Components of ecosystem evaporation in a temperate coniferous rainforest, with canopy transpiration scaled using sapwood density

Abstract

asterisk inside a circle sign Here we develop and test a method to scale sap velocity measurements from individual trees to canopy transpiration (E c) in a low-productivity, old-growth rainforest dominated by the conifer Dacrydium cupressinum. Further, Ec as a component of the ecosystem water balance is quantified in relation to forest floor evaporation rates and measurements of ecosystem evaporation using eddy covariance (E eco) in conditions when the canopy was dry and partly wet. asterisk inside a circle sign Thermal dissipation probes were used to measure sap velocity of individual trees, and scaled to transpiration at the canopy level by dividing trees into classes based on sapwood density and canopy position (sheltered or exposed). asterisk inside a circle sign When compared with ecosystem eddy covariance measurements, Ec accounted for 51% of Eeco on dry days, and 22% of Eeco on wet days. asterisk inside a circle sign Low transpiration rates, and significant contributions to Eeco from wet canopy evaporation and understorey transpiration (35%) and forest floor evaporation (25%), were attributable to the unique characteristics of the forest: in particular, high rainfall, low leaf area index, low stomatal conductance and low productivity associated with severe nutrient limitation. © New Phytologist (2004).