INTRODUCTION

Forests constitute a key natural resource as well as a source of environmental services, and are considered valuable, because they provide a wide range of benefits to the society: products (timber, fuelwood, fodder, green manure, minor produce, medicines, etc.), ecosystem services (soil conservation, hydrological regulation, carbon sequestration, etc.) and repository of biodiversity. Hence, the vegetation studies forms a vital component of any natural resource management.  An ideal forest monitoring should therefore provide information on the levels of each of these stock or benefits being produced by a forest.  Development of sound forest conservation and management strategies requires an understanding of the spatial and temporal patterns in the forest condition. The present study assesses the condition of the forests of Uttara Kannada district of Karnataka State, which is a heavily forested district constituting the Western Ghats and aims at determining the temporal and spatial transformation in the forested area of  Uttara Kannada. The rapidly developing techniques of remote sensing and geographical information systems (GIS) potentially play a significant role in such analysis of forest condition. With the advent of remote sensing technologies, especially the satellite imagery which enables large area coverage, the mid‑80s saw the first attempts to come up with comprehensive forest assessments (NRSA, 1983). The present work focuses on vegetation status in Uttara Kannada district.

Western Ghats:
The Western Ghats are a range of hills extending from the southern portion of Gujarat to Kanyakumari in Tamilnadu, running almost parallel to the Arabian Sea coast.  The hills vary in height from about 200‑3000 m.  On the western side, the distance between the seacoast and the crest of the Ghats varies from 4‑100 km.  On the eastern side ramify into the hills which eventually merge with the Deccan tableland. The Western Ghats one among the 34 global hotspots of biodiversity lies in the western part of peninsular India is a series of hills stretching over a distance of 1,600 km from north to south and covering an area of about 1,60,000 sq.km.  It harbours very rich flora and fauna and there are records of over 4,000 species of flowering plants with 38% endemics, 330 butterflies with 11% endemics, 156 reptiles with 62% endemics, 508 birds with 4% endemics, 120 mammals with 12% endemics (Daniels, 2003), 289 fishes with 41% endemics (Sreekantha et al., 2007) and 135 amphibians with  75% endemics (Gururaja, 2004). Such biodiversity coupled with the higher endemism could be attributed in this regions to prevailing climate (higher rainfall, evapotranpiration, etc.), location (mid latitude), topographic and geological characteristics of the Western Ghats.  The Western Ghats region has some of the richest forests in India.  The major types of forests are the following:

1. Tropical wet evergreen forests, situated along the upper slopes and protected valleys.
2. Semi‑evergreen forests situated along the lower western slopes.
3. Moist deciduous forests which constitute over 50% of the forest in the Western Ghats and contain many commercially valuable species.
4. Dry deciduous forests which form a small percentage of the lower foot of the eastern slopes, and
5. Grassy blanks which occur along the crest of upper slopes, where the vegetation mainly consists of coarse grass.

The forests of the Western Ghats region of peninsular India have undergone significant transformations over the past century, and the nature, extent and causes of these transformations have been due to deforestation, rapid urbanisation, conversion of natural forests into agricultural lands and plantations, etc.  Uttara Kannada district in the Western Ghats is known for their dense forests which cover about 80% of the area of the district (Anon, 1982). The Western Ghats forms a practically unbroken relief dominating the western coast of the Indian peninsula for almost 1600 km.  They extend from the mouth of river Tapti (21^o N latitude) to the tip of South India (8^o N latitude) and the Palghat gap is only gap in the chain. This apparent unity in fact masks the great heterogeneity of the environmental conditions resulting from geographical, geological, and demographic differences. Working plans prepared by the Forest Department for different regions of the Western Ghats prescribe the norms for managing the forest in each area, taking into account the quality of forests, terrain and ecology. Over 13,000 species of higher plants have been recorded from India, of which  about 27% occur in the Western Ghats. There are 58 endemic genera mostly confined to the Western Ghats. Endemic tree genera are Erinocarpus, Meteromyrtus, Otonephelium, Poeciloneuron and Pseudoglochidion.

Geographic Information Systems (GIS) are specialized data systems that preserve location identities of the information they record (Campbell, 1996) and consists of a series of overlays for a specific geographic region. These overlays may depict raw data or may show thematic information, such as soils, landuse or geology. Although these data can be visualised as a set of superimposed images, they are infact stored in digital form, suitable for retrieval and analysis.
Data for GIS can be derived from many alternative sources. For example, topographic data can be derived from topographic maps (such as of Survey of India toposheets), which also provide information on the streams, highways and forested areas. These informations are prepared by digitization. Data can also be derived from aerial photographs or other images from airborne or spaceborne sensors. The other data available is the archived data, generated in digital form. Examples include, the data for India’s Census, available in digital form at the National Informatics Centre (http://www.nic.in), topographic elevation data provided by the Survey of India, land use data provided by Land records departments (State level), and remotely sensed data gathered by IRS (Indian Remote Sensing), LANDSAT (http://glcf.umiacs.umd.edu/data), etc.  

GPS technology aids as convenient, inexpensive and accurate measurement of absolute location. GPS’s have greatly enhanced the usefulness of remote sensing data, especially when it is necessary to integrate image data with field data for geocorrection, geo registration and for ground truthing (collection of field data at a specific location).  A GPS receiver consists of a portable receiving unit sensitive to signals transmitted by a network of earth‑orbiting satellites.  A system of 24 satellites is positioned at an altitude of about 17,600 km, to circle the earth at intervals of 12 hours, spaced in 6 orbital planes to provide complete coverage to the earth's surface. These satellites continuously broadcast one‑way signals within the L‑band region of the microwave spectrum.  These signals permit GPS receivers to estimate latitude, longitude, and elevation.  If a receiver can acquire data as many as 4 satellites, it is possible to estimate both vertical and horizontal positions. In point positioning mode, a single GPS unit can establish horizontal location within 20 m with 95% accuracy, and vertical location within 30 m.

Remote sensing is the practice of deriving information about the earth’s features using images acquired from an overhead perspective, using electromagnetic radiation in one or more regions of the electromagnetic spectrum, reflected or emitted from the earth's surface. Analysed  remote sensing data is combined with other data for a specific application. Remote sensing data aids in natural resource management to maintain sustainable development of a region.