Vegetation structure, phenology, and regeneration in the natural and anthropogenic tree-fall gaps of a reduced impact logged subtropical Bolivian forest

Abstract

Reduced-impact logging is a type of selective logging that incorporates a variety of techniques aimed at lowering levels of damage to the residual stand. In a Bolivian subtropical humid forest we studied differences in gap size, vegetation structure, regeneration and phenology between anthropogenic and natural gaps in a reduced-impact logged and unlogged forest. Harvesting took place between 1 and 4 years previously. Logging gaps were significantly larger than natural gaps (d.f. 1, variance ratio (vr.) 6.38, p = 0.014) and had significantly lower coverage of lianas (d.f. 1, vr. 8.64, p < 0.01). Seedlings were more prevalent in logging gaps than in natural tree-fall gaps (d.f. 1, vr. 13.97, p < 0.001), as were members of the herbaceous genus Heliconia (d.f. 4, vr. 3.05, p = 0.023). In larger gaps microclimatic conditions favour the regeneration of non-commercial pioneer species. We propose that ground disturbance during bole removal causes higher rates of mortality to shade-tolerant species in advanced stages of regeneration. This removes the competitive height advantage needed by shade-tolerant species to compete within gaps, and thus further promotes the opportunity for pioneer species to dominate gap regeneration. These observed differences between anthropogenic and natural tree-fall gaps are of direct importance to forest managers attempting to understand how disturbance associated with reduced-impact logging influences the regeneration of commercial tree species in Bolivian forestry concessions. We discuss the ecological and silvicultural implications of these results.