Natural regeneration and environmental relationships of tree species in logging gaps in a Bolivian tropical forest

Abstract

Successional dynamics and environmental associations of 18 pioneer and 24 commercial tree species were studied in a 4-year chronosequence of logging gaps in a Bolivian tropical forest. Logging gap area ranged from 108 to 1246 m 2. Pioneer regeneration was 71–387 more abundant than that of commercial species in all harvest years. Pioneer saplings (>1.5 m tall and <10 cm dbh) were more abundant in 2- and 4-year-old gaps than in 1-year-old gaps, but pioneer seedlings (≤1.5 m tall) were more abundant in 1-year-old openings. By contrast, there were no significant differences among harvest years in size class distributions of commercial seedlings or saplings. Some pioneers ( Acacia polyphylla, Urera baccifera, Heliocarpus americana, Cecropia concolor, and Inga edulis) were associated with large gaps or coarse soils with high herbaceous cover. Among commercial trees, Ampelocera ruizii, Hura crepitans, and Pseudolmedia laevis were associated with fine textured soils, while Pouteria nemorosa was associated with high fern cover and rock outcrops. Although most logging gaps were dominated by a few pioneer species, the commercial species A. ruizii, H. crepitans, P. nemorosa, and Terminalia oblonga may eventually dominate many gaps. Notably absent among gap regeneration were some of the most commercially valuable tree species, such as Swietenia macrophylla, Cedrela fissilis, Cariniana ianeirensis, and Ficus boliviana. Outplanting programs may be needed to ensure successful regeneration of these rare but valuable species.