Stand dynamics in a logged and silviculturally treated Costs Rican rain forest, 1988-1996

The lowland rain forests of Central America are poorly known from the stand point of management for timber production. We studied the stand dynamics of a logged Costa Rican rain forest under three different regimes of post-log ging silvicultural treatment. The site was located on low hills with Ultiso ls in Holdridge's Tropical Wet Forest life zone. The Pentaclethra macroloba -dominated forest had been high graded before planned management began. Man agement of the 540 x 540 m (29.2 ha) experimental area began with a timber harvest in the whole area during 1989-1990, 4 trees ha(-1) being cut overal l for 10.1 m(3) ha(-1). The experimental plots were 180 x 180 m. (3.24 ha), comprising a 100 x 100 m (1.0 ha) central permanent sample plot (PSP) with a 40-m wide buffer strip. Two types of post-harvest silvicultural treatmen t: liberation/refinement (in 1991) and shelterwood (in 1992) were applied u nder a complete randomized block design with three replicates, using logged but untreated plots as controls. PSP data reported are for the 1988-1996 p eriod for individuals with greater than or equal to 10 cm DBH. The most mar ked changes in forest structure were caused by silvicultural treatment, bas al area under the liberation/refinement treatment being reduced to ca. 65% of its probable mature forest value. Recruitment exceeded mortality in the years following intervention under all three treatments, but forest structu ral recovery was slowest under the liberation/refinement treatment. Post-in tervention mortality rates appeared higher under the liberation/refinement treatment than under the control or shelterwood treatments, though differen ces were not statistically significant. In relation to tree attributes, mor tality rates increased with decreasing DBH increment, crown illumination an d quality of crown form. Commercial DBH increments were higher under the li beration/refinement treatment than in, control plots during the 1993-1996 p eriod. On the basis of its response to intervention during the first seven years of management, the forest appears resilient and productive; trends ov er time in mortality rates under the most intense silvicultural regime requ ire close attention however. Pentaclethra-dominated forests are important c omponents of the productive forest resources of Costa Rica and Nicaragua an d, given current deforestation rates in areas such as southern Nicaragua, i t is now urgent that the existing biophysical knowledge of these forests be applied to forest conservation and management. (C) 1999 Elsevier Science B .V. All rights reserved.