Late-Holocene seasonal moisture variability: Range Creek Canyon, Utah, USA

A 3300 year-long reconstruction of paleoenvironmental moisture conditions was constructed from a sediment core from North Gate Bog (NGB) in the northern section of Range Creek Canyon within the Colorado Plateau. The methods used to analyze the record include loss on ignition (LOI), magnetic susceptibility (MS), elemental analysis with X-ray fluorescence (XRF), charcoal influx, isotopic analysis, elemental ratios and pollen percentages, influx, and ratios. This study adds two new insights to the paleoenvironmental record of the northern section of the Colorado Plateau. First, four climatic zones were established. Zone 1 (3300–2750 cal yr BP) had 100-year wet to dry variations with droughts recorded from 3300–3200, 3000–2900, and 2800–2700 cal yr BP. Zone 2 (2750–1600 cal yr BP) had an overall dry period with an 800-year transition to increased warmth and winter moisture. Zone 3 (1600–850 cal yr BP) had an overall warm, wet, summer precipitation climate conducive to the establishment of Zea Mays and Pinus edulis, two staple foods of the Fremont culture. The Medieval Climate Anomaly (MCA) registered warm and wet in this part of the Colorado Plateau. Zone 4 (850–0 cal yr BP) had a sharp transition to a drier climate from 850 to 400 cal yr BP. During the Little Ice Age (LIA), wetter climate taxon increases such as Artemisia, Cyperaceae, and Pinus edulis. The second overall finding in this study was that NGB was a place of human activity including Fremont farming. The identification of a Zea mays pollen grain confirms the archeological presumptions that this higher elevation site was used to farm corn along with other sites in Range Creek Canyon (RCC). The post Fremont occupation period was marked by a sharp increase in organic material and a return of pinyon-juniper woodlands.

Δ14C PEAKS APPEARING IN EARLYWOOD AND LATEWOOD TREE RINGS (AD 770–780) IN NORTHEASTERN ARIZONA

ABSTRACT The AD 775 peak in Δ14C (henceforth, M12) was first measured by Miyake et al. and has since been confirmed globally. Here we present earlywood and latewood Δ14C values from tree rings of pinyon pine (Pinus edulis) from Mummy Cave, Canyon de Chelly National Monument, Chinle, Arizona, USA, for the period AD 770–780. These data reconfirm the timing of M12 and show a small rise in Δ14C in AD 774 latewood. Allowing for the delay in lateral transfer of radiocarbon produced at high latitude, this suggests that 14C peak production occurred in late winter or spring of AD 774. Additionally, Δ14C decreased slightly in the earlywood of AD 775 and increased in the latewood of AD 775 to a higher level than that observed in AD 774.

Quantifying the demographic vulnerabilities of dry woodlands to climate and competition using range-wide monitoring data

Climate change is expected to alter the distribution and abundance of tree species, impacting ecosystem structure and function. Yet, anticipating where this will occur is often hampered by a lack of understanding of how demographic rates, most notably recruitment, vary in response to climate and competition across a species range. Using large-scale monitoring data on two dry woodland tree species (Pinus edulis and Juniperus osteosperma), we develop an approach to infer recruitment, survival, and growth of both species across their range. In doing so, we account for ecological and statistical dependencies inherent in large-scale monitoring data. We find that warming and drying conditions generally lead to declines in recruitment and survival, but there were some idiosyncrasy in the strength of responses across species. Climate conditions lead to vulnerable regions, such as Pinus edulis in N. Arizona, where both survival and recruitment are low. Our approach provides a path forward for leveraging emerging large-scale monitoring and remotely sensed data to anticipate the impacts of global change on species distributions.