Comparison and assessment of coarse resolution land cover maps for

article i nfo Global Validation GLC-2000 GLOBCOVER MODIS LCCS Information on land cover at global and continental scales is critical for addressing a range of ecological, so- cioeconomic and policy questions. Global land cover maps have evolved rapidly in the last decade, but efforts to evaluate map uncertainties have been limited, especially in remote areas like Northern Eurasia. Northern Eurasia comprises a particularly diverse region covering a wide range of climate zones and ecosystems: from arctic deserts, tundra, boreal forest, and wetlands, to semi-arid steppes and the deserts of Central Asia. In this study, we assessed four of the most recent global land cover datasets: GLC-2000, GLOBCOVER, and the MODIS Collection 4 and Collection 5 Land Cover Product using cross-comparison analyses and Landsat-based refer- ence maps distributed throughout the region. A consistent comparison of these maps was challenging be- cause of disparities in class de" nitions, thematic detail, and spatial resolution. We found that the choice of sampling unit signi" cantly in! uenced accuracy estimates, which indicates that comparisons of reported glob- al map accuracies might be misleading. To minimize classi" cation ambiguities, we devised a generalized leg- end based on dominant life form types (LFT) (tree, shrub, and herbaceous vegetation, barren land and water). LFT served as a necessary common denominator in the analyzed map legends, but signi" cantly decreased the thematic detail. We found signi" cant differences in the spatial representation of LFT's between global maps with high spatial agreement (above 0.8) concentrated in the forest belt of Northern Eurasia and low agree- ment (below 0.5) concentrated in the northern taiga-tundra zone, and the southern dry lands. Total pixel- level agreement between global maps and six test sites was moderate to fair (overall agreement: 0.67-0.74, Kappa: 0.41-0.52) and increased by 0.09-0.45 when only homogenous land cover types were an- alyzed. Low map accuracies at our tundra test site con" rmed regional disagreements and dif" culties of cur- rent global maps in accurately mapping shrub and herbaceous vegetation types at the biome borders of Northern Eurasia. In comparison, tree dominated vegetation classes in the forest belt of the region were ac- curately mapped, but were slightly overestimated (10%-20%), in all maps. Low agreement of global maps in the northern and southern vegetation transition zones of Northern Eurasia is likely to have important impli- cations for global change research, as those areas are vulnerable to both climate and socio-economic changes.