Post-harvest silviculture shapes long-term structural recovery of logging gaps in Amazonia

Reduced-impact logging (RIL) in the Amazon can allow recovery of aggregate timber stocks within conventional 25–35-year cutting cycles, but this does not necessarily restore the abundance and composition of commercial species. Post-harvest silvicultural interventions may overcome this limitation, but empirical evidence remains scarce. We evaluated structural recovery 17–19 years after RIL in 70 canopy gaps created by tree felling under four treatments: Control (standard RIL without additional intervention), Tending (liberation of naturally regenerated commercial trees), Planting-1 (enrichment planting of 10 commercial species without logging-residue removal), and Planting-2 (enrichment planting of five commercial species with logging-residue removal), with both planting treatments subsequently receiving tending. We quantified basal area, commercial volume, diameter structure, and periodic annual increments, and used structural equation modelling to identify drivers of basal-area recovery. Treatments affected basal area and volume (P < 0.001). Planting-2 showed the highest structural recovery, with 4.76 m² ha⁻¹ of basal area and 48.7 m³ ha⁻¹ of volume, followed by Tending, Planting-1, and Control. Annual basal-area and volume increments followed the same pattern, with Planting-2 exceeding Control by more than fivefold. Mortality of monitored commercial trees was the strongest constraint on final basal area (β = −0.58, P < 0.001), whereas treatment exerted predominantly direct effects. Projections to 35 years indicated that recovery in untreated logging gaps is unlikely to restore pre-harvest structural reference conditions, whereas the Planting-2 treatment showed the highest potential for approaching or exceeding the structural range represented by the pre-harvest reference stock classes. These results demonstrate persistent differences in structural recovery trajectories nearly two decades after logging and indicate that post-harvest silviculture can accelerate structural recovery.