title: Precipitation thresholds and drought-induced tree die-off: insights from patterns of Pinus edulis mortality along an environmental stress gradient.
abstract: Recent regional tree die-off events appear to have been triggered by a combination of drought and heat - referred to as 'global-change-type drought'. To complement experiments focused on resolving mechanisms of drought-induced tree mortality, an evaluation of how patterns of tree die-off relate to highly spatially variable precipitation is needed. Here, we explore precipitation relationships with a die-off event of pinyon pine (Pinus edulis Engelm.) in southwestern North America during the 2002-2003 global-change-type drought. Pinyon die-off and its relationship with precipitation was quantified spatially along a precipitation gradient in north-central New Mexico with standard field plot measurements of die-off combined with canopy cover derived from normalized burn ratio (NBR) from Landsat imagery. Pinyon die-off patterns revealed threshold responses to precipitation (cumulative 2002-2003) and vapor pressure deficit (VPD), with little to no mortality (< 10%) above 600 mm and below warm season VPD of c. 1.7 kPa. [Correction added after online publication 17 June 2013; in the preceding sentence, the word 'below' has been inserted.] Our results refine how precipitation patterns within a region influence pinyon die-off, revealing a precipitation and VPD threshold for tree mortality and its uncertainty band where other factors probably come into play - a response type that influences stand demography and landscape heterogeneity and is of general interest, yet has not been documented.
authors.affiliation: Earth and Environmental Science Department, Lehigh University, Bethlehem, PA, 18015, USA.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Clifford
authors.affiliation: Columbia Basin Groundwater Management Area, Kennewick, WA, 99366, USA.|Intera Geoscience and Engineering, Richland, WA, 99354, USA.
authors.forename: Patrick D
authors.initials: PD
authors.lastname: Royer
authors.affiliation: Merriam-Powell Center for Environmental Research, Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ, 86011, USA.
authors.forename: Neil S
authors.initials: NS
authors.lastname: Cobb
authors.affiliation: Department of Ecology & Evolutionary Biology, School of Natural Resources and the Environment, University of Arizona, Tucson, AZ, 85721, USA.
authors.forename: David D
authors.initials: DD
authors.lastname: Breshears
authors.affiliation: USDA Forest Service Rocky Mountain Research Station, Albuquerque, NM, 87102, USA.
authors.forename: Paulette L
authors.initials: PL
authors.lastname: Ford
mesh_terms: D057231:Climate Change; D055864:Droughts; D004777:Environment; D005843:Geography; D018653:Juniperus / Q000502:physiology*; D009516:New Mexico; D028223:Pinus / Q000502:physiology*; D018515:Plant Leaves / Q000502:physiology; D011891:Rain; D013312:Stress, Physiological; D014197:Trees
keywords: Pinus edulis; climate change; die-off; drought; mortality; pinyon pine; pinyon-juniper woodlands; threshold