Global Ecology and Biogeography (1999) 8, 199–209 TROPICAL OPEN WOODLANDS SPECIAL ISSUE Canopy phenology of some mopane and miombo woodlands in eastern Zambia DOUGLAS O. FULLER Department of Geography, The George Washington University, Washington, DC 20052 USA, E-mail: dfuller@gwis2.circ.gwu.edu ABSTRACT rains. Plateau miombo exhibited the lowest range of seasonality in the tree layer, ranging from about Measurements of tree canopy closure and field-layer 40% to 60% closure over one complete seasonal reflectance were made in a series of plots in protected cycle. Phenology of the field layer, expressed as areas of eastern Zambia as part of a multiyear study the normalized difference vegetation index (NDVI), of savanna woodlands. The plots were located in closely followed that of the tree layer, although the the Luangwa Valley and adjacent plateaux, which field layer senesced earlier than trees, especially in contained a range of vegetation types found in plots with relatively low tree canopy closure. The southern Africa. The vegetation consisted of four relationship between tree-canopy closure and field- broad types: 1. plateau miombo woodland; layer NDVI was positive and statistically significant 2. valley miombo woodland; 3. scrub miombo for all sites of the study area, which suggests that woodland; and 4. scrub and woodland mopane. woody biomass and herbaceous biomass are related Hemispherical photographs of the tree layer positively in these savanna woodland ecosystems. provided measurements of tree canopy phenology in the different vegetation plots. The most seasonal Key words. Canopy phenology, Zambezian wood- lands, mopane woodland, miombo woodland, woodland type was mopane, where tree canopy closure ranged from about 15% at the end of the hemispherical photography, NDVI, Luangwa Valley, tree–grass interactions. dry season to just over 60% during the peak of the INTRODUCTION Numerous papers on savanna biogeography have emphasized the spatio-temporal dynamics of trees and The duration and intensity of leaf display, or canopy grasses and particularly changes in woody plant density phenology, can provide an indicator of the many associated with changes in various environmental environmental resources, such as water, soil nutrients, factors (Belsky, 1990; Amundson et al., 1995; Mordelet and solar radiation, which control physiological & Menaut, 1995). Theoretical work by Walker and processes in plants. Canopy phenology also provides colleagues (Walker et al., 1981; Knoop & Walker, 1985) a fundamental descriptor of vegetation type and suggested that competitive interactions between these function. For example, the terms deciduous, two life forms explained many observed changes in semideciduous, and evergreen suggest the type of tree-grass ratios and that competition is strongly biased environment in which plants are found and plant in favour of trees (Scholes & Walker, 1993). Work by adaptive strategies with respect to environmental Belsky and colleagues (Belsky, 1990; Amundson et al., factors like nutrients, water, and solar radiation 1995), Harrison (1984) and Weltzin & Coughenour (Grime, 1979). Changes in canopy phenology over (1990) also showed that habitats beneath trees have a several seasons or years may also indicate more favourable water regime and are more nutrient anthropogenic land-cover change (Millington & rich than habitats in the open. This is because trees Townshend, 1989; Azzali, 1991) or changes associated intercept a significant fraction of incident solar with climatic shifts (Walker, 1991; Goward & Prince, 1995; Fuller & Prince, 1996). radiation and return nutrients to the soil as litter each 199  1999 Blackwell Science Ltd. http://www.blackwell-science.com/geb