[Insert Fig. 5 here]
The applicable range of the HRM depends on the magnitude of error in
measured temperature rise (See Fig. S4 ), which in turn depends
on the precision of the temperature sensor (σ T)
and the amount of heat generated during the heat pulse. The useful range
of the HRM could be extended by increasing heat pulse duration.
3.1.3 Sensitivity to the k
Among the four heat pulse methods, the HRM was the most sensitive to
uncertainty in k . Calculations of V are directly
proportional to k using the HRM. Estimates of V from the
DRM are also sensitive to k at low sap velocities (< 20
cm h-1) because V DRM is
dominated by V 12 (V HRM,
Eqn. 4 ) under such conditions (Fig. 6 ). However, when
sap velocity is high, V DRM equalsV 23, which is much less sensitive to k ;
this is because V 23 is the sum of two terms, of
which only one depends directly on k (Eqn. 6 ). The CHPM
is completely insensitive to uncertainty in k , while the Tmax
method is strongly influenced by noise at high sap velocities. Usingk as estimated using either Eqn. 13 or Eqn. 14considerably improves the accuracy of the DRM (and HRM) at low sap
velocities.