Mumbai: The Delhi high court will hear a petition challenging the felling of 16,000 trees to build houses for government employees in Delhi on Wednesday. The hearing comes in the wake of growing protests over the felling of 16,000 trees. On the face of it, the protests appear surprising in a city which has claimed to have witnessed a spectacular rise in green cover since the turn of the 21st century. According to official estimates of the Forest Survey of India, Delhi has witnessed a whopping 73% rise in forest cover between 2001 and 2017, the third highest gain among all states and Union territories (UTs).

However, a Mint analysis of official and alternative estimates suggests that the Forest Survey of India estimate may be grossly overstating the true extent of forest cover in the national capital, and in the nation.

While the official data suggests that India has been able to increase green cover since the turn of the century, alternative estimates provided by Global Forest Watch, (GFW) —a collaborative project of the University of Maryland, Google, USGS, and Nasa—suggests that green cover has declined sharply in the country.

The main reason for the stark difference in the two estimates seems to lie in the definition of forest cover used by Forest Survey of India.

Forest Survey of India employs satellite imagery to estimate “forest cover", considering “all lands which have a tree canopy density of more than 10% when projected vertically on the horizontal ground, within a minimum areal extent of one hectare" as forests. This definition fails to distinguish between native forests and man-made tree plantations, overstating the extent of forest cover. While the Convention on Biological Diversity has a similar definition of forests, it mentions that the land in question should not be under agricultural or non-forest use.

A 2010 study by researchers from Pondicherry University and James Cook University, Australia, described the Forest Survey of India results as “technically accurate but misleading".

As in the case of Forest Survey of India, the GFW database relies on satellite data for estimation of “tree cover", employs similar criteria as Forest Survey of India, and a similar resolution of satellite imagery. Therefore, the “forest cover" defined by Forest Survey of India and “tree cover", defined by the GFW are comparable in terms of both definition and accuracy. However, the GFW definition is stricter as it only considers vegetation that is taller than 5 metres in height. It is this difference that seems to explain the striking differences in results obtained from the two data sources.

While the latest estimate of tree cover extent from GFW is of 2010, data on loss of forest cover is updated annually. The tree cover loss for Indian states shows an accelerating trend in recent years, with the heavily forested northeastern states, Odisha, and Kerala showing the greatest amount of tree cover loss in the period 2001-2017. However, the official data represents that Kerala gained 30% forest cover in the same period. This can be explained by the fact that Kerala is one of the biggest producers of plantation crops in India, with rapidly growing plantation crops likely compensating for the loss of native forest cover.

According to the GFW data, all states and union territories with the exception of Chandigarh show a decline in the extent of tree cover in the time period 2000-2010. In contrast, in terms of official data, 28 of 36 states and UTs have registered an increase in forest cover.

Since the GFW data adopts a globally consistent definition, it enables international comparison of the extent of tree cover loss, and the results do not paint a pretty picture. India ranks 14th among all countries in tree cover loss in the decade 2000-2010.

Thus, citizens in Delhi and elsewhere have good reasons to be concerned with the depletion in green cover over the years.

Arjun Srinivas is a recipient of the Mint-Hindustan Times-HowIndiaLives Data Fellowship 2018.

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