stem water content

stem water content sensor

  • Low cost stem water content sensors for continuous measurements
  • Simultaneous measurements of stem water content and sap flow
  • Choose between capacitance, TDR or heat pulse sensors
  • Remote access data logging systems with data download over the internet
  • Connect our sensors to your existing system or we can install a complete research monitoring system for you

 

Stem water content, or moisture content, measurements are critical for understanding plant water relations in trees, shrubs and herbs.

Stem water content sensors can improve measurements of transpiration, as well as sap flow methods such as the heat pulse velocity methods.

Edaphic Scientific can provide complete monitoring solutions for the measurement of stem water content from low-cost capacitance sensors, to TDR sensors, to heat pulse sensors for the simultaneous measurements of stem water content and sap flow.

The scientists at Edaphic Scientific have published scientific research in international peer-reviewed journals, such as Tree Physiology, Trees, Annals of Botany, and Water Resources Research, on plant water relations and water content measurements. With our scientific research capabilities, as well as extensive experience with instrumentation and installing scientific research equipment, we can assist you with the design and installation stem water content sensors and data loggers.

 

types of stem water content sensors

Stem water content can be measured between the choice of three types of sensors: capacitance, TDR, or heat pulse velocity sensors. The methods have been borrowed from, or directly applied from, the measurement of soil water content. Therefore, stem water content sensors are based on the same physics and measurement principles as soil moisture sensors. The theory behind capacitance, TDR and heat pulse velocity sensors can be found in The Soil Water Compendium.

 

capacitance

capacitance sensorCapacitance sensors, such as the GS1 Water Content Sensor or the GS3 Water Content, Temperature and Electrical Conductivity Sensor, are a low-cost, easy to install and interpret option for the measurement of stem water content.

The stainless steel probes of capacitance sensors are 5 cm in length. Water content measurements are integrated over the entire 5 cm length of the probe. Therefore, the tree stem must be at least 5 cm in diameter for accurate installation of either the GS1 or GS3 sensor (that is, the stainless steel probes cannot be installed in air and must be entirely embedded within the stem).

Furthermore, for accurate stem water content measurements, it is preferable to install the stainless steel probes entirely within the conducting xylem tissue of the tree rather than both the conducting and non-conducting tissue. For the best measurements, the sapwood depth of the sampled tree should have a length of at least 5 cm. For trees with narrow sapwood, the heat pulse velocity sensors (see below) should be used instead.

 

TDR (Time Domain Reflectometry)

TDR SensorTDR sensors are a highly accurate and reliable method to measure the water content of materials. TDR has been used for many years to measure stem water content. Similarly to capacitance sensors, TDR sensors must be drilled into the stem of the plant. The E-Test TDR Sensors are ideal for stem water content measurements as they are small in diameter and length. The E-Test TDR Sensors can also measure moisture content and electrical conductivity (EC) over 2 probes, rather than the 3 probes of the GS3 capacitance sensor. Therefore, the TDR sensor is ideal to minimise disturbance to the tree stem.

As with the GS1 or GS3 capacitance sensors, the stainless steel probes of the E-Test TDR Sensors are 5 cm in length. Water content measurements are integrated over the entire length of the 5 cm probe. Therefore, the tree stem must be at least 5 cm in diameter for accurate installation of TDR sensors (that is, the stainless steel probes cannot be installed in air and must be entirely embedded within the stem).

Furthermore, for accurate stem water content measurements, it is preferable to install the stainless steel probes entirely within the conducting xylem tissue of the tree rather than both the conducting and non-conducting tissue. For the best measurements, the sapwood depth of the sampled tree should have a length of at least 5 cm. For trees with narrow sapwood, the heat pulse velocity sensors (see below) should be used instead.

 

heat pulse velocity (HPV)

SFM1 Sap Flow MeterHeat pulse velocity (HPV) sensors can simultaneously measure stem water content and sap flow. Therefore, HPV sensors can provide greater insights into plant water relations than capacitance or TDR sensors.

HPV sensors are based on theories thermal conductance and convection in materials. Thermal conductance and convection theories have been in use since, at least, the 1930’s and have been used extensively to measure moisture and thermal properties of soils. The theory can also be extended to measure moisture and thermal properties of plant stems.

HPV sensors are advantageous over capacitance or TDR sensors as they can potentially measure a small area or volume of sapwood. The SF3 sensor has 3 measurement points along a 3.5 cm length probe. Each measurement point as a measurement zone of influence of approximately 0.5 cm radius. Therefore, stem water content can be measured in plants stems with a diameter as narrow as 1 cm.

In larger trees, or with plants stems at least 3.5 cm in radius, stem water content can be measured at 3 depths along the radial profile of the sapwood. Therefore, greater insights into stem water content dynamics can be gained by measuring moisture content at the outer, middle and inner rings of sapwood. Different radial patterns of stem water content could have important implications for drought tolerance or recovery.

 

research monitoring systems

environmental monitoring systemsEdaphic Scientific can provide a complete research monitoring system where stem water content measurements can be performed simultaneously with other parameters of interest including:

The stem water content sensors supplied by Edaphic Scientific can be integrated with your existing system, or we can provide data loggers, with remote access over the mobile/cellular phone network, that are completely pre-programmed and ready to be installed.

Scientists from Edaphic Scientific can even assist you with field installation, training of staff and students, and on-going assistance with data interpretation and analysis.

 

 

 

an example of stem water content measurements

Matheny et al (2015) deployed capacitance GS3 sensors into maple and oak trees in order to measure stem water content alongside sap flow, soil moisture and meteorological measurements.

The Gs3 sensors were calibrated for wood density in maple and oak to measure stem volumetric water content.

Matheny et al also calculated stem water storage by estimating the volume of conductive xylem tissue (i.e. sapwood tissue) in their sampled trees. Stem water storage was then calculated by integrating stem volumetric water content over the conductive volume of the stem.

Matheny et al showed that stem water storage decreases with a decline in soil moisture content for a maple but not an oak tree. The following figure (adapted from Figure 3, Matheny et al 2015), shows that as soil moisture decreases, stem water storage remains constant in oak. However, for maple, there is a correlated decline between stem water storage and soil moisture. The research highlights different physiological responses of tree species which will have further implications for modelling and species response to environment change.

 

Matheny Stem Water Content