Landscape fragmentation & biodiversity conservation Human induced disturbance differs from natural disturbance especially in extension, severity and frequency. The capacity of the landscape to incorporate human disturbance is overwhelmed and the disturbance process is transformed into a stress process, which reduces biodiversity. Human activity has widespread impact on biodiversity, affecting ecological entities from species to whole communities and ecosystems, though heterogeneity in the landscape can be due to moderate disturbance. Disturbance regimes and their impact on communities and landscape can be well understood by analyzing spatial and temporal architecture of disturbance (Moloney & Levin, 1996). At landscape level, disturbance is related to patch structure and spatial arrangement and determines the fate of patches, their size and duration. Severe disturbance or even a prolonged absence of disturbance generally has depressing effect on biodiversity, but intermediate disturbance seems to enhance diversity in a system (Pickett and White, 1985; Anon., 2001). Landscape ecology examines spatial variation in fragmentation at a variety of scales. It includes the biophysical and societal causes and consequences of landscape heterogeneity. Landscape ecology embraces spatial heterogeneity and pattern: how to characterise pattern, how it develops and changes through time, and its implications for populations, communities, and ecosystem processes. Because landscapes are large they are typically measured in kilometers. Human influences are an important influence on landscape pattern and landscape ecology. Hence landscape ecology quite naturally is concerned with anthropogenic aspects of landscape pattern and change. Recent advances in remote sensing and GIS have offered new opportunities for investigation at scales larger than in the past and contemporary research into processes and patterns occurring in the microcosm has reconfirmed the importance of small scales. It has led to a consequent enlargement of temporal scale which, in tracking back processes has allowed us to understand the environmental conditions of the past (Delcourt and Delcourt, 1988). The availability of data across scales has opened new possibilities for integrating patterns and processes, as recently stressed by Lubchenco et al. (1991). Satellite images can be considered as a very convenient tool to measure landscape patterns since they provide a digital mosaic of the spatial arrangement of land covers (Chuvieco, 1999, Coulson et al. 1990). Remotely sensed images can provide critical information on all these three components, but this work focuses on the first one. Size, shapes, perimeter, connectivity, orientation, presence of corridors, visibility or diversity of patches are variables critical for describing the landscape mosaic. Not much work has been devoted to the measurement of these variables from satellite images. Analyses of landscape fragmentation (Turner and Gardner, 1990) have been common goals in the use of satellite data for landscape pattern analysis (IIRS, 2000). Landscape Change and their ecological implications Land use change in Sonitpur (Assam) Tropical regions around the world are currently undergoing rapid and wide-ranging fragmentation in land cover. The present case study has highlighted the ongoing large scale deforestation in the foothill region of Eastern Himalayas. Sonitpur district has been found to be most affected by this large scale deforestation. The spatial distribution of different forest type from 1994 to 2000 show that forests are undergoing massive reduction with time. The reduction in total forests is more from 1999 to 2000 than was observed from 1994 to 1999. 86.75 sqkm (1.70%) area of forest has changed from 1994 to 1999 while 145.44 sqkm (2.86%) has changed from 1999 to 2000. The major change has been due to deforestation. The conversion of forest areas is more towards non-forest category than into other land cover types. The area of semi evergreen forests has not changed considerably due to inaccessibility. No change in riverain forests was observed which could be attributed to considerable distance and also due to isolation and low cover area. The increase in grassland has also been due to conversion of moist deciduous forests and tropical semi evergreen forests. The increase in area of tea gardens is due to proximity of moist deciduous forest to tea garden areas. The change is also due to cutting of crop when mature. The expected loss in the biodiversity value is given in table 1 (Fig. 1).  Fig. 2: Landscape Dynamics in Meghalaya (Talukder et. at., 2001) |