Eko Bhakti Hardiyanto

Genetic improvement of tropical acacias: achievements and challenges §

Three acacia species, Acacia auriculiformis, A. crassicarpa and A. mangium, dominate over 2 million ha of tropical acacia plantations worldwide. Species and provenance trials carried out in the 1980s and 1990s established the fastest-growing regions of provenance for each species, and most current breeding populations comprise open-pollinated families from several, or many, local provenances sourced from these favoured regions. Provenance–progeny trials are thinned to seedling seed orchards (SSOs), which yield both selected progenies for the next generation of breeding and operational seed for plantations. Clonal forestry has been successfully developed for A. auriculiformis and the hybrid between A. mangium and A. auriculiformis. In many instances production of improved seed in seed orchards has not been adequate to meet planting demand; strategies to address this have been (1) the establishment of additional unpedigreed seed production areas of broad and superior genetic base, and (2) clonal family forestry to multiply elite seed families. Controlled pollination of acacias is technically demanding, so is not suitable for advancing main breeding populations. Substantial (50–100%) gains in wood volume production have been demonstrated in trials comparing seed from first-generation SSOs or selected clones with inferior provenances and land races, but volume gains in subsequent cycles of breeding will be smaller. The potential for genetic improvement in form traits and wood properties has also been demonstrated. Genetic improvement objectives must now give heavy weighting to improving disease resistance and tolerance. Ganoderma root rot and Ceratocystis stem wilt have destroyed large areas of acacia plantations in Indonesia and Malaysia. Since clonal deployment of resistant genotypes is the quickest and most effective way of delivering resistant planting material, ongoing research to develop clonal forestry for A. crassicarpa and A. mangium is warranted. Novel interspecific hybrid combinations might deliver useful genetic variation for breeding.

Nitrogen fixation of Acacia mangium Willd. from two seed sources grown at different levels of phosphorus in an Ultisol, South Sumatra, Indonesia

Phosphorus (P) is required to facilitate the fixation of atmospheric nitrogen (N) by leguminous species such as Acacia mangium. We studied the N fixation of A. mangium trees grown from two seed sources. These consisted of bulk seedlots collected from seed orchards in Sumatra, one based on natural provenances from the Cairns region, Queensland, Australia, and the other on the Muting natural provenance, Papua, Indonesia. The seedlots were grown under contrasting P supply (application rates of 0 and 100 kg ha−1) on acidic clay soils in a field experiment at Lematang, South Sumatra. The 15N natural abundance method was used, with Eucalyptus pellita as a non-N-fixing reference species. Foliage samples were collected at age 12 and 18 months. Application of P increased stem volume, foliage N concentrations and the amount of N fixed in both seed sources at 12 and 18 months of age. For the Cairns-origin seed source, the percentage of N derived from atmospheric N was low (c. 14%) without P addition, but increased by more than four-fold with P addition. In contrast, N fixed by the Muting-origin seed source (c. 45–60%) was not significantly affected by P addition. The Cairns-origin seed source partly compensated for lower N fixation by taking up a larger amount of soil N. Thus there were significant differences between seed sources in their N-fixing capacity and the effect of P nutrition on this process. The higher productivity of Muting under low P application appeared to be associated with better P utilisation and greater N fixation, but it was still responsive to P application.

A projected increase in stand volume of introduced provenances of Acacia mangium in seedling seed orchards in South Sumatra, Indonesia

Abstract Increases in stand volume with some currently introduced provenances of Acacia mangium: Papua New Guinea (PNG) and Far North Queensland (FNQ), were projected based on their superiorities in 3-year height growth in seedling seed orchards using the growth model developed for unthinned plantation for pulp and paper production in South Sumatra, Indonesia. The height growth of these provenances was better than that of the local selections from Subanjeriji by 10%–15% at 3 years old and these percentage superiorities would be expected to remain at around 9%–14% until the 8-year rotation. This amount of increase would result in a 7%–10% increase in basal area and hence it would produce a 17%–26% increase in stand volume at rotation age when compared with the Subanjeriji seed source that was being widely used for the plantation establishment of A. mangium in Indonesia.

Minimum distance boundary method: maximum size-density lines for unthinned Acacia mangium plantations in South Sumatra, Indonesia

A minimum-distance boundary method that will minimize the sum of distances between measured points and a fitted self-thinning lines on log-log coordinates of stand density and quadratic mean diameter was proposed in order to estimate the maximum size density line: an upper boundary of self-thinning line. The lines for A. mangium were inferred with this method using data in two areas of unthinned plantations in South Sumatra, Indonesia. Slopes of the lines were deduced as −1.63 and −1.67 within the range of 10–21 cm of quadratic mean dbh. The intensity of self-thinning was examined as a rate of reduction of density in relation to dbh increment. The rates were found to be higher than the slopes in the range close to the maximum line; hence the lines inferred in this study were likely existent. Maximum basal area deduced from the size-density line was 28–30 m2/ha at 12cm of dbh and then it increased up to 34–37 m2/ha at 20 cm of dbh.

Nutrient management of contrasting Acacia mangium genotypes and weed management strategies in South Sumatra, Indonesia

ABSTRACT Tropical plantations are an important source of forest products both to meet the growing demand for wood, and to facilitate the transition from native forests to more sustainably produced forest resources. Management of these plantations for optimal productivity and resource-use efficiency is vitally important, and nutrient management is a critical component of sustainable plantation production. In this study, we explored the response of Acacia mangium plantations in South Sumatra, Indonesia, to fertiliser and their requirement for fertiliser, focusing on phosphorus (P) at establishment. Almost all plantations across a series of 11 sites were highly responsive to P fertiliser, with nine of the 11 sites having more than double the productivity in P-fertilised treatments at age 1 year compared with control treatments. However, the quantity of P required for 90% of maximum growth was generally low by age 2 or 3 years, and 10 kg P ha–1 at establishment was sufficient to ensure that at least 90% of maximum growth was captured across all the experimental sites. At a 12th site, we explored the interactions between genotype and weed control, and found that both effects were additive in the response of the plantations to P, and thus there was no substitutability between management types: weed control, genotype and P needed to be managed in combination to achieve maximum productivity.

A simple step-wise procedure for predicting stand development of Acacia mangium plantations based on the maximum size—density line in South Sumatra, Indonesia

A simple step-wise procedure for predicting the course of stand development on log–log coordinates of stand density and quadratic mean diameter was presented based on a distance of measurement from the maximum size–density line of Acacia mangium. This procedure first predicts annual increment of diameter with a multiple linear regression having the distance, site index, and current diameter as independent variables, and then the associated mortality is calculated with the rate of reduction in stand density to the diameter growth derived from a fitted trend with the distance. The cumulative predictions, starting at 3 years after planting until 9 years of age, agreed well with the observations of group-age means of measurements calculated for the three levels of initial density. Contrasting trend of basal area growth between the three levels of initial density and those for their site index: the differences were decreasing in the former while they remained constant in the latter, was clearly illustrated with the procedure indicating a good potential for use in yield prediction. The simulations for stand growth under different spacing and thinning options were demonstrated in a stand density control diagram suggesting reasonable flexibility for practical application.