Litter decomposition and nutrient dynamics of ten selected tree species in tropical rainforest of Ebom, southwest Cameroon

Litter decomposition processes in tropical rainforests are still poorly understood. Leaf litter decomposition and nutrient dynamics of ten contrasting tree species, Entandraphragma utile, Guibourtia tessmannii, Klainedoxa gabonensis, Musanga cecropioides, Panda oleosa, Plagiostyles africana, Pterocarpus soyauxii, Strombosia scheffleri, Vitex grandifolia and Xylopia aethiopica were studied in the tropical rainforest of Ebom, Southwest Cameroon. After 23 weeks of field incubation in litterbags, mass loss of litter samples varied from 24.08% in E. utile to 92.35% in V. grandifolia. Decomposition rate constants (k) ranged from 0.014 in M. cecropioides to 0.165 week-1 in V. grandifolia. The nutrient content in original litter samples also varied widely among species and showed low levels of Na, P and Mg, and high levels of N, Ca and K. Averagenutrient releases was 89.04%, 60.80%, 46.19%, 40.99% and 24.17% of mean initial content for K, Ca, Mg, N and P, respectively. For nutrient-related litter chemistry, correlations with the mass losses at the end of litter incubation were significant (

Above-ground biomass and nutrient accumulation in the tropical rainforests of southern Cameroon: effects of logging

Impact of logging activities on nutrient cycling in tropical rainforests of southern Cameroon has been little investigated. A study was initiated by the Tropenbos-Cameroon Programme to determine changes in above-ground phytomass and nutrient stock following selective logging in Ebom rainforest of Southern Cameroon. One hundred and twelve (112) trees were sampled in three undisturbed plots of 10m x10m. Their diameters and dry mass were determined. Allometric equations (Y = a + b*D + c*D2 and Y = a’*D b’ ), relating dry mass of foliage, branches, trunks with barks, and total biomass to diameter at breast height (DBH), were developed to estimate the above-ground tree biomass of undisturbed anddisturbed forests. Understorey biomass was estimated by harvesting method. The total above-ground tree biomass is about 583 t.ha-1dry mass in the undisturbed forest. This contains 302 t.ha-1 C and a nutrient capital of 8888 kg.ha-1N, 6953 Ca, 2337 K, 436 P, 311 Mg and 30 kg. ha-1 Na. The stores of nutrient in the above-ground biomass was about 2 (311 and 175 kg ha-1) to 16 (436 and 28 kg. ha-1) times higher than in the top soil stock, respectively for Mg and available P. The losses of carbon and nutrients associated with timber extraction represented less than 7% of store in the above-ground biomass for all nutrients. This means that the impact of logging in the Ebom rainforest remains low. However, additional research is needed on nutrient input in the forest from outside as well as on the impact of logging on nutrient leaching in order to get a complete picture of the nutrient cycles.Key-words: phytomass, nutrient pools, logging, allometric equations, tropical rainforest, Southern Cameroo

Fine root production and distribution in the tropical rainforests of south-western Cameroon: effects of soil type and selective logging

Little information on fine roots that play an important role in nutrient cycling was available in tropical rainforests. Distribution of fine root production and effects of selective logging on root biomass and nutrient content change were studied in the tropical rainforests of south-western Cameroon. Twenty five root samples were excavated in each of two soil depths (0-10 and 10-25 cm) and in each of three undisturbed forests (Ebom, Ebimimbang and Nyangong) and one disturbed forest by logging, using a square metallic frame of 25 x 25 cm and 30 cm high. Root samples were categorized in three diameter classes: fine (<2 mm), small (2-5 mm) and medium roots (5-20 mm). Root biomass of three diameter classes and nutrients (N, Ca, Mg, K, Na and P) of the two first diameter classes were determined. Results have shown that total root biomass varied from 9.62 (Ebom) to 29.88 t ha-1 (Ebimimbang); those of fine roots decreased from Nyangong (7.43 t ha-1) to Ebom (1.74 t ha-1). In the top soil, the fine root biomass was 2 to 4 time lower in Ebom (1.43 t ha-1) than in other undisturbed forests (3.28 and 5.87 t ha-1). From 70 to 80% of fine root biomass were produced in the first 10 centimeters of soil depth. Nutrient amount in fine root biomass were also lower in Ebom than in Ebimimbang and Nyangong, except the P amount (kg ha-1) which remained high in Ebom. On the contrary, no pattern of nutrient content (g kg-1) changes among forest were found, except N and P that decreased from Ebom to Nyangong. Six years after logging, its effects on root biomass and nutrient changes were not significant and during this period, root production of disturbed forest was high due to rapid regeneration of forest particularly heliophilous tree species