Objective:

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.

Novelty:

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.

Design:

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.

Responses:

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

Datasets:

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