chapter 5. vegetation of southern...
TRANSCRIPT
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.
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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
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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,
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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.
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Plate 8. A. A \ levv of a Bamboo forest B. A common grass species {Themeda villosa (Poir.) A,C amus).