Forest Mapping

We have already seen about the area under forest in India which is abysmally low and better than the not so naturally well endowed neighbors. Here we will be see how science and satellite imagery is employed to map a forest.

Forest Survey of India (FSI) started using satellite date for assessment of forest cover since 1986 with a resolution of satellite data being(pixel size 23.5m X 23.5 m), scale of interpretation (1:50, 000) and the technique employed for image processing. Satellite data is procured from the National Remote Sensing Agency (NSRA), Hyderabad in digital form. Data is normally collected to the period from October to December when the cloud cover is low and the deciduous trees still have leaves to provide satisfactory reflectance for the satellite sensors.

Using Digital Image Processing (DIP) software, digital data from satellite is downloaded to the workstation. Radiometric and contrast corrections are applied to remove radiometric defects and for improving visual impact of the False Color Composites (FCC). Geometrical rectification of the data is carried out with the help of scanned SOI toposheets. Based on tone and texture of the forest cover areas are delineated. Interpretation of forest cover for the whole country is done at 1:50,000 scale using polyconic projection. Normalized Difference Vegetation Index (NDVI) transformation is also used for density classification of forest cover. Areas of less than 1 Ha, whether classified as forest within non-forest areas or blanks within forested areas, are excluded by clustering pixels and merged with the surrounding class.

Highly degraded forest or wastelands with stumped trees having canopy density less than 10 percent are classified as scrubs, a category of non-forest cover. Shadow areas in the scenes are treated separately. Density in shadow area is either based on ground information or is assigned due to their unique signature along the coastal areas. This is then followed by extensive ground verification and all the necessary corrections are subsequently incorporated.

But even with remote sensing technology there are some limitations in assessing the forest cover. Young plantations and species having less chlorophyll contents in their crown do not give proper reflectance and as a result are difficult to be interpreted correctly. So will the cloud cover making considerable details becoming obscure. Gregarious occurrence of bushy vegetation and certain agricultural crops, such as sugarcane, cotton, often pose problems in delineation of forest cover, as their reflectance is similar to that of tree canopy.

The post concludes by bringing out the difference between forest cover and forest area

A land may be recorded as forest cover and under management of forest department but may not have any discernible forest cover. On the other hand, all wooded lands or plantations, delineated as forest cover from satellite data may not be legally recorded as forest area as these could be private plantations or institutional wood lots. Although, majority of forested lands happen to be within legally recorded forest areas, all the changes taking place in the forest cover is not necessarily due to changes in the forests managed by the forest departments.

From policy and planning point of view to know the extent and quality of forest cover within recorded forest areas and outside it, the latest geo-referenced forest maps for the whole country showing the latest boundaries of recorded forest areas of 1:250,000 scale should be available using GIS tools for the purpose. On an average, at least 20 percent area within the reserved forests is without forest cover.

*The reference for this post is currently unavailable as I had come across it during one of my reading sprees and didn’t have the foresight to note down the source.

#Next: Posts on animals and aves.

Vanishing Forests

This is Part I of a series of posts giving an insight into the forest cover of India, the scientific methods employed behind its measurement, the flora and fauna.

In school, studying social science was found to be boring, always studded with long drawn information. While going through geography I happened to read about the existing forest cover in India. Forests covering one-third of the total area of a country was considered ideal for the nations overall development. But at the time of reading the geography text India had a forest cover over 23% of its total area. But what does the present statistics lead to?

On further researching I came to know that the 23% forest cover was according to the statistics of the year 1988. In 1988 the National Forest Policy came into being which set a target of 33% of land area under forest and tree cover and maintaining two-third of the area in hills under forest cover in order to prevent erosion and land degradation and also to ensure maintenance of ecological balance and environmental stability.

Forest cover is defined as an area more than 1 ha in extent and having tree canopy density of 10% and above. No distinction with respect to the type of tree crops (natural or man made) or tree species has been attempted due to lack of techniques for making such distinction. So in the forest cover assessment all types of lands, forest, private, community or institutional, will become included if they satisfy the required criteria.

This was taken while on a visit to the Muthanga Wildlife Sanctuary, Wayanad, Kerala

Current Situation

According to the Forest Survey of India (FSI), India’s forest cover stands at 20.6% of the total land area. And the good news is that we had only 0.11% reduction in forest cover since 2002 and the forest cover has remained more or less stable (in 2003 it was 20.64%).

And the main losses, according to FSI, were due to natural disasters and submergence of forests to dams. Though the amount of dense forests cover is a poor 1.66% of total land area, the moderately dense has 10.12% of total land area.

So the statistics surely shows a gradual decrease in forest cover though in the 1990s there was increased deforestation. The afforestation drive and social forestry initiative of the government has done little to improve the forest cover. There has been an addition of only an abysmally low area of 180,000 sq. km in the last 50 years to the forest cover.

In the revised National Forest Policy of 2002 the target to achieve 33% of land area under forest cover was set for the year 2012. So how are we going to have a nearly 60% increase in the forest cover? The forest cover in the hilly areas is a lowly 38.77% against the goal of 66%. What more can explain the increased landslide and soil erosion in the hill regions during rains? A little ray of hope can be found in the forest cover in the tribal areas where it is 60.04% of the total forest cover of the country when the tribal areas constitute only 33.6% of the total land of the country. The N-E states together constitute more than a quarter of the total forest cover(though it constitutes 7% of India’s land area) which is being lost year by year due to shifting cultivation and also wide felling of trees.

From the 1970s, the days of the Chipko Movement, people have become more interested and involved in conservation. Though it doesn’t constitute a good proportion of the vast population of our country, it may become instrumental in wakening others to the threat of going without forests and its rich natural beauty and resources and the flora and fauna it supports.

PS: Kerala has 28.9%, higher than the national average in spite of having the 2^nd highest population density in the country (barring the UTs).

Also India has the 2^nd highest forest cover as a percentage of total land area after Bhutan (58%) while Afghanistan has the lowest at 2% (Pakistan 3%) in South-Asia.

Next: Scientific Methodology behind forest cover estimation.