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

Abstract

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 availability.

Seed fate and seedling dynamics after masting in two African rain forest trees

“…Microberlinia bisulcata (hereafter just Microberlinia) is a large, moderately long-lived canopy-emergent tree that forms extensive buttresses (Newbery et al 2009), whereas Tetraberlinia bifoliolata (hereafter just Tetraberlinia) does not grow as large as Microberlinia and forms rather indiscriminate buttresses (,1.0 m tall or long). Both species produce discoid seeds ( Fig.…”

Transient dominance in a central African rain forest

“…Thus, M. bisulcata led to one or both of the codominants, as well as its own medium-sized trees, being ''displaced,'' which can be interpreted as indirect evidence of its considerable competitive influence. The most likely mechanism behind that competitive dominance is not simply the numerical abundance of M. bisulcata (which was roughly on a par with each of the Tetraberlinia species), but the species' much greater size and biomass, expressed in terms of a combination of its height typical of a main canopy-emergent tree, and its very wide canopy spread and extensive lateral buttresses and rooting extent (Newbery et al 2009), than nearly all other tree species at Korup. Microberlinia bisulcata ''sets the scene,'' biotically and abiotically, above-and belowground.…”

“…Total tree heights for 15 trees of M. bisulcata in the P plot were previously reported in Newbery et al (2009), and heights to lower branches were taken on these and 15 others on 3 July 2010 using a clinometer. Likewise, heights were recorded for 10 randomly selected suitable trees each of T. bifoliolata and T. korupensis on 21 April 2010.…”

“…The species forms tall emergent trees with large domed and spreading crowns and extensive buttressing (Newbery et al 2009). It is found together with two other caesalpiniaceous species that co-dominate the groves, Tetraberlinia bifoliolata and T. korupensis (Newbery et al 1998), and all three species, as well as several others less abundant, are ectomycorrhizal (Newbery et al 1988(Newbery et al , 2000.…”

On the geometry and allometry of big-buttressed trees - a challenge for forest monitoring: new insights from 3D-modeling with terrestrial laser scanning

“…A study in southwest China shows that the percentage of buttressed trees is highest in the larger diameter classes (He et al 2013). Buttresses are complex features that are regarded as an adaptation to poor tropical soils, enabling trees to form a flat root system in the upper, nutrient richer soil layers while maintaining their mechanical stability and anchorage (Richards 1952, Richter 1984, Ennos 1993, Crook et al 1997, Newbery et al 2009, Niklas 2013. Usually Dipterocarpaceae, Ligumninosae and Sterculiaceae show a greater tendency to produce buttresses than other tree species.…”