Sap Flow Technology comes
During 2007 NUFG members realised there was a need to better understand the water use characteristics of the farm forestry plantations at Kamarooka. The watertable began to fall under the 2004 plantation at a time when the only water the trees could access was the underlying saline groundwater. Throughout 2007 the trees continued to draw the watertable down ultimately creating a 3 metre depression under the trees compared with adjacent non-treed lands.
No hydro-geological rationale could explain the depression of the watertable beneath the farm forestry plantation. The explanation that best fitted the data was that the trees were transpiring some of the saline groundwater. Out of the fourteen monitoring bores established across the project site three recorded a substantive fall in watertable much greater than the rest. Two were located within the 2004 farm forestry plantation and the third was among the trees and shrubs that make up the 2004 NUFG/NCCMA biodiversity plot.
The draw-down of the watertable under the woody native vegetation was considered remarkable given that the salinity of the shallow groundwater ranged from half to two thirds the salinity of seawater.
The NUFG recognised the need to look beyond how the watertable responded to the plantations and to prove to the broader scientific fraternity and to landcare groups the veracity of its conclusions. Accordingly, NUFG decided to take the next big step by investing in technology that would monitor and report on the water use of the trees.
Sap flow instrumentation was purchased from ICT International with financial support from the National Landcare Programme and the North Central Catchment Management Authority. The equipment was installed and sap flow monitoring commenced at Kamarooka in mid-January 2008.