Forest degradation affects forest structure, composition and diversity, carbon stocks, functionality and ecosystem processes. It is known to contribute significantly to global carbon emissions, but there is uncertainty about the relative size of these emissions. This is largely because while deforestation, or long-term forest clearance, has been successfully monitored using remote sensing (RS) technology, there are more difficulties in using RS to quantify forest degradation, in which the area remains as forest, but with an altered structure, composition and function. A major challenge in estimating emissions from forest degradation is that in addition to identifying the areas affected, the amount of biomass loss over time in a given area must be estimated. Contributory challenges to mapping, monitoring and quantifying forest degradation include the complexity of the concept of degradation, limitations in the spatial and temporal resolution of RS sensors, and the inherent complexity of detecting degradation caused by different disturbance processes and forest uses. We take the innovative approach of dividing the studies reviewed by the specific type of forest disturbance that is being monitored (selective logging, fires, shifting cultivation and fuelwood extraction etc.), since these different activities will result in different signatures in the canopy and thus may determine the type of RS technology that may best be applied.

Approximately 40% of the global population relies on traditional bioenergy, accounting for 9% of global energy use and 55% of global wood harvest. However, knowledge about the environmental impacts of traditional bioenergy is fragmented. This review addresses several persistent questions and summarizes recent research on land cover change (LCC) and pollution emissions resulting from traditional bioenergy use. We also review recent studies analyzing transitions from traditional bioenergy to cleaner stoves and fuels.Between 27 and 34% of the wood fuel harvest in 2009 was unsustainable, with large geographical variations. Almost 300 million rural people live in wood fuel “hotspots,” concentrated in South Asia and East Africa, creating risks of wood-fuel-driven degradation. Different fuels and stoves show variation in climate-forcing emissions. Many, but not all, nontraditional stoves result in lower emissions than traditional models. Traditional bioenergy makes substantial contributions to anthropogenic black carbon (BC) emissions (18–30%) and small contributions to total anthropogenic climate impacts (2–8%). Transitions from traditional fuels and devices have proven difficult. Stacking, i.e., the use of multiple devices and fuels to satisfy household energy needs, is common, showing the need to shift stove interventions from the common approach that promotes one fuel and one device to integrated approaches that incorporate deep understanding of local needs and practices, and multiple fuels and devices, while monitoring residual use of traditional technologies.