Diameter Growth of a Few African Rainforest Species

ACCROISSEMENTS DIAMÉTRIQUES

S Y N O P S I S

DIAMETER GROWTH OF A FEW AFRICAN RAINFOREST SPECIES

LUC DURRIEU DE MADRON, ROBERT NASI, PIERRE DÉTIENNE

The present paper summarizes the results of overestimated because some growth such as bossé clair (Guarea cedrata) a study on the growth of 17 timber species rings were unclear and therefore diffi- and kotibé (Nesogordonia papaver - that are commonly logged in African rain- cult to measure. There were often false i f e r a). In pioneer species such as obeche forest areas : aningré (Aningeria altissima), rings that were not identified as such, (Triplichiton scleroxylon), limba obeche (Triplochiton scleroxylon), bossé or very fine undetected rings, especial- (Terminalia superba) and okoumé clair (Guarea cedrata), dabema ly in sapelli. There could also have (Aucoumea klaineana), diameter growth (Piptadeniastrum africanum), dibétou been measurement errors due to as- was found to be about 1 cm/year, with (Lovoa trichilioides), iroko (Milicia excelsa), sessment problems in periods when the trunk diameters ranging from 20 to 100 kosipo (Entandrophragma candollei), studied tree had not reached the cm. Within the framework of the Sangha kotibé (Nesogordonia papaverifera), canopy (stunted growth). Much interest- Mbaéré project, the sampling results re- limba (Terminalia superba), longhi ing information was obtained in the vealed constant diameter growth rates (Gambeya boukokoensis), moabi few years beginning in the 1980s, for ayous and sapelli in each diameter (Baillonella toxisperma), niangon (He r i t i e r a when the girths of standing trees were c l a s s . ut i l i s ), okoumé (Aucoumea klaineana), measured periodically, but the mea- sapelli (Entandrophragma cylindricum), surement period was not long enough These results will be useful for the pur- sipo (Entandrophragma utile), tali to cover the lifespan of the trees. poses of tropical rainforest manage- (Erythrophleum ivorense) and tiama Comparisons with growth rates calcu- ment. As no reliable growth data were (Entandrophragma angolense). lated on the basis of growth ring analy- previously available, the periods be- ses involving direct measurements of In addition, the data are compared with tween two felling operations (rotation) trunk circumferences should therefore the results of growth ring analyses that were determined at random, and not be interpreted with caution. were carried out in Cameroon, the based on any biological rationale. The Nevertheless, the growth rates ob- Central African Republic and Gabon. data that we present here could be use- tained were generally close enough to The data were collected in a series of ful for forest managers, but it should be establish quite accurate growth ranges sampling campaigns to monitor trunk kept in mind that only a few species that could prove useful for determining girths in tree plots (Côte d’Ivoire, were covered. Indeed, these data pro- rotations between two logging opera- Cameroon, Central African Republic, vide an indication of the trends, but they t i o n s . Ghana and Gabon). They will provide a should be confirmed by further measure- basis for calculating rotations between ments, e.g. growth data for moabi potential successive logging operations (Baillonella toxisperma). Moreover, RESULTS within the framework of forest develop- f u r ther in-depth studies on this topic ment projects. Comparisons of the results highlighted a would be highly recommended to be mean diameter growth range of 4- able to determine annual growth rates, 5 mm/year for E n t a n d r o p h r a g m a s p . per diameter class, of the main species COMPARISONS (sapelli, sipo, kosipo and tiama) and – this would facilitate calculations The mean growth estimates based on iroko (Milicia excelsa). It ranged from 2- of the periods between two felling growth ring analyses were probably 3 mm/year for slow-growing species o p e r a t i o n s .

74 BOIS ET FORÊTS DES TROPIQUES, 2000, N° 263 (1)