3.4.1. LAI Performance of Different Biome Types and Climate Zones

We then studied the LAI performance for each biome type and climate zone. According to the WestDC land cover classification system, we selected all the vegetation types and merged similar types. For instance, shrubs and open shrubs were merged into shrub, and we regarded woody savannas and savannas as savannas. Finally, we selected nine biome types for further study. According to the Koppen climate classification system, we listed 18 climate zones in China for analysis. Table 4 shows the mean SD and RSD for each biome type and Table 5 shows the similar climate zone results.


**Table 4.** Mean SD and RSD for each biome type.


**Table 5.** Mean SD and RSD for each climate zone.

For biome types (Table 4), the result of mean SD shows that evergreen broad forest (EBF), evergreen needleleaf forest (ENF), and savanna (SAV) have the highest difference, with mean SD of 0.75, 0.72, and 0.54, respectively; while grassland (GRA), deciduous needleleaf forest (DNF), and cropland (CRO) have the lowest mean SD, with mean SD of 0.17, 0.23, and 0.26 respectively. When considering mean RSD, the highest discrepancy occurs in evergreen needleleaf forest (ENF), shrub (SHR), and savanna (GRA), while the lowest difference occurs in deciduous needleleaf forest (DNF), deciduous broadleaf forest (DBF), mixed forest (MF), and cropland (CRO). One thing worth mentioning in Table 4 is that the RSD for almost all biomes is on the order of 0.3, which indicates a typical 30% uncertainty for LAI products.

For climate zones (Table 5), tropical savannah, tropical monsoon, and temperate warm summer no dry season climate show the highest mean SD; the values are 0.80, 0.74, and 0.71. Cold dry cold summer, cold dry warm summer, arid cold desert, and polar tundra show the lowest SD with values of 0.05, 0.06, 0.09, and 0.09. From the perspective of RSD, cold zone dry and cold summer, cold zone dry and warm summer and temperate warm summer/dry winter climate show the highest RSD (values of 0.60, 0.47, and 0.38), while cold dry winter/hot summer, cold dry winter/warm summer, and cold dry winter/cold summer show the lowest RSD, with values of 0.25, 0.24, and 0.24. From Table 5, it is also confirmed that, for most climate zones, the RSD is on the order of 0.3 and in line with the findings from biome types.

Figure 12 shows the bar plots of spatial average LAI differences for each biome type. Compared with MODIS LAI, the other three products all have positive bias for all biome types (Figure 12a–c). It means the three newly developed LAI datasets have larger values than their basis for all land cover types. For GLASS LAI, six of the nine biome types have a difference higher than 0.4: cropland is nearly 0.4, DNF is 0.2, and grassland has the lowest difference with less than 0.1. For GLOBALBNU, the differences of most types are 0.4, DNF and cropland are 0.2, and grassland is also the lowest (less than 0.1). For GLOBMAP, ENF shows the highest difference (more than 1), and grassland and cropland have the lowest difference (less than 0.1). For GLASS and GLOBALBNU (Figure 12d), DNF and grassland are almost the same; differences of the other types are 0.2 or so. For GLASS and GLOBMAP (Figure 12e), cropland has a large positive difference while ENF has a large negative difference, and grassland, savannas, and EBF have the lowest difference. For GLOBALBNU and GLOBMAP (Figure 12f), most of the differences are negative, the highest difference of which occurs in ENF. This means both GLASS and GLOBMAP have larger values than GLOBALBNU for most biome types.

**Figure 12.** LAI value difference between LAI climatologies for each biome type: (**a**) GLASS-MODIS; (**b**) GLOBALBNU-MODIS; (**c**) GLOBMAP-MODIS; (**d**) GLASS-GLOBALBNU; (**e**) GLASS-GLOBMAP; (**f**) GLOBALBNU-GLOBMAP. ENF represents evergreen needleleaf forest, EBF represents evergreen broadleaf forest, DNF represents deciduous needleleaf forest, DBF represents deciduous broadleaf forest, MF represents mixed forest, SHR represents shrubland, SAV represents savannas, GRA represents grassland, and CRO represents cropland).

Figure 13 illustrates LAI difference between six pairs of LAI products for each climate type. GLASS has a more positive bias than MODIS for almost all climate types except Dsc and Dsb, and most of the difference values are in the range of 0–1 (Figure 13a). GLOBALBNU has a positive bias compared with MODIS for all climate types, and the difference values are relatively low (within 0.5 or so) (Figure 13b). For GLOBMAP, the LAI difference values for 11 out of 18 climate types have a positive bias, and seven have a relatively low negative bias (within −0.3 or so): Bwk, Bsh, Bsk, Csb, Dsb, Dsc, and ET. Comparing Figures 12 and 13, it can be found that GLOBALBNU has larger values than MODIS for all biome types and climate zones.

**Figure 13.** LAI value comparison for each climate type: (**a**) GLASS-MODIS; (**b**) GLOBALBNU-MODIS; (**c**) GLOBMAP-MODIS; (**d**) GLASS-GLOBALBNU; (**e**) GLASS-GLOBMAP; (**f**) GLOBALBNU-GLOBMAP.

Compared with GLOBALBNU, GLASS has a positive bias within 0.3 for 12 climate types, and negative bias for the other six climate types (Figure 13d). Compared with GLOBMAP, GLASS has a positive bias for 15 climate types and most of the bias is within 0.4, while there is a negative bias for the other three climate types (Figure 13e). Compared with GLOBMAP, GLOBALBNU has a positive bias within 0.6 for 13 climate types, and negative bias within −0.6 for the other five climate types.
