The influence of topography and soil phosphorus on the vegetation of Korup Forest Reserve, Camerouu*,** J. S. Gartlan 1, D. McC. Newbery2, D. W. Thomas 3 & P. G. Waterman4 z Wisconsin Regional Primate Center, University of Wisconsin, Madison, Wisconsin 53715, U.S.A.***" 2 Department of Biological Science, University of Stirling, Stirling, FK9 4LA, Scotland, U.K. ****" 3 Missouri Botanical Garden, P O. Box 299, St. Louis, Missouri 63166, U.S.A.," 4 Phytochemical Research Laboratory, Department of Pharmaceutical Chemistry, University of Strathclyde, Glasgow, G1 1XW,, Scotland, U.K. Keywords: Africa, Cameroun, Gradient, Korup, Phosphorus, Rain-forest, Topography Abstract All living trees (>_ 30 cm gbh) were enumerated in 135 80× 80 m plots, each subdivided into four 40x40 m subplots, and arranged along four 5 km transect lines in the Korup Forest Reserve, Cameroun. For each plot altitude, slope and the extent of permanent and seasonal swamps were recorded. Four hundred and eleven taxa were recognized of which 66% were identified to species. Mean tree density was 471 ha -1, basal area 27.6 m 2 ha -1 and number of species per plot 75. The subfamily Caesalpinioideae (Leguminosae) was the most abundant family/subfamily in terms of basal area, but the Scytopetalaceae the most frequently represented, mainly on account of Oubanguia alata. Ten plots had at least three quarters of their area permanently swamped, and three, to a similar extent, were seasonally swamped. The ranges in sand, silt and clay content were 60-91, 0-24 and 4-20% respectively. The pH value, organic carbon content and nitrate-nitrogen concentration ranged between 4.0-5.8, 1.3-5.7% and 0-35 ppm respectively. The largest soil variations were in available phosphorus, range 2-29 ppm, and potassium, 38-375 ppm. Correspondence analysis ordination of all plots showed a major indirect floristic gradient correlated with increasing altitude, slope and soil phosphorus and potassium. Removal of the topographic effect by separate re-ordinations of four groups of plots at low, middle (2) and high altitude/slopes highlighted a strong correla- tion of the main floristic gradients of the middle altitude/slope groups with the concentration of available soil phosphorus. Direct gradient analysis using all plots with respect to available soil phosphorus concentration confirmed the indirect analyses. Individual species response to phosphorus were also shown by direct comparisons in the vegetation on plots of high and low available soil phosphorus concentration. Low available phosphorus soils (_< 5 ppm) are strongly associated with species of the subfamily Caesalpinioideae, especially of the tribes Amherstieae and Detarieae. It is suggested that this result is probably due to the ability of these particular legume tribes to form associations with ectotrophic mycorrhizae. * The field work was supported by grant numbers RROO167-17, RROO167-18 and RROO167-19 from the Nation- al Institutes of Health for the operation of the Wisconsin Regional Primate Center, N.A.T.O. Scientific Affairs Division Grant number 1748 (to PGW and JSG), N.E.R.C. grant number GR3/3455 (to PGW), and was greatly facilitated by the skill and dedication of Ferdinand Namata. Meteorological data were kindly provided by E. P. Cundall (Plantations du Cameroun, Lob6). JSG acknowledges the support and encouragement of Sue Gartlan. In the field phase, JSG was a researcher attached to the National Office of Scientific and Technical Research Vegetatio 65: 131-148, 1986 © Dr W. Junk Publishers, Dordrecht - Printed in the Netherlands (ONAREST), Yaound6. We are grateful to I. Alexander and M. D. Swaine for comments on earlier drafts, R. Letouzey for checking the species nomenclature, the Computer Unit of the University of Stirling for facilities, M. Burnett for the typing at Stirling and the Department of Soil Science, University of Wis- consin, for undertaking the soil analyses. ** Nomenclature follows Aubr6ville (1963-1983). *** Publication No. 23-024 of the Wisconsin Regional Pri- mate Center. **** Reprint requests to D.McC.N. at Stirling.