Sap flow in Searsia pendulina and Searsia lancea trees established on gold mining sites in central South Africa

This paper describes a study of the annual pattern of sap flow rates in two species of indigenous tree (Searsia lancea (L. F.) F.A. Barkley and S. pendulina (Jacq.) Moffett, comb. nov.) established in plantation form. These species occur naturally in central and western South Africa. Sap flow was monitored continuously over a full year in eight stems representing each species, using the heat ratio version of the heat pulse velocity technique. Plot sap flow was estimated by scaling up according to the number and size of stems, and utilizing functions relating leaf dry mass and leaf area to stem diameter. The deciduous species S. pendulina was found to use 591 mm of water over a full growing season, while the evergreen species S. lancea was found to use 1044 mm over a full year. Differences in sap flow patterns between these species are attributed largely to different leaf dynamics. We conclude that S. lancea has potential for the hydraulic control of mine seepage water in phytoremediation systems in the WBG.