A half-century of land cover changes in the Caucasus derived from Corona spy satellite and Landsat images

Land cover change substantially affects ecosystems and leaves long-lasting legacies. Unfortunately, land cover analyses typically begin in the mid-1980s, when 30-m Landsat data became available, missing major global changes that occurred in the 1960s and 1970s. We aimed to quantify long-term land cover changes in the Caucasus (240,000 km2) comparing the magnitude of Soviet-era (1965-1987) versus post-Soviet changes (1987-2015). We (a) mapped land cover based on 1965 Corona spy satellite imagery and (b) quantified long-term changes by comparing 1965 Corona with 1987 and 2015 Landsat-based classifications while accounting for the differences in sensors' spatial and spectral resolutions. Our Corona-derived map accuracy was 74.4 +/- 3.7%, and change accuracies were 66.0 +/- 4.2% for 1965-1987 and 61.6 +/- 2.8% for 1965-2015. Overall, 30% of the land changed during the Soviet era compared to 20% during the post-Soviet era, highlighting the importance of mapping those early changes. Change trajectories differed considerably during the Soviet era and thereafter. For example, forests were lost during the Soviet era (- 6%) but gained area post-1987 (+ 5%). Croplands were often lost (- 18%) due to grassland gains (+ 11%), which were continuous, but at different rates (4% versus 7%), whereas croplands were lost in both eras, especially post-1987 (3% versus 16%). There were stark differences among countries: Azerbaijan underwent post-Soviet cropland gains, while the Russian Caucasus and Georgia experienced forest gains. Our results highlight the feasibility and value of early spy satellite data for long-term land cover change analyses, particularly in regions with substantial land cover changes then.