Invasive Exotic Plant Monitoring at Zion National Park: 2023 Field Season
Nash T. 2025. Invasive Exotic Plant Monitoring at Zion National Park: 2023 Field Season. Science Report. NPS/SR—2025/345. National Park Service. Fort Collins, Colorado. https://doi.org/10.36967/2315109
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 ten monitoring protocols to be implemented as part of its long-term monitoring program. NCPN staff conducted surveys at Zion National Park (NP) from May 24 to May 31, 2023, representing the second component of the third monitoring rotation. Of 55 total IEP patches recorded, 22 patches of four priority IEP species were detected along 83.1 km (51.6 miles). The majority of patches (81.8%) were 40 m2 or smaller, with cover low enough to make management feasible. The most prevalent IEP priority species was Scotch thistle (Onopordum acanthium), with whitetop (Cardaria sp.) also common. These two species represented 81.8% of all patches recorded in 2023. On average, trails had more IEP priority patches per kilometer than roads. The trail with the highest density of patches was Sawmill Spring Trail (1.87 patches/km). There were ten trails that had no priority species detected. The road with the highest density of patches was Smith Mesa (0.64 patches/km). Priority species were not found on two roads. IEPs were found on 131 of 260 transects monitored. Almost all of these detections were cheatgrass (Bromus tectorum). Cheatgrass was present in 50.4% of transects, with an estimated cover of 0.50% across all transects sampled. Cheatgrass has decreased in frequency and in percent cover since 2015–2016. Scotch thistle and Siberian elm (Ulmus pulima) have decreased since 2012–2013 and 2015–2016.
- Type
- Published Report
- Authors
- Nash, Tiffany
- Date of Issue
- 2025-08
- Publisher
- National Park Service
- DOI
- 10.36967/2315109
- Units
- NCPN , NRSS , ZION
- Keywords
- Exotic Species, Exotic/Invasive Species - Plants, Invasive Species, Monitoring, NCPN Invasive Plants Monitoring, Plant Studies, Scotch thistle (Onopordum acanthium), whitetop (Cardaria sp.), ZION
- Subjects
- Ecological Framework: Biological Integrity | Invasive Species | Invasive/Exotic plants