Natural regeneration and liberation of timber species in logging gaps in two Bolivian tropical forests

Abstract

One-year-old logging gaps were sampled in dry and humid selectively-logged Bolivian tropical forests to determine the density of commercial tree regeneration. The efficacy of liberation treatments designed to enhance the growth and survival of sapling regeneration was evaluated over a period of 2 years. Liberation treatments included manual cleaning of competing vegetation around commercial tree saplings occurring in logging gaps, or spraying competing vegetation near these saplings with one of two herbicides (2,4-D or glyphosate). Of the nine species harvested in each forest type, only two species in each type had relatively abundant regeneration in logging gaps ( Hura crepitans L. and Schizolobium parahyba (Vell. Conc.) S.F. Blake in the humid forest and Centrolobium microchaete C. Martius ex. Benth. and Caesalpinia pluviosa DC. in the dry forest). After 1 year, liberation treatments significantly increased the diameter growth of saplings in the humid forest, but not during the second year ( P=0.09). In the dry forest, liberation treatments did not affect the diameter of liberated plants. Liberation treatments did not significantly affect sapling survival or height growth in either forest. Treatment costs were relatively low (US$ 1–2.3 per gap), but time until return on investment is long (20–30-year cutting cycles). Adjustments to liberation treatments, such as season and intensity of application may increase effectiveness of treatments. Problems observed in this study with the recruitment of commercial tree regeneration in logging gaps suggests the need for site preparation treatments and more judicious seed tree retention.