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Effect of Disturbance, Habitat Fragmentation and Alien Invasive Plants on Floral Diversity in Dry Tropical Forests of Vindhyan Highland: a Review

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Effect of Disturbance, Habitat Fragmentation and Alien Invasive Plants on Floral Diversity in Dry Tropical Forests of Vindhyan Highland: a Review RAGHUBANSHI & TRIPATHI 57 Tropical Ecology 50 (1): 57-69, 2009 ISSN 0564-3295 © International Society for Tropical Ecology www.tropecol.com Effect of disturbance, habitat fragmentation and alien invasive plants on floral diversity in dry tropical forests of Vindhyan highland: a review A.S. RAGHUBANSHI * & ANSHUMAN TRIPATHI Department of Botany, Banaras Hindu University, Varanasi 221005, India Abstract: Effect of disturbance, habitat fragmentation and exotic plant species invasion on plant diversity is documented for the dry deciduous forests of India’s Vindhyan highlands. Plant communities were identified with the help of satellite imagery and ground data, and community wise diversity was estimated. Analysis of landscape matrices using satellite images and GIS tools showed deforestation of smaller fragments, and fragmentation and degradation of larger ones. Fragments of smaller size had lesser number of plant communities compared to larger fragments. Generally large size fragments were species rich and more diverse as compared to smaller fragments. Lagestoemia -Acacia -Lannea community was richest for both tree and herb strata, whereas Shorea-Buchanania community was the richest when all vascular flora were considered. The study indicates that species rich communities of the dry tropical forests are not only being reduced in area but they are also becoming species poor and less diverse due to rapid deforestation and forest fragmentation. The communities most vulnerable to alien invasive plants were Acacia-Terminalia, Terminalia-Shorea and Hardwickia-Acacia . Ecological implications of plant invasion are discussed and conservation measures suggested. Resumen: Se documenta el efecto del disturbio, la fragmentación del hábitat y la invasión de especies vegetales exóticas sobre la diversidad vegetal para el bosque seco caducifolio de las tierras altas de Vindhyan, India. Las comunidades vegetales fueron identificadas por medio de imágenes de satélite y datos de campo, y se estimó la diversidad de las comunidades. El análisis de las matrices de paisaje que usaron imágenes satelitales y herramientas de SIG mostraron la deforestación de los fragmentos pequeños, y la fragmentación y degradación de los de mayor tamaño. Los fragmentos pequeños tuvieron un menor número de comunidades vegetales que los fragmentos mayores. En general, los fragmentos grandes fueron ricos en especies y más diversos en comparación con los fragmentos pequeños. La comunidad de Lagestoemia -Acacia -Lannea fue la más rica tanto para árboles como para el estrato herbáceo, mientras que la comunidad de Shorea-Buchanania fue la más rica cuando se consideró a toda la flora vascular. El estudio indica que las comunidades ricas en especies del bosque tropical seco no solamente se están reduciendo en área, sino que además se están haciendo menos ricas en especies y menos diversas debido a la rápida deforestación y fragmentación del bosque. Las comunidades más vulnerables a las plantas invasoras exóticas fueron Acacia-Terminalia, Terminalia-Shorea y Hardwickia-Acacia . Se discuten las implicaciones ecológicas de la invasión de plantas y se sugieren medidas para la conservación. Resumo: O efeito das perturbações, fragmentação do habitat e invasão de plantas exóticas está documentado para a floresta seca decídua das terras altas de Vindhyan na Índia. As * Corresponding Author ; e-mail: [email protected] 58 PLANT DIVERSITY IN VINDHYAN FORESTS comunidades vegetais foram identificadas com a ajuda de imagens de satélite e dados de campo, e a diversidade alargada foi estimada. As análises das matrizes de paisagem usando imagens de satélite e ferramentas GIS mostrou a desflorestação de pequenos fragmentos, e fragmentação e degradação das maiores. Os fragmentos de menor dimensão apresentavam menor número de comunidades de plantas quando comparadas com os fragmentos maiores. Geralmente os fragmentos de maior dimensão eram rios em espécies e mais diversos em comparação com os menores. A comunidade Lagestoemia -Acacia -Lannea era a mais rica quer no número de árvores e no estrato herbáceo, enquanto que a comunidade Shorea-Buchanania era mais rica quando toda a flora vascular era considerada. O estudo indica que as comunidades ricas em espécies das florestas secas tropicais não só vêm a sua área sendo reduzida mas se vêm tornando mais pobres em espécies e menos diversas devido à rápida desflorestação e à fragmentação da floresta. As comunidades mais vulneráveis à invasão de espécies exóticas invasivas eram a Acacia- Terminalia, Terminalia-Shorea e Hardwickia-Acacia . As implicações ecológicas da invasão de plantas são discutidas e sugeridas medidas de conservação. Key words: Diversity, deforestation, forest fragmentation, Lantana invasion, plant communities. Introduction substantial portion of these hotspots contain tropical dry forest, which is one of the world’s most Understanding the diversity of nature in endangered forest types (Janzen 1988a; Lerdau et various forms is a fundamental goal of ecological al. 1991; Mittermeier et al. 1999). Data from most research (Lubchenco et al. 1991). Apart from the threatened dry tropics (Janzen 1988a) are scanty. immense economic, ethical and aesthetical Dry tropical forests once occupied more than half benefits, biodiversity is essential for the ecosystem the forest terrestrial tropics (Janzen 1988b; function and stability (Ehrlich & Wilson 1991; Murphy & Lugo 1986). Most of the past studies on Holdgate 1996; Tilman 2000). Biodiversity has habitat fragmentation have focussed their attracted world attention because of the growing attention on animals in temperate forests or in the awareness of its importance on the one hand and rain forests. Little information exists from dry the anticipated massive depletion on the other tropical zone. Few studies have actually measured (Singh 2002). the level of diversity that exists in networks of Globally, concerns are raised over the rapid small forest patches in tropical environments loss of biodiversity in all its forms and at all the (Pither & Kellman 2002; Sagar et al. 2003, 2008). levels. Habitat destruction is the chief cause of the Present paper documents the effects of biodiversity loss. Habitats can either disappear disturbance, habitat fragmentation and exotic completely or they may become degraded and/or plant species invasion on plant diversity in the dry fragmented, both causing serious impact on deciduous forests of Vindhyan highlands. species as well as ecosystem processes. Regionally, species introductions and altered disturbances Vindhyan highlands rates may favour increased local diversity, but habitat loss or modification, outbreaks of Vindhyan highlands are located in between the introduced or native species, and management of highly populated Indo Gangetic - plains and the exploitable systems tend to decrease species Narmada valley, and have natural vegetation of richness and heterogeneity (Lubchenco et al. tropical dry deciduous forests (Champion & Seth 1991). 1968). Although practically no historical Biodiversity hotspots around the world contain information exists on species diversity in the high degree of endemism and are undergoing Vindhyan highlands, it appears that the area was exceptional loss of habitats (Myers et al. 2000). A once very rich in diversity. The potential natural RAGHUBANSHI & TRIPATHI 59 ecosystem of the area is tropical deciduous forest. diversity was estimated. Community classification Earlier ecological work in the Vindhyan highlands was done by cluster analysis procedure as given in shows a profound impact of human activity on the PC-ORD software (McCune & Mefford 1999). natural ecosystems (Singh et al. 1990). There has Hierarchical agglomerative polythetic cluster been rapid industrialization in recent years and analysis was performed with Ward’s divisive activities like quarrying for limestone, method and squared Euclidean distance options to establishment of cement factories, thermal power delineate communities on the basis of basal area stations, widespread mining have resulted in a values of adult trees for all the sampling units. In rapid build up of human population, displacement order to select the appropriate stop level, of original population, deforestation and preliminary cluster was evaluated by Indicator conversion of natural forest ecosystems into Species Analysis procedure in the software as savanna and marginal croplands. Earlier studies proposed by Dufrene & Legendre (1997). indicated that the forested area in the region is Cluster analysis of vegetation data of adult continuously decreasing and the remnant forest tree individuals resulted in 11 plant communities cover exists in the form of non-contiguous patches (Fig. 1). The identified communities were: of varying sizes dominated by single or mixed (1) Tectona-Acacia (2) Lagerstroemia-Terminalia species (Singh et al. 1990). This feature is unique (3) Lagerstroemia-Acacia-Lannea (4) Shorea- and gives a new dimension to the biodiversity Buchanania (5) Tectona-Holarrhena (6) Acacia- pattern. The change detection study (1982-1989) Terminalia (7) Anogeissus-Holarrhena (8) Adina- for a part of Vindhyan hills using satellite images Lannea (9) Terminalia-Shorea (10) Shorea identified that only 31% of the forest area has Community, and (11) Hardwickia-Acacia . Of the remained unchanged since 1982. About 40% of the total forest area was converted from mixed forest with crown cover > 50% to mixed forest with crown cover 30 - < 50%. The good to poor forest conversion occurred at a rate of
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