The genus Terminalia Linn. (family Combretaceae) includes about 200 species of trees and shrubs (Lamb and Ntima 1971; Whitemore 1972) with a distribution throughout the tropical and sub-tropical regions of the world. Besides yielding high value timber, many Terminalia species are the source of various non-wood forest products (NWFP). The present paper provides information on the taxonomy and distribution of Terminalia species in India, their principal non-wood forest products, and strategies for their conservation.
TAXONOMY AND DISTRIBUTION
Species of Terminalia found in India belong to the sections Catappa, Myrobalanus, Chuncea and Pentaptera. Terminalias are predominantly outcrossing (Srivastav 1993; Parkinson 1936), and sexual recombination and segregation, together with mutations, and acted on by natural selection, are the sources of inter- as well as intraspecific variation in this genus. In some cases within-species variation appears so great that more than one species may be involved. Terminalia arjuna, T. tomentosa, T. chebula, T. bellerica and T. citrina are examples of such species complexes (Hooker 1878; Bahadur and Gaur 1980; Parkinson 1936; Srivastav et al. 1992).
According to Parkinson (1936) affinity and intergrading is evident among the various varieties and forms of T. arjuna and T. tomentosa complexes (in section Pentaptera). It is difficult to suggest whether this is due to hybridization which has already been recognized in the genus and is probably common, or evolution/divergence due to changing environmental conditions, or both. While Hooker (1878) has described three varieties under T. tomentosa viz. typica (alata), crenulata and coriacea, Roth, Wight and Arnot (quoted by Hooker, 1878), Gamble (1915, 1920), Blatter (1929), Parkinson (1936), Bahadur & Gaur (1980) and Srivastav et al. (1992) have treated them as distinct species. Likewise, T. arjuna var. arjuna and T. arjuna var. angustifolia described by Hooker (1878) should also be treated as distinct species as T. glabra W. & A. and T. berryi W. & A. respectively (Parkinson, 1936; Srivastav et al. 1992). Hybrids between entities from both complexes have also been reported (Haines, 1922). On the other hand Thwaites (quoted by Hooker, 1878) hints that T. arjuna and T. tomentosa are the same species.
On the basis of natural variations encountered, a total of twelve taxa and/or biotypes may be easily recognized in section Pentaptera. Other species complexes viz. T. chebula, T. bellerica and T. citrina have also become subject of controversy. In T. chebula, fruit varieties have been commercially graded into eight types, viz. Bhimlies (Tamil Nadu), Jubbulpores (Madhya Pradesh), Rajpores (Maharashtra), Vingorlas (Maharashtra), Madras Coast, Survari harde, Bala harde and Java harde (Anonymous, 1976). The existence of various ploidy levels ranging from 2n to 6n in T. chebula and 2n to 4n in T. tomentosa, T. bellerica and T. paniculata is an added complication: increase in ploidy level has been found to increase the size of leaves and fruits (Janaki-Ammal & Sobti 1962; Srivastav et al. 1994).
20 species have been found distributed in tropical and sub-tropical states of India, as shown below:
PRODUCTS FROM TERMINALIA SPECIES
Throughout the Indian sub-continent, Terminalias are valued as sources of an array of non-wood forest products (Srivastav et al. 1993). Different species of Terminalia, viz. T. arjuna, T. alata, T. paniculata, T. chebula, T. bellerica, T. travancorensis, T. procera, T. myriocarpa, T. manii, T. bialata, T. coriacea, T. crenulata, T. citrina, T. catappa, T. pallida yield indigenous drug preparations, tannins, gums, oils, wood (for matchboxes, splints, pulp), fodder and certain organic compounds from their leaves, trunk, bark or fruits. Industries such as pharmaceutical, animal husbandry, leather, dyeing, soap, chemical, resin and gum, paper, railways, match, oil and cosmetic utilize Terminalia species for their raw materials. The Tasar silk industry depends exclusively on members of the genus Terminalia: T. arjuna and T. tomentosa serve as primary food plants for the tasar silkworm (Antheraea mylitta D.), while T. paniculata, T. chebula, T. bellerica and T. catappa serve as secondary food plants. The Tasar silk industry operates in the states of Bihar, Uttar Pradesh, Madhya Pradesh, Andhra Pradesh, Orissa, Maharashtra, West Bengal and Karnataka. Hence, the genus Terminalia may rightly be called the backbone of the Tasar silk industry.
STRATEGIES FOR CONSERVATION OF GENETIC RESOURCES OF TERMINALIAS IN INDIA
Pressure associated with rearing of tasar silkworm (A. mylitta) may result in slow denudation of Terminalia trees if proper maintenance is not undertaken. Furthermore, over-exploitation by leather, timber and pharmaceutical industries in addition to the losses incurred by overgrazing, indiscriminate felling of trees and conversion of forest land into agricultural land and human settlements, has led to a rapid depletion of certain genetic resources of Terminalia. Populations of some species are now highly threatened. The fast depletion of these taxa is also likely to disturb the ecological balance of the tropical forests in which they occur. Hence, a concerted effort to conserve existing genetic diversity of the genus Terminalia is urgently needed. Conservation strategies for Terminalia genetic resources involve both in situ and ex situ approaches.
In situ conservation
In situ conservation areas
These include national parks, wild areas, scientific reservations, natural areas and alike. Kanha National Park in Madhya Pradesh is known to include various types of T. tomentosa and other species. However, such national parks may also be useful in conserving genetic resources of other Terminalia species which are present.
Seed production areas of T. myriocarpa (1.0 ha) and T. arjuna (30 ha) have been already established in Arunachal Pradesh and Uttar Pradesh respectively (Emanuel et al. 1990). There is urgent need to develop seed production areas of other species in a number of other states. Such standard seed production areas should consist of natural stands thinned to leave the best phenotypes in order to minimize pollen contamination from inferior trees.
Superior (plus/elite) trees used in tree improvement programmes may also be conserved in their natural stands. In T. myriocarpa 41 plus trees have been selected by the Forest Department in Arunachal Pradesh (Emanuel et al. 1990; Beniwal & Singh 1990) while in T. arjuna and T. tomentosa a total of 130 plus trees have been selected in Madhya Pradesh, Bihar and Orissa by the Central Tasar Research and Training Institute, Ranchi within the framework of genetic improvement programmes for tasar culture.
Ex situ conservation
Plantings established primarily for the production of seed of proven genetic quality are known as seed orchards (Wright 1976). These orchards are not designed to conserve germplasm per se, but they may serve for such purposes temporarily under selective conservation. Ordinarily all good clones and progenies derived from them will be channelled into a breeding orchard which may be utilized as a valuable bank or living collection of germplasm material for multiplication. In Arunachal Pradesh a three hectare seed orchard of T. myriocarpa has been established by the Forest Department (Emanuel et al. 1990; Beniwal & Singh 1990).
Seedling banks or archives
These are collections similar to clone banks but of seedling origin. They are often derived from experimental crosses made for progeny tests, or they may be representatives of various provenances, ecotypes or special populations and can thus serve as germplasm reserves (Khosla 1988).
Experimental plantings may be established using provenances and individual trees (progeny tests) of given species. These test plantings themselves become a valuable repository of germplasm which is available for use by the tree breeder. In CTRTI, Ranchi experimental plantings of 24 genotypes of plus trees, and progenies of anomalous seedlings, including progenies obtained from 4-12 winged fruits of 34 genotypes, have been raised on one hectare of land for evaluation for tasar culture.
Plantations of T. arjuna and T. tomentosa have been raised in 5 Research Extension Centres, 19 Basic Seed Multiplication & Training Centres and 4 Regional Tasar Research Stations under the Central Tasar Research & Training Institute for tasar culture through seedling progenies. These may also serve as germplasm reserves for their respective states, since they encompass the broad genetic base representing enormous genetic variability existing within and between both the species complexes.
The potential for ex situ conservation of germplasm of Terminalia species using seed, pollen and tissue culture has been little investigated.
Valuable genetic resources of Terminalia species are being rapidly depleted in India, and some populations are on the verge of extinction due to increasing deforestation. Such losses threaten the ecological balance of the tropical forests. The following proposals may be considered for effective conservation of genetic resources of Terminalia:
Anonymous (1976). The wealth of India. Raw materials. Vol. X: S-W. Publication and Information Directorate, C.S.I.R., New Delhi.