Canopy phenology of some mopane and miombo woodlands in eastern Zambia



Measurements of tree canopy closure and field-layer reflectance were made in a series of plots in protected areas of eastern Zambia as part of a multiyear study of savanna woodlands. The plots were located in the Luangwa Valley and adjacent plateaux, which contained a range of vegetation types found in southern Africa. The vegetation consisted of four broad types: 1.plateau miombo woodland; 2.valley miombo woodland; 3.scrub miombo woodland; and 4.scrub and woodland mopane. Hemispherical photographs of the tree layer provided measurements of tree canopy phenology in the different vegetation plots. The most seasonal woodland type was mopane, where tree canopy closure ranged from about 15% at the end of the dry season to just over 60% during the peak of the rains. Plateau miombo exhibited the lowest range of seasonality in the tree layer, ranging from about 40% to 60% closure over one complete seasonal cycle. Phenology of the field layer, expressed as the normalized difference vegetation index (NDVI), closely followed that of the tree layer, although the field layer senesced earlier than trees, especially in plots with relatively low tree canopy closure. The relationship between tree-canopy closure and field-layer NDVI was positive and statistically significant for all sites of the study area, which suggests that woody biomass and herbaceous biomass are related positively in these savanna woodland ecosystems.