HR: 0830h
AN: B31D-0327    [PDF]
TI: Drought Cycles in Northern New Mexico, Isotopic Evidence of Forest Stress
AU: * Fessenden, J E
EM: julianna@lanl.gov
AF: Los Alamos National Laboratory, Earth and Enviornmental Sciences, EES-6, MS D462, Los Alamos, NM 87545 United States
AU: Valdez, C E
EM: cev@lanl.gov
AF: Los Alamos National Laboratory, Earth and Enviornmental Sciences, EES-6, MS D462, Los Alamos, NM 87545 United States
AU: Heikoop, J M
EM: jheikoop@lanl.gov
AF: Los Alamos National Laboratory, Earth and Enviornmental Sciences, EES-6, MS D462, Los Alamos, NM 87545 United States
AU: Breshears, D D
EM: daveb@lanl.gov
AF: Los Alamos National Laboratory, Earth and Enviornmental Sciences, EES-6, MS D462, Los Alamos, NM 87545 United States
AU: Ebinger, M H
EM: mhe@lanl.gov
AF: Los Alamos National Laboratory, Earth and Enviornmental Sciences, EES-6, MS D462, Los Alamos, NM 87545 United States
AU: Allen, C D
EM: craig_allen@usgs.gov
AF: United States Geological Survey, Jemez Mountain Field Station, Fort Collins, CO 80526 United States
AB: Severe droughts in the southwestern United States are shown to occur about every 50 years. Accompanying these droughts, disturbance varieties such as fire or insect infestation produce ecosystem shifts in forest species composition. Specifically, in the Jemez Mountains of northern New Mexico Mountains shifts from Ponderosa pine ({\it Pinus ponderosa}) to pinon ({\it Pinus edulis})/juniper ({\it Juniperus monosperma}) to juniper forests have occurred in the last 100 years. Stable carbon isotope ratios of needle tissues and cellulose from tree rings were measured to determine the periodicity and the severity of regional drought in the Jemez Mountains. Pinon and Ponderosa pines were investigated over an elevation gradient to determine the temperature and precipitation thresholds necessary to cause significant changes in water use efficiency, in isotope ratios, and in large-scale species die-off. Samples of organic $\delta$$^{13}$C in whole leaf tissue were collected from pinon species from attached cohorts where a total of 7 years could be measured. The $\delta$$^{13}$C of cellulose from tree ring samples were collected from both pinon and Ponderosa species where select years over the past 100 years were analyzed. During periods of intense drought, greater than 4 successive years, steady enrichments in $^{13}$C were observed with highest levels of stress occurring at the lowest elevation sites. These results suggest that $\delta$$^{13}$C can be used as a marker for drought in both needle and wood tissues, that the threshold for stress and large scale forest die-off occur at low elevation, and that there is about a 50 year periodicity in severe drought observed in the northern New Mexico region.
DE: 0315 Biosphere/atmosphere interactions
DE: 0400 Biogeosciences
DE: 1812 Drought
DE: 1818 Evapotranspiration
DE: 1851 Plant ecology
SC: Biogeosciences [B]
MN: 2003 Fall Meeting