JOACHIM MEIER-DOERNBERG1, REINHOLD GLAUNER2
1University of Hamburg, Chair of World Forestry, Germany
2Federal Research Centre for Forestry and Forest Products, Institute for World Forestry, Germany
The pioneer species Acacia mangium Willd. is planted pan-tropical for timber and fibre production. In Roraima, increment ranges widely between 4 and 30 m3/ha/yr depending on treatment and site conditions. Anticipated rotation cycles are around 15 years for timber production. In the savannahs of northern Brazil (Cerrados) around 15,000ha of timber plantations have been established for sawlog production. Regularly inventories showed that crown cover closes at a basal area of around ten m2/ha independent of age. Thus, conservative approaches where thinning operations are planned according to top height or age had to be rejected and two methods have been developed solely based on stand quality and basal area.
The objective of both measures is to improve average stand quality for sawlog production and to maintain trees showing good growth performance, evenly shaped crowns and no signs of biotic and abiotic damages.
PCT stands were thinned at an average basal area of 12.4 m2/ha. Stand volume was reduced from 82.4 m3/ha to 64.1 m3/ha. Negative selection was carried out in stands showing 10.2 m2/ha. There growing stock was reduced from 60.3 m3/ha to 47.9 m3/ha. Both stand types comprised of stemsha. After thinning, PCT stands comprise of 1126 trees whereof 364 trees fulfil the criteria of a potential crop tree. In stands where thinning was implemented solely through negative selection, stem number was reduced to 1143 trees.
The second thinning is scheduled when stand have reached around 16-18 m2/ha.
Keywords: Acacia mangium, silviculture, thinning, timber-stand-improvement