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Evaluating the change (1968-2001) in landscape pattern and analyzing disturbance in Baratang Forest Division (Andaman Islands), South East Asia
Dr Nidhi Nagabhatla Post Doctoral Scientist- Landscape Ecology/ Remote Sensing International Water Management Institute (IWMI) Colombo, Sri Lanka nidhi26@gmail.com P.S Roy National Remote Sensing Agency, Balanagar, Hyderabad-500 037, India Rajendra Jagdale S&T Park, University of Pune, Pune - 411 007, Maharastra, India. Abstract: As the 21st century unfolds, accompanied is the range of long term environmental problems forecasting immense consequences for the economic well being of nature. The present approach draws attention towards evaluating the change in landscape pattern and analyzing disturbance in Baratang Islands caused as a result of human activity triggering long-term detrimental effects like climate change, global warming, variation in rainfall pattern, temperature fluctuation and ecosystem imbalance. Advancement in spatial technology has opened new vistas to understand the fundamentals of the complex interrelations between human activity and natural forces. Ecological effects of land use change are tools for anticipating and evaluating the complex interactions between humans and ecological systems. Changes in vegetation cover over time are important spatial data to assist in understanding the change in natural processes and the influence of human contributions, or its subsequent impact, on ecological condition. Natural ecosystems of the Andaman Islands are under severe pressure due to population explosion, forest fragmentation and other natural causes. The forest vegetation with high species diversity is noteworthy but due to human intervention the forest area has remarkably shrunk and ecological balance splintered. Estimating the change in landuse/ landcover over time assist in understanding the landscape dynamics and the influence of human contributions on ecological complexity. The use of two time period data i.e. 1986 and 2001 facilitated in preparation of vegetation cover map and the change matrix analysis was done to find out the change in each type. The change detection analysis reveals that forest vegetation complimented with high species diversity is noteworthy but due to human interventions the forest area has remarkably shrunk. Change detection analysis also highlights the change in landscape pattern and spotlights two major issues of concern viz., the conversion of forest into agriculture and secondly the transformation of primary forest into secondary formations. It also reveals that significant correlation exist between change in natural boundaries of vegetation communities and the causal agents viz., population pressure, extraction, development, and plantation activities. Introduction: Humans have altered the natural environment far as evidences provide us (Thomas, 1956). Increasing population growth coupled with unsustainable resource use is a major factor responsible for change in landscape pattern. Initially ecological approaches started with study on biogeographical patterns and were mostly of taxonomic nature. Ecological science plays an important role in broadly understanding the structure and function of nature. The branch has evolved a science of human sustenance and sustainability (Singh, 2004). The increasing interest in ecosystems spatial dynamics has led the need for new quantitative methods capable of analyzing patterns, determining the importance of spatial processes and developing landscape models (Turner and Gardner, 1991). Williams, (1993) advocated that land use/land cover change acts as a surrogate for the terrain interest points. The information generated on landscape change and configuration facilitates to answer key management questions and help to analyze global ecological and environmental change (Lunetta, 1998). Blaschke et al., (2001) has emphasized the need to measure landscape dynamics quantitatively by incorporating landscape pattern and change from satellite image analysis. Change detection is the measure of landscape-temporal evolution involving comparison of a pair of images to identify areas that have distinctly different brightness values. New images representing change are created by taking the difference between images. Singh, (1989) accounted many change detection procedures including principal component analysis and comparison of classified images. Roy et al., (1996) explains that basic premise of change detection is that spectral signature change commensurate with change in land cover. The information on landscape dynamics highlight specific threats to vegetation and anticipate some of the future threats. Andaman Islands placed under a biogeographical separate zone (10A) (Rodgers and Panwar, 1988) are known to be emergent remnants of a tertiary mountain chain, the Andaman ridge (Ahmad, 1982).These winds swept, isolated, fragile, oceanic islands have volcanic foundations and are characterized by change of sea levels. Rich species diversity is largely attributed to soil variability, climate and colonization of plant species from widely different territories. Luxuriant vegetation shields the island environments from the full amplitude of continental climatic fluctuations. In recent times, the island ecology has undergone serious changes owing to various causes. Tourism has adversely affected sea turtle nesting beaches and the overall ecology (Andrews et al., 2002). Clearing vegetation for cultivation has exposed the soil to high-intensity rainfall resulting in has led to erosion. In turn, the sediments have smothered the mangrove and coral ecosystems (Sirur, 1999, In Andrews and Sankaran, 2002). Kothari et al., (1989), explained the vast encroachments and extensive honeycombing of the forests in Saddle Peak NP (North Andaman). Land use change and extraction practices offers a potential measures for studying its dynamic. Tracing the historical records it was noted that till the middle of 20th century no large intrusion was made into Baratang Islands apart from movement of Jarwas while Ritchie’s archipelago was totally free from any disturbance activities. The colonization started with the penal settlement in 1970 wherein, forest clearance activities resulted in vegetation cover change, starting the first phase of forest degradation. The road construction in 1980’s added to the worse. The developmental activities, increased settlements, agriculture expansion land and the passing of ATR has resulted in increasing the buffer zone of disturbance. However, the remote islands still harbor intact patches of evergreen forest with well-defined storeys and the canopy density of more than sixty percent. Bay islands have undergone an observable change after independence. The changes pertaining to developmental activities, administrative infrastructure, tribal upliftment and economic sustainability have been somewhere responsible for change in the vegetation pattern in these islands. In order to conserve the left intact patches of the tropical forest in the isles, regular monitoring of the landscape is of paramount importance. A comprehensive databases mentioning the causes and the statistics of change will help us to evaluate the change in vegetation cover in the region. Sharma, Naik and Pandian (1988) in their study have visually interpreted major vegetation types in the division using Ariel photographs (acquired by the forest division in 1968). The present study however has made an effort to compare the change in the major vegetation classes using temporal data (1986 & 2000). The vegetation classes have been reframed and the area normalized according to the previous study. Analysis was opted for major communities in the region. Methodology: In the territorial division of Baratang Islands three out of the twenty-eight are inhabited viz. Baratang, Havelock and Neil. These islands were subjected to maximum disturbance and anthropogenic pressure in the last few decades. In the present study these islands were separately analyzed for change in forest and non-forest area. Monitoring change over time using multi-temporal imagery is an important application of spatial technology. Collins and Woodcock (1996) advocated methods for monitoring vegetation change ranging from intensive field sampling with plot inventories to extensive analysis of remotely sensed data. While aerial photography can detect change over relatively small areas, satellite imagery has proven cost effective for large regions. Change detection involves comparison of a pair of images to identify areas that have distinctly different brightness values. The signature trajectories are tracked over time and combined with site-specific rule-base techniques to determine the vegetation trend. In the present attempt, change detection technique is applied to depict information of landscape level changes in vegetation extent in last one and half decades (using two-time period Landsat TM data (1986 & 2001)). Visual interpretation approach was used to identify the changes in the natural boundaries of the vegetation communities and to derive a cover change map (Fig.1). Image elements are significantly taken into consideration during the process. Areas of classified change are related to cover type by GIS overlay analysis by intersecting change classes with cover types and quantifying the change.  Fig 1 Analyzing landuse cover change using temporal data sets |