Co-dominant Detarioideae (Leguminosae) tree species in the rain forests of Korup National Park, Cameroon

The tropical evergreen rain forest in south Korup National Park has been little influenced by human disturbance and past climatic change. Trees of the Leguminosae subfamily Detarioideae are common. Ten new Detarioideae tree species were described in the past eleven years; most of these are (near-) endemic to Korup National Park. They had not been recorded earlier because rainforest trees are easily overlooked and difficult to collect in fertile state. A mapping method was developed to map all Microberlinia bisulcata trees in a large grove. This grove had a size of 272 ha and consisted of 1028 M. bisulcata trees > 50 cm stem diameter. M. bisulcata occurs co-dominant with Tetraberlinia bifoliolata, T. korupensis and at least 21 other, less abundant, grove-forming Detarioideae trees. Many other tree species from many other families are present. There are no significant changes in soil type, topography, or other environmental factors between the M. bisulcata grove and the forest just outside this grove. The tendency of M. bisulcata and other Detarioideae trees to grow in groups is related to the relatively short and strictly limited maximum distance of the ballistic seed dispersal method, characteristic of these species. Co-dominance of Detarioideae trees may also be promoted by other factors such as their ectomycorrhizal habit. Ballistic seed dispersal explains the clear edge of the grove and the complete absence of M. bisulcata from the surrounding forest. The semi-circles of 100 – 200 m diameter of mature M. bisulcata trees at the grove's edge indicate that the grove had been expanding up to the time when these trees established. The presence at the edge of only a few juveniles, indicates that the grove is not expanding much since the present M. bisulcata trees became adults. M. bisulcata has been persistently dominant in the past, but the current deficiency of regeneration indicates M. bisulcata may lose much of its dominance in the near future

Buttress form of the central African rain forest tree Microberlinia bisulcata , and its possible role in nutrient acquisition

Buttressing is a trait special to tropical trees but explanations for its occurrence remain inconclusive. The two main hypotheses are that they provide structural support and/or promote nutrient acquisition. Studies of the first are common but the second has received much less attention. Architectural measurements were made on adult and juvenile trees of the ectomycorrhizal species Microberlinia bisulcata, in Korup (Cameroon). Buttressing on this species is highly distinctive with strong lateral extension of surface roots of the juveniles leading to a mature buttress system of a shallow spreading form on adults. This contrasts with more vertical buttresses, closer to the stem, found on many other tropical tree species. No clear relationship between main buttress and large branch distribution was found. Whilst this does not argue against the essential structural role of buttresses for these very large tropical trees, the form on M. bisulcata does suggest a likely second role, that of aiding nutrient acquisition. At the Korup site, with its deep sandy soils of very low phosphorus status, and where most nutrient cycling takes place in a thin surface layer of fine roots and mycorrhizas, it appears that buttress form could develop from soil-surface root exploration for nutrients by juvenile trees. It may accordingly allow M. bisulcata to attain the higher greater competitive ability, faster growth rate, and maximum tree size that it does compared with other co-occurring tree species. For sites across the tropics in general, the degree of shallowness and spatial extension of buttresses of the dominant species is hypothesized to increase with decreasing nutrient availabilit

Recruitment dynamics of the grove-dominant tree Microberlinia bisulcata in African rain forest: extending the light response versus adult longevity trade-off concept

In groves of ectomycorrhizal caesalpiniaceous species in the Atlantic coastal forest of Central Africa the dominant tree Microberlinia bisulcata, which is shade-intolerant as a seedling but highly light-responding as a sapling, shows very limited regeneration. M. bisulcata saplings were mapped in an 82.5-ha plot at Korup and found to be located significantly far (>40m) away from adults, a result confirmed by direct testing in a second 56-ha plot. Sapling growth over 6years, the distribution of newly emerging seedlings around adults, recruitment of saplings in a large opening and the outward extent of seedlings at the grove edge were also investigated. Two processes appear to have been operating: (1) a very strong and consistent restriction of the very numerous seedlings establishing after masting close to adults, and (2) a strong but highly spatially variable promotion of distant survivors by increased light from the deaths of large trees of species other than M. bisulcata (which itself has very low mortality rate). This leads to an apparent escape-from-adults effect. To maintain saplings in the shade between multiple short periods of release ectomycorrhizal connections to other co-occurring caesalp species may enable a rachet-type mechanism. The recorded sapling dynamics currently contribute an essential part of the long-term cycling of the groves. M. bisulcata is an interesting example of an important group of tropical trees, particularly in Africa, which are both highly light-demanding when young yet capable also of forming very large forest emergents. To more comprehensively explain tropical tree responses, the case is made for adding a new dimension to the trade-off concept of early tree light-response versus adult longevit

Transient dominance in a central African rain forest

The large-crowned emergent tree Microberlinia bisulcata dominates rain forest groves at Korup National Park, Cameroon, along with two codominants, Tetraberlinia bifoliolata and T. korupensis. M. bisulcata has a pronounced modal size frequency distribution around 110 cm stem diameter: its recruitment potential is very poor. It is a long-lived light-demanding species, one of many found in African forests. Tetraberlinia species lack modality, are more shade tolerant, and recruit better. All three species are ectomycorrhizal. M. bisulcata dominates grove basal area, even though it has similar numbers of trees (≥50 cm stem diameter) as each of the other two species. This situation presented a conundrum that prompted a long-term study of grove dynamics. Enumerations of two plots (82.5 and 56.25 ha) between 1990 and 2010 showed mortality and recruitment of M. bisulcata to be very low (both rates 0.2% per year) compared with Tetraberlinia (2.4% and 0.8% per year), and M. bisulcata grows twice as fast as the Tetraberlinia. Ordinations indicated that these three species determined community structure by their strong negative associations while other species showed almost none. Ranked species abundance curves fitted the Zipf-Mandelbrot model well and allowed “overdominance” of M. bisulcata to be estimated. Spatial analysis indicated strong repulsion by clusters of large (50 to <100 cm) and very large (≥100 cm) M. bisulcata of their own medium-sized (10 to <50 cm) trees and all sizes of Tetraberlinia. This was interpreted as competition by M. bisulcata increasing its dominance, but also inhibition of its own replacement potential. Stem coring showed a modal age of 200 years for M. bisulcata, but with large size variation (50–150 cm). Fifty-year model projections suggested little change in medium, decreases in large, and increases in very large trees of M. bisulcata, accompanied by overall decreases in medium and large trees of Tetraberlinia species. Realistically increasing very-large-tree mortality led to grove collapse without short-term replacement. M. bisulcata most likely depends on climatic events to rebuild its stands: the ratio of disturbance interval to median species' longevity is important. A new theory of transient dominance explains how M. bisulcata may be cycling in abundance over time and displaying nonequilibrium dynamics

Knowledge-Sharing Networks in Hunter-Gatherers and the Evolution of Cumulative Culture.

Humans possess the unique ability for cumulative culture [1, 2]. It has been argued that hunter-gatherer's complex social structure [3-9] has facilitated the evolution of cumulative culture by allowing information exchange among large pools of individuals [10-13]. However, empirical evidence for the interaction between social structure and cultural transmission is scant [14]. Here we examine the reported co-occurrence of plant uses between individuals in dyads (which we define as their "shared knowledge" of plant uses) in BaYaka Pygmies from Congo. We studied reported uses of 33 plants of 219 individuals from four camps. We show that (1) plant uses by BaYaka fall into three main domains: medicinal, foraging, and social norms/beliefs; (2) most medicinal plants have known bioactive properties, and some are positively associated with children's BMI, suggesting that their use is adaptive; (3) knowledge of medicinal plants is mainly shared between spouses and biological and affinal kin; and (4) knowledge of plant uses associated with foraging and social norms is shared more widely among campmates, regardless of relatedness, and is important for camp-wide activities that require cooperation. Our results show the interdependence between social structure and knowledge sharing. We propose that long-term pair bonds, affinal kin recognition, exogamy, and multi-locality create ties between unrelated families, facilitating the transmission of medicinal knowledge and its fitness implications. Additionally, multi-family camps with low inter-relatedness between camp members provide a framework for the exchange of functional information related to cooperative activities beyond the family unit, such as foraging and regulation of social life

Two new taxa in Magnistipula (Chrysobalanaceae) from Korup National Park, Cameroon

Background – In the course of the identification work of trees in the permanent plots around the “P transect” in the southern part of Korup National Park, Cameroon, two new taxa in Magnistipula Engl. were discovered. Key results – Magnistipula multinervia Burgt and Magnistipula butayei De Wild. subsp. korupensis Burgt (Chrysobalanaceae) are described and illustrated. M. multinervia is the thirteenth described species of Magnistipula. It is a rainforest tree to 41 m high with relatively small leaves (usually 7–10 cm long), and with stipules to 12 × 4 mm, with 10–20 parallel, longitudinal veins. M. butayei subsp. korupensis is the eleventh described subspecies of M. butayei. It is a rainforest tree to c. 30 m high with relatively elongated flowers and elongated persistent stipules. Conservation status – The two new taxa are only known from the southern part of Korup National Park in Cameroon. Both taxa are very rare; a survey done of 8936 trees over 10 cm stem diameter resulted in respectively four and fourteen trees registered of the two taxa. The numbers of known living trees presently are four and fifteen. The IUCN conservation status of both taxa is assessed as “Critically Endangered” CR D