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The practice of agroforestry is not new; it is as old as the agricultural practices that have existed for millennia. Realising the full potential of integrating commercially managed trees into farming systems is, however, still a long way off. Agroforestry systems can be advantageous over conventional agricultural and forest production systems through increased productivity, economic benefits, social outcomes and the ecological goods and services. Implementation of the National Agroforestry Policy (2014), the Sub-Mission on Agroforestry (2016), and the National Mission on Bamboo (2018) have further accelerated the momentum of adoption and expansion of agroforestry in India. Inclusion of agroforestry as one of the eligible activities for receiving funds through Corporate Social Responsibility Funding (2014), and consideration of 14th Finance Commission of India to include green cover (over forest cover) to provide additional funding to State Governments is expected to further promote agroforestry in the country. During the last two decades the science of agroforestry has progressed fast, both in its techniques and practices. New areas of studies have also emerged. Today, agroforestry has established itself as a viable approach of integrated land management system not only for meeting the deficits of food, fodder, firewood and timber but also for ecological considerations like soil conservation, watershed protection, wasteland management, biodiversity conservation, carbon sequestration and mitigation of climate change effects.

Agroforestry is a very old practice, dating back many years. Tropical farmers have long been growing food crops, timber, and livestock in addition to taking advantage of the variety of products that may be obtained from natural wood lots. Indian culture is deeply rooted in its appreciation of trees and forests. The forests gave birth to the greatest aspects of Indian culture. The sages who developed Hindu philosophy resided in forests, living in perfect harmony with the natural world. In fact, trees have been discussed in our ancient literature so much that people were planting trees on their own in addition to crops for agriculture. Maharishi Kashyap’s book ‘Krishishukti’ divides land into multiple categories and designates regions that are suitable for tree planting. Particular sites for planting trees include all wet and dry regions as well as the vicinity of homes, wells, and tanks. However, foresters and farmers, who have historically worked within very strict disciplinary boundaries and focused on producing their favoured commodities - crops, livestock, and trees - used to disregard such integrated production systems that incorporate many disciplines.

A scientific evaluation of the physical characteristics of the land, the properties of the soil, and the management techniques is called land capacity categorization. Understanding potentiality, capacity, and appropriateness for the best possible use of land is the primary goal of land capability categorization. Measuring land capacity provides an objective assessment for land preservation in certain ecological scenarios. On the one hand, land capacity aids in determining if a piece of land is efficient for a certain use, and on the other, it aids in preventing inappropriate use of the land, which poses a risk of erosion and degrades the quality of the land. Therefore, in order to maximise production, each piece of land’s potential should be assessed taking into account both its pedo-geomorphic characteristics and any constraints resulting from environmental threats. Additionally, under the necessary management practices, capacity categorization allows farmers to use the land appropriately for sustainable output.

It is vital to categorise agroforestry and its many systems in accordance with certain contemporary standards in order to have a thorough grasp of them and to enable future progress. Since each agroforestry system refers to a different set of agroforestry practices involving agriculture (crops), forestry (trees), and pasture (animals), the various uses of land are combined either temporally or spatially. Each agroforestry system has its own unique arrangement of various components, such as crops, animals, perennial trees, etc., and degree of interaction between the components. In terms of structure, composition, age intensity, technology, inputs, etc., one system varies from the other. Creating a useful framework for the synthesis and analysis of data on current systems as well as the creation of new, promising ones should be the primary goal of classification. For this reason, every categorization system needs to have the accompanying the following standards.

Farmers have been growing trees for different purposes for thousands of years. Tree species that are grown to provide more than one significant function are called multipurpose trees. These functions may be productive such as producing fuelwood, timber, fibre, fodder, food, medicine, etc. and/or protective such as soil conservation, shade, shelterbelt, microclimate amelioration, land sustainability, biodiversity preservation, etc. All trees are multipurpose; some, however, are more multipurpose than others. Tree species can be multipurpose in two ways. 1. A single tree can provide more than one function. For example, Gliricidia sepium is grown as living fences that provide fuel, fodder and green manure for agricultural crops - all at the same time. 2. Trees of the same species, when managed differently, can provide different functions. For example, Leucaena leucocephala is managed so that some trees will mainly yield wood while others mainly produce leaf fodder.

The idea of social forestry is not new in India. It may be found in Lord Buddha’s teachings from around 2500 years ago. According to Buddha’s teachings, a devout Buddhist should plant one tree and nurture it for five years so that it matures into a complete tree. By doing this, a person should plant around f ive trees over his lifetime. It is also believed that the Great Emperor Ashoka planted fruit trees and shade trees by the roadsides for the benefit of passing travellers. The rural economy in India has been largely supported by forests. In the past, the local people kept an ecological balance while managing their woods to provide food, fuel, fibre, fodder, timber and herbal remedies. However, India’s forests have rapidly disappeared due to biotic pressure from expanding human and animal populations, a lack of technical skills, insufficient investments, and ownership changes. In addition to biotic pressure, other factors that led to the depletion of forest resources includes inadequate scientific and technical inputs; staff lacking the necessary skills and training to assume their expected new roles; poor investment in forest development; and damage from mining, irrigation projects, industries, roads; and shifting cultivation. As a result, in the early 1970s, new ideas in forestry development were introduced. Therefore, a variety of activities were incorporated in social forestry initiatives, including planting trees on agricultural bunds and roadsides, creating woodlots on shared lands, and integrating local people in the gathering, processing, and management of forest products.

Management approaches to soil, including problems of soil degradation and low soil fertility, have recently undergone major changes. The earlier concept was to concentrate on achieving high levels of production from the more fertile areas, leaving the marginal lands for extensive use only. Steeply sloping and highly drought-prone areas were mostly left without any cultivation as production from these areas was hardly cost effective. Soil constraints were to be overcome by inputs like improved crop varieties, fertilizers, chemical control of pests and diseases, and the use of irrigation. The approach of use of newly developed high yielding crop varieties, improved agronomic management practices, use of chemical fertilizers, efficient water management and timely plant protection measures has been successful in achieving large increases in crop productivity in recent years. On the other hand, continuous application of fertilizers at higher rates leads to environmental problems. Yield responses to fertilizers have declined because of soil physical degradation and micronutrient deficiencies. Above all, large numbers of poor farmers simply can neither afford high levels of fertilizers and other purchased inputs, nor do they have the capital to take on the risk involved in their use. Increasing the area under irrigation has also run into severe constraints in the form of limits to available freshwater resources.

Agroforestry systems are not simply systems where trees and crops or animals give useful products to the farmers, rather systems where trees and crops and/ or animals interact. Interaction literally means influence or mutual or reciprocal action. So, component interaction refers to the influence of one component of a system on the performance of other component as well as the system as a whole. In agroforestry systems, trees are grown in close proximity to crops and pasture. Their performance would largely depend on their ability to share various growth resources in a given environmental situation. Various interactions take place between the woody trees and herbaceous plants (crops or pastures) which is referred to as tree-crop interface. These interactions take place through the media of soil and microclimate and may exert favourable or adverse effects on the crop. Study of interaction helps to know how the components of agroforestry utilize and share the resources of the environment, and how the growth and development of any of the components will influence the others. Interaction occurs both above and below the ground and includes a complex set of interactions relating to radiation exchange, the water balance, nutrient budget and cycling, shelter and other microclimatic modifications.

All agroforestry systems are characterized by three basic sets of attributes; productivity, sustainability, and adoptability (Nair, 2008). Productivity: The majority of agroforestry systems, if not all of them, strive to maintain or raise both land productivity and output (of desired commodities). In several aspects, agroforestry may raise production. These include higher yields of related crops, less input use in the cropping system, enhanced labour efficiency, and higher production of tree products. Sustainability: Agroforestry can achieve and indefinitely maintain conservation and fertility goals by conserving the production potential of the resource base, mainly through the beneficial effects of woody perennials on soils. Adoptability: Improved or new agroforestry technologies that are introduced into new areas should fit the social as well as environmental characteristics of the land use system for which it is designed and should also confirm to local farming system.

Agroforestry is a land use system that involves two or more plant species at least one of which must be a woody perennial. When perennial woody and herbaceous components are grown together on the same piece of land their performance would largely depend on their ability to share various growth resources in a given environmental situation. Due to difference in growth pattern and resource requirement of the components in agroforestry situation, a close interactive relation is obvious. Thus, careful management practices for the components are required to establish a successful agroforestry system. The characteristics of the trees and crops, and their interactions, can be modified with good management practices in order to take advantage of the positive characteristics and minimize the effects of the negative ones. Effective and efficient agroforestry management may be divided into two groups; tree management and agricultural crop management.

Ecology of a place is influenced by a number of biotic and abiotic factors. An agroecological zone is broadly homogeneous in climatic and edaphic factors, but not necessarily contiguous, where a specific crop exhibits roughly the same biological expression. On the other hand, the characteristics of an agroecological zone influence the crops and cropping patterns of the zone. Thus, there are considerable variations in the types and management practices of agroforestry systems being followed in different agroecological zones. AGROFORESTRY FOR HUMID AND SUBHUMID TROPICS Humid and subhumid tropical regions have much variation in biological, social and economic parameters. The characteristics of humid tropics include high mean annual rainfall of more than 1500 mm, dry season of less than four months in a year and mean annual temperature of more than 22°C. Rainfall usually exceeds the evapotranspiration. However, demographic pressure has caused excessive deforestation and overgrazing which developed soil related problems like low soil fertility, low organic matter, high acidity and high rainfall erosivity. The agroforestry practices designed for this region should aim for improved fallows, soil fertility improvement and conservation, food production, etc. Thus, the common agroforestry systems in this zone are taungya, homegardens, alley cropping, plantation-crop combination, windbreaks, silvipastoral systems and various intercropping systems. Shifting cultivation is a common practice in tropics which should be discouraged as it causes environmental degradation and ecological imbalance, soil erosion and soil nutrient loss.

A watershed is a geohydrological unit or all the land and water area bounded by a divide which contributes runoff to a common point. Watershed is considered to be synonymous with ‘catchment basin’ and ‘drainage basin’. In watershed management approach, development is not only confined to agricultural lands but also covers the area, starting from the highest point of the land to the outlet of the natural stream. Watershed management becomes increasingly important as a way to improve livelihood of people while conserving and regenerating their natural resources. Watershed management is the process of creating and implementing plans, programmes and projects to sustain and enhance watershed functions that affect the plant, animal and human communities within a watershed boundary. It implies the judicious use of all the resources,i.e., land, water and vegetation in an area to prevent soil erosion, improve water availability and increase food, fodder, fuel and timber on sustained basis.

In agroforestry systems the various components like tree, crop and pasture exist in different proportions and orientations. It is difficult to find out which agroforestry system is the best suited for a given land situation. Similarly, it is to be decided which technologies are required for refinement and improvement of the existing agroforestry practices. But without sufficient knowledge of the existing system in a particular land situation, it is very difficult to set the research priorities for modification and development of this system. Diagnosis and Design (D & D) is a systematic and objective methodology developed by International Centre for Research in Agroforestry (ICRAF) to initiate, monitor and evaluate agroforestry programmes. D & D is based on the philosophy that knowledge of the existing situation (diagnosis) is essential to plan and evaluate (design) meaningful and effective programmes in agroforestry research for development. The methodology plays a strategic role in all the phases of the agroforestry research process. D & D in agroforestry is unique and it has been specially developed for the following purposes (Raintree, 1987)

Trees have been used in cropping systems since the beginning of agriculture. Throughout the world, at one period or another in its history, it has been the practice to cultivate tree species and agricultural crops in intimate combination. In the tropics, human beings underwent a transition from hunting/gathering to the use of domesticated plants and livestock. As a part of the process, they cut down trees, cleared the debris by burning and sowed crops in the ash enriched soil. It was the ‘slash-and-burn’ agriculture, a primary forerunner of the present-day agroforestry and a practice that might have originated in the Neolithic period, around 7000 BC. There are innumerable examples of traditional land-use practices involving combined production of trees and agricultural species on the same piece of land in many parts of the world. Trees were an integral part of these farming systems and they were deliberately retained on farmlands to support agriculture. These practices are now known as agroforestry. However, the ultimate objective of these practices was not tree production but food production.

Human societies over the ages have depleted natural resources in different ways and degraded their local environments. Indiscriminate cutting down of trees and accelerating the construction works lead to global warming and climate change. Climate scientists believe that human-induced deforestation is responsible for 18-25% of climate change. Accumulation of greenhouse gases in the lower atmosphere is the main cause of global climate change. The concentration of these gases in the earth’s atmosphere is increasing, mainly due to deforestation and the combustion of fossil fuels which release carbon dioxide. The earth receives heat energy constantly from the sun through radiation. Some of the heat is absorbed and some is reflected. Carbon dioxide works like an invisible blanket that wraps around the earth and traps the heat inside, similar to the function of a greenhouse. A greenhouse is a structure that is used in colder climates to grow plants. Even when outside temperatures drop below freezing point, greenhouses are still warm enough inside to grow plants. Greenhouses are made of glass, which allows solar radiation to enter. The heat is trapped inside the greenhouse, allowing plants to grow all the year round. Increasing concentrations of carbon dioxide in the earth’s atmosphere insulate it like a greenhouse, leading to a gradual warming of the earth’s atmosphere. Carbon dioxide is the major greenhouse gas, but there are others as well, including methane and nitrous oxide.

Multipurpose trees and shrubs are defined as all woody perennials that are purposefully grown to provide more than one significant contribution to the production and/or service functions of a land-use system that they occupy. In agroforestry systems, different species of trees and shrubs can be planted with many types of crops in a variety of patterns. Thus, it is required to know about the methods of propagation and nursery raising, planting and other silvicultural management practices along with the diverse uses of multipurpose trees and shrubs of tropical and subtropical areas before their selection for forestry and agroforestry activities. It is important to select the most suitable tree species since it is not easy to replace them once they have been planted. MANGIUM (Acacia mangium) Acacia mangium is a single-stemmed evergreen tree that grows to 25-35 m in height and up to 60 cm in diameter. The bole is usually straight, often fluted near the base, free of branches for up to half its height. Mangium is native to Australia, Indonesia and Papua New Guinea. However, it tolerates varied site conditions and has adaptability to different planting objectives. Mangium shows most vigorous growth on well-drained, fertile soils in high rainfall areas in the humid tropics. It is valued for its rapid growth and has been planted throughout the humid tropics and is a major plantation species in the Asia Pacific. Provenances from Papua New Guinea consistently show better growth in height and diameter.

Abhay Kumar, Yadava, M. S., Shabuam, S., Oraon, P. R., Singh, B. K and Kumar, S. 2020. Recent Trends in Agroforestry. In: Advances in Agricultural Sciences. AkiNik Publications, New Delhi. pp. 35-52. Abrol, I. P. and Dhruva Narayana, V. V. (Eds.). 1990. Technologies for wasteland development. ICAR, New Delhi. Ahmed, P. 1991. Agroforestry: a viable land use of alkali soils. Agroforestry Systems 14: 23-37. Akachuku, A. E. 1985. Cost-benefit analysis of wood and food components of agrisilviculture in Nigerian forest zone. Agroforestry Systems 3: 307-316. Alavalapati, J. R. R., Luckert, M. K. and Gill, D. S. 1995. Adoption of agroforestry practices: a case study from Andhra Pradesh, India. Agroforestry Systems 32: 1-14.