Growth and photosynthesis of seedlings of four tree species from a dry tropical afromontane forest

Growth, photosynthesis and carbon allocation pattern were studied in four d ry afromontane forest tree species (Olea europea subspecies cuspidata, Podo carpus falcatus, Hagenia abyssinica and Juniperus procera) under varied lig ht regimes in a greenhouse. The objective of the study was to assess the po tential of the species for growth under forest canopies and to identify the ir habitat preferences. The light regimes were created using shade cloth an d the) corresponded with deep forest understoreys (2% of the light in the o pen gap); moderate shade (10%), slight shade as is found in edges of forest gaps (20%) and 100% representing open gaps. Seedling biomass was significa ntly influenced by light regimes for all species as were total leaf area an d relative growth rate. H. abyssinica had the highest growth rate but the l owest survival rate in shade. There was a consistent trend for higher speci fic leaf area (SLA) and leaf area ratio (LAR) at lower growth light regimes in O. europea and P. falcatus. O. europea and P. falcatus had similar allo cation patterns whereby between 20-40% of the total biomass uas allocated t o stem, 20-30% to roots and 50-60% to leaves. In H. abyssinica up to 80% wa s allocated to leaves and only a small percentage to stem and to roots. Within species there were significant differences in the light saturated ra te of photosynthesis (A(max)) per unit area among the plants grown at the l owest light level and in the open. For plants grown in the open there were ver): little among species differences in A,,,, per unit area. However, the re were significant differences in the ii,,, of the different species grown at the lowest light level. Chlorophyll fluorescence measurements indicated that open-grown P. falcatus and O. europea experienced moderate photoinhib ition. From the growth and photosynthesis results P. falcatus and O. europe a appeared to be non-pioneer, shade-tolerant species, while J. procera and to a larger extent H. abyssinica showed pioneer, light-demanding characteri stics. The results ar e discussed in terms of the occurrence of the species in the mosaic climaxes of afromontane forests.