Event Title

Potential reconstruction of paleo-vapor pressure deficit and seasonal balance from Rocky Mountain and Utah juniper ring increment

Location

Eccles Conference Center

Event Website

http://water.usu.edu

Start Date

1-4-2014 5:40 PM

End Date

1-4-2014 5:45 PM

Description

Vapor pressure deficit (VPD), controlled mostly by temperature, drives evapotranspiration and in turn governs both agricultural and urban landscape irrigation. Most tree species are sensitive to VPD, closing stomata to reduce transpiration at vapor deficits above 1-2 kPa. At some point temperature-VPD increase affects photosynthesis and tree growth is reduced. Stomatal sensitivity to VPD increases, and photosynthesis and growth reduced, with low precipitation, greater soil water depletion and more water stress. Tree ring growth is widely used as a proxy for hydroclimate, but the role of VPD has been overlooked, particularly as it interacts with low precipitation. We correlated tree ring growth of lower elevation (1700-2100 meter) Rocky Mountain (Juniper scopularum-RMJ) and Utah (J. osteosperma-UJ) junipers from four sites (two sites each species) in the Bear-Wasatch ranges with seasonal VPD and yearly precipitation measured at the USU campus from 1900 to 2010. At two sites, one each RMJ and UJ, soil (precipitation) and atmospheric (VPD) water deficits interacted to limit growth (tree ring indices; r=~0.6 and ~0.5, respectively). At the other two sites dry air/high VPD better explained changes in tree ring index (r=0.45-0.5) than yearly precipitation (~r=0.2), meaning that high summer temperature was the major constraint on growth. RMJ and UJ trees at the driest sites also had 4-10-fold more missing rings, another indicator of greater water stress. Rocky Mountain and Utah juniper species are not commonly used in dendrochronology studies, but these results suggest a direct climate—precipitation/VPD—impact on growth rather than a proxy relationship. Further, this direct relationship illuminates the potential to reconstruct paleo growing season evapotranspiration (ET) and seasonal water deficit (precipitation minus ET) for northern Utah back approximately half a millennia.

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Apr 1st, 5:40 PM Apr 1st, 5:45 PM

Potential reconstruction of paleo-vapor pressure deficit and seasonal balance from Rocky Mountain and Utah juniper ring increment

Eccles Conference Center

Vapor pressure deficit (VPD), controlled mostly by temperature, drives evapotranspiration and in turn governs both agricultural and urban landscape irrigation. Most tree species are sensitive to VPD, closing stomata to reduce transpiration at vapor deficits above 1-2 kPa. At some point temperature-VPD increase affects photosynthesis and tree growth is reduced. Stomatal sensitivity to VPD increases, and photosynthesis and growth reduced, with low precipitation, greater soil water depletion and more water stress. Tree ring growth is widely used as a proxy for hydroclimate, but the role of VPD has been overlooked, particularly as it interacts with low precipitation. We correlated tree ring growth of lower elevation (1700-2100 meter) Rocky Mountain (Juniper scopularum-RMJ) and Utah (J. osteosperma-UJ) junipers from four sites (two sites each species) in the Bear-Wasatch ranges with seasonal VPD and yearly precipitation measured at the USU campus from 1900 to 2010. At two sites, one each RMJ and UJ, soil (precipitation) and atmospheric (VPD) water deficits interacted to limit growth (tree ring indices; r=~0.6 and ~0.5, respectively). At the other two sites dry air/high VPD better explained changes in tree ring index (r=0.45-0.5) than yearly precipitation (~r=0.2), meaning that high summer temperature was the major constraint on growth. RMJ and UJ trees at the driest sites also had 4-10-fold more missing rings, another indicator of greater water stress. Rocky Mountain and Utah juniper species are not commonly used in dendrochronology studies, but these results suggest a direct climate—precipitation/VPD—impact on growth rather than a proxy relationship. Further, this direct relationship illuminates the potential to reconstruct paleo growing season evapotranspiration (ET) and seasonal water deficit (precipitation minus ET) for northern Utah back approximately half a millennia.

http://digitalcommons.usu.edu/runoff/2014/2014Posters/17