Abstract

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 m3 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 (−0.33 ± 1.57 m3 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 m3 ha−1 yr−1 in the logged plots, and 0.81 ± 0.74 m3 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.

Highlights

  • The forests of Central Africa (186.9 million ha, comprising 90% of lowland forests [1]) are facing increasing anthropogenic pressure

  • To get the timber stock (V80), we summed the vs values of trees greater than or equal to 80 cm DBH belonging to 39 timber species, 16 of which had harvestable trees in 1984

  • Almost three decades of observations in 40 ha of initially preserved old-growth forests highlighted that (i) natural forests in the area store high levels of above-ground biomass (AGB) and are still accumulating biomass; (ii) the AGB recovers very fast after logging and thinning, at a rate proportional to the disturbance intensity; and (iii) the timber stock recovers slowly and remains far from initial levels accumulated over long periods

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Summary

Introduction

The forests of Central Africa (186.9 million ha, comprising 90% of lowland forests [1]) are facing increasing anthropogenic pressure. Between 1984 and 1985, seven 4 ha plots were selectively logged, i.e. the harvested trees belonged to 16 timber species and were greater than or equal to 80 cm DBH (list in electronic supplementary material, table S1). To get the timber stock (V80), we summed the vs values of trees greater than or equal to 80 cm DBH belonging to 39 timber species, 16 of which had harvestable trees in 1984 (list in electronic supplementary material, table S1). Because the observations had been made on the same subplot over time, and because the subplots shared the same local environment at plot scale, we again used a linear mixed model to take into account both temporal and spatial autocorrelations (details in electronic supplementary material, method section S3). Linear mixed models were fitted with lme and nlme packages

Results
Discussion
30. Lewis SL et al 2009 Increasing carbon storage
Findings
32. Baker TR et al 2004 Increasing biomass in

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