Science

India Lost Millions Of Mature Farmland Trees Over The Past Decade

Karan Kamble

May 29, 2024, 10:44 AM | Updated 10:41 AM IST

Image sourced from the study published in the journal Nature Sustainability. Basemap in a from Natural Earth. Credit: b, d, Google Earth; c, Planet Labs PBC.
Image sourced from the study published in the journal Nature Sustainability. Basemap in a from Natural Earth. Credit: b, d, Google Earth; c, Planet Labs PBC.

India has lost a considerable number of large farmland trees this past decade, according to a study published in the scientific journal Nature Sustainability.

The researchers reported a loss of 11 per cent, with an uncertainty of about 2 per cent, of trees on farms between the years 2010-2011 and 2018-2022. 

This finding matters because trees on farmlands, located outside of forests or forested ecosystems, are considered “an essential natural climate solution” due to their ability to help combat climate change, support livelihoods, and improve biodiversity.

As high as 56 per cent of India is covered by farmland, and only 20 per cent by forest. A prominent example of a tree grown on farms is the Neem tree.

Martin Brandt, the lead author of the study, revealed in an X post that he and his collaborators picked India for this research because "the large trees within fields are clearly visible in the images". Further, he says he was "surprised how clear the decline of large trees was" when going over Google Earth images.

The study used high-resolution satellite imagery from RapidEye (2010-2011) and PlanetScope (2018-2022) to map and track the changes in 60 crore large farmland trees across India over the past decade. Two deep-learning tree-detection models were trained, one for RapidEye and one for PlanetScope, and deployed for the detection of individual non-forest trees for each year.

RapidEye was a constellation of five satellites in operation from 2009 to 2020. The images it produced threw up a resolution of about 5 metres per pixel. The more recent, more advanced PlanetScope is a constellation of about 130 satellites whose images are about 3 metres per pixel resolution. Both were or are operated by the satellite imagery provider Planet.

A tree was classified as disappeared if it was observed in either 2010 or 2011 but not during 2018-2022. On the other hand, a tree was classified as remaining if it was detected in either 2010 or 2011 and subsequently seen in any year between 2018 and 2022.

Trees mapped with RapidEye have an average crown area of 96 m2, meaning that they were generally mature trees at a later stage of development. Many regions in India lost up to half of these large mature trees within farmlands during 2010-2018. According to the study, “such a high loss rate of mature trees over less than a decade is unexpected.”

Massive losses occurred in central India, in particular in the states Telangana and Maharashtra. Some of the “hotspot areas” in these regions saw losses up to 50 per cent, with up to 22 large farmland trees per square kilometre disappearing. Though comparatively smaller, significant losses were reported in eastern Madhya Pradesh around Indore, as well.

In the tracking of individual trees during 2018-2022 using the higher quality PlanetScope, a tree detected in either 2018 or 2019 but not in the three consecutive years 2020-2022 was classified as disappeared. These trees have a crown size of about 67 m2.

The study found that 5.3 million trees (2.7 trees per square kilometre) observed in 2018 or 2019 were not detected in 2020-2022, with an uncertainty of 21 per cent. 

“This number of disappeared trees, considered a conservative estimate due to the method applied, was still high considering that a majority of the losses must have occurred between 2018 and 2020,” the study said. In some hotspot regions, more than 50 trees per square kilometre were reported lost.

It also bears noting that observed losses in many areas in India were along the expected lines. Still, a trend of farmland tree losses emerged.

In August 2023, researchers involved in the study carried out qualitative interviews with villagers in several states where tree disappearance was notable, such as Telangana, Haryana, Kerala, Maharashtra, and Jammu and Kashmir. The interviews lasted about 20-60 minutes each.

From their personal experience, the villagers verified the considerable depletion of mature trees within and along fields. They said changes in the cultivation practices was the main driver of these tree losses when it is generally considered to be climate change.

New boreholes were dug up to expand paddy rice fields, facilitated by the availability of newly established water supplies, with the objective of boosting crop yields.

“The decision to remove trees within fields is often driven by the perception that their benefits are relatively low and concerns that their shading effect, in particular for trees with a very large crown such as Neem trees, may adversely affect crop yields,” the study reported.

Several interviewees reported that block plantations, a method of plantation wherein single or multiple species are planted in a patch of land available, have increased. The interviewees did not attribute the tree losses to fungi and climate.

In extracting data and insights on farmland trees at an individual level over a period of time, the study has also managed to provide a tool that enables such monitoring.

Sub-metre-resolution satellite imagery would have been useful to map individual trees on farms, but such imagery is not available as time series over areas as large as the country of India.

Other researchers could, therefore, adopt the tools and methods employed in this study to advance research work of a similar nature.

Karan Kamble writes on science and technology. He occasionally wears the hat of a video anchor for Swarajya's online video programmes.


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