Vegetation biomass estimation with remote sensing: focus on forest and other wooded land over the Mediterranean ecosystem

Carbon sequestration service of Mediterranean forest and other wooded land is threatened by their fragile, complex, and highly evolving nature, due to both human disturbances and climate change. Remote-sensing methods for forest biomass estimation have gained increased attention, and substantial research has been conducted worldwide over the past four decades. Yet, the literature body focused on Mediterranean forests is rather limited as a result of their small extent compared to other biomes. We discuss the remote-sensing studies over the Mediterranean forest and other wooded land, discriminating research based on the primary data source used, such as optical imagery, datasets from active sensors, and combination of multisource data. The review indicates that there is a significant research gap in terms of the studies, as well as a need for a reduction of the errors and uncertainty of estimates, which are associated with both the sensors’ characteristics and the Mediterranean forest and other wooded land structure. Biomass estimates based on optical data were generally less accurate R2 close to 0.70, where R2 is the coefficient of determination, however, when data from active sensors were involved, accuracy of estimations was considerably greater usually R2 greater than 0.80. With respect to scale, most of the local scale studies established relationships with R2 over 0.70 and as high as 0.98, while the few regional scale studies exhibited R2 close to 0.80. Further, in-depth analysis can provide more efficient data fusion, classification methods, and procedures for operational regional and national assessment of forest biomass over such Mediterranean areas.