Paul Szejner Abstracts

 

Paul Szener
   Ph.D. Candidate
   Global Change Minor

   Third American Dendrochronological Conference (AmeriDendro 2016)
    Mendoza, Argentina
    March 28 – April 1, 2016

Abstract

Authors: Paul Szejner1, William E. Wright1, Flurin Babst1,2,3, Soumaya Belmecheri1, rouet1, Steve Leavitt1, James R. Ehleringer4, Russell K. Monson1,5

Laboratory of Tree-­Ring Research, University of Arizona, 1215 E Lowell St, Tucson, AZ 85721, USA

Dendroclimatology group, Swiss Federal Research Institute WSL, Zürcherstrasse 111, 8903 Birmensdorf, Switzerland

Institute of Botany, Polish Academy of Sciences, Lubicz 46, 31-­512 Krakow, Poland

Stable Isotope Ratio Facility for Environmental Research, Department of Biology, University of Utah, Salt Lake City, Utah 84112 USA

5 Department of Ecology and Evolutionary Biology, University of Arizona Tucson, AZ 85721, USA

Title:  latitudinal Gradients in the Stable Carbon and Oxygen Isotopes of Tree-Ring Cellulose Reveal Different Climate Influences of the North American Monsoon System.

Summer rainfall plays an important role sustaining different types of ecosystems in the Southwestern US. The arrival of the monsoon breaks the early summer hyper-­arid period in the region providing unique  seasonal conditions for these ecosystems to thrive. It is unknown to what extent monsoon rainfall is used by Ponderosa pine forests, which occupy many mountain ecosystems in the Western US. While these forests  clearly rely on winter snowpack to drive much of their annual net primary productivity, the extent to which they supplement winter moisture, with summer monsoon moisture needs to be clarified. It is likely that there are north–south gradients in the degree to which forests rely on monsoon moisture, as the summer monsoon system tends to become diminished as it moves progressively northward. We addressed these gaps in our knowledge about the monsoon by studying stable Carbon and Oxygen isotopes in earlywood and latewood from cores taken from trees in eleven sites along a latitudinal gradient extending from Southern Arizona and New Mexico toward Utah. Here we show evidence that Ponderosa pine trees from most of these sites use monsoon water to support growth during the late summer, and the fractional use of monsoon precipitation is strongest in the southernmost sites. This study provides new physiological evidence on the influence of the North American monsoon and winter precipitation on tree growth in montane ecosystems of the Western US. Using these  results, we predict differences in the susceptibility of southern and northern montane  forests to future climate change.

Abstract for Lay Audience

Increasing evidence of forest under moisture deficit is often associated with wild-fires, insect

outbreaks and mass tree mortality. The effects of moisture stress on forest have tremendous impacts on the global carbon and water cycle. Luckily, tree-rings are an excellent archive of the environmental conditions and can help to better understand the relation between carbon sequestration and transpiration. This provides insight into how tree are responding to environmental changes over long periods of time. Documenting these responses will allow us to predict how tree growth and productivity will interact on regional changes and under different seasonal time scales (combining Climatology and tree functioning).

This multi-disciplinary study is using a set of tools combining time series and spatial analysis, dendrochronology, plant physiology, climatology and biogeochemistry, to interpret the influence of different seasons on forested ecosystems. I am focusing specifically on the study of the temporal and spatial relationships between the seasonal climate and carbon & oxygen stable isotopes extracted form tree rings collections in the North American Monsoon region. All these set of tools can be applied widely from local to global scale and with a fine temporal resolution giving insights on forest response to climate. However, these techniques haven’t been used widely in may regions and there is an urgent need to transfer this technology where is a great potential for new projects.

Here in the Southwestern US, Summer rainfall plays an important role sustaining different types of ecosystems. The arrival of the monsoon breaks the early summer hyper-arid period in the region providing unique seasonal conditions for these ecosystems to thrive. It is unknown to what extent monsoon rainfall is used by Ponderosa pine forests, which occupy many mountain ecosystems in the Western US. While these forests clearly rely on winter snowpack to drive much of their annual net primary productivity, the extent to which they supplement winter moisture, with summer monsoon moisture needs to be clarified.

We addressed these gaps in our knowledge about the monsoon by studying stable carbon and oxygen isotopes in the first portion of the tree ring (earlywood) and the last portion of the tree-ring (latewood) from tree ring-cores taken from trees in eleven sites along a latitudinal gradient extending from Southern Arizona and New Mexico toward Utah.

Here we show evidence that Ponderosa pine trees from most of these sites use monsoon water to support growth during the late summer, and the fractional use of monsoon precipitation is strongest in the southernmost sites. Finally, this study provides new physiological evidence on the influence of the North American monsoon and winter precipitation on tree growth in montane ecosystems of the Western US, highlighting differences in vulnerability between southern and northern montane forests under future climate change.