Gush, M.B., Dye, P.J., Geldenhuys, C.J. and Bulcock, H.H., 2011. Volumes and efficiencies of water-use within selected indigenous and introduced tree species in South Africa: Current results and potential applications. In : Proceedings of the 5 th Natural Forests and Woodlands Symposium, Richards Bay, 11-14 April. 1 VOLUMES AND EFFICIENCIES OF WATER-USE WITHIN SELECTED INDIGENOUS AND INTRODUCED TREE SPECIES IN SOUTH AFRICA: CURRENT RESULTS AND POTENTIAL APPLICATIONS M.B. Gush¹, P.J. Dye², C.J. Geldenhuys³ and H.H. Bulcock 4 ¹CSIR, Stellenbosch ²University of the Witwatersrand, Johannesburg ³FORESTWOOD cc, Pretoria 4 University of KwaZulu-Natal, Pietermaritzburg Corresponding author: mgush@csir.co.za Abstract South African indigenous forests provide goods and services which are recognised as valuable natural capital, and are well documented. However, the limited extent of these forests has forced South Africa to accelerate the expansion of its own plantation forest industry over the last century, using fast-growing introduced tree species to meet the timber needs of the country. The resultant impacts on streamflow and water resources have been the subject of considerable research, and first led to regulation of this industry in 1972 due to water-use concerns. Conversely, there is widespread belief that indigenous tree species use little water and deserve to be planted more widely. However, research and data on the water-use of indigenous trees and forests has historically been limited. This paper discusses current progress in a Water Research Commission solicited project on the measurement and modelling of water-use and growth in selected South African indigenous tree species. Hourly sap flow rates (water use) over a 12-month period were recorded in a diverse selection of indigenous tree species, while stem circumferences were recorded at the start and end of the monitoring period, to derive biomass increments. Rates of growth and water-use were used to calculate water-use efficiency, defined as mass of utilisable wood produced per unit of water transpired, and were compared to existing data for introduced plantation species. Water-use efficiency in the indigenous species studied was lower than for introduced plantation species, however overall water-use was also generally lower in the indigenous species. It was concluded that the relatively lower water-use efficiency of the indigenous species studied was primarily a consequence of slow growth rates as opposed to high water-use rates. Implications and potential applications of these findings in alternative forms of indigenous forestry and sustainable resource use are discussed. 1. Introduction South Africa is very reliant on its plantations of introduced tree species to meet its pulp and timber needs, and the benefits of this industry in terms of production, income generation and job provision are undisputed (Chamberlain et al., 2005). The downside is that these benefits come at some environmental cost, not least the impact of the industry on water resources (Dye & Versfeld, 2007). Many catchment areas are consequently now closed to further afforestation, but economic growth and development continue unabated. Imports and improved productivity are potential solutions to continue meeting the demand for timber and forest products, but further consideration of the feasibility of expanding indigenous tree resources is also warranted. With over 1000 species of indigenous trees in the country, South Africa is extremely rich in natural arboreal diversity (von Breitenbach, 1990). The numerous benefits of indigenous trees and forests, in terms of the goods and services that they offer, are widely recognised (Lawes et al., 2004; Shackleton et al., 2007). There are also widespread perceptions that indigenous tree species use less water than introduced tree plantations, however up to now these have been unsubstantiated. While data from previous studies are available on the water-use efficiency (WUE) of common introduced plantation species in South Africa (Olbrich et al., 1996; Dye et al., 2001), information on the water-use of indigenous trees and forests is scarce