Drought Impacts at Stunt Ranch

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The scientific application being addressed with the Stunt Ranch deployment is a long-term investigation of the influence of the 2006-07 Southern California drought conditions on the water relations of important chaparral shrub and tree species that differ in their depth of rooting. Rainfall over this past hydrologic year in Southern California has been less than 25% of normal, making it the driest year on record. Measurements will be made using sap flow sensors to continuously monitor the flow of water through the xylem system of replicated stems of four species to compare their access to soil moisture with plant water stress. Core measurements of air temperature, relative humidity, solar irradiance, rainfall, and soil moisture will be monitored continuously at the same site.

The use of sap flow methods in studies of plant water use is becoming increasingly widespread, and they are playing a prominent role in both large-scale ecological research programs such as NEON and AMERIFLUX, as well as in focused research studies. Sap flow studies coupled with appropriate meteorological and ecophysiological measurements have widespread applications in ecology, forestry, agriculture, and horticulture. Sap flow methods have been used to quantify water use by natural vegetation, forest plantations, crop plants, to determine how water uptake by trees influences groundwater discharge, and to determine the effects of atmospheric and other environmental variables on transpiration by individual tree species.

Sap flow in woody plant stems is measured using a modified Granier technique. Two cylindrical probes of 2 mm diameter are inserted radially into the stem, with one probe placed approximately 100 mm above the other. The upper probe contains a heater element and a thermocouple junction that is referenced to another junction in the lower probe. Constant power is applied to the heater and the difference in temperature between the two probes (&Delta T) is then dependent on the rate of sap flow around the probes; as sap flow rates increase, heat is dissipated more rapidly and so (&Delta T) decreases. Sensors measure the amount of heat carried by the sap, which is converted into real-time sap flow in grams or kilograms per hour. The sensors are non-intrusive and not harmful since the plants are heated up only a few ° C.

Deployment

Data from the experiment is wirelessly collected with a networked data logger. By using the CompactRIO system as part of the SensorKit platform, scientists can use just one data logger and monitor multiple inputs from different plants, providing a broader and more complete data set. The data is then streamed wirelessly back to the lab with the use of a satellite.

About Stunt Ranch

Stunt Ranch is a 310-acre reserve in the Santa Monica Mountains, located within the Santa Monica Mountains National Recreation Area of the National Park Service. The reserve includes mixed communities of chaparral, live oak woodland, and riparian habitats. Stunt Ranch is managed by UCLA as part of the University of California Natural Reserve System.