Testing liana cutting and controlled burning as silvicultural treatments for a logged forest in the eastern Amazon.
In the eastern Brazilian Amazon, logged forests frequently include patches where liana density is particularly high. In these so-called liana tangles, competition from lianas is predicted to reduce tree growth significantly, thus effectively impeding future timber production. To begin to develop a silvicultural strategy for these patches, the impact of liana cutting and controlled burning on liana density, tree growth and tree regeneration in liana-dominated patches was investigated in a logged forest in the eastern Brazilian Amazon. The two treatments (liana cutting and controlled burning) and a control were installed in 40×40-m plots in a randomized complete block design of six blocks near Paragominas, Pará. Treatments were conducted during October 1997, and tree diameter growth and mortality, canopy cover, regeneration and liana density were monitored over 2 years. Mean mortality following burning was significantly higher for lianas (79%) than for trees (48%), as was the mean coppicing rate of top-killed stems (42% for lianas vs. 20% for trees). Coppicing combined with some recruitment from seed resulted in liana densities in the burned plots returning to 70% of the values in the control plots only 2 years post-treatment. Canopy light transmittance, estimated from hemispherical canopy photographs taken at 1 m above the ground, increased significantly from approximately 4% in controls to 8% in cut and 12% in burned treatments, and these differences persisted over the 2-year study period. In the absence of silvicultural intervention, mean tree diameter increments were low (1.3 mm year-1), suggesting that the successional transition to higher stature forest was occurring very slowly. Each of the treatments resulted in a more than doubling of mean annual tree growth (3 and 2.8 mm year-1 for liana-cut and burned treatments, respectively). The treatments also significantly reduced the occurrence of trees that showed no growth over the study period, from 56% in controls to 30% in cut and 32% in burned treatments. The results of this study suggest that although burning resulted in increased tree growth, rapid recolonization of surviving trees by lianas and the high vulnerability of burned stands to unwanted repeat burns are likely to cancel out any of the possible benefits of controlled burning as a silvicultural treatment for liana-dominated patches. Liana cutting, on the other hand, showed promise and its adoption as part of a larger strategy for the recuperation of the timber production potential of logged tropical forests seems warranted.