S. Gupta, A.R.Ghosh, S.Bandopadhayay and S. Chowdhury
Department of Environmental Science
The University of Burdwan
Temporal change detection (1961 – 2006) study of the predefined forest cover of Burdwan district, West Bengal is carried out by the help of GIS. From the overlay analysis it is found that in the duration of 1961 – 1991 there are 24% deforestation followed by 18% afforestation during 1991 – 2000 and again 9% deforestation during 2000 – 2006 with an overall decreasing trend of 15% during the entire study period (1961 – 2006). For sustainable development of forest resource protected forest development along with agro-forestry and social forestry in the older alluvium soil and red and yellow soil region of this district may be recommended.
Introduction In the name of development and agricultural need or other this resource has been exploiting for several years. Remote Sensing and GIS can be used to manage and assess this resource for a healthy environment in future. Abbasi and Khajedin (2006) have made a study on the application remote sensing and GIS technology in identification of wood types Cupressus sempervirens, for re-habilitation of deforested area in Armand watershed, Iran. Bajpai and Dasgupta (2006) and Dasgupta et al (2006) have made a study on technological advances using remote sensing and GIS in forestry sector of India. They made another study on use of remote sensing and GIS in assessment of trees outside forests.
The study area lies in the western part of West Bengal, covering an area of 7024 km2 and is encompassed within latitudes 22055´N – 23051´N and longitudes 86048´E – 88023´E in the Survey of India topographical maps (73I/13,14; 73M/1,2,6,7,10,11,12,13,14,15,16; 73N/9,13 and 79A/2,3,4,6,7,8).
The forest of Burdwan district can be divided into three groups, viz reserve forest, protected forest and un-classed forest. Of the total area of Burdwan, 2.97% is covered by forest.
Forest Distribution on Soil Type
The soil type of Burdwan can be divided into four large groups i.e i) Alfisols Older Alluvium, ii) Entisols Younger Alluvium, iii) Lateritic Ultisols and iv) Red and Yellow Ultisols. The younger alluvium is most suitable for agriculture as this type of soil is very fertile. On lateritic soil and red and yellow soil agriculture is not so suitable. Majority of forest area is under the Lateritic Ultisols. For the development of forest the most important cause is that the predominant tree species of these forests is sal and sal associates, which are very suitable for this type of soil (Fig 1 ).
Figure 1 Distribution of forest on various soil types.
As stated earlier that the forests of Burdwan district are predominantly developed on the lateritic soil, the 80% forests are mainly covered by Sal (Shorea robusta Gaertn) and Sal-associates like Mohua (Madhnea latifolia), Palas (Butea monosperma), Simul (Salmalia malabarica), Neem (Azadirachta indica), Amlaki (Phyllanthus embica) etc. The species of the forests are divided into three main categories like
The entire study is worked out by three stages viz i) data collection, ii) data editing, manipulation, and iii) out put generation. All the stages are described below.
As the main view of this study is to make a change detection study on the state of the forest area, both types of data viz present and past data are collected. The data are collected from divisional forest office, district land and land reform office etc. In case of the spatial data, forest cover maps of Burdwan of 1961 (SOI toposheet), 1991 (NATMO product) are used. The satellite image of 2000 and 2006 of forest-covered portion of Burdwan is an IRS 1C, LISS-III image with 23-meter resolution.
This stage can farther be subdivided into various sub stages, like Software: – In this study the used software packages are ARC GIS 8.3, ARC View GIS 3.2a (GIS Packages) and ERDAS IMAGINE 8.6 (Image processing and GIS package).
Spatial Data Entry: – The toposheet and the maps are scanned and fed into the computer. In ERDAS Imagine the map is registered in Everest 1956 spheroid. Then the registered map is digitized, manipulated the output is saved as shape file in ARC GIS. The satellite image is also registered in ERDAS imagine software.
Non Spatial Data Entry:
In this study two types of database file (*.dbf) are used. One is info database, which is created automatically during digitizing. It store entity data and other data are selectively add. Another type of database is created which is not linked with the entities. But it stores all the other information regarding that particular beat wise area coverage of forest. Classification: –
The satellite images are classified in ERDAS Imagine through Supervised Classification method. The training sites are collected from field visit and fed in signature editor of ERDAS Imagine. By these signature images are classified.
Change Detection Study:
For a change detection study the maps are overlapped and the specific display system is used in which only the changes are showed. From this the changes can clearly identify.
Out Put Generation:
The out put map is created on ARC GIS and ARC VIEW GIS by overlapping various maps and integrating the databases.
Results & Discussion
On the basis of overlay analysis temporal changes of forest cover area from 1961 to 2006 are represented in table 1.
From table 1 it is found that 24% deforestation has been made from 1961 – 1991, whereas during 1991 – 2000 substantial amount i.e. 18% forest cover have been increased particularly in reserve forest area. But again a decreasing trend of 9% was found from 2000 – 2006. But the most interesting thing is that the shape of the forests area remains same (Fig 3).
Figure 3 Vector overlay of the forest cover of 1961, 1991, 2000 and 2006 of Burdwan
In 1961 map Shebdanga and Orgram Beat are visible but in 1991 map both the beats cannot be seen, though both of the maps are created on same scale and same coordinate system. Some forests are renamed and some forest area such as Aduria and Ausgram beat are increased. Since 1961 to 2006 there is an overall reduction of 15% in forest coverage. Population expansion and uncontrolled grazing (degrading specially the low canopy areas) are one of the major causes of degradation of forest in this district during 1961 – 1991. In conjugation with population expansion the agricultural need was also increased. During 2000 – 2006 major cause of forest degradation is rapid urbanization of the district. Moreover unplanned urban sprawl is damaging the primary drainage system thereby generating excess runoff water during rainy season, which is detrimental for plant growth.
Figure 4 Probable areas for developing protected forest, agro forestry and social forestry
For sustainable development of forest cover in Burdwan district agro-forestry, social-forestry and development of protected forest area can be recommended. Older alluvium region of this district, which is very fertile for agriculture, is also very much suitable for developing for agro-forestry whereas lateritic ultisols and younger alluvium, relatively less fertile are favourable for developing social-forestry. Protected forest area can be developed in red and yellow ultisols region of this district (Figure 4).
The authors gratefully acknowledge Prof. J.K.Datta, Department of Environmental Science, Burdwan University, for his critical evaluation and suggestions, which greatly helped to improve the manuscript.
Abbasi, A. P and S.J. Khajedin Commissioning the potential habitat of Pinus Nigrawith using of RS and GIS techniques for recultivation of deforested area occasional study (Watershed of Sarkhoon, Chaharmahal Bakhtiyari Province- Iran); Map Asia, 2006 Bajpai, R.K and S. Dasgupta Technological advances using Remote sensing and GIS in forestry sector of India ; Map Asia, 2006 Dasgupta, S, P.Lakhchaura and D. Panday Use of remote sensing and GIS in assessment of TOF-A case study from Panjab, India; Map Asia, 2006