资源环境科技发展态势分析平台

Lianas (woody climbing plants) often abound in tropical forests after selective logging and other disturbances. Liana cutting is an often-prescribed but seldom applied silvicultural treatment designed to foster the growth of future crop trees (hereafter: FCTs). Small-scale studies indicate that this treatment is effective, but little is known about its efficiency (i.e., proportions of lianas missed) or financial cost effectiveness at operational scales. To fill these gaps, we worked in a commercial forest concession in Belize where FCTs and trees to be felled were liberated from lianas in 500-1000 ha annual timber harvest blocks. We found that field crews assigned this and inventory-related tasks spent 11.8% of their time cutting lianas from FCTs at a cost of $0.11 per tree. Workers failed to cut 31.9% of the lianas that infested the 701 FCTs they were supposed to liberate; most of the missed lianas grew into the FCT crowns from neighbors or hung down far from the bole [an additional 48 FCTs (6%) were completely missed]. In a logging block treated 9-years prior to this study, 39% of the liberated Swietenia macrophylla FCTs 29-56 cm DBH were still liana-free whereas in an untreated stand, 94% of similar-sized conspecific control FCTs were liana-infested. Based on tree ring data for the same 9-year period, the liberated FCTs grew 38-63% faster than control FCTs. If the mean growth benefit is sustained over the entire 40-year cutting cycle, each liberated FCT will yield an average of 1.51 m(3) (639 board feet) more roundwood than comparable FCTs in unliberated forest. Over this 40-year period with an annual discount rate of 4.5%, this added volume gives the $0.11 investment per tree a net present value of US $161.38 and a profitability index of 1467 for export quality timber. These results argue for the application of this inexpensive and effective treatment in managed forests where lianas abound.