The Woody Wonders of Arunachal Pradesh and How to Identify Them

Arunachal Pradesh, is a land of vast forests, hills and mountains with deep gorges, through which many rivers and streams flow. It is among the last regions with exceptional biodiversity that has persisted along with diverse indigenous communities, in part due to its remoteness and relatively inaccessible terrain. The diversity is due to its unique location at the junction of three biogeographical realms, high rainfall and its wide elevational gradient. In addition, its recent geological history, has played an important role in the speciation and evolution of some floral and faunal groups.

It has been a place of wonder and exploration for biologists. Exploration by the British started in the 1800s with formal documentation of its rich floristic diversity by Frank Kingdon-Ward (1913, 1930) among others.

However, much before that, its flora and fauna were known to the indigenous communities that live there and continue to use the flora and fauna of the region intimately.

Arunachal Pradesh (which means the land of the dawn-lit mountains) is a state in North-east India with an area of 83,743 km2, the largest in area among the states of North-east India and the largest mountainous state of India. Arunachal is located between 26.28° N and 29.30° N latitude and 91.20° E and 97.30° E longitude. Earlier, Arunachal was considered as part of Assam state, and was initially known as the North-east Frontier Tract before independence. It was later designated as the North-east Frontier Agency (NEFA) in 1954 after independence, but was still part of Assam. It was christened Arunachal Pradesh and became a union territory in 1972, and was given statehood in 1987.

In the days when it was NEFA, the area was divided into five frontier divisions named after the main rivers (Kameng, Subansiri, Siang, Lohit, Tirap). The number of districts has grown over the years from 13 in the nineties to 26 in the present day. The states of Assam and Nagaland adjoin Arunachal on its southern boundary, while Bhutan (160 km) lies to its west, Myanmar (440 km) to its east and China to its north and northeast (1080 km). The border with China remains disputed and is marked by the McMahon Line.

The major rivers of Arunachal Pradesh are the Kameng, Subansiri, Siang (which becomes the Brahmaputra once it reaches Dibrugarh in Assam), Dibang, Lohit and Noa-Dihing. All these rivers are snow-fed and originate in the Himalaya and drain into the Brahmaputra on reaching the plains in Assam.

The elevation ranges from 50 to 100 m in the plains bordering Assam to above 7000 m on its northern parts bordering China. The mountain ranges and hills of Arunachal are part of the Eastern Himalaya, with different names in different parts. The ranges and hills to the west were known as the Aka or Dafla Hills, while in the central part which falls in the Siang region, it was known as the Abor Hills. The mountain ranges until the Siang are part of the Eastern Himalaya, while between the Siang and the Noa-Dihing rivers, the hills are known as the Mishmi hills, and to the south of the Noa-Dihing, lies the lower hills of the Patkai range (in the south-eastern districts of Tirap, Longding and part of Changlang). The villages of Dong in Upper Dibang Valley and Vijaynagar (Dawodi) in Changlang district receives the first sunrise each day in India. 

The climate varies considerably across the elevational gradient. The lower altitude (100 to around 500 m) areas have a hot and humid tropical climate. The areas around the middle belt are cooler. The high elevation areas have a subtropical climate or a cold alpine climate with snowfall during winter. The average mean minimum and maximum temperature ranges between 17.7°C and 29.5°C in the tropical humid regions, and 2.4°C and 21.4°C in the colder temperate and alpine regions. The monsoon or rainy season is from May and often lasts up to September, with 70- 80% of the annual rainfall in these months. The total rainfall generally ranges from 2000 to 5000 m annually. It can vary from 1000 mm in the higher elevations to 5750 mm in the foothill areas. East Siang and Lohit district experience the highest rainfall, whereas, rainfall is the lowest in West Kameng district. The relatively dry cooler months are from October to March, with many deciduous tree species showing leaf fall. March-April are the drier hot months with some showers and thunderstorms. In the lower elevations, even during the monsoon months from June to September, the climate is very warm and humid. July and August are the warmest months with the average maximum temperature during Arunachal Pradesh falls within the Himalaya and Indo-Myanmar Biodiversity Hotspots (Mittermeier et al. 2004). It accounts for one-third of the habitat area of the Himalaya biodiversity hotspot. The state is located at the junction of three biogeographical realms—the Paleoarctic, Indo-Chinese, and Indo-Malayan with biotic elements from all these regions contributing to its exceptionally this period being about 30°C. Generally, the winter months (December–February) are the coldest.

Arunachal Pradesh falls within the Himalaya and Indo-Myanmar Biodiversity Hotspots (Mittermeier et al. 2004). It accounts for one-third of the habitat area of the Himalaya biodiversity hotspot. The state is located at the junction of three biogeographical realms—the Paleoarctic, Indo-Chinese, and Indo-Malayan with biotic elements from all these regions contributing to its exceptionally high species diversity. Biogeographically, it is in the Eastern Himalayan province, which is the most species-rich biogeographical province of the Himalayan zone.  

Plant diversity and vegetation types

North-east India includes the states of Arunachal Pradesh, Assam, Nagaland, Manipur, Mizoram, Tripura, Meghalaya and Sikkim with approximately 7000 plant species (ca. 50% species of known flowering plants in India). The flora primarily has an Indo-Malayan affinity; however, floral elements of other parts of India and neighbouring countries have also contributed to its richness and diversity (Chauhan et al. 1996). Arunachal Pradesh alone is known to harbour over 6000 plant species, which are distributed along one of the largest elevation gradients in the world, ranging from lowland tropical forests to alpine vegetation in the Himalaya. These vegetation types comprise nearly 5000 species of angiosperms, 34 species of gymnosperms (including 23 species of conifers), 400 species of pteridophytes and bryophytes. The most speciose plant groups include orchids with more than 600 species, more than 450 grass species, around 68 bamboo species, around 65 rhododendron species, and 42 species of Impatiens, and 34 species of Hedychium. There is also a high diversity of Musa, Citrus, Piper, Dioscorea, and canes.

Arunachal Pradesh has a diversity of forest types ranging from tropical wet evergreen, tropical semi-evergreen, sub-tropical, pine, temperate forests and alpine meadows and scrub. Tropical forests occur up to an elevation of 900 m. They are present in all the districts along the foothills and are considered as the world’s northernmost tropical forests (Proctor et al. 1998). Tropical semi-evergreen forests occur all along the foothills and river banks up to an elevation of 600 m. The emergent trees in this forest type are mainly deciduous, where evergreen species dominate in the lower canopy. Bamboos grow along the foothills, higher elevations, and successional habitats. Grasslands cover the riparian tracts. 

How to use the book

This book is designed for field identification of woody plants seen mostly, although not exclusively, in the low elevation forests of Western Arunachal and adjoining areas of Assam. [It] is divided into two sections; the first part consists of leaf-, flower- and fruit-based identification keys. The second part consists of species pages which give morphological and ecological accounts along with images of species featured in this book. A user can identify a plant of interest using identification keys based on leaves, flowers or fruits. Alternatively, if the user knows the family, genus or the local name of the species, then it can be looked up in the index of scientific names or vernacular names respectively.

Flower keys

Flower keys can be useful when one encounters flowers fallen on the forest floor and it may not be possible to trace their plant of origin. One may also encounter flowers on a leafless tree, in which case flower keys may prove handy in the absence of other characters. We have classified 207 species for use in identification.

Fruit keys

The fruit keys showcase some of the prominent and striking fruits observed in the lowland forests of Western Arunachal. The collection of fruits that feature here are by no means comprehensive, but nonetheless may prove useful for identifying certain fruits when associated leaf or flower information is not available. We have classified around 168 species for use in identification. This categorization is based on easily recognized physical features that a lay person can observe in the field and use for identification.

Excerpted with permission from Trees of Arunachal Pradesh: A Field Guide. Published by the Nature Conservation Foundation. Price Rs 1000. You can buy the book here.

Photo sources: Magnolia leaves, Magnolia seeds, Phoebe cooperiana flowers, Phoebe cooperiana fruit.