Patterns and drivers of recent disturbance in tropical forest reserves of Southwestern Ghana

Despite the high rates of tropical forest loss in the Upper Guinean Forest Region, Ghana has retained a substantial area of closed forests, most of which are found in protected reserves. These forests, however, are experiencing substantial land use pressures that have led to widespread forest degradation, which may increase the risk of future disturbance. We mapped annual patterns of forest disturbance and recovery from 2013 to 2020 using maps of forest cover derived from Landsat imagery. Fire disturbance was distinguished from non-fire disturbance using VIIRS active fire data. We used boosted regression trees to model these disturbances in closed and open forests as a function of climate, topography, landscape structure, and socio-economic variables. A total of 3,562 km2 of forest reserves were disturbed, of which 86% (3,067 km2) were non-fire. Of the 495 km2 of fire disturbances, 62% were found in the moist semi-deciduous (northwest subtype) vegetation zone. Degradation (change from closed to open forest) and open forest loss accounted for 68% and 28% of all disturbances, respectively. Over the same period, 2,702 km2 of forest reserves recovered, with 1,948 km2 of these recovering fully to closed forests. Modeling results showed that fire disturbances were strongly associated with precipitation anomalies and occurred mostly in drier years, whereas non-fire disturbances had weaker relationships with precipitation. Disturbances in closed forests tended to occur where closed forest cover was already low. In contrast, disturbances in open forests were most common in locations with intermediate levels of population pressure from nearby cities and proximity of non-forest land cover. These results support the hypothesis that forest disturbance in Ghana is a multi-stage process with strong feedbacks. Most disturbances of closed canopy forests result in degradation rather than outright forest loss, but there is substantial loss of open forests. Reductions in closed forest cover result in fragmentation that increases the rate of degradation at nearby locations. Open forest loss is associated with multiple indicators that quantify the potential for human encroachment and activities such as logging, agriculture, mining, and burning.