## 7 The Arctic in Global Land Cover Maps
Figures 3-5 provide a direct comparison of their classes with the CAVM. ECOCLIMAP contains significantly more global classes than the other maps, which use the FAO system. Their number is however similar in the Arctic domain. The actual thematic detail is lower for ECOCLIMAP, as it provides separate classes for North America and Asia for the same land cover type, but it is the only map that includes a tundra class. This class covers however only a very small proportion within the CAVM domain. It has been demonstrated that global land cover datasets disagree especially in the transition zone from boreal to tundra [129,130]. Furthermore, the classes bare and shrub covered have been differently assigned [129]. This has been demonstrated when compared to selected Landsat-based land cover maps. It has also been pointed out by [PERSON] et al. [1] that shrublands cannot be resolved in coarse resolution global maps. Figure 4: Comparison of ECOCLIMAP classes with CAVM [5]. Figure 5: Comparison of CCI Land Cover 2010 classes with CAVM [5]. Already a visual comparison of the CAVM with global maps demonstrates the limited thematic content of global maps in the Arctic (Figure 2). The classes available from the CAVM (which represent vegetation communities) show largely different spatial patterns than the classes in the global maps, as they differ significantly by their definition (Table 3). The CCI land cover product has received increasing attention in recent studies. It includes a high latitude dedicated'mosses and lichens' class. The full name is 'closed to open (>15%) herbaceous vegetation (grassland, savannas or lichens/mosses)'. It is expected by users that mosses and lichens have a certain thickness and are cooling the ground [131]. This class corresponds however largely to mountain complexes with cryptogam crusts over the CAVM domain in the CCI map. These are very thin and often show a large active layer thickness [68; 71]. A large proportion of this class also corresponds to dwarf shrub tundra, mostly of the graminoid type (see Figure 5). Lichens and mosses can be found within most land cover types in the high latitudes [100]. The species composition and amount differ between vegetation communities. A certain lichen coverage is associated with land cover types that can be identified with Landsat. [PERSON] and [PERSON] [103] demonstrated that lichen coverage increases reflectance across all Landsat channels. The higher the reflectance, the higher the lichen coverage. Grazing reduces the lichen height and, thus, also reflectance [95]. Large areas are affected by reindeer herding, as well as wild herds. Thematic detail with respect to shrubs is highest for the ECOCLIMAP map. It distinguishes between closed and open shrublands. The closed shrublands correspond mostly to dwarf and low shrub tundra. The majority of shrub categories of the CAVM are however classified as open shrubland, which can be found in almost all CAVM classes (Figure 4) and is also the most common one with 37%. The GLC2000 also separates herbaceous from shrub cover over the Arctic. The most dominant class is'sparse herbaceous or sparse shrub cover' (about 40%; Figure 3). Similar classes are included in the CCI land cover legend, but not mapped over the Arctic. This class named 'closed to open (>15%) (broadleaved or needle-leaved, evergreen or deciduous) shrubland (<5 m)' can be found in steppe zones and covers large areas of the Tibetan plateau, which is also a permafrost-affected region. Moreover, Western Greenland is inconsistent with the Arctic class pattern in the CCI product. It is the only region in the Arctic mapped as grassland. The majority (approximately 33%) is mapped as sparse vegetation (with less than 15% vegetation coverage). Although dominant classes are similar in quantity across the different maps, they overlap only partially. Water surfaces in all global maps are better resolved than in the CAVM. Table 3 lists classes of the global maps, as well as CAVM within the extent of the multi-purpose maps described in Section 3.