Wetter Summers Mitigated Temperature Stress on Rocky Mountain Forests During the Last Interglacial Warm Period. Issue 18 (21st September 2021)

• Record Type: Journal Article
• Authors: Berkelhammer, M.; Insel, N.; Stefanescu, I.
• Is Part Of: Geophysical research letters. Volume 48:Issue 18(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-09-21
• Subjects: ecohydrology -- paleoclimate -- tree rings -- stable isotopes -- interglacial climate; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2021GL093678
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Recent droughts have highlighted concerns of how rising summer temperatures will increase tree mortality rates across the western United States. We analyzed subfossil wood samples from Colorado dating to the last interglacial to assess the response of two common conifers to a previous warm period. The trees experienced comparable growth rates and water use efficiency during the interglacial relative to modern despite evidence from model simulations of a ∼ 30% increase in evaporative demand during the peak of the growing season. High‐resolution isotopic analysis of the wood samples show an enrichment in the late season cellulosic δ 18 O relative to modern samples, which we find was associated with increased reliance on summer rain. The data are consistent with model simulations showing the interglacial was associated with wetter summers across the western US. We propose enhanced summer rain during this period compensated for drought stress imposed by higher evaporative demand. Plain Language Summary: Rising temperatures are expected to put stress on forests across the western US both by reducing spring snowpack and increasing the rate that soil moisture is lost to evaporation. We typically use field observations and tree ring records to understand the stress levels forests experience from warming events. However, these records provide a limited context because they do not go back in time far enough to when temperatures were persistently warmer than today. We take advantage of a collection of subfossil wood samples from Colorado that date back to the last interglacial period—116, 000–130, 000 years ago—to assess whether trees altered their water use strategies during the most recent period when summer temperatures were persistently warmer than today. We found that because of higher summer rain during the interglacial, the trees were able to mitigate stress that would be imposed from the added evaporative demand during warmer summers. Future changes in summer rain are therefore likely to be extremely important to whether forests of the western US become subjected to high levels of stress from projected warming. Key Points: Subfossil wood from the last interglacial was analyzed to assess ecohydrological response of fir and spruce to previous warm period Isotopic analysis of subfossil samples show summer rain was a more critical component of the trees' water source during the interglacial Access to and use of summer rain retained favorable growing conditions for the trees despite higher evaporative stress during warm period