One of the PhD students in Woody Weeds Project, Mr Hailu Shiferaw, measures the amount of water consumed by Prosopis trees in the Afar Region of Ethiopia. He assesses the amount of water being used by Prosopis using eco-physiological and micrometeorological instrumentation.

The main technique used to understand water consumption at the tree level is measuring the flow of water through the stem of replicate Prosopis trees in a field study. The transpiration rate is measured using the stem sap flow method, in which sap flow through individual Prosopis trees is measured in trees of different diameter classes.

Sap flow measurements to calculate transpiration from individual Prosopis trees: sap flow measurement setup (left) and setup for data storage (right).

The second part of the field study is aimed at calculating evapotranspiration (ET) of a Prosopis-dominated plant community, so that triangulation with transpiration from individual Prosopis trees will be possible. Evapotranspiration is assessed using Eddy Covariance measures taken above the vegetation canopy, which reveal the amount of water transpired by the entire vegetation. The data is collected from a homogenous Prosopis-dominated vegetation block where the instrument is installed.

Eddy Covariance measurement to calculate evapotranspiration from Prosopis-dominated vegetation. Measurement instruments (left) and monitoring and downloading equipment (right) are mounted on an elevated position.

A preliminary analysis of the data shows that a single Prosopis tree consumes several liters of water per day during high photosynthetic active periods, suggesting an important impact of Prosopis on water availability at the study area. Hailu will continue his measurements and analyses to arrive at more definitive estimations of water consumption by individual Prosopis trees, but also by Prosopis at community level.