Forestry & Forest Sciences · Silviculture · also Afforestation of Problem Sites, Wasteland Development, Ecological Restoration
Re-establishing tree cover and ecosystem function on degraded and hostile sites, including mangroves, sand dunes, ravines, saline land, mine spoils and cold deserts, and controlling invasive species.
In the exams: ICAR AICE-JRF 59 Unit 2 (afforestation on difficult sites) and Unit 8 (wastelands); IFoS Forestry Paper I Section A (mangrove and cold-desert silviculture); ICAR AIEEA-PG Group 09 (wasteland management)
A large part of the land that foresters are asked to reforest is not ordinary forest land. It is salt-affected, sandy, rocky, gullied, waterlogged, mined, frozen for much of the year or overrun by invasive weeds. Planting on such sites with the methods used on good forest soils usually fails. Success depends on understanding why the site is hostile, treating the main limiting factor, choosing species that tolerate the conditions, and protecting and maintaining the planting until it can sustain itself. Beyond planting trees, the goal is increasingly ecological restoration: recovering a functioning ecosystem with native species and the services it provides.
This subject covers the principles of ecological restoration and forest landscape restoration; the afforestation of saline and alkaline soils, coastal and inland sand dunes, lateritic, rocky and dry sites, ravines and gullies, wetlands and waterlogged sites, mangroves, cold deserts and mine spoils; the control of invasive plant species; assisted natural regeneration and the framework-species method; and the extent, characteristics and reclamation of wastelands. It draws on forest-ecology for succession and disturbance, on forest-nursery-plantation and silviculture-principles for nursery and planting practice, on conservation-biology-genetic-resources for native species and genetic considerations, and on wildlife-management-protected-areas and wildlife-biology-ecology for habitat restoration and the role of animals in seed dispersal. Mangrove and cold-desert forest types are described in forest-types-biogeography.
The manual is written for students preparing for the ICAR AICE-JRF forestry paper (afforestation of difficult sites and wastelands), the Indian Forest Service (mangrove and cold-desert silviculture) and the ICAR AIEEA-PG forestry paper, and for foresters, restoration practitioners and project staff. Areas and figures from national surveys are approximate and are revised periodically.
The Society for Ecological Restoration (SER) defines ecological restoration as the process of assisting the recovery of an ecosystem that has been degraded, damaged or destroyed. Restoration aims for an ecosystem resembling a reference ecosystem, a model based on local native ecosystems, adjusted for expected change. SER's International Principles and Standards (first published in 2016, second edition 2019) describe a restorative continuum: reducing societal impacts, remediation (removing pollutants or hazards), rehabilitation (restoring some functions and productivity, often with non-native species), and ecological restoration (aiming for the full native ecosystem). Many afforestation projects on difficult sites are rehabilitation rather than full restoration, and that is often appropriate where the original ecosystem cannot be recovered.
SER's standards use six key attributes to judge recovery: absence of threats, physical conditions (soil, water), species composition, structural diversity, ecosystem function, and external exchanges (connections with the surrounding landscape). Recovery is often summarised with a five-star rating against these attributes. Restoration should be planned with clear objectives and measurable targets and monitored to see whether they are met.
Restoration builds on succession: if the causes of degradation are removed, many ecosystems recover naturally (passive restoration). Where degradation has crossed a threshold, for example when topsoil is lost, invasive species dominate, or seed sources and dispersers are absent, the system may be stuck in an alternative stable state and needs active intervention: soil treatment, removal of invaders, planting or seeding, and reintroduction of missing species. Choosing between passive and active approaches depends on the degree of degradation, the presence of remnant vegetation and seed sources, and cost. Succession and disturbance are covered in forest-ecology.
Forest landscape restoration (FLR), developed by IUCN, WWF and partners from around 2000, is a planned process that aims to regain ecological functionality and enhance human well-being across deforested or degraded landscapes. It works at landscape scale, with a mosaic of interventions such as natural regeneration, agroforestry, planting, protection and improved land management, chosen with local stakeholders. The Bonn Challenge, launched in 2011, set a global goal of bringing 150 million hectares of degraded and deforested land into restoration by 2020 and 350 million hectares by 2030; India pledged to restore 21 million hectares, raised to 26 million hectares by 2030 in 2019. The Restoration Opportunities Assessment Methodology (ROAM), developed by IUCN and the World Resources Institute, helps countries identify where and how to restore. The United Nations declared 2021-2030 the Decade on Ecosystem Restoration.
Good restoration practice emphasises native species and local genetic material, diverse rather than single-species plantings, involvement of local people who use the land, attention to land tenure, and long-term monitoring. Planting large numbers of trees without these elements, sometimes counted only as seedlings distributed, often fails.
Salt-affected soils are classified using the electrical conductivity of the saturation extract (ECe), the exchangeable sodium percentage (ESP) and pH, following the US Salinity Laboratory (Richards, 1954). Saline soils have ECe above 4 dS/m, ESP below 15 and pH usually below 8.5; their problem is high soluble salts, which cause osmotic stress and specific ion toxicity. Sodic (alkali) soils have ESP above 15, pH usually above 8.5 and ECe below 4 dS/m; their problem is excess exchangeable sodium, which disperses clay, destroys soil structure, makes the soil hard and impermeable, and often goes with a calcium carbonate hardpan (kankar). Saline-sodic soils have both high ECe and high ESP. India has roughly 6.7 million hectares of salt-affected soils, somewhat more than half of them sodic, mainly in the Indo-Gangetic plains, and saline soils in arid, coastal and canal-irrigated areas. Research on their reclamation is led by the ICAR-Central Soil Salinity Research Institute (CSSRI) at Karnal.
The key technique for planting on sodic soils with a kankar layer is the auger-hole method developed at CSSRI. A tractor-mounted or manual auger makes holes of roughly 15 to 25 cm diameter and 1 to 2 m deep, breaking through the hardpan so roots can reach softer, less sodic subsoil and water. The holes are filled with a mixture of the original soil, gypsum and farmyard manure (sometimes with sand), and a nursery-raised seedling, preferably tall and in a large container, is planted. Gypsum supplies calcium to replace exchangeable sodium. Irrigation in the first years improves survival.
Gypsum requirement can be estimated from the change in ESP and the cation exchange capacity (CEC). For pure gypsum, roughly 1.9 tonnes per hectare is needed to replace 1 cmol(+)/kg of exchangeable sodium in the top 15 cm of soil with bulk density about 1.5 g/cm3. For example, reducing ESP from 40 to 10 in a soil with CEC 10 cmol(+)/kg requires replacing 3 cmol(+)/kg of sodium, about 3 x 1.9 = 5.8 tonnes of gypsum per hectare for that depth. In auger-hole planting only the hole is treated, so the amount per tree is small.
Species tolerant of sodicity include Prosopis juliflora (the most tolerant and widely planted, though invasive), Acacia nilotica, Salvadora persica, Tamarix articulata, Terminalia arjuna, Eucalyptus tereticornis and E. camaldulensis, Albizia lebbeck, Pongamia pinnata, Casuarina equisetifolia and Azadirachta indica, the last few on moderately sodic sites. Tolerance depends on ESP and pH; trials show survival and growth falling sharply as pH rises above about 9.5 to 10 for most species.
On saline soils, the aim is to leach salts and to choose salt-tolerant species. Species tolerant of salinity include Salvadora persica, Tamarix species, Prosopis juliflora, Acacia farnesiana, Casuarina glauca and Eucalyptus camaldulensis. Planting on ridges and raised beds, with furrow irrigation using good-quality water, keeps the root zone less saline. In canal command areas where seepage has raised the water table and caused waterlogging and secondary salinisation, biodrainage, planting fast-growing, high-water-using trees such as Eucalyptus in strips along canals and in fields, has been used to lower the water table through transpiration, for example in Haryana and the Indira Gandhi canal area of Rajasthan. Biodrainage works best where water is fresh enough for trees to use and must be designed to avoid salt accumulation in the root zone.
Coastal dunes form where sand blown from beaches accumulates behind the shore. They are mobile when unvegetated, threatening fields, roads and settlements, and they protect inland areas from storm surges when stable. The dune system usually has a foredune near the shore, colonised by pioneer creeping plants, and older, more stable dunes inland. Stabilisation follows the natural sequence: first reduce sand movement, then establish pioneer vegetation, then plant shrubs and trees.
Mechanical methods include brushwood fences, palisades and sand-trapping fences placed across the direction of the wind to trap sand and build up foredunes, and covering surfaces with brushwood or mulch. Pioneer sand-binding plants on Indian coasts include Spinifex littoreus, Ipomoea pes-caprae (beach morning glory), and grasses such as Saccharum spontaneum. Shrub and tree species for coastal sands include Casuarina equisetifolia, the most widely planted coastal species in India, Anacardium occidentale (cashew), Pongamia pinnata, Calophyllum inophyllum, Thespesia populnea, Pandanus and coconut palms. Casuarina grows well on coastal sands because it tolerates salt spray and fixes nitrogen with Frankia.
After the Indian Ocean tsunami of 2004, coastal vegetation belts, called bioshields, were promoted along the coasts of Tamil Nadu and other states; studies suggested that dense coastal vegetation and mangroves reduced damage in some places, although their protective effect against very large waves is limited and debated. Coastal shelterbelts of Casuarina and other species also protect farms from salt-laden winds and cyclones. Monoculture Casuarina belts on beaches can, however, displace native dune vegetation and turtle nesting habitat, so planting should avoid the active beach and foredune where these are important.
Inland dunes in the Thar desert of Rajasthan threaten farmland, canals, roads and railways. The Central Arid Zone Research Institute (CAZRI) at Jodhpur developed a dune stabilisation technique with several steps: protecting the dune from grazing and other biotic interference by fencing; establishing micro-windbreaks of brushwood, often in parallel strips or a checkerboard pattern several metres apart, across the prevailing wind; sowing or planting sand-binding grasses such as Lasiurus sindicus (sewan), Cenchrus ciliaris and Cenchrus setigerus; and planting drought-hardy trees and shrubs such as Prosopis juliflora, Acacia tortilis, Acacia senegal, Calligonum polygonoides, Ziziphus nummularia, Tecomella undulata and Colophospermum mopane in the inter-strip spaces during the monsoon. Large areas of dunes have been stabilised in this way, although protection must be maintained, and the invasiveness of Prosopis juliflora is a concern.
Lateritic soils, formed by intense weathering in warm, wet-dry climates, are rich in iron and aluminium oxides, acidic and low in nutrients and organic matter, and may contain a hard laterite crust or murram layer near the surface. They are common in parts of Kerala, Karnataka, Goa, Odisha, Jharkhand and West Bengal. Rocky and shallow sites, with little soil over rock, and dry sites in low-rainfall regions have very little water-holding capacity. On all of these, the main limiting factors are rooting depth, water and nutrients, and plantings fail if water is not harvested and conserved.
Site preparation on such sites aims to break hard layers and to harvest rainwater for each seedling. Techniques include deep pits dug with crowbars or machinery through the hard layer, filled with soil and organic matter; continuous or staggered contour trenches, which intercept runoff along the contour and store it in the soil, with seedlings planted on the berm or in the trench; V-ditches and half-moon (crescent) basins opening uphill; saucer-shaped basins around seedlings; and microcatchments, small runoff-producing areas draining to a planting pit. The water harvested by a microcatchment can be estimated as catchment area x rainfall x runoff coefficient: a 50 square metre microcatchment with 300 mm of rainfall and a runoff coefficient of 0.3 delivers 50 x 0.3 x 0.3 = 4.5 cubic metres, or 4,500 litres, to one tree. Mulching with stones or organic matter reduces evaporation.
Species for lateritic and degraded acidic soils include Acacia auriculiformis (widely planted, though its value for biodiversity is limited), cashew, Eucalyptus, Casuarina, Gmelina arborea, Pongamia, Simarouba glauca, and native species such as Terminalia, Xylia xylocarpa and Pterocarpus marsupium where conditions allow. For rocky and dry sites, hardy species include Acacia catechu, Acacia nilotica, Anogeissus pendula and A. latifolia, Hardwickia binata, Albizia amara, Ailanthus excelsa, Azadirachta indica, Dichrostachys cinerea, Wrightia tinctoria and Ziziphus, with bamboo (Dendrocalamus strictus) in some areas. Using large, hardened seedlings raised in deep containers, planting at the start of the monsoon, early weeding and protection from grazing and fire are critical. Where seed sources remain, protection alone may allow rootstocks and coppice to regenerate, an approach described in the chapter on assisted natural regeneration.
Gullies are channels cut by concentrated runoff, too deep to be removed by normal tillage; ravines are networks of deep gullies along rivers, formed where erodible alluvial soils, intense monsoon rain and a steep drop to a river combine. India has several million hectares of ravine land, often cited as around 3.6 to 4 million hectares, especially along the Chambal, Yamuna, Mahi, Sabarmati and their tributaries in Madhya Pradesh, Rajasthan, Uttar Pradesh and Gujarat. Ravines advance headward into fertile tablelands, destroying farmland, and they have historically harboured dacoits. Ravines are classified by depth, width and bed slope into shallow, medium and deep classes, which determine treatment.
Ravine reclamation combines engineering and vegetation, treating the catchment first. Peripheral or contour bunds on the tableland above the ravine stop runoff from entering the gully heads and arrest headward advance; runoff is led safely through stabilised outlets. Within gullies, check dams of brushwood, loose boulders, earth, gabions (stone-filled wire mesh) or masonry reduce flow velocity, trap silt and raise the gully bed, with spacing set so that the top of one dam is level with the toe of the next. Small and shallow gullies can be levelled and cropped; medium gullies can be shaped and used for horticulture or silvopasture; and deep ravines are best put under permanent vegetation.
Vegetation stabilises slopes and beds. Grasses such as Saccharum munja (sarkanda), Dichanthium annulatum and vetiver (Chrysopogon zizanioides), and shrubs such as Ipomoea carnea and Agave, are planted on beds and slopes. Trees for ravine slopes include Prosopis juliflora, Acacia nilotica, Azadirachta indica, Dalbergia sissoo, Dendrocalamus strictus, Holoptelea integrifolia and Emblica officinalis. The ICAR-Indian Institute of Soil and Water Conservation (formerly the Central Soil and Water Conservation Research and Training Institute) at Dehradun, with regional centres at Agra, Kota and Vasad, developed many ravine reclamation technologies.
Ravine reclamation is costly and must be planned on a watershed basis with the participation of landholders and villages, because benefits such as protected farmland and reduced siltation accrue to many people. Grazing control is essential, since livestock trampling and grazing on ravine slopes renew erosion. Large-scale levelling of ravines for farming, promoted at times, has been criticised for its cost and for destroying ravine habitats that support wildlife such as gharials, chinkara and birds in the Chambal ravines.
A site is waterlogged when the soil is saturated long enough to exclude oxygen from the root zone; in India, land with a water table within about 2 m of the surface is often classed as waterlogged, though definitions vary. Waterlogging arises naturally in depressions and floodplains and artificially from canal seepage, over-irrigation and poor drainage, and is often associated with salinity. Under anaerobic conditions, roots cannot respire, toxic compounds such as reduced iron and manganese and hydrogen sulphide accumulate, and nitrogen is lost by denitrification. Most trees die or grow poorly unless they have adaptations such as aerenchyma, adventitious roots, lenticels or tolerance of anaerobic metabolism.
Techniques for planting on waterlogged sites include raised mounds or ridges, on which seedlings are planted above the water table; planting tall, well-hardened stock at the end of the wet season, when water levels fall; and drainage where feasible. Species tolerant of waterlogging include Terminalia arjuna, Syzygium cumini, Salix (willows), Populus deltoides on moist sites, Eucalyptus camaldulensis, Casuarina glauca, Barringtonia acutangula, Lagerstroemia speciosa, Pongamia pinnata, Bischofia javanica, Anthocephalus cadamba and bamboos such as Bambusa vulgaris in some areas, with Acacia nilotica tolerating seasonal flooding. In canal command areas, biodrainage plantations, described in the chapter on saline soils, lower the water table.
Wetlands themselves, such as marshes, floodplain lakes and swamp forests, are ecosystems to be restored, not sites to be drained and afforested. Restoration of wetlands focuses on restoring natural hydrology (reconnecting floodplains, removing drains or embankments where possible, managing water inflows), controlling invasive aquatic weeds such as water hyacinth (Eichhornia crassipes) and invasive grasses, reducing pollution and siltation from the catchment, and re-establishing native vegetation. Freshwater swamp forests, such as the Myristica swamps of the Western Ghats, are rare and need protection. Planting trees in natural grassland wetlands or wet meadows, sometimes done in the name of greening, can destroy valuable habitats for birds and other wildlife and should be avoided. Wetlands of international importance under the Ramsar Convention are discussed in wildlife-management-protected-areas.
Mangroves are salt-tolerant trees and shrubs of tropical and subtropical intertidal zones. Worldwide they cover roughly 14 to 15 million hectares; India has about 5,000 square kilometres, with the largest share in the Sundarbans of West Bengal and major areas in Gujarat, the Andaman and Nicobar Islands, Odisha (Bhitarkanika), Andhra Pradesh and Maharashtra. Mangroves protect coasts from erosion and storms, support fisheries as nurseries for fish and shrimp, store large amounts of carbon in their soils (blue carbon) and provide timber, fuel and other products.
Mangroves have special adaptations. Pneumatophores, upward-growing aerial roots, supply oxygen to roots in anaerobic mud, as in Avicennia and Sonneratia; stilt or prop roots support Rhizophora; knee roots occur in Bruguiera; and buttresses in Heritiera. Salt is managed by exclusion at the roots (Rhizophora, Bruguiera), excretion through salt glands in the leaves (Avicennia, Aegiceras) or accumulation in leaves that are later shed. Vivipary, in which the seed germinates while still attached to the parent and the seedling (propagule) grows before falling, is characteristic of the Rhizophoraceae (Rhizophora, Bruguiera, Ceriops, Kandelia); crypto-vivipary occurs in Avicennia and Aegiceras. Species are often zoned along gradients of tidal inundation and salinity. The mangrove forest type is described in forest-types-biogeography.
Mangrove plantation methods depend on species. Viviparous propagules of Rhizophora, Bruguiera and Ceriops can be planted directly in the mud at suitable tidal levels, with about a third to half their length inserted. Avicennia and other species with smaller seeds are usually raised in nurseries in polythene bags with tidal or brackish watering and then planted out. Planting is done at the right tidal elevation for each species, since too frequent or too infrequent inundation kills seedlings.
Many mangrove plantings have failed because they were placed on mudflats below the natural mangrove zone or in sites where hydrology had been changed. Lewis and others have advocated ecological mangrove restoration: first understanding and restoring the hydrology and elevation that allow mangroves to grow, so that natural recruitment from propagules can occur, and planting only where natural recruitment is insufficient. In degraded, hypersaline areas cut off from tidal flushing, the fishbone canal method developed by the M. S. Swaminathan Research Foundation at Pichavaram in Tamil Nadu digs a main canal and feeder canals in a fishbone pattern to bring tidal water into the area, reducing salinity and allowing planted mangroves to survive; it has been applied in several states. India launched the MISHTI programme in 2023 to promote mangrove plantation along the coast.
Mangroves are threatened by conversion to aquaculture ponds, agriculture and urban development, by reduced freshwater inflow because of upstream dams, by pollution, by overharvesting and by sea-level rise where they cannot migrate landward. Protection under coastal regulation zone rules, community management and restoration of hydrology are central to their conservation.
Cold deserts are high-altitude arid regions, in India mainly in Ladakh, Lahaul and Spiti in Himachal Pradesh and parts of Uttarakhand and Sikkim, in the rain shadow of the Great Himalaya. Annual precipitation is low, often below about 100 to 300 mm, much of it as snow; winters are long and extremely cold, the growing season is short, solar radiation and wind are intense, soils are coarse, shallow, low in organic matter and often alkaline, and water for irrigation comes from snow and glacier melt. Natural woody vegetation is sparse and restricted to stream banks and moist places.
Afforestation in cold deserts relies on a small number of hardy species, nearly always planted near water. Willows (Salix alba, S. fragilis and others) and poplars (Populus alba, P. nigra, P. ciliata and others) are the main species, planted as large cuttings or stakes along irrigation channels (kuhls), streams and field boundaries; they provide fuelwood, fodder, timber for house construction and shelter. Seabuckthorn (Hippophae rhamnoides and related species), a thorny shrub that fixes nitrogen with Frankia, stabilises slopes and riverbanks, and its berries are rich in vitamin C and used for juice and other products. Other species include Myricaria, Elaeagnus, Ulmus, Robinia pseudoacacia, Juniperus (whose natural stands are slow-growing and need protection) and Caragana.
Planting is usually done in spring, after the soil thaws and before the main growing season, with cuttings soaked and planted deep enough to reach moist soil. Irrigation through channels during the first years, protection from goats, sheep and yaks by walls or fencing, and protection from frost heave and desiccating winds improve survival. Soil and moisture conservation works such as contour trenches can store snowmelt.
Water is the overriding constraint, and afforestation competes with agriculture for scarce irrigation water, so plantations are concentrated on community and riverbank land. Local communities in Ladakh and Spiti have long traditions of planting willow and poplar around villages and managing them for fuel and timber. Climate change, altering snow and glacier melt, threatens water supplies. Large plantations of exotic species in naturally treeless high-altitude grasslands and steppe can harm native wildlife such as Tibetan wild ass, snow leopard prey and birds, so afforestation should focus on village and riverine areas rather than converting natural steppe.
Surface mining for coal, iron ore, bauxite, limestone and other minerals removes vegetation and topsoil and leaves overburden dumps, pits and tailings. Mine spoils are hostile for plants because they lack topsoil and organic matter, have poor structure and are often compacted or very coarse, are low in nitrogen and phosphorus and in soil organisms, may be acidic (from oxidation of pyrite, producing acid mine drainage) or alkaline, may contain toxic levels of heavy metals, have steep unstable slopes that erode easily, and can become very hot on the surface. Reclamation aims to create a stable, non-polluting landform that supports vegetation and, where possible, a self-sustaining ecosystem or productive land use.
Good reclamation begins before mining. Topsoil should be stripped separately, stored in low heaps for as short a time as possible (seeded with grasses to keep it alive) and respread on reshaped spoils; it is the most valuable resource for revegetation, holding seeds, organic matter and soil organisms. For example, stripping 30 cm of topsoil from 10 hectares yields 10 x 10,000 x 0.3 = 30,000 cubic metres to be stored and returned. Overburden dumps are regraded to stable slopes, terraced and provided with drainage to control erosion. Amendments correct the main deficiencies: lime for acidic spoils, gypsum for sodic ones, organic matter such as farmyard manure, compost, sewage sludge or fly ash in some cases, fertilisers, and inoculation with biofertilisers and mycorrhizal fungi.
Revegetation commonly starts with a cover of fast-growing grasses and legumes that stabilise the surface and add organic matter and nitrogen, followed by trees and shrubs. Species used on Indian mine spoils include Dalbergia sissoo, Acacia auriculiformis, Acacia nilotica, Pongamia pinnata, Albizia lebbeck and A. procera, Cassia siamea, Leucaena leucocephala, Gmelina arborea, Eucalyptus, Bamboo, and native species of the region; on metal-contaminated sites, metal-tolerant species and phytostabilisation (using plants to immobilise metals in the root zone) are used. NEERI and other Indian institutes developed an integrated biotechnological approach combining organic amendments, biofertilisers and mycorrhizae with plantation on mine spoils.
A well-known Indian example is the restoration of limestone mines in the Mussoorie hills, where, after the Supreme Court ordered the closure of many mines in the 1980s in a case brought by the Rural Litigation and Entitlement Kendra, an Eco Task Force battalion of the Territorial Army planted and protected large areas of degraded mined land. Coal mining companies have reclaimed overburden dumps in Jharkhand, Odisha and Madhya Pradesh with mixed success. Mining leases in India require approved mining plans and progressive and final mine closure plans, with financial assurance for reclamation, and forest clearance conditions for mining on forest land include reclamation and compensatory afforestation. Monitoring of reclaimed sites should check not only tree survival but soil development, species diversity and ecosystem function against restoration targets.
Invasive alien plants are introduced species that establish, spread and cause ecological or economic harm. Invasion proceeds through stages of introduction, establishment (naturalisation), spread and impact; Williamson's tens rule suggests that roughly one in ten introduced species becomes established and one in ten established species becomes a pest, though rates vary. Invasive plants suppress native regeneration, alter fire regimes, change soil properties, reduce forage for herbivores and can dominate entire landscapes.
Among the most damaging invasives in Indian forests and grasslands are Lantana camara, which has invaded a large share of India's forests including tiger habitats; Prosopis juliflora in arid, semi-arid and coastal areas, including the Banni grasslands of Kutch; Chromolaena odorata and Mikania micrantha in moist forests of the Western Ghats and North-east; Parthenium hysterophorus on disturbed land, which also causes allergies; Senna spectabilis, which has spread rapidly in the Mudumalai-Bandipur-Wayanad landscape; Ageratina adenophora in the Himalaya; Mimosa diplotricha; and aquatic invaders such as water hyacinth (Eichhornia crassipes).
Prevention, through quarantine and avoiding introduction of potentially invasive species in plantations and gardens, is cheapest. Early detection and rapid response eradicates new invasions before they spread. For established invaders, control combines methods. Mechanical control includes uprooting, cutting and repeated slashing; for lantana, the cut-root-stock method, cutting the plant below the root collar so that it cannot resprout, has been widely used in Indian protected areas and is more effective than surface cutting. Chemical control uses herbicides such as glyphosate or triclopyr, applied as cut-stump or foliar treatments, with care to avoid harming native plants and water. Biological control introduces host-specific natural enemies from the invader's native range after testing: the Mexican beetle Zygogramma bicolorata against Parthenium, weevils of the genus Neochetina against water hyacinth, and insects such as Teleonemia scrupulosa against lantana, with variable success. Fire is used against some invaders but can favour others.
Control alone is rarely enough. Cleared areas must be restored with native grasses, shrubs and trees, otherwise the invader or another weed returns, and follow-up treatments are needed for several years to exhaust the seed bank. Some invasives can be used for products: lantana stems for furniture and baskets, Prosopis juliflora for charcoal and fuel, and water hyacinth for handicrafts, which can help pay for clearing but may also create interests in keeping the invader. Priorities should be set by impact and feasibility, focusing on high-value areas and new outbreaks.
Assisted natural regeneration (ANR) accelerates natural succession by removing barriers to regeneration and protecting existing seedlings, saplings, stumps and rootstocks, rather than planting all trees. It is suited to sites where remnant trees, coppicing stumps or seed sources remain and where natural seed dispersal can still occur. Techniques include protection from fire, grazing and cutting; marking and releasing existing regeneration by weeding around it; pressing or flattening competing grasses, as with Imperata cylindrica (cogon grass) in the Philippines, where ANR was developed and promoted with FAO support; and enrichment planting of species that are missing, such as large-seeded trees whose dispersers have been lost. ANR is generally much cheaper than full planting and produces a forest with local species and structure, but it is slower and less predictable, and needs sustained protection. In India, protection of degraded forests under joint forest management has allowed rootstocks of sal, teak and other species to regenerate in many areas.
The framework-species method, developed in tropical Australia and refined by the Forest Restoration Research Unit (FORRU) at Chiang Mai University in Thailand, plants a mixture of indigenous forest tree species chosen to restore forest structure quickly and attract seed-dispersing animals that bring in seeds of many other species. Framework species should be native to the forest type, have high survival and fast growth on degraded sites, develop dense, spreading crowns that shade out weeds, and provide fruit, nectar or nesting sites for birds and bats early in life. Typically 20 to 30 species are planted at close spacing, often about 1.8 m apart (about 3,100 trees per hectare), with weeding and fertilisation for the first two years until the canopy closes. Natural seed rain then adds many more species. The method works where remnant forest and seed-dispersing animals are within reach; far from forest, more species must be planted.
Applied nucleation plants small clusters or islands of trees, which act as foci for seed dispersal and spread over time, at lower cost than planting the whole area. The maximum diversity method plants as many native species as possible where dispersal is limited. The Miyawaki method, which plants many native species very densely (often around three seedlings per square metre) on improved soil, has become popular for urban forests; it gives fast canopy closure on small areas but is costly, and evidence for its claimed benefits over other methods is limited. Choosing among ANR, framework planting, nucleation and plantation depends on the degree of degradation, distance to seed sources, budget, objectives and local people's needs. These approaches draw on seed and nursery practice described in tree-seed-technology and forest-nursery-plantation.
Wastelands in Indian usage are degraded lands that can be brought under vegetative cover with reasonable effort, are currently underutilised, and are deteriorating for lack of appropriate water and soil management or because of natural causes. They include gullied and ravinous land, land with or without scrub, waterlogged and marshy land, saline and alkaline land, shifting cultivation areas, degraded forest, degraded pastures and grazing land, degraded plantation land, sands, mining wastelands, industrial wastelands, barren rocky areas and snow-covered or glacial areas, among 23 categories in the national mapping. The Wastelands Atlas of India 2019, prepared by the National Remote Sensing Centre and the Department of Land Resources, estimated about 55.8 million hectares of wastelands in 2015-16, roughly 17 percent of the country's geographical area (55.76 / 328.7 = 16.96 percent). The Desertification and Land Degradation Atlas of India, prepared by the Space Applications Centre, estimated that about 97.85 million hectares, nearly 30 percent of the country, was undergoing land degradation in 2018-19, with water erosion the leading process.
Wasteland development in India has been pursued through several programmes. The National Wastelands Development Board was set up in 1985 to promote afforestation of wastelands. The Integrated Wastelands Development Programme and later the Integrated Watershed Management Programme, now the watershed development component of the Pradhan Mantri Krishi Sinchayee Yojana, treat land on a watershed basis with soil and water conservation, afforestation, pasture development and livelihood support. Afforestation schemes such as the National Afforestation Programme and the Green India Mission include restoration of degraded forests and wastelands, and compensatory afforestation is often directed to degraded land. Under the UN Convention to Combat Desertification, India has committed to achieving land degradation neutrality, in line with Sustainable Development Goal target 15.3, and to restoring 26 million hectares of degraded land by 2030.
Reclaiming a wasteland begins with diagnosing its main limitations: salinity or sodicity, waterlogging, erosion, shallow or rocky soil, low rainfall, mining damage, invasive weeds or overgrazing. The techniques in the previous chapters are then applied. A watershed approach, treating the ridge to the valley, combines soil and water conservation structures with vegetation. Silvopasture and agroforestry, described in agroforestry-systems-design, are often the most productive uses of common and private wastelands. Community participation and secure rights to the products of reclaimed land are essential, because many wastelands are common lands used for grazing and fuel; programmes that planted trees on commons without involving users often failed. Monitoring with remote sensing and field surveys tracks whether vegetation cover and soil condition improve over time.
Learn the classification of salt-affected soils, the auger-hole method and gypsum calculation, the steps of dune stabilisation, ravine and gully treatments, mangrove adaptations and planting methods, cold-desert species, mine reclamation steps, invasive species and their control, ANR and framework-species principles, and wasteland statistics and programmes. Practise matching species to sites.
As a range officer or project forester you diagnose site limitations, design site preparation and water harvesting, choose species and planting stock, plant mangroves at the right tidal level, clear invasives and restore with natives, organise protection with communities, and monitor survival and growth. Judgement is needed to avoid planting where it harms existing habitats and to use natural regeneration where it will work.
At senior level you plan landscape restoration programmes, compensatory afforestation and mine closure, set targets and monitoring standards, and coordinate watershed, forestry and rural development schemes. Decisions include where to restore and by which method, species policy (native versus exotic), invasive species strategy, and how to secure community participation and rights.
Research questions include thresholds and alternative states in degraded ecosystems, species and provenance performance on hostile sites, soil and microbial recovery on mine spoils and sodic soils, mangrove hydrology and recruitment, invasive species ecology and control, the cost-effectiveness of ANR versus planting, and remote-sensing assessment of restoration outcomes.
Areas of salt-affected soils, ravines, mangroves and wastelands differ between surveys and years and are approximate. Species tolerance limits for salinity, sodicity and waterlogging vary with provenance, site and management, and the species lists are indicative. Dimensions of auger holes, trenches and check dams vary with site and agency practice. Detailed nursery practice is in forest-nursery-plantation, species silviculture in silviculture-of-species, and forest types in forest-types-biogeography. Evidence on some popular methods, such as the Miyawaki method and coastal bioshields, is limited or contested 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.
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