Application of Remote Sensing and GIS in the Sustainable Management of Mangrove Forests Y.L.P.Rao Conservator of Forests Working Plan Division Forest Department Government of Maharashtra Forest Colony , Wanavdi, PUNE PIN Code– 411 022 ylprao @ hotmail .com G.Anupama Ms.G.Anupama Environmental Consultant Pune, Maharashtra state , India . anupamay @ yahoo.com Abstract : - Mangroves display high degree of structural and functional diversity placing mangroves amongst the most complex ecosystems . Mangroves differ from other forest eco systems in that they receive large inputs of matter and energy from both land and sea .They also store large quantities of organic carbon . Mangroves are important tropical costal ecosystems .Mangrove forests are regularly used by the local people to meet their fuel wood , food and other requirements .Sustainable use and management of mangrove forests can not be done without knowing the extent , distribution of mangroves and impacts of human activities on them . RS & GIS are very useful tools to carry out such study . The Village maps , topographic maps , were geo-referenced and digitized .The satellite imagery was classified to extract mangrove forests. Ground reference data for mangroves was collected using GPS hand sets. A mangrove stock database was created with various attributes like species , various products used by the local people , socio economic data etc. The paper concludes by making certain management guidelines for the mangroves by involving the local people through Joint Forest Management and other protection and conservation measures. 1. Introduction :- Mangrove forests are unique tropical eco-systems occurring along the sheltered shore line with muddy to sandy bottoms. They are variously described as coastal woodland, tidal Forests and mangrove forests. Mangroves depend on terrestrial and tidal waters for their nourishment , and on coastal soils and soil deposits from up land as substrate for support. The tides nourish the forests ,and mineral rich river-borne sediments enrich the swamp. Thus the mangroves derive the form and nature from both marine and terrestrial influence. Mangrove forests are among the most productive terrestrial eco systems and are natural and are a renewable resource. Mangroves are loosing their habitats as rivers are damned, their waters diverted, and the inter tidal zone extensively developed for aquaculture or agriculture and generally dried up. Large tracts have been converted into rice fields, fish and shrimp ponds, industrial use and land development and other non forest activities. Mangroves are over exploited at many places for the fuel wood, charcoal making etc. In thickly populated coastal villages with fuel wood shortage, even small branches and saplings are cut for domestic fuel. Mangroves are feeding, breeding, and nursery grounds for numerous commercial fish and shellfish. Mangrove represents the last refuse for a number of rare and endangered species. The tidal swamp is an ideal sanctuary for avifauna some of which are migratory. The importance of the resource stems from the many products taken directly from the mangroves, including wood products and non wood products. Wood products are fuel wood charcoal, construction material, timber for boats, pulp, tannin etc. The non wood products are apiculture fisheries products etc. Mangroves provide services like protection of coasts against wave and wind erosion , moderating the effects of coastal storms and cyclones, shelter and habitat for diverse wildlife particularly avifauna, entrapment of upland run up sediments thus protecting near shore reefs and reducing water turbidity. Mangroves also provide opportunities for education, scientific research and eco tourism. Increased human population in coastal areas is resulting in increased pressure on mangrove eco systems. With the growing demand for timber, fuel wood, and other non wood products. To ensure the environmental benefits together with a sustainable supply of various forest wood, non wood products and services sustainable management of mangrove eco system is needed. Sustainable management will lead to new opportunities for self employment such as , eco tourism, fishing, bee keeping and cottage industries based on mangrove forest product, helping to improve the socio economic condition of the local people. The detailed information on the extent and distribution of mangrove is required for their conservation and sustainable management. Remote sensing and GIS can be used to assess the distribution and extent of the mangrove and change in their extent , density etc over period of time . This study was carried out to assess the extent ,distribution of mangroves in Alibag sub district , and factors causing the reduction in density and extent . Alibag sub district is situated in Raigad district , Maharasthstra State, India. The results of Remote Sensing and GIS analysis were used in preparing a management plan for the mangrove forests in the area . 2.Study Area :- The study area selected is Alibag sub district in Raigad district of Maharashtra State, India. Alibag sub district is situated on the West coast of India. It has 50148 ha of geographic area, and has about 54.5 km long coast line. The Alibag sub-district has 189 villages and 2 towns with a population of 221661 as per 2001 census. The area extends between latitudes 180 56’ N to 180 29’ N and longitudes 720 50’ E to 730 04’ E. The area is surrounded by sea coast on its North East, North, and Southern part. The map of study area with its location in India is shown in figure-1 .The climate of the area is typical of that on the west coast of India, with plentiful and regular seasonable rainfall, oppressive weather in the hot months and high humidity throughout the year. The highest maximum temperature is 380 C and lowest minimum is 8.40 C. The air is humid throughout the year. Relative humidity is on an average over 80% during the south west monsoon season. In the rest of the year the relative humidity is between 65 % and 75 %. The average annual rainfall is between 2000 to 2200 mm. The mangroves are mainly found in the Dharamtar creek , Paulo creek, Kundalika creek, and at Alibag, Kihim, Thal, Varsoli, and Revdanda locations. All these estuaries originate from the Sahyadris hill ranges of Western ghats and flow towards the west and join the Arabian sea. Mangrove forests inter spurs with the coastal shrubs or the principal vegetation along the coast.  Fig 1 : Map of Alibag Sub-District and its Location Since 1970 the Alibag coast has come under intense pressure due to increase in the population, rapid industrialization in the area and neighboring towns like Panvel, Pen, Karjat . There are 34 villages with mangrove forests having an area of 1591 ha The ownership of the mangroves in these areas is mostly with the local residents and partly with the Revenue Department, Government of Maharashtra. There is no mangrove management plan till now for these areas for scientific management .As per the Government of Maharashtra ,Forest Department circular dated 21st October 2005 all these mangroves must be taken over by the Forest Department for scientific management from the Revenue department within six months and a management plan has to be prepared for their management using RS and GIS. The process of taking over these areas from the Revenue Department is in progress , till now over 80% of the area owned by Revenue department is taken over by the forest department . No mangrove map for this area is available .The exact extent of mangroves is also not known. To know the extent of the area , and to locate the parcel number , density , species , basal area and growing stock , RS and GIS were used .Reference data was collected with the GPS hand sets during field work . 3. Materials and Methods :- The satellite imagery of December 2004 in digital format was used. The satellite imagery was geo-referenced using UTM projection system and WGS 84 datum. A sub set of the image was obtained from the scene to extract the study area. The digital data was visually interpreted and digitally classified using Geomedia Grid software. Satellite imagery pertaining to December 1990 was also classified by comparing both the images it was observed that the mangrove area decreased and changed to other land uses like residential purpose , industries etc. The forest management maps and Survey of India toposheets were digitized. The GIS software used was Geomedia Professional 5.2. In order to assure the map accuracy in terms of the relationship between specific pixels and map co-ordinates the images were geometrically corrected .Village maps all along the coast line and around the creeks were geo-referenced with the village boundaries on forest management maps and GCPs. All the Village boundaries and parcels (survey numbers ) in these coastal villages were digitized and the parcel number and ownership details were fed as attributes to the parcel polygons . By overlaying the parcel information on classified satellite imagery, the parcels containing the mangroves were identified and extracted using GIS functions. A database was generated for each village with attributes , Village name , Survey no , mangrove area in ha , name of the owner and growing stock volume . This table facilitated to approach the Revenue Department to takeover the mangroves for scientific management. A village census GIS was prepared using the year 2001census data for all the 189 villages in the subdivision , with 42 attributes consisting of the following attributes .
To assess the growth , basal area , species , tree height etc ,26 sample plots were laid in the mangrove forests distributed throughout the area .The coordinates of sample plots were noted with the GPS . Sampling units are of 10m x 10 m quadrant for trees and 5m x 5m seedlings. Sampling for grown up trees was restricted to stems with diameter greater than 5cms. All the trees with diameter less than 5 cms were categorized as seedlings. Vegetation measurements taken on tree height, and stem diameter at breast height from these tree basal area and growing stock, species density, were calculated. Photographs of all sample plots laid in the mangroves for enumeration work were collected and their location was noted with GPS. A point feature named Photographs was created and the digital photograph file (*.jpeg) path was hyper linked to one of the attributes to photograph point features ,the other attributes given to the photograph features are latitude, longitude of photograph, date of photograph and the camera direction (bearing) . These photographs will help to know the mangrove type and status at a particular location on a particular date and will be useful in monitoring the change in the mangrove composition and density over a period of time . Various species found in the study area are , Avicennis alba Blume-Tree , Avicennis officinalis Linn.-Tree , Acanthus ilicifolius Linn.- Shrub ,Bruguiera gomnorrhiza Lam. –Tree , Excoecaria agallocha L. –Tree ,Luminitzera racemosa -Willd – (Shrub/ Tree) , Rhizophora mucronata Lam. – Tree etc. 4. Results and Discussion :- There is 1591 ha of mangrove forest area in the study area . A mangrove map in each parcel along the cost was prepared .From the Government land records 790.55 ha of mangroves are with the Revenue department . This map facilitated to identify the owner .The Revenue department has already handed over 80% of this area to the Forest Department . The following are the various threats to the mangroves in the study area. Over exploitation of the mangroves by the local people for fuel wood and timber especially to the mangroves close to the settlements. Conversion of mangroves on public lands for agriculture, human habitation and industrial development and using them as dumping grounds for garbage and other waste building material. Encroachment on Mangrove forest lands for, cultivation of paddy .At many places uprooting of natural seedlings was observed. Private land owners are not interested in conserving and developing their mangrove lands. Many owners are either preoccupied with other trade or , living in urban areas. Discharge of industrial pollutants into the creeks, rivers, and estuaries due to heavy industrialization in and around the study area. Obstruction and diversion of water for culvert construction along the main streams and rivers for paddy cultivation. Absence of proper survey and demarcation of mangrove parcels in the area and confusion regarding ownership of the land under mangroves, this is leading towards encroachment on the land and over exploitation of the resource. After studying the extent and distribution of mangroves in the area and the problems associated with them the following prescriptions are given for scientific management in the management plan. Since the area was over exploited over a long period initially the emphasis was put on the protection and conservation of mangroves.
In the Alibag sub district major threats to the mangrove forests are due to over exploitation of mangroves by the local people for the fuel wood , timber and as a dumping grounds by the local villages. The main problem that prevented the scientific management of mangroves is due to the private ownership and ownership with the revenue department with no technical person to guide them on scientific management of mangroves. A clear cut map showing the extent and distribution of the mangroves in the area is not available. Using the remote sensing and GIS the mangroves have been identified and the parcels and the ownerships of the mangroves is taken from the GIS. The management problems are compounded by inadequate knowledge of silvicultural of mangroves, of multiple use potential of resources. Mangrove restoration has great potential to increase the mangrove resources, provide employment to the local population, protect fragile tropical coast lines and also to enhance the bio-diversity and fisheries productivity. 6. References : -
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