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Drivers of radial growth and carbon isotope discrimination of bur oak (Quercus macrocarpa Michx.) across continental gradients in precipitation, vapour pressure deficit and irradiance
Voelker, S., F. Meinzer, B. Lachenbruch, J. Renée Brooks, AND R. Guyette. Drivers of radial growth and carbon isotope discrimination of bur oak (Quercus macrocarpa Michx.) across continental gradients in precipitation, vapour pressure deficit and irradiance. PLANT, CELL, AND ENVIRONMENT. Blackwell Publishing, Malden, MA, 37:766-779, (2014).
Tree-ring characteristics including stable isotope composition are commonly used to reconstruct climate variables and establish mechanisms that underlie oscillations in modes of climate variability. However, divergence from the assumption of a single, primary biophysical control over these tree-ring variables may reduce the accuracy of climate reconstructions or obscure true oscillatory patterns. Here we examine patterns of ring-width indices (RWI) and carbon stable isotope discrimination signals (Δ13C) from tree-rings of bur oak (Quercus macrocarpa Michx.) within and beyond its current bioclimatic envelope to identify the conditions under which a switch may occur in the environmental controls on these paleoclimate proxies. Our results indicate that for modern bur oaks, controls on both RWI and Δ 13C differed substantially across the range of this species. At the center and western edge of the range, RWI was controlled by both atmospheric drought and soil water deficits, whereas at the northern and wettest site the influence of these variables was weak. Across tree-rings from each site, leaf internal to atmospheric vapor pressure difference (VPD) was the primary control on tree-ring Δ13C. The scaling of Δ13C with VPD was much closer to previously reported canopy-level eddy flux measurements than our own leaf gas exchange measurements on bur oaks. Among sites, photosynthetically active radiation (PAR) was a secondary influence on Δ13C. In combination, VPD and PAR closely predicted Δ13C among sites (r2=0.81, P=0.039). Correlations between RWI and Δ13C differed in strength and direction among sites and scaled with VPD or the average fraction of precipitation that was transpired. We therefore propose that the strength and direction of correlations between RWI and Δ13C can be used to more reliably infer past wetness or aridity from paleo wood by determining the degree to which tree carbon gain and growth has been more limited by moisture or irradiance over decadal or greater timescales.
Scientists often look to past climates to predict how ecosystems and their services will respond to future climate change, and one highly successful method for doing such hindcasting is dendrochronology. However, climate predictions from dendrochronology assume that trees respond similarly to climate drivers across a broad range of past climates. In this paper, we examine growth and physiological responses of Burr Oak across the breadth of climates within its growing range and some outside its current range. We find that this assumption of similar responses across climates does not hold for Burr Oak, but that the use of other proxies such as stable isotopes contained within tree rings can help identify whether trees are shifting their response to various drivers through time. This work will help verify the robustness of dendrochronological methods for hindcasting ecological responses.
BROOKS DRIVERS OF RADIAL GROWTH AND CARBON ISOTOPE DISCRIMINATION OF BUR OAK.PDF (PDF,NA pp, 57.885 KB, about PDF)
Record Details:Record Type: DOCUMENT (JOURNAL/PEER REVIEWED JOURNAL)
Organization:U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
NATIONAL HEALTH AND ENVIRONMENTAL EFFECTS RESEARCH LAB
WESTERN ECOLOGY DIVISION
FRESHWATER ECOLOGY BRANCH