Leaf litter breakdown in natural and plantation forests of the Lama forest reserve in Benin

The Lama forest reserve in southern Benin, West Africa, comprises timber and fuelwood plantations as well as some of the country's last vestiges of semi-deciduous lowland forest. The reserve is intended to protect the fauna and flora and to promote the sustainable use of tree plantations. An important aspect in its management is the preservation of soil quality, which in turn is related to key ecosystem processes such as decomposition. In the present study, we examined the breakdown of leaf litter from two indigenous species Afzelial is africana (A. africana) and Ceiba pentandra (C. pentandra), and two exotic tree species Tectona grandis (T grandis) and Senna siatnea (S. siamea), using the litterbag technique (1920 litterbags altogether). We also studied the relationship between litter breakdown and the relative abundance (frequency of occurrence) of litter-dwelling invertebrates. The study was conducted over a 140-day period, focusing on four different forest types: semi-deciduous natural forest, young teak, old teak and fuelwood (mainly S. siatnea) plantations. Both main factors, litter species and forest type, had a significant effect on litter breakdown. The residual litter weight was lowest in A. africana, intermediate in S. siatnea and C. pentandra and highest in T. grandis. Differences were significant for all but one pairwise comparison (A. africana versus S. siamea). With regard to forest type, the breakdown was highest in natural forest, followed by young teak, old teak and firewood plantations. Except for teak plantations (young versus old teak), all comparisons were significant. We also found a significant litter x forest interaction, indicating dissimilar changes in litter breakdown across forest types. With the exception of teak, decay rate coefficients (k) were higher than in most tropical forests, ranging from k = 1.3 (T grandis in firewood plantations) to k = 4.7 (A. africana in natural forest). The frequency of occurrence of invertebrates differed among leaf litters and forests. while there was no significant litter x forest interaction. Higher frequencies were observed in indigenous than in exotic litter. Likewise, litterbags in natural forest attracted more invertebrates than those in forest plantations. We found a significant inverse linear relationship between invertebrate frequency and residual litter weight, indicating that the breakdown of litter was strongly related to the activity of invertebrates. Our study concludes that management practices should aim to enhance decomposer communities to safeguard the productivity and sustainable use of Lama forest. (C) 2004 Elsevier B.V. All rights reserved.