Sustainability & Environment (Agri-Food Systems) · Sustainable Agriculture & Agroecology · also Agroforestry Systems, Silvopasture and Silvoarable Systems
Trees in farmland as a sustainability tool: system types, tree-crop interactions, carbon, soil and biodiversity benefits. Silviculture, forest management and REDD+ are covered in depth in the Forestry track; this subject keeps to trees on farms.
In the exams: ICAR AIEEA-PG Forestry group 9.2; ICAR AICE Agroforestry; overlaps with the Forestry track
Agroforestry is the deliberate integration of trees and shrubs with crops, livestock or both on the same unit of land, so that ecological and economic interactions between the components are put to use. It is not new: parklands of Faidherbia and shea in the Sahel, homegardens in Kerala and Java, khejri trees in the fields of Rajasthan, the dehesa oak pastures of Spain and the shaded coffee and cacao farms of the tropics are all centuries old. What is newer is the recognition, since the 1970s, that trees on farms are a central tool for sustainability: they store carbon, protect soil and water, support biodiversity, diversify income and buffer farms against climate shocks.
Trees on farms are also far more extensive than most people realise. Global mapping by Zomer and colleagues found that a large share of the world's agricultural land, more than 40 percent, has at least 10 percent tree cover, and that these trees hold a substantial share of the carbon in agricultural landscapes. In India, trees outside forests supply a large part of the country's timber and much of its fuelwood, and India in 2014 became the first country to adopt a national agroforestry policy.
This manual looks at agroforestry through a sustainability lens. It covers the classification of agroforestry systems, the interactions between trees and crops that decide whether a system works, silvopastoral and silvoarable systems, shelterbelts and boundary plantings, the roles of trees in soil fertility and erosion control, carbon storage and how it is estimated, biodiversity, livelihoods and markets, and the policy and tenure barriers that keep trees off farms. The design methodology, multipurpose tree species, agro-ecological zone systems and tree management on farms are covered in depth in the Forestry track subjects agroforestry-systems-design and agroforestry-management-economics; this subject refers to them rather than repeating them. Agroecological principles are treated in agroecology-principles, soil carbon in soil-carbon-sequestration, and carbon crediting in carbon-markets-offsets.
The World Agroforestry Centre (ICRAF, founded in Nairobi in 1978 as the International Council for Research in Agroforestry) adopted a widely used definition in the early 1980s, associated with Lundgren and Raintree: agroforestry is a collective name for land-use systems and technologies in which woody perennials (trees, shrubs, palms, bamboos) are deliberately used on the same land-management unit as agricultural crops and/or animals, in some form of spatial arrangement or temporal sequence, and in which there are both ecological and economic interactions between the different components. Two features distinguish agroforestry from simply having trees and crops near each other: the integration is deliberate, and the components interact.
Later definitions widened the scale. ICRAF has described agroforestry as a dynamic, ecologically based natural resource management system that, through the integration of trees on farms and in the agricultural landscape, diversifies and sustains production for increased social, economic and environmental benefits. This landscape view includes scattered trees, boundary plantings, woodlots and riparian strips, not only intimate tree-crop mixtures on a single field.
P. K. R. Nair's classification, set out in the 1980s and 1990s, remains the standard framework for exams. It classifies systems on four bases. The structural basis looks at the nature of the components and their arrangement: agrisilvicultural systems combine trees and crops; silvopastoral systems combine trees and pasture or animals; agrosilvopastoral systems combine all three; and 'other' systems include apiculture with trees, aquaforestry and multipurpose woodlots. Arrangement can be spatial (dense mixed, sparse, strips or boundaries) or temporal (coincident, concomitant, overlapping, sequential or interpolated, as in rotational fallows and taungya).
The functional basis looks at the main role of the woody component: productive (food, fodder, fuelwood, timber, other products) or protective (windbreaks, shelterbelts, soil conservation, moisture conservation, soil improvement, shade). The socio-economic basis groups systems by scale and management: commercial, intermediate or subsistence. The ecological basis groups them by agro-ecological zone: humid lowland tropics, semi-arid tropics, highlands, temperate zones and so on. A single system can be described on all four bases; for example, a poplar-wheat system in Punjab is agrisilvicultural, productive, commercial and semi-arid subtropical.
Common named practices include: alley cropping (hedgerow intercropping), in which crops are grown in alleys between regularly pruned rows of trees or shrubs, often legumes; improved fallows, in which fast-growing, usually nitrogen-fixing trees are planted to restore fertility in a fallow; taungya, in which farmers grow crops between young forest tree seedlings for the first years of a plantation, which originated in Burma in the nineteenth century; homegardens, multistorey mixtures of trees, shrubs, crops and often animals around homesteads; parklands, with scattered trees retained on cropped fields; boundary plantings, windbreaks and shelterbelts; plantation crop combinations, such as coconut with cacao, pepper or pineapple and shade trees over coffee and tea; trees on pasture and fodder banks in silvopastoral systems; and woodlots and riparian buffers at landscape scale. In temperate regions, five main practices are commonly listed: alley cropping, silvopasture, windbreaks, riparian forest buffers and forest farming. The detailed design of these practices, and how to choose among them for a given site, is covered in agroforestry-systems-design.
Whether an agroforestry system produces more than separate trees and crops depends on how the components interact. Ong and colleagues summarised this with a simple expression, I = F - C, where I is the net interaction effect of trees on crop yield, F is the facilitation (positive effects such as improved soil fertility, microclimate and reduced erosion) and C is the competition for light, water and nutrients. A system benefits the crop only when facilitation exceeds competition. In many semi-arid systems with trees close to crops, competition for water dominates and crop yields near trees fall; in humid systems with good rainfall, or where trees are well managed, facilitation may dominate.
Cannell, van Noordwijk and Ong proposed a central hypothesis for agroforestry: trees will increase overall productivity only if they capture resources that the crops would not otherwise use, for example water and nutrients from deep soil layers, rainfall outside the crop season or light above the crop canopy. If trees simply take resources the crop would have used, the mixture gives no gain. This hypothesis explains why species and arrangement must be chosen carefully.
Competition for light depends on canopy size, density, orientation of rows and the shade tolerance of the crop. Shade-tolerant crops such as turmeric, ginger, coffee and cacao suit agroforestry better than sun-demanding cereals. Competition for water is greatest where rooting zones overlap; root pruning, trenching between trees and crops and selecting deep-rooted trees reduce it. Competition for nutrients, especially nitrogen, can be offset where trees fix nitrogen or recycle nutrients through litter and prunings. Some trees release allelopathic compounds that inhibit crops; eucalyptus and some others have been studied for such effects, although competition for water is often a larger cause of yield loss near eucalyptus.
Facilitation includes nitrogen fixation by leguminous trees, uptake of nutrients from deep layers and their return in litter (the 'safety-net' and 'nutrient pump' roles), improved soil structure and organic matter, reduced wind speed and evaporation, moderated temperature extremes, hydraulic lift (movement of water by roots from moist deep soil to dry surface layers at night), and habitat for natural enemies of pests. The classic example of complementarity is Faidherbia albida, which has 'reverse phenology': it sheds its leaves during the rainy season and is in leaf during the dry season, so it competes little with crops for light during cropping and drops nitrogen-rich leaves onto the field. Studies in eastern and southern Africa and the Sahel have often found higher crop yields under Faidherbia canopies than in the open, although the size of the effect varies with site and rainfall.
The land equivalent ratio (LER) measures whether a mixture uses land more efficiently than sole stands: LER is the sum, over components, of yield in the mixture divided by yield in the sole stand. If a tree-crop system gives a crop yield of 70 percent of the sole crop and tree production of 60 percent of a sole plantation, LER = 0.7 + 0.6 = 1.3, meaning that 1.3 hectares of separate sole stands would be needed to produce what 1 hectare of the mixture produces. European silvoarable studies of walnut or poplar with cereals have estimated LERs of the order of 1.2 to 1.4 over the tree rotation, although such figures come largely from modelling and depend on management. LER does not account for differences in value or timing between products, and agroforestry trees often take years to yield, so LER should be combined with economic analysis, covered in agroforestry-management-economics.
Silvopastoral systems combine trees with pasture and livestock. Trees provide fodder (especially valuable in the dry season when grasses are scarce), shade that reduces heat stress in animals, timber, fuelwood and fruit, while animals graze the understorey and recycle nutrients. Forms include scattered trees on pasture, trees planted in rows on grazing land, fodder banks of densely planted shrubs that are cut and carried to animals, live fences and grazing in plantations.
Examples span climates. In arid Rajasthan, khejri (Prosopis cineraria) is retained in fields and pastures for fodder (loong), pods (sangri), fuel and soil improvement. Hardwickia binata and Albizia lebbeck are used as fodder trees in drier India. The dehesa of Spain and montado of Portugal are open woodlands of holm and cork oak grazed by cattle, sheep and pigs, which feed on acorns, and harvested for cork; they are recognised as high-nature-value farmland. In Latin America, intensive silvopastoral systems in Colombia and elsewhere combine high densities of the fodder shrub Leucaena leucocephala with improved grasses and timber trees; studies there have reported higher stocking rates and milk production per hectare than in grass-only pastures, although results depend on management. In Australia and Latin America Leucaena is also grown in hedgerows for cattle; its mimosine content limits intake by animals that lack rumen microbes able to degrade it.
From a sustainability perspective, silvopasture can raise carbon storage on grazing land, reduce erosion and improve animal welfare through shade. It can also be a step from degraded open pasture towards more diverse land use. Livestock grazing in young plantations must be controlled to avoid damage to seedlings.
Silvoarable systems combine trees with arable crops. In the tropics and subtropics these include parklands, alley cropping and commercial row plantings such as poplar with wheat and sugarcane in north-western India, where poplar is planted in blocks or boundaries and harvested after a rotation of roughly six to eight years for plywood and match industries, while wheat and other winter crops grow during the poplar's leafless winter. Eucalyptus clones and Melia dubia are grown in similar ways in other states. In Europe, research projects since the early 2000s have studied walnut, poplar, wild cherry and other timber trees in widely spaced rows with cereals, showing productive mixtures in modelling and field trials, while noting that machinery access and subsidy rules have limited uptake.
Design choices in silvoarable systems involve row spacing wide enough for machinery and light, row orientation (north-south rows often share light more evenly across the day), tree species with deep roots and late leafing, and pruning to produce clean timber and reduce shade. Sustainability gains include soil protection, carbon storage and diversification; trade-offs include crop yield losses near trees and delayed returns from timber.
Agrosilvopastoral systems combine all three components. Homegardens are the most complex: around homesteads in Kerala, Sri Lanka, Java and elsewhere, several canopy layers of coconut, arecanut, jackfruit, mango, banana, pepper, tubers and vegetables are combined with cattle, goats or poultry. They provide food, income and fuel year-round, recycle household wastes and support high plant diversity on small areas. Studies of Kerala homegardens have recorded dozens of useful species on single farms. Pressures from commercialisation, fragmentation and simplification towards a few cash crops threaten their diversity.
Windbreaks are rows of trees or shrubs planted to reduce wind speed; shelterbelts are usually wider, multi-row belts protecting larger areas. A barrier slows wind on both sides, with the greatest reduction on the leeward side. The protected distance is expressed in multiples of barrier height (H): wind speed is markedly reduced for a distance of roughly 10 to 20 H downwind, with some effect further, and a small distance upwind. The exact distance depends on barrier height, porosity, length, wind direction and terrain.
Porosity, the proportion of open space in the barrier, is the key design variable. A dense, solid barrier creates strong reduction close behind it but also turbulence and a shorter protected zone. A moderately porous barrier, often cited as around 40 to 50 percent porosity for crop protection, gives a longer protected zone with less turbulence. Barriers should be long relative to their height (gaps and ends allow wind to funnel around them), oriented at right angles to the damaging wind, and multi-row with a mix of species and heights where space allows. For example, a windbreak 12 m tall protects roughly 120 to 240 m downwind if the 10 to 20 H rule is used, which suggests the spacing between parallel belts in a field shelterbelt network.
Reduced wind lowers evaporation and crop water loss, reduces mechanical damage and lodging, limits soil erosion by wind, improves pollination by insects and can moderate temperatures. Reviews from North America, Europe, China and elsewhere have generally found crop yield increases in the sheltered zone that outweigh losses in the competition zone close to the trees, although the net gain varies widely with crop, climate and design. Shelterbelts also shelter livestock from wind chill and heat, catch drifting snow in cold climates, reduce spray drift and odour from farms and provide habitat corridors and wood.
The costs are land taken out of crops, competition for water, nutrients and light in a strip roughly one to two tree heights wide next to the belt, and establishment and maintenance costs. Root pruning or a trench along the crop side of the belt reduces competition.
Large shelterbelt programmes have been established in arid and semi-arid regions. In the Indian Thar desert, shelterbelts and strip plantations along roads, canals and field boundaries have been planted since the mid-twentieth century, with species such as Acacia tortilis, Prosopis juliflora, Azadirachta indica, Dalbergia sissoo and Tamarix. China's Three-North Shelter Forest Programme, begun in 1978, is among the largest afforestation programmes in the world; its effectiveness has been debated, especially where trees were planted in areas too dry to support them. The Great Plains Shelterbelt Project in the United States in the 1930s responded to the Dust Bowl. Africa's Great Green Wall initiative aims to restore land across the Sahel, increasingly through farmer-managed regeneration and mosaics of land uses rather than a single belt of trees.
Boundary plantations are lines of trees along field or farm boundaries. They are common where farmers want trees but not shade over the whole field, and where boundary trees also mark ownership. In India, eucalyptus, poplar, Melia, teak and Dalbergia are widely planted on bunds and boundaries. They demand less land than block plantations, but competition with neighbouring crops, including neighbours' crops, can cause disputes, and species choice should consider water use, especially for fast-growing eucalyptus in dry areas.
Trees improve soil fertility through several mechanisms: biological nitrogen fixation by leguminous trees and actinorhizal trees such as Casuarina (with Frankia); addition of organic matter through litter, prunings and root turnover; uptake of nutrients from deep soil layers and their return to the surface in litter; reduced leaching, as deep roots catch nutrients moving below the crop root zone; improved soil structure, infiltration and water holding; and support of soil biota, including mycorrhizal fungi. Trees cannot create phosphorus or potassium; they redistribute and recycle them, so in nutrient-depleted soils additional inputs may still be needed.
Biomass transfer moves leaves from trees grown elsewhere, for example Tithonia diversifolia hedges, into fields as green manure. Green leaf manuring with Gliricidia sepium loppings from field bunds is widely practised in South Asia. Cross-reference to organic-farming-certification and agroecology-principles for nutrient cycling more broadly.
Alley cropping was developed and promoted from the late 1970s, notably at the International Institute of Tropical Agriculture in Nigeria, using hedgerows of Leucaena leucocephala or Gliricidia sepium pruned regularly, with prunings used as mulch and green manure for maize and other crops in the alleys. It sustained yields in some humid and subhumid trials, but adoption was low: it needs a lot of labour for pruning, it competes with crops for water in drier areas, the benefits take time to appear, and secure land tenure is needed to invest in hedgerows. Alley cropping is now seen as suitable mainly in specific niches, such as sloping land where hedgerows also control erosion.
Improved fallows have been more widely adopted in parts of southern and eastern Africa. Fast-growing nitrogen-fixing shrubs such as Sesbania sesban, Tephrosia vogelii, Gliricidia sepium and Cajanus cajan are planted and left for one to three years, then cut, with the leaves and roots enriching the soil for subsequent maize crops. Research in eastern Zambia and elsewhere reported substantial maize yield increases after such fallows compared with continuous unfertilised maize, although yields usually remained below those obtained with recommended fertiliser. 'Fertiliser tree' systems, including intercropping Gliricidia with maize and parklands of Faidherbia, are promoted in Malawi and other countries as part of 'evergreen agriculture'.
Trees control erosion by protecting the soil surface with canopy and litter, increasing infiltration, binding soil with roots and acting as barriers to runoff. On sloping land, contour hedgerows of trees or shrubs, planted along the contour with crops in between, trap sediment, and terraces gradually form behind the hedgerows; the Sloping Agricultural Land Technology (SALT) promoted in the Philippines is a well-known example. Vegetative barriers can be combined with grass strips such as vetiver. Trees on bunds and gully plantations stabilise conservation structures. Riparian buffers of trees and shrubs along streams trap sediment, nutrients and pesticides from fields before they reach water and shade streams; their design is covered in agroforestry-systems-design.
Erosion experiments measure soil loss in runoff plots; across many studies, systems with permanent tree cover and litter have much lower soil losses than clean-tilled annual crops on the same slope, but hedgerows alone may not control erosion if litter is removed and the cropped alleys are tilled bare. Conservation agriculture practices, covered in conservation-regenerative-agriculture, complement trees in erosion control.
Agroforestry stores carbon in above-ground tree biomass, below-ground roots, dead wood and litter, and soil organic carbon. Compared with treeless cropland or pasture, adding trees usually increases the total stock, mainly in biomass; soil carbon gains are slower and more variable. Global estimates by Zomer and colleagues suggested that trees on agricultural land hold a large stock of carbon, and that tree cover on farmland increased over the first decade of this century. Because so much farmland has some trees, agroforestry is included in many countries' climate pledges and in the IPCC's mitigation options.
Rates of carbon sequestration reported in the literature vary enormously with climate, species, tree density, age and management. Reviews have reported rates from well under 1 to more than 10 tonnes of carbon per hectare per year, with many systems in the range of roughly 1 to 4 t C/ha/yr during the growing phase. Stocks stop increasing when trees mature or are harvested, so sequestration is time-limited, and carbon in harvested timber is only retained if the wood goes into long-lived products. Converting natural forest to agroforestry loses carbon; agroforestry gains carbon relative to cropland or degraded land, not relative to intact forest.
Tree carbon on farms is usually estimated from measurements of trunk diameter at breast height (DBH, at 1.3 m) and sometimes height, using allometric equations that relate these to above-ground biomass for a species or forest type. Below-ground biomass is estimated with a root-to-shoot ratio; IPCC default ratios vary by ecological zone and biomass, often in the range of roughly 0.2 to 0.4. Carbon is calculated as a fraction of dry biomass; the IPCC default carbon fraction is 0.47 (0.5 is also commonly used), and carbon is converted to carbon dioxide by multiplying by 44/12, about 3.67.
For example, suppose an agroforestry plot has 100 trees per hectare, each with above-ground dry biomass of 300 kg, and a root-to-shoot ratio of 0.25 is assumed. Total biomass is 100 x 300 x 1.25 = 37,500 kg, or 37.5 t per hectare. Using a carbon fraction of 0.47, carbon is 17.6 t C/ha, equivalent to 17.6 x 44/12 = 64.6 t CO2/ha. If the trees took ten years to reach this size from negligible biomass, the average sequestration rate was about 1.8 t C/ha/yr. Mistakes to avoid are forgetting the root fraction, using fresh instead of dry weight, or confusing carbon with carbon dioxide.
Soil organic carbon under agroforestry tends to rise more slowly than tree biomass carbon, and measured changes vary from large gains to none. Gains are most likely where trees replace degraded cropland or overgrazed pasture, where litter and prunings are returned to the soil, and where deep roots add carbon below the plough layer; many studies sample only the top 30 cm, which can miss carbon added deeper down. Soil carbon also responds to tillage, residue removal and grazing pressure in the crop or pasture component. Measuring a change requires repeated sampling of the same points with bulk density measured at each time, or paired comparisons of similar soils with and without trees, because the change in a few years is small relative to natural variation. Soil carbon accounting and its uncertainties are discussed in soil-carbon-sequestration.
Agroforestry projects can earn carbon credits under voluntary standards and some compliance schemes, but they face particular challenges: many small, scattered farms make monitoring costly; trees are harvested or die, so permanence is uncertain; baselines are hard to set where farmers would have planted some trees anyway (additionality); and leakage may occur if land use shifts elsewhere. Remote sensing and sample-based monitoring reduce costs. Carbon crediting concepts are covered in carbon-markets-offsets and inventory methods in carbon-accounting-ghg-inventories. For farmers, carbon payments are usually small relative to the value of tree products, so carbon is best seen as a co-benefit of agroforestry that is worth doing for other reasons.
Trees on farms provide habitat, food and nesting sites for birds, bats, insects, epiphytes and other organisms, and connect forest fragments across farmed landscapes. Structurally complex systems such as shaded coffee and cacao, multistrata homegardens and jungle rubber hold more species than open monocultures, often including many forest species, although usually fewer forest specialists than intact forest. Studies in Latin America have found that traditional shaded coffee supports many more bird species than sun coffee, and bird-friendly certification schemes reward shade cover and tree diversity.
Scattered trees in pastures and fields act as 'keystone structures', disproportionately important for wildlife relative to the area they occupy, as stepping stones for movement, perches for seed-dispersing birds that start forest regeneration, and roosts for bats. Hedgerows and windbreaks act as corridors. Biodiversity value rises with the number and diversity of native tree species, the presence of several canopy layers, the retention of dead wood and old trees, and lower pesticide use.
Biodiversity in agroforestry supports ecosystem services to farmers. Pollinators nest and forage in tree-rich landscapes; coffee near forest has been shown to receive more pollinator visits and set more fruit. Birds and bats eat insect pests in coffee and cacao, with exclusion experiments showing increased pest damage when they are kept out. Predators and parasitoids find alternative food and shelter. Some studies also show disadvantages: trees can host crop pests and diseases or attract crop-raiding animals, so effects depend on species and context. Conservation biological control is discussed in agroecology-principles.
Agroforestry is central to the debate between land sharing (wildlife-friendly farming over large areas at lower yields) and land sparing (high-yield farming on less land so that more natural habitat can be protected). Agroforestry is a form of sharing. Studies in Ghana and India by Phalan and colleagues suggested that many species, especially those dependent on forest, did better under sparing, while other studies emphasise that wildlife-friendly matrices are needed for connectivity and that sparing rarely happens in practice. Most researchers now conclude that the best strategy depends on context and that agroforestry plays its biggest role where it replaces degraded open farmland rather than forest, and where it connects protected areas. Cross-reference to agroecology-principles for a fuller treatment of this debate.
Agrobiodiversity is also conserved in agroforestry. Homegardens maintain traditional varieties of fruit, tubers and vegetables, and farmers' fields are reservoirs of genetic diversity of trees such as tamarind, mango and jackfruit. However, many tree planting programmes rely on very few species, often exotic and fast-growing, which limits biodiversity benefits; diverse, native and locally valued species are preferred for biodiversity outcomes.
Trees on farms supply fruit, nuts, oils, fodder, fuelwood, timber, poles, fibre, gums, resins, medicines and honey. These products diversify income, spread labour and income over the year and act as 'savings banks' that can be harvested when cash is needed for weddings, school fees or emergencies. In Africa, shea butter from Vitellaria paradoxa parklands is an important source of income for women in the Sahel; in India, farm-grown poplar, eucalyptus, Melia and other species supply a large share of the wood used by plywood, paper, match and furniture industries. National studies have estimated that trees outside forests supply a large part of India's industrial wood. Fodder trees reduce the cost of feeding livestock in the dry season.
Trees also reduce risk. When a crop fails in drought, deep-rooted trees often continue to produce fruit or fodder, and tree products can be sold in years of crop failure. Studies have associated tree cover on farms with greater dietary diversity, especially where fruit trees are present. These risk and nutrition benefits are often missed in narrow economic analyses that compare only the yields of a single crop.
Farm-grown wood depends on markets. Where processing industries and traders are close by, as with poplar in Punjab, Haryana and western Uttar Pradesh or eucalyptus near pulp mills in Andhra Pradesh and Telangana, farmers have planted on a large scale. Contract or buy-back arrangements with industries have reduced risk by guaranteeing a market and supplying quality planting stock. But prices of farm wood fluctuate strongly: when many farmers plant at once, prices can collapse at harvest, as poplar growers have experienced, which discourages further planting. Information on prices, certified planting material, and fair grading and measurement of logs are recurring needs.
Non-timber products such as fruit, gums and medicinal plants need post-harvest handling, quality standards and market linkages. Producer groups and cooperatives can help smallholders reach better markets. Economic evaluation methods, including discounted cash flow, net present value and internal rate of return for long-rotation tree crops, are covered in agroforestry-management-economics.
Adoption of agroforestry depends on whether it fits farmers' resources and goals. Factors that favour adoption include secure land tenure, access to markets, availability of quality seedlings, knowledge and extension, and the time farmers can wait for returns. Barriers include the long delay before trees pay, competition with crops, rights to harvest and sell trees, labour needs and lack of credit. Gender shapes who benefits: women often manage tree products such as fruit, fodder and shea, but men more often control land and timber, so programmes that ignore gender can shift benefits away from women.
Farmer-managed natural regeneration (FMNR), in which farmers protect and prune stumps and seedlings of native trees that regrow naturally in their fields, has spread widely in Niger and other Sahelian countries since the 1980s. Studies by Reij and colleagues estimated that millions of hectares in Niger were re-greened, largely after changes in perceived tree rights encouraged farmers to protect trees. FMNR is low-cost, uses locally adapted species and illustrates how changes in policy and incentives, more than technology, can drive tree cover on farms.
Even where agroforestry is profitable, rules on growing, cutting and transporting trees can make it unattractive. Many countries' forest laws were written to protect natural forests and treat timber of certain species as government property or require permission to fell and transport trees, regardless of whether they were grown on private farmland. Farmers who fear they will not be allowed to harvest or sell their trees have little reason to plant or protect them. Insecure land tenure has a similar effect: tenants and those without formal title are unlikely to invest in trees that take years to mature, and in some customary systems planting trees can be seen as a claim to land, which landowners may resist.
Other barriers include agricultural subsidy rules that count tree-covered land as ineligible or reduce payments, credit and insurance products designed for annual crops, extension services organised separately for agriculture and forestry, lack of quality planting material, and the absence of trees outside forests from national statistics.
India adopted the National Agroforestry Policy in 2014, the first country to do so. It recognised the role of trees on farms for productivity, livelihoods and environment, and called for: coordination between ministries; simplification of rules for felling and transit of trees grown on farms; secure tenure and access to quality planting material; research, extension and capacity building; access to credit and insurance; and market linkages. Following the policy, the Sub-Mission on Agroforestry was launched in 2016-17 under the National Mission for Sustainable Agriculture to support farmers in planting trees, and many states relaxed transit rules for common farm-grown species. In 2017, the Indian Forest Act of 1927 was amended so that bamboo grown outside forest areas was no longer defined as a tree, removing the need for felling and transit permits for farm-grown bamboo.
Research on agroforestry in India is led by the ICAR-Central Agroforestry Research Institute at Jhansi, established in 1988 as the National Research Centre for Agroforestry, together with an All India Coordinated Research Project on agroforestry begun in 1983. Rules still differ between states, and farmers in several states report difficulty obtaining permits for some species, so implementation remains uneven.
Several other countries have adopted measures to support trees on farms. Kenya's Farm Forestry Rules of 2009 set a target of maintaining at least 10 percent tree cover on agricultural land. In Niger, changes in the interpretation of forest rules from the 1980s onwards, giving farmers greater confidence that they could benefit from trees they protected, were followed by the spread of farmer-managed natural regeneration. The European Union has supported establishment of agroforestry through rural development measures under its Common Agricultural Policy, and France adopted a national agroforestry development plan in 2015. In the United States, agroforestry practices are supported by conservation programmes of the Department of Agriculture.
Internationally, trees on farms contribute to restoration commitments such as the Bonn Challenge, launched in 2011 with a goal of restoring 150 million hectares by 2020 and 350 million hectares by 2030, and to the African Forest Landscape Restoration Initiative (AFR100). Many countries' nationally determined contributions under the Paris Agreement mention agroforestry. The lesson from experience is that securing rights to trees and simplifying rules often does more to increase tree cover on farms than subsidies for planting, and that planting targets measured only in seedlings distributed say little about how many trees survive.
Learn Nair's four bases of classification and the named systems, the interaction equation I = F - C and the central hypothesis, the windbreak height rule and porosity, the main fertility and erosion-control practices, and the carbon calculation chain from biomass to CO2. Know the National Agroforestry Policy, the Sub-Mission on Agroforestry and the 2017 bamboo amendment. Visit a poplar or eucalyptus boundary planting, a homegarden or a silvopasture to see interactions on the ground.
As an extension officer, project agronomist or NGO staff member you help farmers choose trees and arrangements, source planting material, plan windbreaks and boundary plantings, manage competition through pruning and root pruning, estimate tree carbon for projects, and navigate felling and transit rules and buy-back arrangements. Judgement is needed to match species to water availability and markets and to avoid promoting trees farmers cannot legally harvest.
At senior level you design state or national agroforestry programmes, carbon or restoration projects, or corporate sourcing of farm wood. Decisions include species and market strategy, simplifying tree rules, monitoring survival rather than seedlings distributed, safeguarding tenure and gender equity, and presenting carbon and biodiversity claims honestly given permanence and baseline issues.
Research questions include quantifying tree-crop interactions under climate change, carbon stocks and sequestration across systems with remote sensing and allometry, biodiversity value of different agroforestry designs, adoption and the role of tenure and markets, and the economics of agroforestry versus land sparing. Rigorous research combines long-term trials, farm surveys, mapping and modelling, and reports uncertainty explicitly.
Sequestration rates, LER values, windbreak protected distances and porosity optima vary widely with site, species and design; the ranges given are indicative and should not be applied to a site without local data. State rules on felling and transit of farm-grown trees in India change often and differ between states; they are not listed individually. Design methodology, multipurpose tree species, agro-ecological zone systems, tree management and economic evaluation are covered in the Forestry track subjects agroforestry-systems-design and agroforestry-management-economics rather than here. Evidence on some claims, such as nutrition benefits of trees and the effectiveness of large shelterbelt programmes, is mixed and is presented as such.
Original practice questions written to the syllabus and pattern of the exams named in each question's examTags. They are not past papers and do not reproduce any board's questions.
These notes are free to read here, with no account.
What the Laisha app adds:
Free for ten days, then a subscription. We would rather write that here than have you find it later.