In a mere three years, from 2019 to 2022, India may have lost close to 5.8 million full-grown trees in agricultural lands, says a satellite-imagery based analysis by researchers at the University of Copenhagen, Denmark, and published this week in the peer-reviewed journal Nature Sustainability.
Additionally, 11% of such trees detected via satellite during 2010-2011 were no longer visible when reviewed from 2018 to 2022, leading the researchers to conclude that these trees had “disappeared.”
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However, this doesn’t necessarily imply that India’s overall tree cover, or trees outside forest, is declining as the analysis was specific to only large trees above a certain size.
The Forest Survey of India (FSI) conducts regular surveys of tree cover – both inside and outside forests – but only publishes data on the changes in acreage and not individual trees. The latest FSI report says that India’s tree cover has increased in 2021 over 2019.
The present analysis however focusses on Indian farmland and tracks individual trees, albeit only big ones, relying on maps from multiple ‘micro-satellites’, and machine learning analysis to estimate trends, beginning 2010.
About 56% of India is covered by farmland and 22% by forest. With the largest agricultural area in the world, changes in tree cover here, while critical, have been largely “overlooked,” the authors say.
For their analysis, the researchers combined satellite-imagery from two repositories – RapidEye and PlanetScope – to estimate changes in tree number from 2010 to 2022. These have resolutions of three to five metres, meaning that the satellite can “see” large trees, three to five metre apart, as individual trees. The FSI relies on data from the Sentinel satellite that has a coarser resolution of 10 metre – implying that they can tell apart blocks of trees but not individual ones.
Hotspots
Trees detected by RapidEye had an average crown size (the leafy outgrowth of tree) of 96 sq.m and such a high loss rate of mature trees over less than a decade is “unexpected”, the authors note.
“The disappearance of mature farmland trees was observed in many areas, but numbers rarely exceed five to 10%, except for areas in central India, in particular in the States of Telangana and Maharashtra, where we document massive losses of large trees. Here, several hotspot areas have lost up to 50% of their large farmland trees, with up to 22 trees per square kilometre disappearing. Smaller hotspot areas of loss are also observed, such as in eastern Madhya Pradesh around Indore.”
The tree loss estimate was on the “conservative” side and most of the losses were likely between 2018 and 2020, they noted.
One of the authors told The Hindu that the absolute number of trees lost since 2010 could not be estimated as “.. images from 2010 to 2011 are not always good and it was not a wall-to-wall (tree) mapping exercise. Trees may be missed due to bad image quality. An absolute number would thus have a high uncertainty. We trust the images from 2018 to 2022, so if a tree was detected in 2010 but not over 2018-2022, there is little uncertainty that it was lost. But not all trees in 2010 were mapped,” said Martin Brandt, of the University of Copenhagen and one of the study authors. “Similarly for the 2018-2022 period: it’s not a consistent thinning all over India, but often clustered, with some areas losing a considerable number of trees within a few years. You can see it visually on GoogleEarth using the historic images, it’s unbelievable seeing how many large trees disappeared.”
A plausible reason for large trees being lost was the conversion of farmland to paddy field. “A certain loss rate is natural, and the cutting of trees is also part of agroforestry management systems, and not every lost tree is related to climatic disturbances or human appropriation...an observable trend is emerging in several areas where established agroforestry systems are replaced with paddy rice fields, which are being expanded and intensified, a development facilitated by the availability of newly established water supplies. Large and mature trees within these fields are removed, and trees are now being cultivated within separate block plantations typically with lower ecological value,” the authors noted.
Published - May 17, 2024 11:23 pm IST
