The objective of this study was to manipulate trees in a piñon-juniper woodland to understand the mechanistic basis of the differential mortality often observed during extreme drought in this dominant ecosystem of the southwestern USA.


Initiated in 2006, this study imposed treatments at a scale that is unusually large among such experiments. We maintained treatments for a six-year period (2007-2013) that is also beyond the scale of many such experiments. After extensive mortality in two of the three drought treatments during 2008-2009, an additional control and drought plot were added in 2010, each treated to control bark beetles to assess the role of drought vs. drought + beetle impacts on piñon mortality.


The original study was based on a factorial design featuring three blocks of four plots, with plots assigned to one of four treatments: untreated control, a drought treatment applied by removal of ~45% of ambient rainfall, an irrigation treatment applied by the addition of five to six rainfall events of 19 mm simulated using aerial sprinklers, or a ‘cover control’ treatment consisting of 45% coverage of a full-sized plot with the same plastic used in the drought treatment structure to allow ambient rainfall to reach the plot surface.


We recorded environmental data (precipitation, soil moisture, soil temperature, micrometeorology), tree water potential, tree sap flow, non-structural carbohydrate content of piñon and juniper to evaluate possible mechanisms of response and mortality.

Key publications:

McDowell, N. G., W. T. Pockman, C. D. Allen, D. D. Breshears, N. Cobb, T. Kolb, J. Plaut, J. S. Sperry, A. West, D. G. Williams, and E. A. Yepez. 2008. Mechanisms of plant survival and mortality during drought: Why do some plants survive while others succumb to drought? New Phytologist 178:719–739. https://doi.org/10.1111/j.1469-8137.2008.02436.x


Ecosystem-scale rainfall manipulation in a Piñon-Juniper Woodland: Volumetric Water Content (VWC) Profile Data (2009-2013). https://portal.edirepository.org/nis/mapbrowse?scope=knb-lter-sev&identifier=287

Ecosystem-scale rainfall manipulation in a Piñon-Juniper woodland: Tree Sapwood and Leaf Area Data (2011). https://portal.edirepository.org/nis/mapbrowse?scope=knb-lter-sev&identifier=288

Ecosystem-Scale Rainfall Manipulation in a Piñon-Juniper Forest at the Sevilleta National Wildlife Refuge, New Mexico: Sap Flow Data (2006-2013). https://portal.edirepository.org/nis/mapbrowse?scope=knb-lter-sev&identifier=277