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

Abstract

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*D
2 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 and
disturbed 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 Cameroon