Forestry & Forest Sciences · Foundations · also Dendrology, Tree Identification, Forest Dendrology
Identifying trees in the field by bark, leaf, flower, fruit, wood and habit, and knowing the range, ecology and uses of the commercially and ecologically important species of each forest region.
In the exams: ICAR AIEEA-PG Group 09 (dendrology, hardwoods, softwoods, multipurpose tree species); IFoS Forestry Paper I Section A (silviculture of named species); Korea Forestry Engineer written subject Silviculture; SAF and state forester field identification
Dendrology is the study and identification of trees and other woody plants. For a forester it is a practical skill: recognising a tree in the field, often without flowers or fruit and sometimes without leaves, from its bark, blaze, leaves, buds, exudates, form and habitat; knowing its range, ecology, phenology and uses; and telling it apart from look-alikes. Every other forestry task depends on it. An inventory with misidentified species gives wrong volumes and values, a working plan that confuses species prescribes the wrong silviculture, a timber sale that mislabels a species can be fraudulent or illegal, and a seed collection from the wrong tree wastes years of work.
This manual builds on forest botany and plant systematics, which covers plant morphology, families and nomenclature, and on wood anatomy and properties, which covers identification of timber. It describes the field characters used to identify trees and how keys work, and then surveys the important trees of each kind of forest: temperate and boreal conifers; tropical hardwoods such as teak, sal, dipterocarps and mahoganies; dry-zone and arid species; plantation genera such as eucalypts, poplars and casuarinas; and bamboos and rattans. It ends with phenology, native ranges and exotics, and the identification of trees in the leafless state. The distribution of forest types in which these species grow is described in forest types and biogeography.
Dendrology is examined in ICAR's AIEEA-PG forestry paper (dendrology, hardwoods, softwoods and multipurpose tree species), in the UPSC Indian Forest Service Forestry optional through the silviculture of named species, in the silviculture paper of Korea's Forestry Engineer qualification, and in field identification tests for state forest services, Society of American Foresters and other professional credentials. Scientific names follow current usage, with widely used older names given where they help.
Identification starts with the whole tree: its height and form, whether it is evergreen or deciduous, the shape and density of the crown, whether the trunk is straight, buttressed, fluted or crooked, and where it grows. Bark is often the most useful single character in tropical forests, where leaves and flowers may be far out of reach. Bark is described by its colour; texture, from smooth through flaking, peeling, scaly, fissured and furrowed to corky; the pattern and depth of fissures; thickness; and features such as lenticels, prickles and spines. Some barks are unmistakable: the deeply cracked, crocodile-skin pattern of Terminalia elliptica (saja); the smooth, pale, often mottled bark of Terminalia arjuna and of Lagerstroemia; the papery, peeling bark of Boswellia serrata; the smooth whitish bark of Sterculia urens, which gives it the name ghost tree; the prickly trunk of young Bombax ceiba; and the smooth, shedding bark of many eucalypts (gums) contrasted with the persistent fibrous bark of stringybarks and the hard, furrowed bark of ironbarks.
A blaze is a small, shallow cut made into the bark with a knife or machete to expose the inner bark and the outer sapwood. It is a standard tool of tropical dendrology, because the colour, texture, smell and exudate of the inner bark are often characteristic and do not depend on season. The forester notes the colour of the outer and inner bark at the cut and whether it changes on exposure to air, the texture (granular, fibrous, laminated), any smell, and the exudate. Blazes should be small, made only where needed and not on valuable trees or in research plots, because they create wounds through which pathogens can enter.
Leaf characters remain the most widely used. The first questions are whether leaves are simple or compound, and whether they are arranged alternately, oppositely or in whorls; these two characters alone split most floras into manageable groups. Then come the shape, size, margin, apex, base, venation, texture, surface hairs and glands. Pellucid dots, oil glands seen as translucent points when a leaf is held against light, indicate families such as Myrtaceae and Rutaceae. Stipules, small appendages at the base of the petiole, and the scars they leave, are important: Rubiaceae have interpetiolar stipules between opposite leaves; Polygonaceae have a sheathing ochrea; many Fabaceae and Malvaceae have conspicuous stipules; and in some acacias the stipules are modified into paired spines. Crushed leaves often have a characteristic smell, as in eucalypts, neem and citrus.
Many trees produce exudates when cut. Latex, a milky or coloured fluid, flows from cut bark and leaves in Moraceae (figs, jackfruit), Apocynaceae, many Euphorbiaceae, and Sapotaceae such as mahua. Resins, sticky and aromatic, come from Pinaceae, Dipterocarpaceae (dammar from sal and Vateria) and Burseraceae. Gums, water-soluble exudates, include gum arabic from Acacia senegal, gum ghatti from Anogeissus latifolia and gum karaya from Sterculia urens. Kinos are red, astringent exudates, such as those of Pterocarpus marsupium and Butea monosperma (Bengal kino). Some trees exude red or coloured sap, as in Myristica. Noting whether an exudate is present, its colour, consistency and how fast it flows is part of every blaze description.
A key is a tool that leads the user to the name of a plant by a series of choices among characters. A dichotomous key presents a series of couplets, each consisting of two mutually exclusive statements (leads); the user chooses the statement that fits the specimen and follows it either to a name or to the next couplet. Dichotomous keys are the commonest kind in floras and field guides. In an indented key, the two leads of a couplet are given the same indentation and the couplets that follow each lead are indented beneath it, so the structure of the key is easy to see but long keys move across the page. In a bracketed key, the two leads of each couplet are printed together and numbered, with each lead ending in a number or a name, which saves space but hides the structure.
A good dichotomous key uses characters that are easy to see in the field or on the specimen, preferably vegetative characters for trees; makes the two leads of a couplet truly contrasting and parallel in wording; uses precise terms and measurements rather than vague comparisons such as large or small; puts the most reliable character first in each lead; and is tested on real specimens. Keys fail when the specimen lacks the character asked, such as flowers, or when the plant is outside the area or group the key covers.
A multi-access (polyclave) key allows characters to be used in any order. Originally made as punched cards, these keys are now computer programs: the user enters whatever characters can be observed, such as leaf arrangement, bark type or fruit, and the program narrows the list of possible species, often showing images. Multi-access keys are well suited to trees, because the user can start with whatever is visible, and to tropical forests with many species. Their quality depends on the accuracy and completeness of the character data entered for each species.
Field guides combine keys with descriptions and photographs. Mobile applications that identify plants from photographs using machine learning can suggest names quickly, but their accuracy varies by region and group, and their suggestions must be confirmed with a key, a flora or a specialist. DNA barcoding identifies samples by short standard DNA sequences; for land plants the core barcode, agreed in 2009 by the Consortium for the Barcode of Life plant working group, consists of parts of the chloroplast genes rbcL and matK, often supplemented by other regions. Barcoding is used to identify seedlings, fragments and traded products, and to check timber species in enforcement. Wood identification by anatomy, using reference collections and keys, is covered in wood anatomy and properties. Whatever method is used, a voucher specimen should be kept when the identification matters.
Pines (Pinus) have needles in bundles (fascicles) of usually two, three or five, with a papery sheath at the base, and woody cones that take about two years to mature. Hard (diploxylon) pines usually have two or three needles per bundle, a persistent sheath and harder wood; soft (haploxylon) pines usually have five needles, a deciduous sheath and softer wood. In the Himalaya, chir pine (Pinus roxburghii) has long needles in threes, thick, deeply fissured reddish-grey bark in plates, and large cones; it forms the subtropical pine forests and is tapped for resin. Blue pine (P. wallichiana) has slender, drooping, blue-green needles in fives and long, hanging, resinous cones; it grows in the temperate zone. Chilgoza pine (P. gerardiana) of dry inner valleys has needles in threes and smooth, flaking bark with grey-green and whitish patches, and edible seeds. Khasi pine (P. kesiya) of the North-East has needles in threes. Around the world, Scots pine (P. sylvestris) has twisted paired needles and orange upper bark; radiata pine (P. radiata) has needles mostly in threes; and loblolly, slash and ponderosa pines are major American species.
Deodar (Cedrus deodara), the national tree of Pakistan, has needles in tufts on short shoots and singly on long shoots, a drooping leading shoot and branch tips, and erect, barrel-shaped cones that break up on the tree; its fragrant, durable heartwood was the classic building timber of the western Himalaya. Firs (Abies) have flat, soft needles that leave round, flat scars on the twig, and erect cones that disintegrate on the tree; the West Himalayan silver fir (A. pindrow) has long needles notched at the tip and the East Himalayan fir (A. spectabilis) forms subalpine forests. Spruces (Picea) have stiff, often four-angled needles each set on a woody peg (sterigma) that remains on the twig, making it rough, and hanging cones that fall whole; the West Himalayan spruce (P. smithiana) has long, drooping branchlets. Larches (Larix) are deciduous, with soft needles in tufts on short shoots, turning yellow in autumn; Himalayan larch (L. griffithii) grows in the eastern Himalaya. Hemlocks (Tsuga) have short flat needles on short stalks and small cones; Douglas-fir (Pseudotsuga menziesii) of western North America has pointed buds and cones with three-pointed bracts.
Himalayan cypress (Cupressus torulosa) has small scale leaves on slender, drooping branchlets and small round cones. Junipers (Juniperus) have needle or scale leaves and fleshy, berry-like seed cones; they dominate dry temperate and alpine scrub. Himalayan yew (Taxus wallichiana) has flat, dark green needles in two ranks, red, fleshy arils around the seeds, and toxic foliage. Cryptomeria japonica, planted in the Darjeeling hills and the North-East, has awl-shaped leaves spiralled around the shoot.
In the boreal forest the main conifers are Norway spruce (Picea abies) and Scots pine in northern Europe; white spruce (P. glauca), black spruce (P. mariana), balsam fir (Abies balsamea), jack pine (Pinus banksiana) and tamarack (Larix laricina) in North America; and Siberian larch (Larix sibirica), Dahurian larch (L. gmelinii), Siberian spruce and Siberian pine in Russia. Black spruce, a slow-growing tree of boggy ground with semi-serotinous cones, and jack pine, with serotinous cones that open after fire, are classic examples of fire-adapted boreal trees.
The conifers of the Himalaya grow with many broadleaved trees that a forester must also know. Ban oak (Quercus leucotrichophora) has leaves with toothed margins, dark green above and white-woolly beneath; moru oak (Q. floribunda) has glossy leaves, spiny on young trees; and kharsu oak (Q. semecarpifolia) has leathery leaves, spiny-toothed when young and entire on old trees, brown-hairy beneath. Rhododendron arboreum, with red flowers in spring, is the state tree or flower of several Himalayan states and Nepal's national flower. Himalayan alder (Alnus nepalensis) colonises landslides and fixes nitrogen with Frankia; it bears small woody cone-like fruits. Other common trees include Himalayan birch (Betula utilis) at the treeline, walnut (Juglans regia), Indian horse chestnut (Aesculus indica) with palmately compound leaves and erect flower spikes, maples (Acer) with opposite lobed leaves and paired winged fruits, elms (Ulmus), hackberry (Celtis australis), much lopped for fodder, and Himalayan cherry (Prunus cerasoides), which flowers pink in autumn or early winter.
Teak (Tectona grandis, Lamiaceae) is a large deciduous tree with very large, rough, opposite leaves, often 30 centimetres or more long, covered beneath with star-shaped (stellate) hairs; young leaves, when crushed, stain red. It flowers in the monsoon, bearing large terminal panicles of small white flowers, and the fruits, ripening in the cool season, are hard drupes enclosed in an inflated, papery calyx. The bark is grey-brown, fibrous and peeling in thin strips. Teak occurs naturally in peninsular India, Myanmar, Thailand and Laos and is planted throughout the tropics; its golden-brown, oily, durable heartwood is among the world's most valued timbers.
Sal (Shorea robusta, Dipterocarpaceae) is a large, gregarious tree with simple, alternate, leathery, broadly ovate leaves with a pointed tip and fine parallel lateral veins. It is briefly deciduous in the hot dry season, when new reddish leaves flush. Its fruits have five sepal wings, three long and two short, and germinate as soon as they fall at the start of the monsoon. The bark is thick, dark and longitudinally fissured, and the tree exudes a resin (sal dammar). Sal forms extensive forests in northern, central and eastern India and Nepal.
Other dipterocarps dominate the rain forests of South-East Asia and are important in India's evergreen forests. Dipterocarpus species, such as gurjan (D. turbinatus) of the North-East and Andamans and D. indicus of the Western Ghats, have large leaves with prominent parallel veins, large stipules that leave ring scars around the twig, an oleoresin (gurjan balsam) and fruits with two long wings. Hopea species have smaller leaves and small two-winged fruits. Vateria indica (white dammar) of the Western Ghats yields a resin used for varnish and incense. In Malesia, Shorea species supply the meranti, lauan and seraya timbers of trade, Dryobalanops yields Borneo camphor, and Neobalanocarpus heimii (chengal) is a heavy, durable timber. Many dipterocarps flower and fruit in irregular mast years, which complicates seed supply and regeneration.
The true mahoganies (Meliaceae) are Swietenia macrophylla, big-leaf mahogany, and S. mahagoni of tropical America, with pinnate leaves of a few pairs of asymmetric leaflets and woody, upright capsules releasing winged seeds; both are widely planted in India and listed under CITES because of overexploitation. African mahoganies belong to Khaya. Indian red cedar (Toona ciliata) has large pinnate leaves with many leaflets and a fragrant reddish wood; Chukrasia tabularis and neem (Azadirachta indica) are other Meliaceae.
Other important Indian hardwoods include Indian rosewood (Dalbergia latifolia) and shisham (D. sissoo), legumes with pinnate leaves of a few broad leaflets and flat, thin pods; red sanders (Pterocarpus santalinus), an endemic of the southern Eastern Ghats with trifoliate leaves and a deep red heartwood, protected and heavily smuggled; bijasal (P. marsupium), with a red kino; laurel or saja (Terminalia elliptica), with crocodile bark; arjun (T. arjuna), with smooth pale bark and riverside habit; Gmelina arborea; Lagerstroemia speciosa, with large mauve flowers and smooth peeling bark; Xylia xylocarpa; and sandalwood (Santalum album), a small evergreen tree that is a root hemiparasite on other plants and whose fragrant heartwood is among the most valuable woods in the world.
Many other trees are characteristic of India's moist and evergreen forests. Mesua ferrea (ironwood or nahor), the national tree of Sri Lanka, has narrow, leathery leaves that flush bright red, large white fragrant flowers and very hard wood. Artocarpus species, including jackfruit (A. heterophyllus) and the wild jack (A. hirsutus) of the Western Ghats, have milky latex and large multiple fruits. Calophyllum species have closely parallel lateral veins and yellow latex. Michelia champaca (now usually placed in Magnolia as M. champaca) has fragrant yellow flowers and is planted near temples. Terminalia myriocarpa (hollock) is a tall tree of north-east India with drooping panicles of small flowers. Canarium species yield aromatic resins. Bombax insigne and Tetrameles nudiflora, a huge buttressed deciduous tree, emerge above the canopy in semi-evergreen forests. In wetter forests, palms, tree ferns and climbing rattans add to the diversity, and field identification relies heavily on bark, blaze and exudate.
The acacias of dry South Asia, now divided among several genera, are thorny legumes with bipinnate leaves, small flowers in round heads or spikes, and pods. Babul (Vachellia nilotica, formerly Acacia nilotica) has dark, fissured bark, paired straight white stipular spines, bright yellow globose flower heads and constricted, necklace-like (moniliform) pods; it is valued for fuel, tannin, fodder and agricultural tools. Khair (Senegalia catechu, formerly Acacia catechu) has hooked prickles, white or pale yellow flower spikes, flat pods and a dark red heartwood boiled to produce katha and cutch. Acacia senegal (Senegalia senegal) yields gum arabic. Israeli babul (Vachellia tortilis), with coiled pods and umbrella-shaped crowns, has been planted on dry sites in India. Albizia lebbeck (siris), with large flat pods that rattle in the wind, and Leucaena leucocephala are related legumes of dry and moist zones.
Khejri (Prosopis cineraria) is the most important native tree of the Thar desert: a thorny tree with small bipinnate leaves, short prickles, small yellowish flower spikes and long, slender pods (sangri) eaten as a vegetable. Its deep roots allow crops to grow beneath it without much competition, and its leaves are lopped for fodder. Mesquite (Prosopis juliflora), introduced from the Americas in the nineteenth century, has longer, paired spines, larger leaflets and sweet pods eaten by livestock, which spread its seeds; it has become an aggressive invasive in dry India, Pakistan and East Africa, valued for fuelwood but displacing native vegetation.
Anjan (Hardwickia binata) is a tall, graceful legume of dry forests in peninsular India; each leaf has a single pair of broad, kidney-shaped leaflets that resemble butterfly wings, and its very hard, heavy heartwood is used for posts and implements; its leaves are lopped for fodder. Dhaura or axlewood (Anogeissus latifolia, Combretaceae) has smooth, pale, flaking bark, simple opposite to alternate leaves that turn red before falling, small winged fruits in round heads and gum ghatti; its tough wood was used for axles. Kardhai (Anogeissus pendula) forms open forests on the rocky hills of the Aravallis. Other typical dry-zone trees include ber (Ziziphus mauritiana), with zigzag branches, paired spines and edible fruits; Balanites aegyptiaca; Salvadora persica and S. oleoides; rohida (Tecomella undulata), with showy orange-yellow flowers and valuable timber; Capparis decidua, almost leafless with green twigs; guggul (Commiphora wightii), source of a medicinal resin and now threatened; and neem, widely planted in dry areas.
Eucalypts (Eucalyptus and the related Corymbia) are evergreen trees native mainly to Australia, with several hundred species. They show marked leaf dimorphism: juvenile leaves are often opposite, sessile and broad, while adult leaves are usually alternate, stalked, narrow and hanging, dotted with oil glands that give the crushed leaf a strong smell. Flower buds are capped by an operculum that falls at flowering to release many stamens, and the fruit is a woody capsule (gumnut). Species are distinguished by bark, bud and fruit shape and size, and leaf characters. In India the most planted species include E. tereticornis (often under the name Mysore gum), E. camaldulensis (river red gum), E. grandis, E. globulus (Tasmanian blue gum, planted in the Nilgiris) and hybrid clones; Corymbia citriodora, the lemon-scented gum, is grown for its oil. Smooth-barked species shed their bark in strips or plates, revealing coloured patches.
Poplars (Populus, Salicaceae) are fast-growing, deciduous, dioecious trees with alternate, often triangular or heart-shaped leaves on long petioles, flowers in catkins, and capsules releasing cottony seeds. Populus deltoides (eastern cottonwood) from North America, grown as selected clones, is the main poplar of agroforestry in north-western India, planted with crops in Punjab, Haryana, Uttar Pradesh and Uttarakhand. Native Himalayan poplars include Populus ciliata. Willows (Salix) have narrower leaves and catkins and grow along streams; Salix alba and related willows are used for cricket bats (Kashmir willow) and fuel. Both genera regenerate readily from cuttings and sprout from roots.
Casuarina equisetifolia, of coastal South-East Asia and Australia, looks like a conifer: its drooping, jointed, green branchlets bear whorls of tiny scale leaves, and its small woody, cone-like fruits contain winged seeds. It fixes nitrogen through Frankia in root nodules and is widely planted along the Indian coast for poles, fuel and shelterbelts; C. junghuhniana and hybrids are also grown. Australian acacias such as Acacia auriculiformis and A. mangium, with phyllodes in place of compound leaves and coiled or twisted pods, are planted for pulp, fuel and land rehabilitation. Other plantation trees include Leucaena leucocephala (subabul), Melia dubia (Malabar neem), a fast-growing tree for plywood and pulp; Ailanthus excelsa of dry areas; Gmelina arborea; silver oak (Grevillea robusta), planted as shade in coffee and tea estates; Caribbean pine (Pinus caribaea) and other tropical pines; and Cryptomeria in the eastern Himalaya. Each is identified by its leaves, fruits and bark, as described in floras and in silviculture of species.
Many trees are grown on farms and around villages for several products at once. Neem (Azadirachta indica) provides shade, timber, and oil and leaves used as natural insecticides. Pongamia (Millettia pinnata), with glossy pinnate leaves and thick woody pods, yields seed oil and is planted along roads and canals. Mahua (Madhuca longifolia) has fleshy, sweet flowers collected for food and liquor and seeds yielding fat, and is central to the livelihoods of many forest communities. Tamarind, mango, jackfruit and jamun provide fruit and timber. Shisham (Dalbergia sissoo) and Albizia species are planted for timber and fodder. Moringa oleifera supplies leaves and pods as vegetables. Subabul (Leucaena leucocephala) supplies fodder and fuel. Ficus species such as peepal (F. religiosa) and banyan (F. benghalensis) are planted for shade and worship. Identifying these trees and knowing their uses is essential for agroforestry and extension work, described in agroforestry systems design.
Bamboos are woody grasses of the family Poaceae, subfamily Bambusoideae. Their stems, called culms, are usually hollow between solid nodes, and they grow from underground rhizomes. A new culm emerges as a shoot and reaches its full height within a single growing season, with no later increase in diameter, because bamboos lack a vascular cambium; culms become harder and stronger as they mature over the next few years. Identification relies on culm characters (height, diameter, wall thickness, colour, surface, presence of thorns), branching at the nodes, and above all the culm sheaths, the papery or leathery sheaths that cover young culms, whose shape, hairs, auricles and blade are diagnostic. Flowers are rarely available.
Rhizomes are of two main types. Pachymorph or sympodial rhizomes are short and thick, each turning up into a culm, producing clumps; they are typical of tropical bamboos such as Bambusa and Dendrocalamus. Leptomorph or monopodial rhizomes run long distances underground, producing culms singly and spreading; they are typical of temperate bamboos such as Phyllostachys.
Dendrocalamus strictus, the male or solid bamboo, is the commonest bamboo of India's dry deciduous forests, with thick-walled, nearly solid culms used for poles and paper. Bambusa bambos (B. arundinacea), the giant thorny bamboo, forms dense clumps with spiny branches in moist forests. Dendrocalamus giganteus is among the largest bamboos. Melocanna baccifera (muli) of the North-East and adjoining Myanmar and Bangladesh spreads by long rhizome necks and produces large, fleshy fruits. Many bamboos flower gregariously, all culms of a species in a region flowering together after long intervals, sometimes decades, and then dying. The gregarious flowering of Melocanna baccifera in Mizoram and neighbouring areas, at intervals of about half a century, has been followed by explosions of rats feeding on the abundant fruit and by famines, known locally as mautam. India has one of the largest bamboo resources in the world. In 2017 the Indian Forest Act was amended so that bamboo grown outside forest areas is no longer treated as a tree, freeing its harvest and transport from felling and transit permits on such land.
Rattans are climbing palms (Arecaceae, subfamily Calamoideae), chiefly of the genera Calamus and Daemonorops in Asia. Their slender, solid stems climb into the canopy using whip-like climbing organs armed with recurved hooks: cirri, extensions of the leaf rachis, or flagella, modified inflorescences arising from the leaf sheath. Leaf sheaths are usually covered in spines, and the fruits are covered in overlapping scales, a feature of the subfamily. Rattan canes, stripped of their sheaths, are used for furniture, baskets and handicrafts, and form a major non-timber forest product in South-East Asia, north-east India, the Western Ghats and the Andamans. Overharvesting has depleted many wild populations, and rattans are being cultivated in some areas.
Phenology is the study of the timing of recurring biological events and of their causes. For trees, the main phenophases are bud break and leaf flush, leaf maturation, leaf senescence and leaf fall, flower bud formation, flowering, fruit setting, fruit ripening and seed dispersal. Trees are evergreen (with leaves all year, shed and replaced gradually), deciduous (leafless for a period), or brevideciduous (leafless only briefly, often while new leaves flush, as in sal). Phenology is recorded by regular observation of marked trees, by litter traps, by repeated photography and by satellite indices of canopy greenness. Phenological calendars, charts showing the months of each phenophase for each species in a region, are used to plan seed collection, to choose the best season for identification, and to time silvicultural operations.
In temperate and boreal trees, leaf flush is triggered mainly by rising temperatures after winter chilling has been satisfied, and leaf fall and dormancy by shortening days and falling temperatures. In tropical seasonal forests, water status is the main driver: many trees shed leaves as the dry season deepens and flush before or at the onset of the rains, sometimes in response to rising day length or to the first showers. Many dry deciduous trees flower while leafless, which makes them conspicuous and helps pollinators: flame of the forest (Butea monosperma), with orange-red flowers, silk cotton (Bombax ceiba), with large red flowers, and Erythrina flower in the late dry season. Teak flowers during the monsoon and its fruits ripen in the following cool season. Sal sheds its leaves in the hot dry season and flushes almost at once, flowering about the same time and fruiting at the beginning of the monsoon. Mast fruiting in dipterocarps and gregarious flowering in bamboos are phenological events on scales of years or decades.
Exact months vary with latitude, elevation and year, so calendars must be local. Long-term phenological records show that, in many temperate regions, spring events such as leaf flush and flowering have advanced as climate has warmed; similar trends are being studied in tropical forests, where changes in rainfall timing may matter more.
Phenological knowledge supports many forestry tasks. Seed collection must be timed to fruit ripening and before dispersal, as described in tree seed technology. Identification is easiest when flowers or fruits are present, so dendrology field courses are timed accordingly. Fire risk in dry deciduous forests peaks when leaf litter accumulates after leaf fall. Fodder lopping, honey production, tendu leaf collection and other non-timber activities follow phenology. Plant-animal interactions, such as the timing of fig fruiting for frugivores, depend on it. Recording phenology on permanent plots is also a simple and valuable way to detect the effects of climate change.
A species is native (indigenous) to a region if it occurs there naturally, without human introduction. An exotic (alien, introduced, non-native) species has been brought to a region by people, deliberately or accidentally. Among exotics, ecologists distinguish casual species, which survive only where planted or occasionally reproduce; naturalised species, which reproduce and sustain populations without human help; and invasive species, a subset of naturalised species that spread widely from where they were introduced, often with harmful effects on native ecosystems or the economy. This scheme was set out by Richardson and colleagues in 2000 and is widely used. A species can be native in one part of a country and exotic in another; for example, a Himalayan conifer planted in the Western Ghats is exotic there.
Knowing native ranges matters for seed sourcing, conservation and the interpretation of species lists. Teak is native to peninsular India, Myanmar, Thailand and Laos; sal to northern, central and eastern India, Nepal and Bangladesh; deodar to the western Himalaya and adjoining mountains of Afghanistan and Pakistan; chir pine to the Himalaya from Afghanistan to Bhutan; red sanders to a small area of the southern Eastern Ghats; and sandalwood is generally regarded as native to peninsular India, though some authors have suggested an early introduction. Eucalypts are native to Australia and a few islands to its north; Pinus radiata to a few sites in California and Mexican islands; mahoganies to tropical America; Casuarina equisetifolia to South-East Asia, northern Australia and the Pacific; Leucaena leucocephala to Central America; and Prosopis juliflora to Central and South America. Databases such as Plants of the World Online summarise native and introduced ranges.
India has a long history of tree introductions. Eucalypts were introduced in the eighteenth and nineteenth centuries and are now among the most widely planted trees; teak and other native species have been moved far within the country. Exotics that have naturalised or become invasive include Prosopis juliflora in dry regions, Leucaena leucocephala, Acacia mearnsii (black wattle) in the Nilgiris and other hills, and Lantana camara, a shrub that has invaded much of India's forest understorey. Exotic trees can be valuable for wood, fuel and rehabilitation, but their planting should be preceded by assessment of invasiveness, and plantations of potentially invasive species should be managed to limit spread. The ecology and management of invasive species are discussed in forest ecology and conservation subjects.
Some trees are protected by national law or international trade rules because of overexploitation, and their identification has legal consequences. Red sanders and sandalwood are protected in India, and their felling, transport and trade are tightly controlled; red sanders is listed in Appendix II of the Convention on International Trade in Endangered Species (CITES). Big-leaf mahogany is in CITES Appendix II. Many rosewoods of the genus Dalbergia were listed in CITES Appendix II in 2017, with later amendments to exemptions for finished products. Himalayan yew is protected because of over-harvesting for taxol. Agarwood (Aquilaria malaccensis), whose fungus-infected resinous heartwood is used for incense and perfume, is listed in CITES Appendix II. Customs and forest officers need reliable identification, often supported by wood anatomy and DNA methods, to enforce these rules and to distinguish protected species from look-alike substitutes.
Deciduous trees must often be identified without leaves, in winter in temperate regions or in the dry season in the tropics. The twig then carries most of the information. Buds may be terminal or lateral; covered by one, two or many overlapping (imbricate) scales or by scales meeting at the edges (valvate), or naked without scales; and they vary in colour, size, shape and hairiness. Leaf scars, left where leaves fell, vary in shape, and within them the bundle scars, marks of the vascular strands, vary in number and arrangement. Opposite leaf scars indicate an opposite-leaved tree. Stipule scars, lenticels, the colour and hairiness of the twig, thorns and spines, and the pith (solid, hollow or chambered, and its colour) are also used. Classic examples from temperate forests include the black buds of European ash (Fraxinus excelsior) in opposite pairs; the large, sticky buds of horse chestnut; the long, slender, pointed buds of beech; the clusters of buds at the twig tip in oaks; and the chambered pith of walnuts (Juglans), divided into small compartments by thin plates.
Without leaves, bark and form become more important: the white, peeling bark of birches; the smooth grey bark of beech; the patchwork bark of plane trees; and the branching pattern and silhouette of the crown. Persistent fruits help too: the woody capsules of eucalypts, the cones of conifers, the pods of legumes, the winged fruits of maples and ashes, and the cone-like fruits of alders.
In the tropical dry season, many deciduous trees are identified by bark, blaze and fruit. Terminalia elliptica has crocodile-skin bark; Boswellia serrata has papery, peeling, greenish bark; Sterculia urens has smooth, white, papery bark and red fruits; Bombax ceiba has prickles on young trunks and buttressed bases, with red flowers on bare branches; Butea monosperma has crooked branches and orange flowers on bare twigs; Lagerstroemia parviflora has smooth, flaking bark; Anogeissus latifolia has smooth, grey to pale bark with flakes; and teak keeps its dry, papery fruits and has fibrous bark. Field identification courses in South Asia are often held in both wet and dry seasons so that students learn trees in both states.
Reliable identification in all seasons comes from repeated field practice: learning a core list of common species thoroughly, using all the senses (bark texture, smell of crushed leaves or blaze, taste is not advised), comparing similar species side by side, keeping a field notebook with sketches and photographs, and checking difficult cases against herbarium specimens or experts. Local people, forest guards and collectors often know local trees intimately by vernacular names, and learning these names, while linking them to scientific names, builds trust and skill. The forester's goal is to recognise the commercially and ecologically important species of a region at a glance, and to know how to identify the rest.
A student should be able to describe a tree using standard terms, make and read a blaze, use dichotomous and multi-access keys, and recognise in the field the important conifers, tropical hardwoods, dry-zone species, plantation trees, bamboos and rattans of the region by bark, leaves, exudates and fruits. Learn the native range, phenology and main uses of each species, the current and older scientific names, and how to identify common deciduous trees in the leafless state. Keep a field notebook and a small reference collection.
A forester five years into practice identifies trees confidently during inventories, marking, timber sales and seed collection; recognises protected and high-value species such as red sanders and sandalwood and their substitutes; detects invasive species early; plans seed collection and other operations by local phenology; and trains forest guards and crews in identification, including vernacular names.
A senior forester or dendrologist builds regional identification resources (field guides, keys, reference collections), supports enforcement against illegal logging and timber fraud with reliable identification and expert evidence, advises on species choice and native ranges for planting programmes, and maintains phenological records for climate monitoring.
A researcher in dendrology and systematics revises the taxonomy of important tree genera, develops multi-access keys, image recognition and DNA barcode libraries for tropical trees, studies phenology and its response to climate, and maps native and introduced ranges. Such work underpins reliable species identification in forestry, trade regulation and conservation.
This manual describes representative species and identification principles; it is not a complete field guide or key to the trees of any region, and local floras and field guides are essential. Exact phenological months, sizes and colours vary with region and year and are given only in general terms. Wood identification is covered in wood-anatomy-properties, silviculture of individual species in silviculture-of-species, and forest distribution in forest-types-biogeography. Name changes in genera such as Acacia are followed where well established; some recent changes may not yet be reflected.
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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