Response of Larrea tridentata to a Natural Extreme Cold Event at the Sevilleta National Wildlife Refuge, New Mexico

Shrub expansion into grasslands can cause abrupt changes in ecosystem processes. Creosote (Larrea tridentata) is a native shrub in warm, arid deserts of the southwestern US and has taken over C4 grasslands. A limited freeze tolerance is thought to dictate the northern boundary of creosote and the Sevilleta National Wildlife Refuge occurs near to the northern extent of creosote. Cold temperatures are known to damage creosote. In laboratory trials, temperatures of -25 for 1 hour lead to xylem damaging embolism in nearly 100% of stems and temperatures of -24 C lead to seedling death in the lab. Sevilleta LTER meteorological data from a station located within creosote shrublands indicated a low temperature of -20 C between 1999 and 2010. On February 3, 2011 temperatures hit record lows in central New Mexico, reaching -30 C at shrublands within the SNWR. To address how creosote responds to a natural extreme cold events, plots were established to monitor creosote initial response and regrowth following the cold event. Initial surveys will determine canopy death and subsequent surveys of the same individuals will allow us to determine how creosote responds to record cold temperatures.