Multiple versus single row: To be most effective, your windbreak should include at least two rows of trees. This is because you want a wind barrier from the ground, up. Tall trees will protect a larger area of field, but they have high canopies and will thus leave an understory gap. Smaller trees are needed to this gap.
If you cannot sacrifice the land-area that a multi row windbreak requires, plant a single-row windbreak. A single row of trees can form a reasonable windbreak - and it is certainly better than nothing.
Windbreak height and between windbreak spacing: For every 1 m of height, your windbreak will protect 10 m of field area. A windbreak that is 10 m high will protect a field area 100 m downwind - so a windbreak 10 m high and 100 m long will protect a one hectare field
Individual tree spacing and placement: Plan trees closely enough within rows so that tree mature tree crowns will overlap. The tees spacing for medium sized trees is 3 to 4 m. Plan smaller trees at 2 to 3 m spacings and large
You can use the same range for between-row spacing. Again consider tree canopy size. Do not space the rows so closely that the larger row will shade-out the smaller row.
Always plant trees in each row so that they are inline with gaps between trees of parallel rows. This staggering produces more effective windbreak sooner.
· Species selection: You can plant your windbreaks with a variety of species. Obviously, trees used for windbreaks should be wind-strong, and deeply rooted. The best species for windbreaks also have low branching habits and relatively narrow crowns.
Individual tree/free-row spacing and placement
Choose species that are well adapted to your particular site and suited to your needs. If you need more fodder for your animals or fuelwood for your home, choose species tolerate strong winds while also yielding fodder and fuelwood. For consistency in height and ease of management, you should include only one species in each single row.
If you are able to plant a double - or multi-row windbreak, choose smaller trees for the most windward row and medium to larger trees for the next row.
The area protected will be larger if the windbreak is partially permeable rather than too dense. This is because too-dense a barrier can result in more turbulent air movement downwind. Some species make ideal windbreaks because their foliage filters rather than blocks the wind. The conifer-like foliage of Casuarina is one example.
· Grid design: This rather new
windbreak technology is gaining popularity. Single-row windbreaks are laid out
in a grid pattern on a field creating several smaller cells or squares. This
technique is especially effective where the wind often shifts
Windbreak grid-pattern layout
You will not necessarily have to manage your windbreak once it is established. Depending on the species you include however, you can prune, pollard, otherwise treat trees in various rows to provide alternative products or maintain a more desirable height relative to other rows.
The management or harvesting practices you choose for each row will obviously influence the height and form of that row relative to the others. You should plan accordingly. For example, you can use shorter rows for things like fodder or fuelwood production because you will be pruning or pollarding them regularly. You can leave the taller rows alone to grow to their maximum height. You can also use the taller trees in ways that do not reduce their height - for fruit, nut production.
Management treatments can affect a tree's resistance to strong winds. Shoots that grow up from a pollarded stem, will be very susceptible breakage at the stem joint once they reach a certain size. If you pollard the most windward row of your windbreak for several years and then leave it alone to grow in height sprouting branches will probably break in strong winds.
Pollarded trees will be susceptible to wind damage it left to return to, full size
You can even harvest complete rows in you windbreak on a rotational basis if the trees are good timber producers. In this case, you would plant a new row to be functional at the time the mature row is harvested.
Problems/Limitations and Alternatives
Field boundary conflicts: It is unlikely that the ideal orientation for your windbreak will conform perfectly to your field boundary. If the boundary is nearly perpendicular to the prevailing wind, you can simply plant a windbreak as a form of boundary planting. IF it is not, a boundary planting will not protect your crop from the wind. It may in fact, speed wind in your field because the wind may be forced along - rather than against it. The most effective windbreaks are those that stretch across boundaries and are the cooperative efforts Of a number of formers.
Problems and winds limitations
Loss of lard: Windbreaks of two or more tree rows will take a substantial portion of your land out of crop production. Most successful windbreaks though, boost crop yields enough to compensate for this loss of area. Once your windbreak is in place, you may even be able to grow a more marketable or valuable grow crop/ variety
· Competition with crops: Windbreaks may reduce the yield of crop plants in the area immediately next to them. This is due to competition for sunlight or water. Again, the increase in yield resulting in field interiors should compensate for this.
Pest problems: Some trees make nice homes for birds that will
eat some crops - especially grains.
The following are species which have proven themselves as effective windbreak components. They are grouped by typical size at maturity. For each, common additional uses are noted.
The species in bold are especially tolerant to salt spray Species with asterisk are more shallow rooted and may blow over in typhoons.
Sesbania sesban - green manure, animal fodder
Sophora tomentosa - fuelwood, nitrogen-fixing
Tournefortia argentea - fuelwood, shade
Medium size trees
· Acacia aurieuliformis -
· Acacia confuse - shade, firewood, nitrogenfixing
· Acacia mangium - fuelwood, nitrogenfixing Albizzia lebbeck - timber, nitrogen-fixing
· Azadirachta indica (neem) - fuelwood, timber, insecticide
· Cassia fistula: fuelwood Casuarina equisetifolia - fuelwood, poles, nitrogen-fixing
· Erythrinapoeppigiana - green manure, shade, nitrogen fixing
· Erythrina variegate - green manure, nitrogen-fixing
· Gliricidia septium - green manure, animal fodder, fuelwood, nitrogen fixing Intsia bijuga - sturdy construction timber
· Melia azedarach - fuelwood, timber, tools, shade
· Pinus caribaea - timber, shade
· Pithecellobium dulce-fuelwood animal fodder
· Calophyllum inophyllum - boat
timber, lampoil, shade, medicine
· Cassia siamea - fuelwood, small timber, animal fodder (toxic to pigs), edible leaves & flowers · · Cordia alliodora - timber
· Cordia suacordata - timber, edible seed 'l'amarindus indica (tamarind edible pods, charcoal, animal fodder, nitrogenfixing