Predicting the water-use of Eucalyptus nitens plantations in ...

Stemflow (L)
500
450
400
350
300
250
Figure 10. Relationship between stem diameter and stem flow for 4 trees at Forestier
Canopy interception was then calculated to account for 182 mm of the rainfall occurring at
the site:
Canopy interception = Rainfall – Throughfall – Stemflow = 854 – 632 – 40 = 182 mm/yr.
3.7. Transpiration
Transpiration is the product of sapwood area and sap velocity. Plot sapwood area, plot sap
velocity and plot transpiration were calculated for each day, and transpiration was summed
for the period of the study.
Plot sapwood area was estimated for each day by assuming linear growth in sapwood
between the sapwood estimates derived from plot inventory.
Sap velocity was measured at 4 locations in each of 4 trees from 24/2/2011 to 7/2/2012.
Sensors were allocated to different depths below the cambium to generate sap velocity
estimates that were representative of the range of flow rates observed in the sapwood band.
Sap velocity was estimated for each day by taking the average value of all operating sensors
for that day. There were very few days with no data. Data from 1/11/11 onwards were
modified to account for the large step change in sap velocity that occurred when sensors were
moved to new positions on this date – it appears that the potting mix that insulates the
thermistors in the sensors had degraded and that moving the probes caused the potting mix to
fracture leading to the erratic behaviour seen in some probes from this time onwards. Figure
11 shows the daily average sap velocity values after the last months of data were modified.
17
y = 18.2x + 43.9
R² = 0.99
200
10 12 14 16 18
Stem diameter (cm)
20 22 24 26