Enrichment planting as a silvicultural option in the eastern Amazon: Case study of Fazenda Cauaxi

Liana-dominated forest patches constitute 15-20% of old-growth forests in the Eastern Amazon but are generally excluded from management for timber production. Here we ask if liana-dominated patches may be brought into production by clearing lianas and conducting enrichment planting (EP) of native timber species. We present growth results from 8 years of such EP trials. Rapid growth and low mortality of all species in this study suggest that EP in cleared liana patches can contribute to timber stocks in second and third harvests of managed forests. The most vigorous individuals of Parkia gigantocarpa and Schizolobium amazonicum in each enrichment site grew more than 1cm diameter per year (rates were initially >2cmyr⁻¹), and attained dominant canopy positions and diameters equal to those of small canopy trees in the surrounding forest within 8 years of planting (mean dbh ~18cm and ~20cm, respectively, at year 8). Limited data on Ceiba pentandra plantings indicate a similar trajectory for this species (dbh ~40cm in 8 years). The most vigorous Swietenia macrophylla grew at least 1cm per year in enrichment plots (mean dbh ~10cm in 8 years), but take longer to attain dominant positions. Tabebuia serratifolia may take much longer to reach the canopy than other species tested (rates <1myr⁻¹). We attribute the excellent performance to light availability; planting in intact soil with minimal compaction and abundant organic material; and low competition rates maintained by periodic thinning of competing vegetation. Operational, ecological, and regulation questions must be addressed before EP of liana patches can be added to the menu of silvicultural options for Amazonian forests. Enrichment planting involves ecological and financial costs and uncertainties, and techniques need refinement. We caution against authorizing this silvicultural practice on more than a pilot scale until adequate information and resources exist for effective, responsible use of this technique.