Invasive exotic plant monitoring at Dinosaur National Monument: Results of the 2019 field season on the Green River, and the third completed monitoring rotation

Invasive exotic plant (IEP) species are a significant threat to natural ecosystem integrity and biodiversity, and controlling them is a high priority for the National Park Service. The Northern Colorado Plateau Network (NCPN) selected the early detection of IEPs as one of 11 monitoring protocols to be implemented as part of its long-term monitoring program. We also calculated a patch management index (PMI) to quantify the extent and density of invasive patches into a single value that helps identify the scale of the problem. Park managers can use this tool to help prioritize IEP treatment. At Dinosaur National Monument, the NCPN monitors IEPs in the Green and Yampa river corridors. This report summarizes data from monitoring on the Green River in 2019, and monitoring on the Yampa River in 2017, to represent the completion of the third monitoring rotation of the entire river corridor (2002–2005, 2010–2011, 2017–2019). During surveys conducted from June 26 to July 2, 2019, NCPN staff detected 12 priority IEP species and two non-priority species in a 84.6-hectare (209-acre) area along 74.4 kilometers of the Green River above (“upper”) and below (“low-er”) its confluence with the Yampa. A total of 2,535 IEP patches were detected. Of those patches, 24.2% and 15.6% were smaller than 40 m2 on the upper and lower Green River reaches, respectively. The patch management index (PMI) was low or very low for 95.7% of patches on the upper Green River and 90.9% of patches on the lower Green River. Tamarisk (Tamarix sp.), broad-leaf pepperwort (Lepidium latifolium), and yellow sweetclover (Meli-lotus officinalis) were the most widespread species. For the first time, NCPN monitoring detected teasel (Dipsacus sylvestris) on the upper Green River. Yellow sweetclover has increased on all three river reaches during the survey years. Musk thistle (Carduus nutans) was found at considerably lower levels than yellow sweetclover but has also increased on all three river reaches. Leafy spurge is increasing on the lower Green River and Yampa River. Cheatgrass was not monitored in the first rotation, but increased substantially in cover and percent frequency on all three river sections from 2010–2011 to 2017–2019. This increase may be due to a lack of recent high-flow scouring events. The highly regulated upper Green River generally has the highest number of IEPs, while the lower Green River has a moderate amount of IEPs. The largely unregulated flows of the Yampa River continue to result in a lower number of patches per kilometer, lower percent cover, and lower percent frequency than the upper or lower Green River. Network staff will return to the monument in 2022 to begin the fourth monitoring rotation.

Silicified logs of Agathoxylon hoodii (Tidwell et Medlyn) comb. nov. from Rainbow Draw, near Dinosaur National Monument, Uintah County, Utah, USA, and their implications for araucariaceous conifer forests in the Upper Jurassic Morrison Formation

A new local flora of silicified logs and wood has been discovered in the Upper Jurassic Morrison Formation in the Rainbow Draw area near Dinosaur National Monument, northeastern Utah, USA. Fossil logs and wood were found in the Salt Wash Member at nine sites at Rainbow Draw and at one site near Miners Draw, south of Blue Mountain. The fossil logs are large and relatively intact, the longest measuring 11 m. The wood is well preserved, coniferous, and can be identified to the species level. Diagnostic anatomical features include resin plugs in the ray cells and axial tracheids, araucarioid tracheary pitting and crossfield pitting, and the lack of resin canals and true, regularly occurring growth rings. This taxon of fossil wood, originally described as Araucarioxylon hoodii Tidwell et Medlyn, is recognized here as a new combination, Agathoxylon hoodii (Tidwell et Medlyn) Gee, Sprinkel, Bennis et Gray, which pertains to the conifer family Araucariaceae. Based on the preserved girth of the logs, the minimum height of the trees could be reconstructed. The largest fossil logs measured at least 127 cm in diameter and hence reached a minimum height of 28 m. Judging from the growth habit of all naturally occurring araucariaceous trees today, the fossil plants likely formed forests of moderately tall trees and were well over 100 years old. The lack of true growth rings shows that there was no seasonality in the local paleoclimate, neither variations in summer–winter temperatures, nor wet–dry cycles. Thus, during the Late Jurassic, tall conifer forests with Agathoxylon hoodii grew in at least two areas in what is now Utah: east of the city of Vernal and near Mt. Ellen in the Henry Mountains. Coupled with the fossil evidence of conifer seed cones and pollen found in the Morrison Formation throughout eastern Utah, the newly discovered fossil logs and wood argue for the reconstruction of Upper Jurassic habitats in this region as mesic and wooded, and the climate as equable, not seasonal, nor semi-arid or arid.

Stratigraphic setting of fossil log sites in the Morrison Formation (Upper Jurassic) near Dinosaur National Monument, Uintah County, Utah, USA

The outcrop belt of the Upper Jurassic Morrison Formation in the northeastern Uinta Basin and southeastern flank of the Uinta Mountains is particularly rich in dinosaurian and non-dinosaurian faunas, as well as in fossil plants. The discovery of several well-preserved, relatively intact, fossil logs at several locations in Rainbow Draw and one location in Miners Draw, both near Dinosaur National Monument (Utah), has provided an opportunity to study the local paleobotany, stratigraphy, and sedimentology of the Morrison Formation in northeastern Utah. The Morrison Formation in northeastern Utah consists of four members. In ascending chronostratigraphic order, they are the Windy Hill, Tidwell, Salt Wash, and Brushy Basin Members. The lithology (including the presenceof glauconite grains) and fossil assemblage of the lower two members (Windy Hill and Tidwell) indicate a marine to marginal marine (coastal plain) depositional environment, whereas the lithology, fossil flora and faunaassemblage of the upper two members (Salt Wash and Brushy Basin) indicate a fluvial–lacustrine depositional environment. At least 10 fossil log sites in Rainbow Draw have been documented so far, and geologic mapping indicates that the logs and wood all occur in the same stratigraphic interval within the Salt Wash Member, approximately 17 to 27 m above the base of the member. The unit containing the logs and wood is about 11 m thick and consists of very fine to fine-grained sandstone and siltstone with indistinct bedding and no discernible sedimentary features.The logs are siliceous, some have a coaly exterior, and they range in exposed length from 0.5 to 11 m and reach diameters up to 1.1 m. In the Miners Draw area, a single siliceous log is documented in the upper part of the Salt Wash Member within a silty sandstone unit that is 4 m thick; its exposed length is about 6 m. Although the correlation of the Miners Draw log-bearing interval to the interval in Rainbow Draw is uncertain, both units are lithologically similar and both occur in the upper part of the Salt Wash Member. The logs have been identified as araucariaceous conifers that pertain to the same taxon originally described as Araucarioxylon hoodii Tidwell et Medlyn 1993 from Mt. Ellen in the Henry Mountains of southern Utah. Concurrent systematic work will prompt a nomenclatural transfer of this species to the genus Agathoxylon. Based on the abundance of large fossil logs and wood in the same stratigraphic interval in Rainbow Draw, wehypothesize that the area was covered by stands of moderately large trees of araucariaceous conifers. The sedimentological evidence suggests that the trees were not transported far from their original site of growth before they were deposited in a low-energy floodplain environment.

Stratigraphic Setting of Fossil Log Sites in the Morrison Formation (Upper Jurassic) near Dinosaur National Monument, Uintah County, Utah, USA

The outcrop belt of the Upper Jurassic Morrison Formation in the northeastern Uinta Basin and southeastern flank of the Uinta Mountains is particularly rich in dinosaurian and non-dinosaurian faunas, as well as in fossil plants. The discovery of several well-preserved, relatively intact, fossil logs at several locations in Rainbow Draw and one location in Miners Draw, both near Dinosaur National Monument (Utah), has provided an opportunity to study the local paleobotany, stratigraphy, and sedimentology of the Morrison Formation in northeastern Utah.

Multidecadal Climate Variability and the Florescence of Fremont Societies in Eastern Utah

Fremont societies of the Uinta Basin incorporated domesticates into a foraging lifeway over a 1,000-year period from AD 300 to 1300. Fremont research provides a unique opportunity to critically examine the social and ecological processes behind the adoption and abandonment of domesticates by hunter-gatherers. We develop and integrate a 2,115-year precipitation reconstruction with a Bayesian chronological model for the growth of Fremont societies in the Cub Creek reach of Dinosaur National Monument. Comparison of the archaeological chronology with the precipitation record suggests that the florescence of Fremont societies was an adaptation to multidecadal precipitation variability with an approximately 30-plus-year periodicity over most, but not all, of the last 2,115 years. Fremont societies adopted domesticates to enhance their resilience to periodic droughts. We propose that reduced precipitation variability from AD 750 to AD 1050, superimposed over consistent mean precipitation availability, was the tipping point that increased maize production, initiated agricultural intensification, and resulted in increased population and development of pithouse communities. Our study develops a multidecadal/multigenerational model within which to evaluate the strategies underwriting the adoption of domesticates by foragers, the formation of Fremont communities, and the inherent vulnerabilities to resource intensification that implicate the eventual dissolution of those communities.