Since 1984 in the field, and based on data analyses from 1981, we have made a long-term integrated effort towards understanding how high forest is maintained on very poor soils under strongly seasonal weather conditions. In Korup an important group of tree species in the Caesalpiniaceae (Leguminosae) form large groves (patches co-dominated by three main species) within a matrix of other forest trees. These groves are distinct, the main one in southern Korup - which has been the focus of our interests - being ca. 2 km long and 1 km wide. The three main caesalps, Microberlinia bisulcata, Tetraberlinia bifoliolata and T. moreliana (=korupensis) are very large, frequently buttressed, deciduous and strongly ectomycorrhizal species. They form the groves on the soils with the lowest phosphorus (P) concentrations. Much of our earlier work concentrated on establishing the phosphorus cycle, on mycorrhizal studies, on soils and the surface root mat which led to a clear understanding of how the tight but mobile P cycle was maintained in the face of extreme wet season leaching and dry season leaf loss. This work has involved studies of phosphorus fractionation in soils, litter fall, decomposition, and seedling transplants.

The main work of 1984-1990 benefited greatly from the existence of a set of 135 80-m x 80-m plots enumerated by a team in the late 1970's led by Dr JS Gartlan. Analysis of those data with further field work led to new hypotheses of how this forest might function. Then with two grants form the European Union - DGXII it was possible to advance by setting up the present large 82.5 ha plot, follow tree phenology over many years, undertake extensive nursery experiments, further detailed nutrient-cycling studies, a fertilization trial (in a another smaller grove outside of the Park), and studies of size distribution, growth and dynamics of the trees with several seedling demographic studies.

The work continues presently with support from the Swiss National Science Foundation to set up a second large (56-ha plot) in a connecting grove, further phenological studies, extended tree dynamics for mortality and growth, measurement of a plantation trial of 1986 using M. bisulcata, and nursery work on water stress with saplings. The main research began in 1984 when DM Newbery was in Stirling University, Scotland, and has continued with his move to Bern University, Switzerland, in 1996. Please refer to the publications list.

M. bisulcata is the dominant species in the groves but its regeneration is very poor. The species is mast fruiting (every ca. 3 yr) and of the extensive carpets of seedlings almost none survive over 5 yr. Nursery experimentation and field transplants of this and other species point to a low tolerance to shade combined with herbivory and or pathogen attack. Yet in the light M. bisulcata is highly responsive. Saplings can grow in the complete open. There are very few medium and small trees in the forest which suggest that this species has established stands in the past in response to climatic events which opened the forest and favoured it. We have suggested that major drought periods in previous centuries have been the driving factor. This situation is not unusual at least among African canopy species and illustrates the Aubréville-Letouzey phenomenon: cycles of dominance and replacement on the landscape determined by extreme events. Our recent and present work has concentrated on trying to understand this dynamics and how it interfaces with the ecosystem P-cycle. The mast fruiting is related to climatic variability especially the timing and intensity of the dry season in Korup: a fascinating aspect of the forest which links to P-flux (leaf litter - P shunts), to seedling demography and to carbon balance considerations. The two Tetraberlinia species coexist with M. bisulcata but have smaller sizes, faster dynamics (mortality rates much higher), and better regeneration. Nevertheless, we now have shown that M. bisulcata has a very fast tree growth rate once it has established.

The key summarizing phrases of the work are: ecosystem phosphorus cycle, grove formation and tree dynamics, regeneration release, mast fruiting, forest cycles and climate drivers, and fragile stability and the surface soil layer.

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