India is endowed with rich and diverse forest vegetation. The forests of the country vary. India is the second most populous and seventh largest country in the world having a population of over one billion with 1.8% of world's forest cover. It is, however, important to differentiate between the forest cover and the tree cover, i.e., Trees outside Forests (TOF). There exists a significant tree cover wealth outside the conventional forest area, most of which is less than one hectare in extents they include small patches of trees in plantations, and woodlands, or scattered trees on farms, homestead and urban areas or trees along linear features such as roads, canals, bunds etc.
Trees outside Forests (TOF) are considered an alternative but significant source of fuel, fodder and timber. They give economic stability, support development and also provide environmental relief to the local people. With the improvement in satellite data resolution and with adoption of digital image processing, it is possible to assess forest cover patches as small as one hectare that are termed as tree cover. The tree cover estimate comprises tree patches outside the recorded forest area which are not captured by remote sensing satellites during forest cover assessment.
The Forest Survey of India (FSI) started estimating the tree cover in the country in the year 2001 to have a complete picture of the forest and tree cover to compare it with the national goal of 33% forest and tree cover. Trees outside forest areas are fragmented, scattered and there is no accurate knowledge of their geo-locations. They have a low density and their assessment by conventional methods becomes costly and time-consuming. The assessment of tree cover of a district has two components. One component consists of areas identified from satellite data under block and linear forms. The high resolution satellite imageries map tree blocks (patches between 1 and 0.1 ha) and linear plantations in the rural areas. The actual area covered by such patches is computed from the classified digital map using GIS methods. The second component is the computed area from scattered trees growing in rural and urban strata, which are not mapped/identified even with high-resolution satellite data (5.8m) currently used.
For computing area of tree cover from scattered trees, an exercise was conducted in 2001 to establish relationship between diameter (DBH) and tree crown of different species growing in different physiographic zones. This relation was used to derive the number of trees of a species in making the area with 70% density. To estimate the area of tree cover under scattered trees- in-rural and urban strata, adequate numbers of sample plots are laid and numbers of trees occurring in the sample plots are enumerated by diameter, class and species. This helps in estimating the number of trees per ha in scattered and urban strata. Using the number of trees by diameter and species constituting the area as published; the tree cover under scattered stratum is estimated.
On the basis of the tree cover of sampled districts, the tree cover for the physiographic zone is estimated. Adding tree cover estimate for all the physiographic zones provides the estimated tree cover of the country. Presently the total tree cover of the country constitutes 2.79 per cent of the country’s geographic area.