Tropical forest recovery from logging: a 24 year silvicultural experiment from Central Africa

Large areas of African moist forests are being logged in the context of supposedly sustainable management plans. It remains however controversial whether harvesting a few trees per hectare can be maintained in the long term while preserving other forest services as well. We used a unique 24 year silvicultural experiment, encompassing 10 4 ha plots established in the Central African Republic, to assess the effect of disturbance linked to logging (two to nine trees ha(-1) greater than or equal to 80 cm DBH) and thinning (11-41 trees ha(-1) greater than or equal to 50 cm DBH) on the structure and dynamics of the forest. Before silvicultural treatments, above-ground biomass (AGB) and timber stock (i.e. the volume of commercial trees greater than or equal to 80 cm DBH) in the plots amounted 374.5 +/- 58.2 Mg ha(-1) and 79.7 +/- 45.9 m(3) ha(-1), respectively. We found that (i) natural control forest was increasing in AGB (2.58 +/- 1.73 Mg dry mass ha(-1) yr(-1)) and decreasing in timber stock (20.33 +/- 1.57 m(3) ha(-1) yr(-1)); (ii) the AGB recovered very quickly after logging and thinning, at a rate proportional to the disturbance intensity (mean recovery after 24 years: 144%). Compared with controls, the gain almost doubled in the logged plots (4.82 +/- 1.22 Mg ha(-1) yr(-1)) and tripled in the logged + thinned plots (8.03 +/- 1.41 Mg ha(-1) yr(-1)); (iii) the timber stock recovered slowly (mean recovery after 24 years: 41%), at a rate of 0.75 +/- 0.51 m(3) ha(-1) yr(-1) in the logged plots, and 0.81 +/- 0.74 m(3) ha(-1) yr(-1) in the logged + thinned plots. Although thinning significantly increased the gain in biomass, it had no effect on the gain in timber stock. However, thinning did foster the growth and survival of small-and medium-sized timber trees and should have a positive effect over the next felling cycle.