Forest restoration assessment in selected critical watersheds in the Philippines using NDVI and Google Earth Engine

Forest cover in the Philippines has reduced drastically over the past decades. To address the problem, the government embarked on a massive forest restoration program called the National Greening Program (NGP) that started in 2011 and recently extended until 2028. The performance of NGP was evaluated using a cloud-based technique called Google Earth Engine (GEE). Landsat imageries were used within the cloud library of GEE, and vegetation index data were computed annually covering the period 1996 until 2021. Reforestation sites were considered in the monitoring of vegetation quality using Normalized Difference Vegetation Index (NDVI). The annual trends in the vegetation index were analyzed for these sites. Sen’s slope and Mann-Kendall trend test were employed to assess the statistical significance of the trends. Results reveal that from 2011 onwards, areas implemented purely with NGP could not yield statistically significant trends in all the watersheds chosen for the study, with p-values of 0.0736 for Salug Daku and Padada watersheds and 0.1611 for Labangxan watershed. Ground truthing may reveal further insights into the effects of the program on the vegetation coverage. Further studies are recommended to observe the consistency of the results, as the duration of the time series used in this study is limited.