“…Numerous studies on air pollution effects and pests and diseases impacts on forest condition are reported in the literature since 1980 [2,7,44,50,64,65,73,80,87,88,91,96,97,107], among others) and show that "severe" damage (affecting a "sufficient" number of trees) can be easily detected, while scattered tree decline is difficult to see with the limited resolution of space remotely sensed data [6,24], and without ground assessment. Finally, the feasibility of depicting forest decline is closely depending on the topography of the study area, on the structure of forest stands, on the date and frequency of data acquisition and on the spatial resolution of the remotely sensed data.…”