Satellite study reveals 40 per cent of SGNP forests in poor health

From left: Sanjay Gandhi National Park forest area deemed 1. moderately dense, 2. dense and 3. open by the study

A study based on high-resolution satellite imagery to establish forest health at the Sanjay Gandhi National Park (SGNP) has found that low-health forests accounted for 39.52 per cent, healthy forests accounted for 36.51 per cent and very healthy forests accounted for 3.36 per cent of the total area of the park.

The study - ‘Assessing Forest Health of Sanjay Gandhi National Park, Mumbai, Maharashtra, India' - was conducted in January 2024 by Dr Ravindra Medhe, with assistance from his student Chaitanya Kolekar, using remote sensing data and GIS software for the analysis. The report was published in IntechOpen on May 8, 2025.

SGNP is located in a highly urbanised and ecologically sensitive region. According to the researchers, the integration of remote sensing and GIS techniques using Sentinel-2A satellite data for analysing forest health through key vegetative indices is both timely and methodologically sound.

The study excels in its multi-index approach by utilising Normalised Difference Vegetation Index (NDVI) to measures vegetation "greenness" and vigor, Green Normalised Difference Vegetation Index (GNDVI) - similar to NDVI but more sensitive to chlorophyll content and photosynthetic activity - Modified Soil Adjusted Vegetation Index (MSAVI) technique - which reduces the influence of bare soil in vegetation analysis - and Moisture Stress Index (MSI) technique which indicates moisture stress in vegetation.

Dr Medhe, assistant professor of geoinformatics, Department of Geography, Savitribai Phule Pune University, said, "Particularly commendable is the decision to include MSI to incorporate a hydrological perspective, adding depth to the traditional greenness-based assessments. The weighted overlay method, while only applied to the vegetative indices, provides a robust classification of forest health into three categories: low-health, healthy, and very healthy forests. This classification is clear, intuitive, and relevant for urban forestry management."

The authors of the study also effectively emphasise the impact of urbanisation and moisture stress on forest health, which is a critical concern for conservation planning in metropolitan regions.

The study also shows comparisons to similar studies conducted in India and abroad. Moreover, the graphical outputs and index-specific discussions enhance the reader's understanding of spatial patterns and forest conditions within SGNP.

Commenting on the revelations of the study, which indicated that only 3.36 per cent of the total area of SGNP is "very healthy", Dr Medhe said, "This is not satisfactory, as very healthy forest area is too little. We must work to improve the quality and amount of SGNP forest land. The forest health of SGNP is currently in a fragile state and not fully satisfactory. Immediate and sustained conservation efforts are needed to restore low-health areas and protect the remaining healthy zones."

Questioned about the reason for the fragile state of SGNP, Dr Medhe said, "As a researcher, I recognise the importance of supporting claims with rigorous, multi-temporal, and interdisciplinary data. While the study provides a valuable baseline assessment of forest health in SGNP, it also highlights several areas where further investigation is essential to fully understand the drivers behind the observed forest degradation, based on the existing literature, spatial patterns, and ecological
context of SGNP."

3.36%
Forest area classified as very healthy

Possible reasons for degradation

Urban pressure, encroachment
The park's location within one of the most densely populated metropolitan regions subjects it to continual land-use change, illegal settlements, and infrastructure development

Water stress and climate variability
Evidence from the Moisture Stress Index in this study, combined with known regional climate variability, suggests that periodic drought and declining groundwater availability could limit forest regeneration and productivity

Tourism, human activities
SGNP is a forest reserve, tourist attraction, and religious site, which increases footfall and contributes to ecosystem disturbances like trail erosion

Limited buffer zone/management challenges
A relatively narrow buffer zone and a complex urban-ecological interface present ongoing challenges to forest protection, and long-term planning

Invasive species/soil issues
Anecdotal observations and prior studies from similar tropical dry deciduous forests suggest the presence of invasive plants and degraded topsoil, especially in human-disturbed zones