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Patterns of species dominance, diversity and dispersion in 'Khasi hill sal' forest ecosystem in northeast India
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The 'Khasi hill sal' forest ecosystem in Meghalaya, India represents the easternmost limit of sal distribution. We tested if tree diversity and compositional heterogeneity of this ecosystem was higher than other sal-dominated forests due to moister environment.
Vegetation was sampled in 11 transects of 10 m width and up to 500 m length covering 5.2 ha area. All stems ≥ 10 cm girth at breast height were enumerated.
We found a pattern of mixed dominance of Shorea robusta (sal) and Schima wallichii and co-dominance of Pinus kesiya and Careya arborea. The Shannon's diversity index (H′) was 3.395 nats. This value is remarkably high and competitive to that of moist sal forests of eastern Himalayan foothills and sal-dominated forests of Tripura. A high value of H′ was manifested by: a) high species richness (S = 123), b) good equitability (70.6%), c) 'fair' resource apportionment, and d) abundance of rare species (84% species with less than one per cent of total individuals, 67% species with two or less individuals ha-1 and 59% species with one or less individuals ha-1). The compositional heterogeneity was 'fair' (Whittaker's βw = 3.15). The presence of Fagaceae with six species commanding 4.3% of importance value (IVI) and of a pine (P. kesiya) in sal forest was remarkable. As many as 58 species showed 'low density (≤ 10 individuals ha-1), uniform dispersion', five species achieved 'higher density (> 10 individuals ha-1), uniform dispersion' and six of the top 10 species were 'clumped'. The forest showed an exponential demographic curve illustrating 'good' regeneration of an expanding community. Vertical stratification was simple with a poor canopy and fair subcanopy, which together with low basal area (15.65 m2 · ha-1 for individuals ≥ 10 cm gbh) indicated logging of mature sal trees in the past.
The 'Khasi hill sal' forest ecosystem is richer in alpha and beta diversity than most sal-dominated forests, but past logging has reduced basal area. Selective removal of small timber and firewood, slash-and-burn agriculture and recurrent burning of forest floor are the principal anthropogenic factors controlling forest structure and regeneration of species.
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Patterns of species dominance, diversity and dispersion in 'Khasi hill sal' forest ecosystem in northeast India
)
Abstract
The 'Khasi hill sal' forest ecosystem in Meghalaya, India represents the easternmost limit of sal distribution. We tested if tree diversity and compositional heterogeneity of this ecosystem was higher than other sal-dominated forests due to moister environment.
Vegetation was sampled in 11 transects of 10 m width and up to 500 m length covering 5.2 ha area. All stems ≥ 10 cm girth at breast height were enumerated.
We found a pattern of mixed dominance of Shorea robusta (sal) and Schima wallichii and co-dominance of Pinus kesiya and Careya arborea. The Shannon's diversity index (H′) was 3.395 nats. This value is remarkably high and competitive to that of moist sal forests of eastern Himalayan foothills and sal-dominated forests of Tripura. A high value of H′ was manifested by: a) high species richness (S = 123), b) good equitability (70.6%), c) 'fair' resource apportionment, and d) abundance of rare species (84% species with less than one per cent of total individuals, 67% species with two or less individuals ha-1 and 59% species with one or less individuals ha-1). The compositional heterogeneity was 'fair' (Whittaker's βw = 3.15). The presence of Fagaceae with six species commanding 4.3% of importance value (IVI) and of a pine (P. kesiya) in sal forest was remarkable. As many as 58 species showed 'low density (≤ 10 individuals ha-1), uniform dispersion', five species achieved 'higher density (> 10 individuals ha-1), uniform dispersion' and six of the top 10 species were 'clumped'. The forest showed an exponential demographic curve illustrating 'good' regeneration of an expanding community. Vertical stratification was simple with a poor canopy and fair subcanopy, which together with low basal area (15.65 m2 · ha-1 for individuals ≥ 10 cm gbh) indicated logging of mature sal trees in the past.
The 'Khasi hill sal' forest ecosystem is richer in alpha and beta diversity than most sal-dominated forests, but past logging has reduced basal area. Selective removal of small timber and firewood, slash-and-burn agriculture and recurrent burning of forest floor are the principal anthropogenic factors controlling forest structure and regeneration of species.
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Acknowledgements
The Department of Biotechnology (DBT), Government of India, New Delhi provided principal funding for this work through a project grant to US (grant number BT/PR7928/NDB/52/9/2006). AKT sincerely acknowledges a research fellowship from this project and from UGC's meritorious fellowship programme. The authors are grateful to Prof. K.N. Ganeshaiah, UAS, Bangalore for project design and encouragement and thank the custodians of forests in Meghalaya to permit field work, the Botanical Survey of India (BSI), Shillong for access to herbarium, and the Head, Department of Botany, North-Eastern Hill University, Shillong for logistics. Invaluable help in the work rendered by D. Kumar, S. Borah and K. Nongrum is thankfully acknowledged.
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