Acacia mearnsii industry overview: Current status, key research and development issues §

Abstract

Acacia mearnsii De Wild (black wattle) is an important plantation species for tannin production and woodchip exports in South Africa and Brazil. This study provides an updated overview of the black wattle industries in both countries, including planted areas and land ownership, silviculture and management, bark extract production, woodchip exports, as well as key research and development issues. The current  total planted area to black wattle is 110 000 ha in South Africa and c. 170 000 ha in Brazil. In both countries black wattle is mainly cultivated by farmers (c. 76–78% of the total area). Due to the high prices fetched by the wattle woodchips in the international market, black wattle is a profitable crop. In South Africa, the timber provides 85% of the revenue and the bark the other 15%, and thus the commercial emphasis has shifted from bark to timber. At present the only significant secondary products are charcoal and firewood. Acacia mearnsii bark tannins are used in the leather industry, adhesives for wood composites, water flocculants and specialty products for the chemical, food and beverage industries. The world demand for  vegetable tannins has remained unchanged over the past two decades due to intense competition from synthetic tannins. South Africa produces about 45 000 t of bark extract annually, whereas Brazil produces 30 000–40 000 t. The annual value of A. mearnsii extract from South Africa and Brazil is about US$100 million. The total wattle woodchip exports from South Africa and Brazil in 2013 was 800 000 bone dry metric tonnes (BDMT) and 570 000 BDMT, respectively, with an estimated value of US$208 million. Acacia mearnsii offers important economic advantages for pulp production (higher wood density and pulp yield, which translate into higher digester productivity and factory output), and is highly suitable for hardwood  bleached kraft pulping, dissolving and semi-chemical pulps. These factors make A. mearnsii a sought-after species and have ensured a sustained demand for wattle woodchips in the Japanese market, and today continue to attract new customers in emerging markets (China and India). The most important challenges for the black wattle industry in South Africa are (1) to maintain the wattle land base and improve productivity from the existing resource and (2) considering that black wattle is a highly labour-intensive crop and the recent increases in labour costs, it is  necessary to revisit current silviculture practices from a costs–yield perspective and to develop mechanised harvesting/bark stripping systems. The Brazilian wattle industry faces important challenges in silviculture, tree improvement, and pests and diseases, which require further research and collaboration between the few players involved. It is important for both Brazil and South Africa to develop domestic  markets for wattle solid wood as additional sources of income for the many farmers growing wattle.

Keywords: Acacia mearnsii, Brazil, hardwood pulps, pulping and papermaking  properties, South Africa, vegetable tannins, woodchip markets