Mapping smallholder forest plantations in Andhra Pradesh, India using
multitemporal Harmonized Landsat Sentinel-2 S10 data
Abstract
This study’s objective was to develop a method by which smallholder
forest plantations can be mapped accurately in Andhra Pradesh, India,
using multitemporal visible and near-infrared (VNIR) bands from the
Sentinel-2 MultiSpectral Instruments (MSIs). Conversion to agriculture,
coupled with secondary dependencies on and scarcity of wood products,
has driven the deforestation and degradation of natural forests in
Southeast Asia. Concomitantly, forest plantations have been established
both within and outside of forests, with the latter (as contiguous
blocks) being the focus of this study. Accurately mapping smallholder
forest plantations in South and Southeast Asia is difficult using
remotely sensed data due to the plantations’ small size (average of 2
hectares), short rotation ages (4-7 years for timber species), and
spectral similarities to croplands and natural forests. Cloud-free
Harmonized Landsat Sentinel-2 (HLS) S10 data was acquired over six
dates, from different seasons, over four years (2015-2018). Available in
situ data on forest plantations was supplemented with additional
training data resulting in 2,230 high-quality samples aggregated into
three land use classes: non-forest, natural forest, and forest
plantations. Image classification used random forests on a thirty-band
stack consisting of the VNIR bands and NDVI images for all six dates.
The median classification accuracy from the 5-fold cross-validation was
94.3%. Our results, predicated on high-quality training data,
demonstrate that (mostly smallholder) forest plantations can be
separated from natural forests even using only the Sentinel-2 VNIR bands
when multitemporal data (across both years and seasons) are used.