Effect of provenance variation and singling and pruning on early growth of Acacia mangium Willd. plantation on Imperata cylindrica (L.) Beauv. dominated grassland.

Abstract

Early growth of 20 provenances (mainly Papua New Guinea and Queensland (Australia), with one from Irian Jaya, Indonesia) of Acacia mangium was studied on Imperata cylindrica dominated grassland in South Kalimantan, Indonesia. Effect of climatic factors of the natural habitats of the provenances on growth on the trial site was tested. In addition, the effects of singling (i.e., reducing the number of stems to one per tree) and pruning (all branches removed up to a height of 2 m) on the early growth were assessed. Randomized complete block design with four replications was used. At the age of 26 months the yield of the best provenances was almost threefold compared with that from bulk seed from Subanjeriji, the most widely used Acacia mangium seed origin in Indonesia. Provenances from Papua New Guinea showed the best growth (60-90 m³ ha^-1 ) and the lowest growth (30-50 m³ ha^-1) was recorded for those from southerly parts of Queensland, and local sources. Field performance was closely related to rainfall seasonality emphasizing the need for careful matching between the rainfall patterns of seed collection sites and those of the planting site. The driest quarter precipitation explained 74% of the growth rate. Growth after singling and pruning was only about 70% of that of untreated plots. Therefore, singling and pruning at 8 months cannot be recommended for plantations if growth rate is the first priority. Studies of the long-term effect of pruning and singling are needed.