Stratification of Vegetation in the Barpeta District of Assam, India
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Pleione 9(2): 325 - 347. 2015. ISSN: 0973-9467 © East Himalayan Society for Spermatophyte Taxonomy Stratification of Vegetation in the Barpeta District of Assam, India K. K. Sarmah1 and S. K. Borthakur2 Department of Botany, Gauhati University, Guwahati, 781 014 Assam, India 1Department of Botany, B. B. K. College, Nagaon, Barpeta, 781 311, Assam, India 2Corresponding author. e.mail: [email protected] [Received 25.10.2015; Revised 14.12.2015; Accepted 15.12.2015; Published 31.12.2015] Abstract Study carried out in the Barpeta district of Assam, India during the years 2011 – 2013 to record the stratification pattern in its vegetation recorded the presence of 722 Angiospermic taxa of species and infra-specific ranks. Of these, 546 species were dicotyledonous belonging to 346 genera from 101 families and the remaining 176 taxa were monocotyledonous belonging to 94 genera under 20 families. Different species were found to occur in nearly well demarcated horizontal layers especially in the areas covered by natural vegetation inside the Manas National Park. The remaining areas were characterized by open and scattered vegetation. These plants were found to represent 4 horizontal zones viz. canopy, middle storey, under-storey/shrub and the ground layer, accounting for 68, 107,138 and 409 species and infra-specific taxa respectively. Evidently shrubs and ground layer elements were found to much outnumber the remaining categories thus indicating a good extent of anthropogenic interference in the study area. Key words: Assam, Barpeta District, Angiosperms, stratification INTRODUCTION Economic development of a country without plant utilization is quite unthinkable (Guha & Chattoraj 2009). The economic activities of man are greatly influenced by forests. Being the major component of vegetation of India, the Angiosperms are expected to bear much influence in this regard. Study of these plants is very important as the information gathered in such studies on any aspect of vegetation of the country is expected to become invaluable for formulating different plans by the Ministry of Environment, Forests and Climate Change (Anonymous 2015). Study of plant community is an important aspect of research as it provides many important positive results. It is because a given plant community is always an orderly arrangement of organisms having certain trophic relationships amongst themselves. Determination of the degree of productivity and also of capacity of a given plant community to support a particular animal community are among the findings of such studies. The organized nature of plant species in a community can distinctly be observed in their vertical arrangement. The vertical distribution of different species occupying different levels is the stratification or layering. The latter indicates the configuration of the given vegetation type (Ambasht & Ambasht 2004) The present day Assam, being a part of the Eastern Himalayas, is located within the Himalaya Biodiversity Hotspot. With limited scope of mineral based industrialization, the State is having no other alternative but to opt for agro-based economy. For this purpose, 326 Vegetation stratification in Barpeta District detailed study of the vegetation of Assam is necessary. The present study was carried out with this background as stratification indicates the nature of vegetation and also the relative number of different categories of plants with their utilitarian potential. The district of Barpeta in Assam was selected as the study area as it is contiguous with the foot-hill region of Bhutan Himalaya in the north and encompasses a short stretch of the mighty river Brahmaputra in the south and as such the study area was expected to serve the objective of the present study. Barpeta district, with an area of 3245 sq km (before the creation of BTAD) lies between 26 o 6' - 26o51' N. latitudes and 90 o 38' -91o21' E. longitudes with altitudes ranging between 40 – 81 m AMSL (Anonymous 2009). The district represents a nearly uniform but low-lying plain with numerous water-bodies like rivers, ‘beels’, swamps, ponds, pools, etc. Inundation by flood is almost an annual disaster (Plate – I: Fig. - 5). The area is almost inhabited by rural people. High fertility of soil is mainly responsible for its meagre urbanization. It is dominated by countryside with vast stretches of cultivated fields that indicates intense biotic interference (Plate – I: Figs. - 3, 5). The vegetation of the study area, as a whole, was found to be characterized by 10 different types viz., Tropical Semi-Evergreen Forest (Plate - I: Fig.-2), Tropical Deciduous Forest (Plate – I: Fig.-3), Riparian Forest, Tropical Grasslands (Plate - I: Fig.-4), Tropical Savannah, Swamp Vegetation, Aquatic Vegetation, Roadside Vegetation (Plate – I: Fig.-6), Plants of Household Compound and Vegetation of ‘Char’ Areas (Champion 1935; Rowntree 1954; Rajkhowa 1961; Rao & Panigrahi 1961; Champion & Seth 1968; Rao 1974 and Jain & Hajra 1975). Area under natural vegetation was very limited due to extensive anthropogenic interference. The present study was carried out with the sole objective of providing a preliminary account of the overall stratification pattern. In order to maintain brevity, detailed phytosociological study was avoided and as such it was not possible to record any overlapping species among the layers. MATERIALS AND METHODS The present work was started with consultation of relevant literature (Rajkhowa 1961; Pandey 2008; Guha & Chattoraj 2009; Anonymous 2009, 2015). Extensive exploration accompanied by collection of specimens was carried out for around 2 years at intervals of 4 – 6 months so as to cover all the seasons. Only the terrestrial Angiosperms were selected for the work as they were the most important and dominant components of the vegetation of the study area. Minute observation was made to record all available morphological features including habit, habitat and height. Herbarium specimens were prepared by following the techniques of Jain & Rao (1977). Families were delimited according to the sequential arrangements of Bentham and Hooker’s (1862 – 1883) system followed by adoption of recent modifications (Basak 1983). Identification of herbarium specimens was carried out through direct consultation with herbarium sheets in ASSAM, Shillong. Relevant literature was consulted whenever necessary (Hooker 1872 – 1897; Kanjilal et al. 1934 – 1940; Bor 1940; Santapau 1964; Barooah & Borthakur 2003). Names were initially checked for any change by consulting Bennet (1987) and then confirmed from www.theplantlist.org. Identified specimens were deposited in the GUBH Herbarium. For convenience, plants were grouped into four horizontal layers viz., canopy, middle storey, under-storey/shrub and ground layers (Appendices I & II; Plate – I: Figs. - 1, 2). For this purpose, the grouping of life-forms proposed by Raunkiaer (1934) was employed along K.K. Sarmah & S.K. Borthakur 327 with the height of the plants (Raunkiaer 1934; Ambasht & Ambasht 2002). All the 5 major life forms viz., Phanerophytes, Chamaephytes, Hemicryptophytes, Geophytes and Therophytes were taken into account including the three subcategories of Phanerophytes viz., Mesophanerophytes, Microphanerophytes and Nanophanerophytes. The subcategory named ‘Megaphanerophytes’ was omitted due to absence of plants of that height. After going through the above mentioned criteria, the Angiospermic plants of the study area were delimited into four distinct horizontal strata as follows: Canopy Layer: Plants of 8 to 30 metres high, usually including the mesophanerophytes; Middle Layer: Plants of 3 to 8 metres high, usually including the microphanerophytes; Under-storey/Shrub Layer: Plants of 1.5 to 3 metres high, mostly comprising the nanophanerophytes; Ground Layer: Plants bellow 1.5 metres high, usually represented by herbs and under-shrubs belonging to chamaephytes, hemicryptophytes, geophytes and therophytes. Stratification was recorded in detail for the study area as a whole with an intention to provide a glimpse of the relative numerical strength of different taxa in their respective horizontal layer. A detailed composition of stratification was recorded for a natural forest type viz., ‘Tropical Semi-evergreen Forest’ (Plate – I: Fig. 2) as an example of occurrence of typical stratification. RESULTS AND DISCUSSION The study resulted in the recognition of 722 Angiospermic species and infra-specific taxa out of which 546 were dicotyledonous belonging to 346 genera under 101 families while the remaining 176 monocotyledonous elements belonged to 94 genera under 20 families. Evidently the study area was found to possess a rich floristic diversity (Appendix-II; Plate – I: Figs.-1, 2, 3, 4 & 6). Stratification was clearly observed only in two vegetation types viz., ‘Tropical Semi- Table – 1. Number of Angiospermic Species and Infra-specific Taxa Belonging to Different Life-forms LIFE-FORMS ANGIOSPERMIC SPECIES & INFRASPECIFIC TAXA TOTAL DICOTYLEDONS MONOCOTYLEDONS (101 Families, 346 Genera) (20 Families, 94 Genera) Mesophanerophytes 61 02 63 (11.17% of M; 8.42% of H) (8.70% of H) Microphanerophytes 118 08 126 (21.61% of M; 16.30% of H) (17.40% of H) Nanophanerophytes 140 00 140 (25.64% of M; 19.33% of H) (19.34% of H) Chamaephytes 16 02 18 (2.49% of H) Hemicryptophytes 02 57 59 (32.02% of N; 7.87% of (8.14% of H) H) Cryptophytes/ 01 78 79 Geophytes (43.82% of N; 10.77% of H) (10.91% of H) Therophytes 208 29 237 (38.07% of M; 28.72% of H) (17.41% of N; 4.48% of H (33.01% of H) TOTAL 546 (M) 176 (N) 722 (H) (75.41% of H) (24.58% of H) (121 Families, 440 Genera) 328 Vegetation stratification in Barpeta District 1 2 3 4 5 6 PLATE – I: Fig. – 1. Number of species & infra-specific taxa in different layers of stratification; Fig. – 2. Stratification in Tropical Semi-evergreen Forest in MNP; Fig. – 3. Vast tract of cultivated field near Barpeta town; Fig. – 4. Grassland inside MNP near Bansbari Range office; Fig. – 5. Cultivated field under flood near Pathsala town; Fig. – 6. Rich growth of roadside vegetation at Keotkuchi, near Barpeta town. Evergreen Forests’ (Appendix- I; Plate – I: Fig. - 2) and ‘Tropical Deciduous Forests’.