HR: 0800h
AN: B31B-02    [Abstracts]
TI: Causes and consequences of tree mortality in Piñon-Juniper woodlands. Introducing an ecosystem scale rainfall manipulation.
AU: * Yepez, E A
EM: yepezglz@unm.edu
AF: University of New Mexico, Department of Biology Castetter Hall Room 167, Albuquerque, NM 87131, United States
AU: Elliot, J
EM: jelliott@nmt.edu
AF: University of New Mexico, Department of Biology Castetter Hall Room 167, Albuquerque, NM 87131, United States
AU: White, S A
EM: sawhite@unm.edu
AF: University of New Mexico, Department of Biology Castetter Hall Room 167, Albuquerque, NM 87131, United States
AU: Plaut, J A
EM: jplaut@unm.edu
AF: University of New Mexico, Department of Biology Castetter Hall Room 167, Albuquerque, NM 87131, United States
AU: McDowell, N G
EM: mcdowell@lanl.gov
AF: Los Alamos National Laboratory, Earth and Environmental Sciences Division MS-J495, Los Alamos, NM 87545, United States
AU: Pockman, W T
EM: pockman@unm.edu
AF: University of New Mexico, Department of Biology Castetter Hall Room 167, Albuquerque, NM 87131, United States
AB: Tree mortality as a consequence of drought is widespread worldwide. In Piñon-Juniper woodlands of the semiarid North American Southwest this phenomenon is patent but the consequences for the functioning of these ecosystems remain largely unknown. Although several factors have been proposed to explain tree mortality following drought (e.g. plant desiccation, bark beetle attack), no substantial experimental evidence has been produced to give mechanistic explanations for the occurrence of these events, nor for the potential effects on the ecosystem carbon and water cycles following this rapid landscape transformation. In this work, we introduce a plant-to-ecosystem rainfall manipulation experiment in Piñon-Juniper woodlands at the Sevilleta LTER in central New Mexico, USA. The goal of our study is to understand the causes (plant-level) and consequences (ecosystem-level) of tree mortality and/or survival following experimental drought in these woodlands. Framed in hydraulic concepts involving the soil-plant-atmosphere continuum, we are investigating how Pinus edulis and Juniperus monosperma would respond to treatments of rainfall diversion and addition in replicated (n=3) 1600 m² plots. Within this experimental framework, we are first describing the hydraulic architecture of both species to predict plant allocation patterns (e.g. root vs. leaf area) and assess tree-level water transport capacity and/or failure. We believe that a thorough understanding of the tree hydraulic characteristics controlling transpiration will allow us to make robust predictions about the likelihood of plant death or survival during drought episodes and concomitant effects on the ecosystem rain use efficiency. Pre-treatment results (summer-fall 2006) indicate that transpiration rates per unit of leaf area were highly sensitive to variation in hydraulic conductance in the soil and plants and varied according to the contrasting vulnerabilities to xylem cavitation between P. edulis and J. monosperma. In light of these preliminary results we expect to see effects on the transpiration to evapotranspiration ratio and the soil water storage at depth as trees are subjected to chronic drought
UR: http:per.ornl.gov/McDowell.html
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 0495 Water/energy interactions (1878)
SC: Biogeosciences [B]
MN: 2007 Joint Assembly