Monitoring tree growth and mortality in central Africa

Tree growth and mortality are two central processes in mixed and structurally complex moist tropical forests. Yet, accurate estimates of the variables needed to model them remain sparse and scattered. It is thus still difficult to predict forest evolution at a local scale and build reliable management plans. To help fill this gap, from 2009 and up to now, we have annually monitored up to 21,000 trees belonging to 42 species exploited for timber production in Central Africa. To this end we set up a particular sampling scheme. We sampled tree individuals without establishing plots, while ensuring that at least 20 trees were measured per species, site and logging history. With this data, we successfully provided new species-specific estimates of diameter increments and mortality rates, and we could investigate the relationships between tree growth, tree size and logging history. The resulting estimates could help to make more accurate forest projections (e.g. with matrix population models) and draw up sustainable management plans. Yet, the within and between-site variability were substantial, and further long-term data collected in different sites would be needed to predict tree growth and especially tree mortality with accuracy under different ecological conditions. The pros and cons of this monitoring systems are then be discussed and compared to other approaches used to monitor forest dynamics.