A field and remote sensing assessment of rates and drivers of tree cover loss in island catchments: variation in global model accuracy

This study seeks to shed light on the rates and drivers of tree cover loss in island catchments focusing on a case study from Fiji. Global Forest Watch (GFW) is critically assessed as a framework for quantifying terrestrial tree cover loss and associated forest carbon stocks. The study assesses the role of the drivers of tree cover loss identified by GFW global models including anthropogenic deforestation: shifting agriculture, wildfires, urbanisation and plantation forestry as well as other drivers outside of the globally standardised list. According to GFW, from 2000 to 2023, Fiji lost 530.9 km² of tree cover equivalent to an annual average loss of 23.1 km². The study finds that global models provide useful insights into the rates of tree cover loss at the national level. However, the impacts of local drivers of tree cover loss are found to diverge from global model predictions. Specifically, tropical cyclones driving and harvesting cycles within timber plantations driving 15.3–24.5% and 75.9–83.2% of tree cover loss in the Ba River Catchment, respectively. These ranges are significantly greater than the rates predicted by global models. Further collection of 5209 ground cover points, generation of land cover models and forest inventories across 115 sites and 1070 trees sheds light on biomass carbon implications of this tree cover loss. Based on the forest inventory estimates, the 40.5 km² of tree cover resulted in approximately 466,000 tonnes of dry matter (t DM) or 856,000 tonnes carbon dioxide equivalent (tCO₂e) in the Ba River Catchment between 2000 and 2023.