Volume I Number I February (2012) pp. 121-26 The Clarion ISSN: 2277-1697
Analysis of Changing Forest Cover and its Impact on Environment with Special Reference to Umtrew Basin, North East India
Dhanjit Deka1, Pradip Sharma2
1Department of Geography, B.Borooah College, Guwahati
2Department of Geography, Cotton College, Guwahati
The pattern of forest cover has been changing more or less continuously in all parts of North East India. The changes have been accelerated in last few years partly due to natural causes and mainly due to human activities. The human activities including agricultural expansion, illegal felling of trees for timber wood mainly deplete the forest land and most of which in course of time turns into agricultural land. All these changes have brought about many environmental as well as socio economic problems in the region. The trend of such changes and their impact on natural environment as well as on socio-economic condition of the people are identified as the prime concern at this stage. The Umtrew Basin of North East India is a river basin covering an area of 1253.1sq km where the study has been carried out using satellite data and GIS techniques. The satellite data of Landsat MSS and IRS-1C LISS III for the years 1977, 1999, 2004 and 2007 respectively have been utilized for the study. In the present study an attempt has been made to identify the pattern of forest cover change using GIS analysis through which we could identify the degraded areas. In course of the present study an attempt has been made to formulate a strategy for maintaining environmental quality of the study area. A humble starting from the Umtrew Basin for such programme with an aim to replicate in other similar areas of the country has been considered as the application part of the study.
Keywords: Afforestation, Forest cover change, GIS, GPS, Remote Sensing, Satellite imagery, Umtrew
North East India is very rich in biodiversity, and it is known as one of the 17 biodiversity hotspots of the world. Physiography, climate and soils of the region have in combination provided a suitable condition for luxuriant growth of forest in the region. But, unchecked economic activities and population growth have left their scars on the landscape in many of the drainage basins of North East India, particularly from the last few decades. Over the last ten years significant changes have been taken place on the issue of forest cover changes. Such changes are the result of the relocation of the people to river sides, extensive deforestation, farm and grazing abandonment etc. Intensification of agriculture and huge industrial activities supplemented with the above resulting in climate change, soil erosion, flood, siltation, reducing precipitation, habitat extinction etc. Anthropogenic interference in forest cover is being increasingly recognized as one of the critical factors that influencing global climate change (P.K. Sarma, 2008).This widespread deforestation and its resultant factors have continuously violating the environmental quality of the drainage basins. Therefore, it needs some evaluation to formulate a strategy by which some improvement on environmental quality could be maintained. The main criteria for maintaining the environmental quality is to increase the forest cover in the degraded areas through proper planning and monitoring. River basin development approach is identified as the most useful approach for the above mentioned purpose. To increase the forest cover or to take up afforestation programmes the criteria like selection of potential site, selection of suitable species are very much necessary and for this, the study of past and present forest pattern is indispensable. Remote sensing integrated with GIS using LISS-III data is an effective tool for precise analysis of such study at global as well as local levels (E. R. Rhoades, 1998). It is found to be more suitable in small river basins. It helps in finding out the accurate and precise results in lesser cost and time. It is an effective technique for assessment of status of natural resources, which has been tried to apply in the Umtrew Basin of North East India.
The Umtrew river basin of North East India lies in between 250 30’ 15” north and 260 14’ 18” north latitude and 910 41’ 15” east and 920 0’ 15” east longitudes. The upper course of the river basin lies in Ri-Bhoi district of Meghalaya where it is locally known as Umtrew. The lower course of the basin lies in Kamrup district of Assam. The total area of the basin is 1253.1 sq km. Of this, upper and lower Umtrew basins cover 1035.6 sq km and 217.5 sq km respectively. The lower part of the basin consist of 68 numbers of villages with definite geographical boundary, where as the upper part consists as many as 65 villages/places which does not have any administrative boundary.
Figure 1: Location Map of the study area
Aims and Objectives
The study focuses on thevarious geo-environmental issues of the Umtrew Basin with special emphasis to forest cover changes.
The following are the specific objectives of the study-
- Assessment of changing pattern of forest cover, particularly in last three decades using satellite data.
- Assessment of the cause and effect of changes, which have been taken place on the geo-environmental condition of the region.
- Assessment and selection of potential sites for afforestation programme in the degraded areas.
The methodology for analyzing forest cover changes was based on the comparison between the satellite imageries taken on different dates. The whole basin has been surveyed with a eTrex vista GPS receiver and using a set of questionnaires designed for the purpose. As many as 50 GPS points were collected for ground truthing and verification. GPS points give the location (latitude and longitude) and. From the available imageries of the years 1977 (LANDSAT MSS), 2004(IRS 1 C LISS III) and 2007 (IRS 1C LISS III), the change detection of the said area has been analysed. For the preliminary processing of the satellite imageries and detecting the basin boundary Survey of India topographical sheets (Nos- 78 N/16, 78 O/9, 78 O/13 and 78 O/14) of scale 1: 50000 have been used. The satellite imageries brought from NRSC first rectified or geometrically corrected using GCPs and GPS points. The scene was geo-referenced to latitude-longitude coordinate system using Polyconic Projection system and Polynomial Equation. The sheet was enhanced by the process of histogram matching and radiometric correction. Finally for forest cover change detection, we have followed the method of digital classification i.e. supervised classification.
Analysis and Findings
The analysis has been done using digital classification technique in GIS environment. The imageries used here for detection of forest cover change are LANDSAT MSS and IRS-1C-LISS III, out of which LISS III have the spatial resolution of 23.5 meter and it is very good for such study. But one imagery (1977, LANDSAT MSS), which has been used here has the spatial resolution of 80 meters only. So, as it is not matching with the earlier imageries, this has been used only as basic database for the study. Two types of forest cover have been identified viz. dense and open based on the algorithm provided by the GIS interface. The dense forest includes the area which have more than 40 percent canopy layer whereas the open forest consist the area having less than 40 percent canopy layer including scrub ones. It is well established from the analysis that the forest cover of the study area has continuously decreasing except between 1977-1999. The area shows a declining trend particularly in case of open forest from 1977 to 2004 at an average rate of 1 sq.km per year. From 2004 to 2007 this rate has been accelerate to 14sq.km per year. In comparison to the open forest, the area under dense forest have been showing an increasing trend from 1977-1999 probably because of the extensive afforestation programme held during 1980s by the Meghalaya government. But from 1999 to 2007 this takes a reverse trend and the area under dense forest decreasing at a rate of 34sq.km per year.
Figure 2: Map showing pattern of forest cover change during 1977-2007
|Land use class/Area||1977(sq km)||1999(sq km)||2004(sq km)||2007(sq km)|
Table 1: Statistics showing forest cover change
Causes and Effects
River basin is one of the complex units to understand the cause effect relationship of any kind of phenomena. It is obvious that today’s world is facing high rate of growth of population. Similar condition prevails in Umtrew river basin. It is well examined from the analysis that lower part of the basin has a high rate of population growth over the years and the plain condition of this part resulted in large amount of developmental activities which in turn effect the environment at a massive scale. With the growth of various economic activities influx of population from the neighbouring areas and Guwahati city has threatened the process of environmental equilibrium in the lower part of the basin. In contrast the upper part of the basin is not so much affected at a massive scale but area specific degradation of forest is a common phenomenon in the upper part. Because as the upper part lies in the hilly tracts of Meghalaya plateau, the local tribes of that area still depend on jhoom cultivation, and with increasing population pressure the previous 6/7 years jhoom cycle has come down to 3/4years i.e. a plot of hill land used for shifting cultivation left fellow for 6to 7 years for restoration of natural soil quality is now being used with a gap of only 3 to 4 years. The impact of these fragile hill slopes is responsible for acceleration of topsoil erosion as well as deterioration of soil quality and also siltation and sedimentation in the lower course of the river.
Figure 3: Population density map of the lower part Fig: 4 Area-wise magnitude of places in the upper part
Until about a few years ago, there was a lack of comprehensive knowledge on the degradation of forest cover and the resultant consequences. During the last decade, however, rigorous efforts have been made to rehabilitate the forest cover through launching of afforestation programmes. These programmes can be implemented well only if the problems related to this are well understood. One of the important aspects of such programmes is the location of those areas where such schemes can be implemented without adversely affecting the present land use pattern. This is particularly necessary because most of the forest land, encroached in the past, is currently being used for agriculture. It is imperative that such schemes are either taken up in degraded forest lands or on those lands which are currently not being put to any use but lying as wastelands. So the programme should be implemented in those areas where maximum waste land and scrub land occur. This would not only increase the wooded area to meet ever increasing demand for timber, fuel wood etc., but would also improve the quality of natural environment. It is well established from the study that the degradation of forest land mainly takes place in the hilly areas of lower part of the basin as well as areas surrounding the villages and nearby areas of the national highway no.40 in the upper part. So based on the forest maps and related statistics, there could have some ideal and potential locations and sites in the lower part as well as the upper part where the river itself might be an important component for forest area development. It is already mentioned that an afforestation programme was held under the Meghalaya government in 1980s for which a large area came under forest, as one can observe comparing the forest maps of 1977 and 1999. So, this area has natural potentialities for growing forest cover if properly planned. There are two very important advantages in selecting such lands for tree plantation. Firstly, acquisition of available land for tree plantation and secondly it will arrest the process of further land degradation in the neighbouring areas, which may also otherwise lose their productivity due to ecological degradation. Tree plantation would make these lands productive, check further degradation and thereby restoring ecological balance so that there is no drop of agricultural potential in the surrounding lands. If more people participate and made them aware and government initiatives are there it may definitely help in faster restoration of natural environment and improve human economic support. Continuous monitoring of the afforested area is of umpteen needs for success of the programmes. Usually the programme of tree plantation is made satisfactorily, but the rates of survival of the trees, which play an important role in the actual success of such schemes, are normally disheartening. This is generally ignored in computing the statistics. It is thus suggested here that, apart from monitoring afforested areas, temporal assessment of wooded area should also be undertaken.
The study elucidates that the population growth, migration, developmental activities and agricultural activities are the main driven force deforestation; however there is a spatial variation in contribution to the causative factors. Change in local population is directly related to forest degradation. In some places jhooming is one of the important problem. Agricultural expansion, development of industries caused the deforestation in many ways.It is observed from the analysis of satellite data of last thirty years; it becomes clear that the forest cover has been tremendously decreasing in the Umtrew basin. As a result, soil erosion and siltation on the river bed has already been increased manifold in the said area. The geo-environmental condition of this part has already been deteriorated. There is every possibility of micro climatic change due to such changes. So, this area needs more afforestation including the social forestry programme for restoring the conditions as prevailed earlier. Therefore, considering the trend of forest change there is an umpteen need to take protection measures in the Umtrew Basin to maintain the environmental quality, restricting the possibilities of micro climatic change and meet the national demand of forest cover.
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