Post-fire tree regeneration in lowland Bolivia: implications for fire management

Abstract

Abstract Tree regeneration was compared in burned and unburned portions of a tropical dry forest (1110 mm ppt/year) and a tropical humid forest (1542 mm ppt/year) in southeastern Bolivia. Both forests burned 5 years prior to our study, and both forests were also lightly selectively logged ( intensity m 3 /ha ) —the dry forest during the 1970 and 1980s and the humid forest just prior to the wildfire. The objective of this study was to compare abundance, size, and mode (seedling or resprout) of tree regeneration in burned and unburned areas of these forests, focusing on the most common canopy tree species and the commercial timber species at each site. Regeneration of 13 species of trees was quantified in the humid forest and 12 species in the dry forest. Tree regeneration 20 cm tall was more abundant in the dry forest ( x =1807 stems/ha ) than in the wet forest (x=490 stems/ha ) . In both forests, resprouts were generally larger but less abundant than seedlings. In the dry forest, regeneration of the following commercial tree species was significantly more abundant in the burned areas: Cedrela fissilis, Anadenanthera colubrina, Astronium urundueva, and Centrolobium microchaete. However, Acosmium cardenasii, a canopy tree species not marketed for timber in Bolivia, represented the majority of regeneration (63%) in the dry forest and was equally abundant in burned and unburned areas (∼1100 stems/ha). In the humid forest, only one timber species, Aspidosperma rigidum, was more abundant in burned than unburned areas (51 vs. 0 stems/ha, respectively). Another timber species that is rarely harvested in the region, Pseudolmedia laevis, was significantly less abundant in the burned than unburned area (22 vs. 173 stems/ha, respectively). The results of this study suggest that controlled burning could increase the abundance of timber tree regeneration at the dry forest site and to a lesser extent at the humid forest site. No data were collected to assess the likelihood that this increased density of regeneration will result in increased harvestable timber. However, local forest management institutions do not presently appear capable or motivated to conduct fire management—whether for enhancing timber regeneration or for limiting the damage caused by accidental wildfires.