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Monitoring changes in Sunderban Mangrove Forest using RS/GIS
Methodology
IRS IC/ID, LISS-III data of December, 1999, March 2001 in 4 bands (Green, Red, Near IR and SW IR) were requisitioned from NRSA, Hyderabad for the scenes (row-path nos.) 107-57, 108-57& 108-56 which covered the entire Sunderbans mangroves of Indian portion and major parts in Bangladesh. After applying the histogram stretch and appropriate brightness contrast, the standard FCC was classified through supervised classification using "Maximum Likelihood classifier", on the basis of known ground truth points (A.O.I.). The entire imagery was classified with the following classes: dense and open mangrove vegetation, water with high sediment, clear water, non-forest uses, sands and muddy channels/mud flats. Extensive Ground Truth Verification was carried out by the author with the help of field officers and staff of Sunderbans Tiger Reserve.
The Reserved Forest boundaries of 24-Parganas Forest Division and Sunderbans Tiger Project were digitised, geo-referenced using ARC/INFO software and overlayed on the classified imagery, both the raster and vector coverage being in polyconic projection with 88šE & 24šN as central meridian / projection origin.
Results & Discussions
The objective of the study was to clearly delineate the dense, open and degraded mangrove areas as well as to re-map the courses of rivers and creeks, which have undergone major shifts over the last few decades.
Analysis of the classified imageries shows that the effects of erosion by ebb tides and formation of muddy channels gradually extending to the interior of the islands, is very high in Goasaba 1, 2 and 3 blocks of STR. Goasaba-3 is the most affected compartment, which contains large patches of mud flats at the heads of these muddy channels. Though there is no harvesting or felling of trees in these parts of STR, yet considerable parts of the block is either devoid of trees, or is open type of forest with sporadic growth of bushes or dwarf trees like Ceriops decandra ( local name-Jhanti Goran ).
The density status of Sunderbans mangrove, including the Tiger Project and Territorial Forest Division is as follows: -
| Class name |
|
Dec 1999 |
March 2001 |
| Dense Mangrove |
|
= 1570.35 |
sq km |
|
| Open mangrove |
|
= 577.70 |
,, |
|
| Sand/ Grass/ Charland |
|
= 180.59 |
,, |
|
| Non Forest use |
|
= 26.57 |
,, |
|
| Clear Water |
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= 109.58 |
,, |
|
| Muddy Water |
|
= 1817.59 |
,, |
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| Total |
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= 4282.38 |
,, |
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Such detailed mapping of Sunderbans estuary, showing the periodic changes and the latest positions of river courses, landmasses and water bodies, as well as quantum of dense and open mangroves, could be completed on real-time basis, which was not possible in the past. While conventional survey allows such detailed mapping, perhaps once in five decades, the new technology as mentioned in this paper allows such detailed mapping of a highly dynamic, inaccessible and fragile ecosystem at least once a year. The cost involved was also reasonably moderate which includes the data cost, paid to NRSA, cost of hiring one Project personnel, office expenses and cost of field verification. The cost of such mapping and survey is also low as compared to conventional manual method. While calculating the cost, the overhead cost of computer hardware & GIS software has not been taken into account as the hardware and software have been in use for many other jobs.
Recommendations: -
It is recommended that regular mapping, at least biennially, of Sunderbans forests be carried out, using the GIS and Remote Sensing technology, to monitor the changes in Sunderbans ecosystem which is the Habitat of the highly endangered spp of Royal Bengal Tiger. The utility of this technology in real-time monitoring of the changes in the remote and mostly inaccessible habitat has been proved beyond doubt.
References
- Working Plan Division, West Bengal - First Working Plan for the 24 Parganas Forest Division, 1949-50 to 1958-59, Southern Circle, Forest Deptt.
- Field Director, Sunderban Tiger Reserve- Draft Management Plan of STR for the period 2000-2001 to 2005-2006.
- W.W.Hunter- A Stastical Account Of Bengal, Sunderbans- Vol. I, Pt. II, W.W.District Gazetteers, Deptt of Higher Education, G.O.W.B. ( 1998 )
- A.B.Chaudhuri- Wetland Ecology- Resources, Research and Conservation- An Indian Scenario- MEPS Publishers (1998 )
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