Abstract:

Stable forests exhibit high vegetation integrity and a relatively stable microclimate. Revealing the effect of changes in the greenness of stable forests on surface albedo can provide a quantitative basis for understanding energy exchange processes and forest responses to climate change. This study focused on the stable forests of Guizhou province, utilizing MODIS surface albedo, Enhanced vegetation index (EVI) and Fractional vegetation cover (FVC) data from 2001 to 2022. By employing Theil-Sen trend analysis, Mann-Kendall trend testing, correlation analysis and relative importance analysis, the temporal and spatial variations of surface albedo, EVI and FVC in Guizhou's stable forests were explored at monthly, annual and growing season scales, as well as the influence of greenness changes across different forest types on surface albedo. The results showed that: (1) from 2001 to 2022, the monthly surface albedo of evergreen broadleaved forests, evergreen needle−leaved forests and deciduous broadleaved forests in Guizhou exhibited insignificant patterns, peaking in July. The monthly average surface albedo ranked as follows: deciduous broadleaved forests > evergreen broadleaved forests > evergreen needle-leaved forests. (2) During 2001-2022, Guizhou's stable forests exhibited a significant interannual greening trend (P < 0.05). The spatial variations of surface albedo on both interannual and growing-season scales showed an increasing trend in the northwest and a decreasing trend in the southeast. Evergreen broadleaved forests were the dominant type driving the increase in surface albedo and forest greening (contributing >55%). (3) From 2001 to 2022, the surface albedo of Guizhou's stable forests exhibited a significant positive correlation (P<0.05) with EVI and FVC, indicating that forest greening did not reduce surface albedo but rather enhanced its shortwave radiation reflectance capacity. Among forest types, evergreen broadleaved forests demonstrate the most pronounced positive driving effect. 

Key words: Surface albedo, Enhanced vegetation index, Fractional vegetation cover, Spatiotemporal variation, Vegetation greenness