Forest trees of Odisha, India: An updated checklist

An exhaustive taxonomic inventory of forest trees of Odisha in the Eastern Ghats of India was made during 2015 – 2020, which revealed the presence of a total of 501 species of wild and naturalised trees belonging to 293 genera under 81 families. The family Fabaceae was the most species - rich represented by 58 species, followed by Rubiaceae (28), Moraceae (26), Rutaceae (21), Meliaceae (21), Phyllanthaceae (21) Verbenaceae (19) and Lauraceae (15). The genus Ficus (Moraceae) had highest number of 21 tree species, followed by Diospyros (10 species), Terminalia (8 species), Syzygium (7 species), Sene-galia (7 species), Vitex (7 species) and Albizia (6 species). Nothopodytes nim-moniana , Alphonsea lutea , Lasiococca comberi , Siphonodon celastrineus , Searsia paniculata , Syzygium schmidii , Cassipourea ceylanica , Prunus pyge-oides , Sonneratia griffithii , Eriolaena hookeriana var. viridis , Tritaxis glabella , Garcinia xanthochymus and Litsea glutinosa have been identified as regionally threatened species needing conservation intervention. Cocculus lauri-folius is reported here as a new distributional record for the state. Field observation on the occurrence and dominance of tree species in different forest types of Odisha has been discussed. A checklist of the tree species of Odisha is presented in this article, along with the correct botanical name, synonym(s), local name, flowering and fruiting time, locality of occurrence and citation of voucher herbarium specimens.


Introduction
Tropical forests are the most species-rich terrestrial ecosystems in the world. Though they cover only 6 ̶ 7% of the landmass on Earth, more than half of the described and unknown species of plants, animals and microorganisms of the globe are reported to occur in the tropics (1,2). Due to a wide range of variation in topographic, climatic and edaphic conditions, the world's tropical forests hold strikingly rich genetic diversity at species and intra-specific levels (3). However, many tropical forests are under tremendous anthropogenic pressure and require management intervention to maintain the overall biodiversity, productivity and sustainability (4). Understanding tree composition and structure of the forest is a vital instrument in assessing the sustainability of the forest, species conservation and management of forest ecosystems (5). Long-term biodiversity conservation depends on the knowledge of the structure, species richness and the ecological characteristics of vegetation, especially trees (6).
Because of their dominance, density and biomass, the trees form the main structural and functional components of tropical forests. They are considered robust indicators of climatic change and man-made alterations at the landscape level (7). Trees are one of the main features of most forest ecosystems of the world, and they make available habitats, food and other resources for a range of epiphytes, mosses, fungi, lichens, birds, insects and other forest-dwelling organisms (8). The biological diversity of tree species in tropics varies according to the geographical location, forest types, habitat conditions and intensity of disturbance (9).
Though trees find a place in general floristic accounts of Odisha (10,11), no exclusive publications on trees of Odisha have been brought out except that of the Similipal Biosphere Reserve (12). As regards the trees of Odisha state, the Botany of Bihar and Orissa (10) provides an account of the flora and vegetation of the then Bihar and Odisha and as many as 386 tree species have been listed therein. Subsequently, occurrence of 475 species of tree has been reported from the state in "Flora of Orissa" (11) and the same authors later recorded the distribution of Siphonodon celastrineus Griff. from Odisha (13). Another work "Wild edible fruit plants of Eastern India" mentioned about 98 wild tree species producing edible fruits. The book on "Floral diversity of Nandankanan Wildlife Sanctuary" records the presence of 175 tree species (15). Subsequently, several tree species such as Sloanea sterculiacea (Benth.) Rehder & Wilson (16), Dysoxylum gotadhora (Buch.-Ham.) Mabb. (17), Searsia paniculata (Wall. ex G. Don) Moffett (18) and Nothapodytes nimmoniana (J. Graham) Mabb. (19) have been added to the list of trees of Odisha. Till date, there is no publication dealing exclusively on diversity, distribution and phenology of forest trees of Odisha state.

Study area
The study area covers the entire state of Odisha, located between 17.49' N and 22.34' N latitudes and 81.27' E and 87.29' E longitudes on the east coast of India (Fig. 1). This coastal state covers an area of 155820 km 2 . It is surrounded by the States of Jharkhand, West Bengal, Chhattisgarh, Andhra Pradesh and the Bay of Bengal. One-third of the area of the state is under forest cover and three-fourths of the area is covered with hills and mountainous ranges. Based on homogeneity, continuity and physiographic characteristics, Odisha has been divided into 5 major regions such as (i) The Odisha coastal plains, (ii) The middle mountainous and highlands, (iii) The Central plateau, (iv) The western rolling uplands and (v) the major flood plains. Eleven major rivers and their tributaries flow in the state and drain into the Bay of Bengal. Odisha enjoys a tropical monsoon type of climate characterized by high temperature and humidity, medium to high rainfall, and short and mild winters. The average summer temperature can be as high as 45 °C and a minimum of 5 °C in winter. The period from mid-June to September is the monsoon season and the state receives an average annual rainfall about 1500 mm.
Despite degradation, both in extent and density, the existing forests of Odisha can be classified under 5 broad forest types and sub-types as per the classification of Champion and Seth (20). These are (i) Orissa Semi-Evergreen Forests, (ii) Tropical Moist Deciduous Forests, (iii) Tropical Dry Deciduous Forests, (iv) Central Indian Hill Forests and (v) Littoral and Tidal Swamp Forests.

Field and herbarium methods
Regular collection trips were organised in all the 30 districts of Odisha in different seasons of the year, with special emphasis on protected areas like Biosphere Reserve, National Parks, Wildlife sanctuaries and other floristically diversified habitats. Since most of the tree species flower during the summer months, extensive field trips were conducted during this season to collect and photograph flowering specimens. Before collection, general observations on the type of vegetation, dominant species, habitat condition, soil type, plant association, dominance and distribution, level of disturbance etc., of each site were recorded. Authentic field notes were recorded on the spot, which includes place of collection, local name, tree height, GBH, phenology and other characters which cannot be detected in dried specimens. Herbarium specimens were prepared following the standard herbarium techniques (21,22). Some flowering and fruiting twigs were preserved in polythene bags and brought to the laboratory for subsequent diagnosis, botanical description and correct identification. The voucher specimens have been deposited in the Herbarium of the Regional Plant Resource Centre (RPRC), Bhubaneswar, India.
The identity of the plants was ascertained in consultation with the artificial identification keys and descriptions provided in the local floras such as "The Botany of Bihar & Orissa" (10), its "Supplement" (23), "Flora of Orissa" (11), other floras, monographs and revisions. Some doubtful specimens were taken to Central National Herbarium, Calcutta (CAL) and were matched with authentic materials to ascertain identity The enumeration of 501 species of forest trees in Odisha is provided in Supplementary Table 1. The families are alphabetically arranged, and the species under a family also follow alphabetic order. For each species, correct botanical name, synonym(s), family to which it belongs, local name, flowering and fruiting time, locality of collection from Odisha and herbarium voucher specimen number have been given. The correct name used in this paper is according to the name cited in the online world plant database (http://www.worldfloraonline.org) and the synonym as available in the "Flora of Orissa" (11), "The Botany of Bihar and Odisha" (10) and "Supplement to the Botany of Bihar and Orissa" (23) only have been cited. Photographs of some important tree species collected from the forests of Odisha have been provided (Figs. 2-8).

Discussion
The present study reports the presence of as many 501 tree species against 386 species reported earlier (10) and 475 species listed (11). The occurrence of several interesting and threatened tree species like Nothopodytes nimmoniana (J. Graham) Mabb., Cocculus laurifolius DC., Searsia paniculata (Wall. ex G. Don) Moffett has been reported in this study. The natural distribution of many species of trees was observed to be restricted to specific forest types and habitat conditions. While the dominant trees in the top storey of semi-evergreen forests were Artocarpus lacucha Roxb. ex Buch.

Conclusion
The forest tree inventory of Odisha in this article is the first comprehensive study in the state based on intensive fieldwork, herbarium and literature consultations for about 6 years. It enumerates 501 species of wild and naturalised trees, representing 19.25% of India's tree diversity, estimated as 2603 species (24) and lists several threatened taxa needing conservation actions. The present work will help the forest managers and conservationists to formulate suitable strategies for conservation of threatened tree species and a better understanding of the tree flora of the state.