Diversity and aboveground biomass in three tropical forest types in the Dja Biosphere Reserve, Cameroon

We present tree community diversity, species composition, basal area and aboveground biomass of three forest types in the Dja Biosphere Reserve, in South-East Cameroon, part of the contiguous tropical forest of the Congo Basin. A total of fourteen, 1 ha, plots were established in heterogeneous terra firme forests (TFF), Gilbertiodendron dewevrei forests (GDF) and periodically flooded forests (PFF). A total of 281 tree species with diameter >= 10 cm were recorded. The Shannon diversity index was significantly higher in TFF (5.7 +/- 0.28) and PFF (5.6 +/- 0.23) than in GDF (2.29 +/- 0.48) (ANOVA, F-2,F-11 = 139.75, P < 0.001). While tree density did not differ between forest types (F-2,F-11 = 3.50, P = 0.06), basal area differed significantly (F-2,F-11 = 7.38, P = 0.009), as did aboveground biomass (F-2,F-11 = 17.95, P < 0.001). Mean AGB values were respectively, 596.1 +/- 62.24, 401.67 +/- 58.06 and 383.14 +/- 61.91 Mg ha-1 in GDF, TFF and PFF. Variation in the abundance of trees with large diameter was the main reason for these differences. Few dominant species made the greatest contribution to the AGB. G. dewevrei, accounted for 83% of AGB in GDF, Penthaclethra macrophylla for 9.9% in TFF and Uapaca heudolotii for 10.6% in PFF. The importance of preserving G. dewevrei forest in the context of 'Reducing Emissions from Deforestation and forest Degradation' (REDD) policies is discussed.Resume Nous presentons la diversite des communautes d'arbres, la composition des guildes, la surface terriere et la biomasse aerienne de trois types forestiers de la Reserve de Biosphere du Dja, dans le sud-est du Cameroun, qui fait partie de la foret tropicale contigue du Bassin du Congo. Nous avons etabli un total de 14 parcelles, d'un hectare chacune, dans des forets heterogenes sur terra firma (FTF), dans des forets a Gilbertiodendron dewevrei (FGD) et dans des forets periodiquement inondees (FPI). Nous avons releve au total la presence de 281 especes d'arbres d'un diametre >= 10 cm. L'index de diversite de Shannon etait significativement plus eleve dans les FTF (5 7 +/- 0,28) et les FPI (5,6 +/- 0,23) que dans les FGD (2,29 +/- 0,48) (ANOVA, F-2,F-11 = 139,75, P < 0.001). Alors que la densite des arbres ne differait pas significativement entre les types forestiers (F-2,F-11= 3,50; P = 0,06), la surface terriere differait de facon significative (F-2,F-11 = 7,38; P = 0,009), tout comme la biomasse aerienne (F-2,F-11 =17,95; P < 0,001). Les valeurs de la biomasse etaient respectivement de 596,1 +/- 62,24, 401,67 +/- 58,06 et 383,14 +/- 61,91 Mg ha-1 dans les FGD, FTF et FPI. Une variation de l'abondance d'arbres de grand diametre etait la principale raison de ces differences. Quelques especes dominantes constituaient la plus forte contribution a la biomasse aerienne. G. dewevrei comptait pour 83% de la biomasse aerienne dans les FGD, Penthaclethra macrophylla pour 9,9% dans les FTF, et Uapaca heudolotii pour 10,6% dans les FPI. L'on discute de l'importance qu'il y a de preserver la foret a Gilbertiodendron dewevrei dans le cadre des politiques REDD (Reduction des emissions resultant du deboisement et de la degradation forestiere).