CHAPTER 5.

VEGETATION OF SOUTHERN ASSAM

CHAPTER 5. Vegetation of Southern Assam

The region comprises 12 Reserve Forests and I Wild Life Sanctuary comprising a

total forest area of about 2338.65 km" i.e., 33.78 % of the total geographical area of the

valley (see Map 3 & Table 11).

Table 11: Protected Area Network of Southern Assam District Reserve

Forest/Wild Life sanctuary

Area in Sq. Total Forest Total area of Percentage Km. Area of the the district of forest

District in in sq. km area sq. km

Cachar

Hailakandi

Karimganj

Borail Wild Life 326.5 Sanctuary Upper JiriR.F. 63.31 Lower Jiri R.F. 36.46 Barak R.F 204.54 Sonai R.F. 35.97 Innerline R.F. 443.00 (Part-1). Katakhal R.F. 6.30 (Part-II) Katakhal R.F. 132.70 (Part-1) Innerline R.F. 609.01 (Part-II). SinglaR.F. 124.39 LongaiR.F. 151.51 Badsahi tilla R.F. 75.12 DuhaliaR.F 34.81 TilbhumR.F 18.50 Patharia R.F 76.53

16.08

741.71

Total

480.86

2338.65

3786

1327

1809

6922

29.48

55.89

26.58

33.78

Based on the floristic composition the Vegetation Types of Southern Assam broadly classified into the following categories 1. Tropical wet Evergreen Forests

2. Tropical Semi-Evergreen Forests

3. Tropical moist deciduous forests

4. Swamp forests

5. Riparian forests

6. Bamboo and cane-brakes

7. Grass lands.

5.1. TROPICAL WET EVERGREEN FORESTS: This type of forest is prevalent in the

Northern and Eastern slopes of Southern Assam like Borail Hill Ranges, Barak R.F.,

Inner Line R.F. Rajkhowa (1961) classified this type of forest as ''Mesua-Dipterocarpus-

Palaquium formation''' and "mixed evergreen type'' by Mohanlal (1938). The rainfall of

these areas ranges from 2500-3500 mm. Luxuriant growth of fioristic elements are due to

heavy rainfall. The areas under forests land with variation of altitude from 100-1500 m

and adjoining low hills that merge into plains. Mostly the forests Reserves with dense

preserve are not of lofty broad leafed tree species of Angiosperms but also a number of

Tree ferns growing majestically. The forests are rich in species contents showing

gregarious growth and are studded with epiphytic Orchids, ferns and other Angiosperms.

A characteristic feature of the forests is the stratification of fioristic elements into three

distinct storey's.

The dominant species growing in the top canopy are Actinodaphne obovata Amoora

rohituka, Aporosa ohlonga, Artocarpus chuplasha, Alhizzia procera, Alphonsia ventricosa..

Calophyllur)i polyanthum, Canurium sp. Cuslanopsis lanceifolia, Dipterocarpus tnrhinatus,

Duabanga grandiflora, Dysoxylum bineclariferum, D. hamillonii. D. procerum, Diospyros

toposia, Diospyros lanceaefolia, Syzygiiim cumini, Ealeocarpus sp., Gmelina arborea. Melia

azedarach, Micheliu champaca, Mesua ferrea, Mangifera indica, Palaquium polyanthum,

Premna bengalensis, Sterculia villosa, Toona ciliala, Trewia nudiflora, Vatica lanceaefolia,

Xerospermum glabratum etc.

The common species composing the middle storey are Callicarpa arborea,

Holarrhena antidysenterica, Milragyna diversifolia, Schima M>alUchii, Macaranga

denticulate, M. indica, Microcos paniculata, Bauhina purpurea, Lagerstroemia parviflora,

Ficus auriculata etc.

The lower storey is often found in association of sparsely distributed species viz.,

Catunaregam spinosa, Mallolus albus, Villebrunea integrifolia, Balakata haccata, Ficus

roxburghii etc. The forest floor is covered with species of Zingiberaceae, Costaceae,

Taccaceae etc viz. Curcuma angustifolia, Co.stus specious, Alpinia allughas, Etlingera

linguiformis, Phrynium capitatum, Alpinia malaccensis, Tacca laevis, Peliosanthes tela

Dracaena angustifolia, D. ellptica etc.

42

Plate LA. A view of the Borail Hill Ranges. B> A view of the Tropical Wet-Evcrgrgen Forest

Plate 2„ Some dominant trees of Tropical Wet-Evergreen Forest A. Xernspermum glahratum Wall. B, Melia azedarach L. C. Gmelina arborea Roxb- D, Trewia uudiflora L.

Plate 3. Some dominant trees of Tropical Wet-Evergreen Forest A. Duahauga grmidiflora (DC) Walp, B. Castauopsis lanceifoUa (Oerst.) Hickel & A.Camus C. Tooua ciliata M.Roem. D„ Sterculia viUosa Roxb.

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Plate 4. Some dominant climbers of Tropical Wet-Evergreen Forest A. Entada gigas (L.) Fawc. & Rendle B. Archidendrnu clypearia (Jack) I.C.Nielsen C. Hodgsonia hetewcUta (Roxb.) Hook.f. & Thomson D. Dalhoiisiea hracteata (Roxb.) Benth.

The common shrubs in these forests are Allophylus cohhe, Leea indica, Chassalia

curviflora, Morinda angusHfolia, Mycetia longifolia, Myrioncuron nutans, Chloranthus

officinalis etc.

The common lianous climbers are Entada gigas, Archidendron clypearia, Dalhousiea

bracteata are common, besides above other climbers like Tinospora cordifolia, 7 malaharica,

Dioscorea hulhifera, D. hamiltonii, Smilax roxburgrhiana are also commonly available.

5.2. TROPICAL SEMI-EVERGREEN FORESTS: This type of forest is prevalent in Southern

and Western side of Southern Assam, viz, Katakhal R.F., Singla R.F, Badsha Tilla R.F.,

Longai R.F., Tilbum. R.F., Dohalia, R.F. and Patheria R.F. In these regions rainfall ranges

between 2000-3000 mm. The upper canopy of this forest is 18-24 m usually not dense,

though almost closed on tops and ridges of hills. The common species growing in the f' and

2" storeys are Schima M'allichii, Holigarna longifolia, Terminalia chebula, Saurauia

roxburghii, Artocarpus chaplasha, A. lakoocha, Dipterocarpus turbinatus, Palaquium

polyanthum, Cynometra polyandra, Vitex peduncidaris, Pterospermum acerifidium,

Pterygota alata. Chukrasia velutina, Adina cordifolia, Protium scrratum, Albizzia procera.

Premna bengalensis, Gmelina arborca, Sterospermum pcrsonalum Vangueria spinosa,

Alstonia scholaris, Macaranga indica, Adallotus nepalansis, M. roxburghiianus, Phyllanthus

embelica, , Ficus bengalensis etc.

Shrubs species like Actinidia callosa. Camellia drupifera, Eurya acuminata,

Abelmoschus munihot. Hibiscus macrophyllus, Sida acuta, S. rhombifolia, Urena lobata etc

are common.

The common climbers growing in these forests are Cissampelos pareira,

Pericampylus incanus, Cissus assamica, Cissus repens, Tetrastigma rumicispermum,

Tetrastigma serrulatum, Vitis japonica, Uncaria macrophylla, Uncaria pilosa Hoya

parasitica, Ipomoea obscura, I. coccinea, I. uniflora etc.

5.3. TROPICAL MOIST DECIDUOUS FORESTS: This type is characterized by the average

annual rainfall of 1000 to 2000 mm and comprises the 'sal forest' and major parts of scrub

forest. The dominant species in the Sal areas is Shorea robusta. Other important trees are

Schima wallichii, Lagerstromia parvifiora, Toona ciliata. Bombax ceiba, Gmelina arborea

43

Plate 5. A. A view of the Tropical Semi-Evergreen Forest. B. A view of the Tropical Moist Deciduous Forest.

Plate 6. Some dominant trees of Tropical Semi-Evergreen Forest A, HoUgarua longifolia Buch.-Ham, ex Roxb. B. Diplerocarpus fiirbwatus F.Gaertn C. Schima waUkhii Choisy D. TermiuaUa chebida Retz.

accompanied with the smaller trees like Malloluspaniculalus, Macamnga denticulata, Adina

cordifolia, Mitragyna diversifolia. Ficus roxhurghii and other sal associates.

5.4. SWAMP FORESTS: This type includes undrained depressions generally known as Beels.

Aquatic families such as Araceae, Cyperaceae, Eriocaulonaceae, Lemnaceae, Najadaceae,

Nymphaeaceae are common in these beels. Extensive growth of Monocharia haestifolia, M.

hasta, M. vaginalis, Eichhornia crassipes and floating herbes like Ottelia, Nymphaea,

Jussiaea are also found in these swamps. Several species belonging to family Cyperaceae

like Scleria terrestris, Cyperus iria, C. pumilus, C. exaltatus, C. hrevifolius , C. nutans, C.

tenuispica, Hypoletrum nemorum, Carex thomsonii, C. indica, C. olivacea etc are found to

be wide spread. Ipomoea aquatica also has extended its formations throughout the region as

one of the obnoxious weeds. The following trees and shrubs are characteristic on the border

of Beels & Haors Lagerstroemia speciosa, Hyptianlhera stricta, Ficus pyriformis, F.

heterophylla, F. cunia etc. as well as the following grasses Arundinella, Thysanolaena,

Agrostis etc. Some of the grasses eg. Hygrorhiza etc. float on the surface and covers

considerable parts of the water along the border.

5.5 RIPARIAN FOREST: These forests occur all over the evergreen and scmievergreen zones

of southern Assam along river banks and extend in several areas. In low lying areas, Dellinia

indica, Anthocephalus cadamba, Samania saman, Bischofia javanica. Duahanga

granidiflora, Lagerostromia speciosa are the common species most frequently met with.

Shrubs species like Cassia tora, C. occidentalis, C. nodosa. C. alata, I. nigricans,

Mussaenda roxhurghii, Maesa indica, Clerodendron colebrookianum, C. indicum. C

infortunatum, Lantana indica, Lippia gcminata etc are common.

5.6. BAMBOO AND CANE-BRAKES: The most characteristics of secondary growth in both the

evergreen and semi-evergreen types in the presence of bamboos, either as an understory, or

mainly bamboos, with a few scattered trees standing over them. The bamboo forests tend to

become more and more pure as the intensity of shifting cultivation increases and especially

in lateritic soils (eg. Badshahi tilla, Singla R.F., of the present Karimganj district). The

common species of bamboo growing in these forests are e.g. Bamhusa halcooa, B. hamhos,

44

Plate 7. A. A view of a Swamp forest. B. A view of a Riparian forest.

B. multiplex, B. nutans, B. pallida. B. polymorpha, B. tulda, B. vulgaris, B. reptans,

Dendrocalamus giganteus, D. longispathus, D. strictus, Dinochloa macclellandii,

Gigantochloa albociliata, G. nigrociliata, G. parvifolia, Melocalamus compacliflorus,

Melocanna baccifera and Pseudostachyum polymorphum.

5.7. GRASSLANDS: The grasslands occur in alluvial plains and riparian flats throughout the

valley and generally inundated every year during monsoon period. The common grass

species growing in these grasslands are e.g. Arundinella bengalensis, Axonopus compres.sus,

Brachiaria reptans, B. subquadripara, Centotheca lappacea, Chloris barbata, Chrysopogon

aciculatus, C. zizanioides, Cynodon dactylon, Cyrtococcum oxyphyllum, C. patens var.

latifolium, Digitaria ciliaris, D. jubata, D. violascens, Echinochloa colonum, E. crusgalli, E.

stagnina. Eleusine indica, Enteropogon dolichostachyus, Eragrostis unioloides, £'. zeylanica,

Hackelochloa granularis, Hemarthria longiflora, H. protensa. Ichnanthus pallens var.

majus, Imperata cylindrica, Isachne elarkei, 1. miliacea, I. sylvestris, Leersia hexandra,

Leptochloa chinensis, L. fdiformis, Lophatherum gracile, Neyraudia reynaudiana,

Oplismenus compositus, Ottochloa nodosa, Panicum auritum. P. brevifolium, P. humidorum,

P. khasianum, P. latifolium, P. luzonense, P. notatum, P. paludosum, P. repens, P.

sarmentosum, Paspalidium punctatum, Paspalum conjugatum, P. scrobiculatum, Phragmites

karka, Pogonatherum crinitum, Pseudoraphis minuta, Saccharum longisetosum , S.

procerum. S. spontaneum, Sacciolepis interrupta. Setaria clivalis, S. palmifolia, S. pumila,

Sporobohts diandrus, S. fertilis, S. indicus, Themeda villosa and Thysanolaena latifolia.

45

Plate 8. A. A \ levv of a Bamboo forest B. A common grass species {Themeda villosa (Poir.) A,C amus).