Abstract
This study documents tree mortality in Big Bend National Park in Texas in response to the most acute one-year drought on record, which occurred following a five-day winter freeze. I estimated changes in forest stand structure and species composition due to freezing and drought in the Chisos Mountains of Big Bend National Park using permanent monitoring plot data. The drought killed over half (63%) of the sampled trees over the entire elevation gradient. Significant mortality occurred in trees up to 20 cm diameter (P < 0.05). Pinus cembroides Zucc. experienced the highest seedling and tree mortality (P < 0.0001) (55% of piñon pines died), and over five times as many standing dead pines were observed in 2012 than in 2009. Juniperus deppeana vonSteudal and Quercus emoryi Leibmann also experienced significant declines in tree density (P < 0.02) (30.9% and 20.7%, respectively). Subsequent droughts under climate change will likely cause even greater damage to trees that survived this record drought, especially if such events follow freezes. The results from this study highlight the vulnerability of trees in the Southwest to climatic change and that future shifts in forest structure can have large-scale community consequences.
Highlights
Recent widespread tree mortality has been documented across the globe in response to increasingly warmer and drier climatic conditions (Allen & Breshears, 1998; Breshears et al, 2009; van Mantgem et al, 2009; Allen et al, 2010)
While multi-year droughts have been widely identified as agents of tree mortality (Guarin & Taylor, 2005; van Mantgem et al, 2009; Ganey & Vojta, 2011), short-duration acute droughts of one to two years in duration can be responsible for extensive tree death (Breshears et al, 2005; Hogg, Brandt & Michaellian, 2008)
The tree mortality that occurred in response to this short-duration freezing event and one-year drought is striking because relatively few trees in Chisos Mountains (CM) succumbed to the longer decadal drought of the 1990s in this region
Summary
Recent widespread tree mortality has been documented across the globe in response to increasingly warmer and drier climatic conditions (Allen & Breshears, 1998; Breshears et al, 2009; van Mantgem et al, 2009; Allen et al, 2010). Global-change-type droughts, which are severe droughts coupled with elevated summer temperatures, have resulted in landscapeand regional-scale shifts in forest stand structure and species composition (Breshears et al, 2005; Shaw, Steed & DeBlander, 2005). While multi-year droughts have been widely identified as agents of tree mortality (Guarin & Taylor, 2005; van Mantgem et al, 2009; Ganey & Vojta, 2011), short-duration acute droughts of one to two years in duration can be responsible for extensive tree death (Breshears et al, 2005; Hogg, Brandt & Michaellian, 2008). How to cite this article Poulos (2014), Tree mortality from a short-duration freezing event and global-change-type drought in a Southwestern pinon-juniper woodland, USA. Rapid changes in temperature present a unique challenge to trees because cold snaps can cause air bubbles and sap ice to form which can result in stem breakage and hinder water transport (Scholander, Hemmingsen & Garey, 1961; Hammel, 1967; Sucoff, 1969; Zimmermann, 1983)
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