A 20-year tree liberation experiment in the Amazon: Highlights for diameter growth rates and species-specific management

Abstract

We address tree diameter growth, linking it to a species-specific approach to managing terra firme forests in the Amazon, based on a long-term forest experiment testing the effect of tree liberation on diameter growth. Five species were selected for diameter growth modeling: Astronium lecointei, Chrysophyllum lucentifolium, Lecythis lurida, Manilkara paraensis, and Manilkara elata. The aims were to (i) investigate the tree diameter growth rates with and without liberation and (ii) determine species-specific minimum cutting diameters (MCDs) and cutting cycles (CCs). Individual tree non-age-explicit growth models were tested with calibration data from trees of ≥35 cm dbh whose growth was monitored over 20 years. The diameter growth was projected to 100 years. We found that liberation can reduce the time necessary for trees of 35 cm to attain an MCD of 50 cm by up to 70 years and can accelerate diameter growth even after growth stagnation. Its effect may be strong on both small and large trees, depending on the species. Both the diameter growth and the liberation effect depend on the species, thus reinforcing the need for more discussion of specific-species management in the Amazon. M. elata had the fastest diameter growth rate among the studied species. A. lecointei can grow under liberation as fast as M. elata. An MCD of 50 cm is suitable for both species because trees reach this dbh while still growing quickly. The number and length of the CCs for A. lecointei and M. elata should allow trees to reach a dbh between 60 and 70 cm. The species C. lucentifolium and L. lurida experienced growth stagnation at dbhs of 40–50 cm; however, liberation accelerated the slowed growth of trees in that diameter range. Similar studies in the Amazon are encouraged in order to confirm the slow growth of C. lucentifolium and L. lurida at other sites and then recommend reducing their MCD with a species-specific regulation. The number and length of the CCs for these two species should allow trees to reach a dbh no larger than the MCD. M. paraensis was the only species for which the effect of the liberation increased with tree size. An MCD of 50 cm is suitable for this species. CCs should allow M. paraensis trees to reach a dbh no larger than 60 cm without liberation and 70 cm with liberation.