Precipitation thresholds and drought-induced tree die-off:insights from patterns of Pinus edulis mortality along anenvironmental stress gradient

摘要

Recent regional tree die-off events appear to have been triggered by a combination ofdrought and heat – referred to as ‘global-change-type drought’. To complement experimentsfocused on resolving mechanisms of drought-induced tree mortality, an evaluation of howpatterns 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 edulisEngelm.) 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-offcombined 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 mmand below warm season VPD of c. 1.7 kPa. [Correction added after online publication 17 June2013; 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 whereother factors probably come into play – a response type that influences stand demographyand landscape heterogeneity and is of general interest, yet has not been documented.