Abstract

Two trees were instrumented with heat pulse sapflux sensors in the Southern Sierra Critical Zone Observatory (SSCZO) within the Kings River Experimental Watershed (KREW) to better understand transpiration as it relates to water availability from deeper sources. At the first instrumented site, CZT-1, a White Fir (Abies concolor) was instrumented on a flat ridge with access to deep soil moisture. Extensive monitoring of shallow and deep soil regions confirm that there is significant soil water available from 100-400cm as the tree exhausts water from shallower depths. A root excavation of an adjacent tree shows the roots distributed from 30-150cm with limited roots available to access deeper soil water and water stored in the saprolite. At the second instrumented site, CZT-2, a Ponderosa Pine (Pinus Ponderosa) was instrumented with a similar suite of sap flow and soil sensors. The CZT-2 site is on a slight slope and is characterized by shallow soils (<90cm) with extensive cobbles and bedrock outcrops with limited access to deeper soil or saprolite water. The second site also sits in the open while the first site is more protected in a closed forest. The two sites show different responses to changes in rain and snow loading from above as well as soil drainage and water depletion from below. They also have different thresholds for transpiration shut down both due to late season water deficit and also during winter periods where air temperatures are high enough to permit photosynthesis. Sap flux data are supplemented by extensive soil water content and potential measurements around both trees as well as evapotranspiration measurements from a 50m flux tower located between the two instrumented trees.

Citation

Hartsough, P.C. Roudneva, E., Malazian, A.I., Meadows, M.W., Kelly, A.E., Bales, R.C., Goulden, M., Hopmans, J.W. (2011): Comparison of sap flux data from two instrumented tree species in a forested catchment with different levels of water stress. Fall meeting, American Geophysical Union, December 2011. Abstract GC31A-1023. .