New-generation permanent sampling sites to monitor forest dynamics in central Africa: Results from the Republic of Congo

Abstract

Managing tropical production forests sus-tainably requires knowledge of their diver-sity and dynamics, and of logging impacts on their characteristics. The necessary knowledge can be obtained by establi-shing large permanent sampling plots wit-hin which trees can be regularly measured. Such a monitoring experimental site exists in central Africa. It was settled in 1982 at M'Baïki, Central African Republic, and has provided reference standards to develop forest management and planning rules for many logging concessions in the region. Several projects have since established new monitoring experimental sites, focu-sing mainly on areas with different geo-logical substrates. Two of these sites are located in managed logging concessions in the north of the Republic of Congo, on Cenozoic alluvia (Loundoungou) and on Mesozoic Carnot sandstone (Mokabi). Each site comprises two 400 ha blocks, each containing a trail of about 4,000 trees belonging to twenty commercial species and two 9 ha plots in which all trees more than 10 cm in diameter are measured. One block is logged after a few years of moni-toring, with the second remaining as a control. Establishing a monitoring experi-mental site and making the first inventory required, on average, 34 months of work with a team of 8 people, at an average total cost of 94,500 €. The characteristics of the stands in the Loundoungou and Mokabi plots were, respectively: 240 and 230 tree species; densities of 346.8 (± 5.8) and 426.8 (± 3.6) trees/ha; biomass 432.6 (± 13.8) and 457.3 (± 9.3) Mg/ha. This paper analyses the difficulties encoun-tered in establishing the sites (position, location of the plots, setting up the trails, applying the inventory protocol, logistics, etc.) and puts forward several recommen-dations to improve both the establishment of such monitoring experimental sites and the inventory protocol.