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A Survey of Buttresses and Aerial Roots of Tropical Trees for Presence of Reaction Wood

1982; Wiley; Volume: 14; Issue: 1 Linguagem: Inglês

10.2307/2387760

1744-7429

Jack B. Fisher,

Plant Physiology and Cultivation Studies

Wood from buttresses of 48 species in 20 families of tropical trees was examined microscopically for the presence of reaction wood (RW), indicated by gelatinous fibers in place of normal wood fibers. Only Eschlweilera (Lecythidaceae), Derris (Fabaceae), and three spp. of Ficus (Moraceae) had RW. All other species, including one specimen of Guarea (Meliaceae) in which the buttress was under tension due to a leaning trunk, had normal wood structure. Wood from aerial roots, including stilt roots and flying buttresses, of 18 species in six families was similarly examined. A cylinder of well-developed RW occurred in aerial roots of nine species of Ficus and in stilt roots of Cecropia (Moraceae). Reaction wood also occurred on the upper side of stilt roots of Cecropia and Pourouma (Urticaceae). Contraction of the aerial roots of Ficus is related to RW. However, although RW has been correlated wIth stresses in the wood of trunks and branches of many trees, RW cannot be related generally to a supportive role of buttresses in which stresses have been postulated previously. THE WIDESPREAD AND NOTICEABLE occurrence of buttressed trunks in tropical trees has long been interesting to biologists, and a variety of hypotheses have been offered to explain their cause and function (Richards 1952). One ccmmon assumption was that buttresses aided in the physical support of a tree, especially, when growing on shallow or wet soils, and Henwood (1973) demonstrated, on engineering principles, that buttresses do give added support to trees growing on poorly anchoring substrates and do reduce the stresses oin roolts caused by wind or uneven crown load as compared to trees with unbuttressed, cylindrical bases. Several publications are relevant to the supportive role of buttresses and suggest a survey of wood structure in buttresses and aerial roots. Reaction wood (RW) has been related to internal strains and stresses in trunk and branch wood (Trenard and Gueneau 1975, Scurfield 1973, Wilson and Archer 1977, 1979). Fayle (1976) found that secondary growth and RW formation were reduced in pine roots when plants were tied, thus preventing normal mechanical stresses. Mechanical stress has been suggested (but not widely accepted) as an inducer of RW by Boyd (1977). Since RW has been associated with stresses in branch, trunk, and root wood, and since buttresses should be subject to stresses in their supportive role, RW might be present and of importance in the buttresses of tropical trees. Chalk and Akpalu (1963) noted that several anatomical features were associated with species that produced buttresses, but they did not examine buttress wood for presence of RW nor compared trunk and buttress woods. To date, there has been only one careful study of buttress wood anatomy (Stahel 1971) in which some quantitative differences in percentages of cell types between trunk and buttress woods were found. In addition, Stahel ( 1971 ) looked for but found no RW in buttresses of the two species examined, Khaya (Meliaceae) and Piptadeniastrum