The opportunity of climate change mitigation through global tree afforestation/reforestation programs has become the flavour of the decade. With the likelihood of increasingly frequent and severe droughts and heat waves being a major cause for concern, understanding how trees respond to temperature extremes and limited water availability is critical to forecasting both short and long-term impacts of climate change on forest systems in South Africa. This study evaluates the effects of ambient air temperature in concert with available water availability on the water use efficiency (WUE), physiology, and isotopic discrimination of two Myrtacae species; Eucalyptus grandis (a species originally from New South Wales) and Syzygium guineense (a local species found predominantly in the eastern parts of South Africa). The trees are placed in a high tunnel structure where they are exposed to a temperature gradient stimulated by a built-in wet wall. Two water treatments are applied to the trees to help determine whether WUE varies between the two species under different temperatures and whether δ13C can be used as a reliable signal of historic WUE.
