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Our sap flow sensors provide an accurate way to measure a tree's transpiration rate, and include the following:

Simple, sturdy design allows for this sensor to be used for long periods for time.

Durable pull-cord for easy displacement from the tree after measurement.

Grafting Wax included to minimize damage to the tree.

Portable and easy to use, these sensors don't require complex calibrations or set up.

Includes both prewritten programs for the dataloggers and macros to interpret the data quickly and easily.


1. Transpiration of desert riparian forest canopies estimated from sap flux.

2. Rainfall Partitioning within Juniper Communities

3. Seasonal Patterns of Water-use Measured with a Dual Heat Pulse Sap Flow Technique on Mature Grapevines Growing in a Weighing Lysimeter

Sap flow sensors measure tranpiration rate in trees. Available in 2 or 3 needle configurations.


  • Monitoring water use in irrigated orchards.
  • Scheduling irrigation in orchards.
  • Estimating water use by trees in agroforestry.
  • Monitoring species specific water requirements of trees in watersheds.
  • Note: Probes are reusable unless they become cemented in the tree. This is dependent on the tree species and "wound response".


Temperature Sensors: 10K Precision Thermistor

Dimensions: Handle is 45mm long, 15mm dia. Needles are 35mm long, 1.27mm dia.

Heater Resistance: 44 ohms.

Cable length: 2m standard (additional cable available.)

Accessories needed:

Heater control interface: One interface will run up to 5 sensors. Click here to view a schematic diagram.


Drilling Guide for precise spacing of needles in the tree.


The East 30 Sensors Sap Flow Sensor consists of a pair of 35mm long stainless-steel needles spaced 6mm apart. One needle contains an Evanohm heater and the other contains three precision thermistor sensors evenly spaced at 5mm, 17.5mm, and 30mm. The needles are inserted into holes drilled in the trunk of a tree with the heater placed below (upstream from) the thermocouples. A current is applied to the heater for 8 seconds, after which the temperature of the thermistors is monitored. The flowing sap carries the heat pulse to the sensors. The time taken for the pulse peak to reach the temperature sensors is monitored. This time is directly related to the sap flow velocity. The velocity is used, along with the sapwood area, to compute the transpiration rate of the tree. The three thermistors provide measurements of flow at three depths in the sapwood, from which the velocity profile can be deduced.


Cohen, Y., M. Fuchs, and G.C. Green 1981. Improvement of the heat pulse method for determining sap flow in trees. Plant, Cell and Environment 4:391-397