ORIGINAL PAPER Hydraulic redistribution in Eucalyptus kochii subsp. borealis with variable access to fresh groundwater K. Brooksbank • D. A. White • E. J. Veneklaas • J. L. Carter Received: 22 July 2010 / Revised: 11 February 2011 / Accepted: 12 February 2011 Ó Springer-Verlag 2011 Abstract Salinity caused by land clearing is an important cause of land degradation in the Western Australian wheatbelt. Returning a proportion of the cleared land to higher water use perennial vegetation is one option for reducing or slowing the salinisation of land. Over the course of a year patterns of water use by Eucalyptus kochii subsp borealis (C. Gardner) D. Nicolle, a mallee eucalypt species, were monitored in three landscape positions with different water availability. One treatment had groundwater at 2 m, a second at 4.5 m and a third had groundwater below a silcrete hardpan thought to be impenetrable to roots. Hydraulic redistribution was observed in all land- scape positions, and rates were positively correlated with the magnitude of soil water potential gradients within the soil. High rates of hydraulic redistribution, facilitated by abundant deep water may increase tree water use by wet- ting surface soils and reducing stomatal closure. This effect may be countered by increased soil evaporation of water moved from root to soil following hydraulic redistribution; the net volumes of redistributed water though lateral roots was calculated to be the equivalent of up to 27% of transpiration. Keywords Sap flow Á Salinity Á Hydraulic redistribution Á Mallee eucalypt Á Root architecture Introduction In the low rainfall agricultural region of south Western Australia, replacement of deep-rooted native vegetation with a farming system based on annual grain crops and pastures has altered local hydrology, causing water tables to rise and mobilize salt stored in the soil profile (George et al. 1999). Salinisation and waterlogging significantly reduces agricultural productivity (George 1991) and is predicted to affect more than 25% of Western Australia’s agricultural land before a new hydrologic equilibrium is reached (McFarlane et al. 2004). Re-establishing deep-rooted perennial vegetation, such as tree crops has potential to at least partially address this environmental degradation (Stirzaker et al. 1999). It is widely recognized that commercial options are needed to facilitate tree planting on a scale sufficient to restore hydrologic balance in the annual cropping zone of Aus- tralia (Pate and Verboom 2009). One prospective com- mercial tree crop is a group of native multi-stemmed or mallee-form eucalypts collectively known as oil mallees. Since the early 1990s, over 23 million oil mallees have been planted in this cropping zone, mostly in narrow belts separated by wider alleys of annual crops and pastures (M. Kerkmans, pers comm). Integrating trees into the existing farming system distributes the hydrological bene- fits of these plantings across the landscape (Stirzaker et al. 1999). Communicated by C. Lovelock. K. Brooksbank (&) Á D. A. White Á E. J. Veneklaas School of Plant Biology, University of Western Australia, 35 Stirling Hwy, Crawley, Perth, WA 6009, Australia e-mail: kbrooksbank@agric.wa.gov.au K. Brooksbank Á D. A. White Á E. J. Veneklaas Á J. L. Carter CRC for Future Farm Industries, University of Western Australia, 35 Stirling Hwy, Crawley, Perth, WA 6009, Australia D. A. White Á J. L. Carter CSIRO Sustainable Ecosystems, CSIRO Centre for Environment and Life Sciences, Private Bag 5, Wembley, WA 6913, Australia 123 Trees DOI 10.1007/s00468-011-0551-0