Forest ecosystem water use : does species identity and ecosystem composition matter?

Abstract

Transpirational water use by trees has been long known to be regulated by evaporative demand and temperature, solar radiation, stomatal conductance and tree leaf area. More recently control of transpiration by plant hydraulic traits has been highlighted, and these as well as stomatal conductance and its response to air saturation vapour pressure deficit remain unstudied for the majority of Australian native tree species. To predict how forested ecosystem water use may change under future climates and enable better estimates of catchment water losses, we must understand stomatal and hydraulic behaviour of trees in the field under a range of conditions. In this study, I quantified traits describing stomatal and hydraulic behaviour for five Eucalyptus species from differing climates. Patterns in whole tree water use, stomatal sensitivity and responses to low water availability of these species in a common garden were correlated with species identity and with their characteristic climate of origin. I found that different Eucalyptus species employed different strategies to deal with water deficits which were linked to hydraulic, anatomical and leaf tissue water relations characteristics, and also with the original climatic range of the species. Tree water use, growth and tolerance of low water availability were enhanced in species mixtures compared to monocultures, an effect ascribed to asymmetric competition of component species in these mixtures. A basis for incorporating species stomatal and hydraulic parameters into forest stand-level water use models is provided. Ultimately, doing so will enhance predictions of water use, and enable estimates of stand water-use efficiency and productivity under current and future climate conditions. The findings are key to inform plantation and land management decisions, and can assist in the identification of vulnerable species or ecosystems, and the conservation of catchment water supplies in a changing climate.

Date of Award	2015
Original language	English