Invasive exotic plant monitoring in Zion National Park: 2018 field season

Perkins, Dustin; Washuta, Amy

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 10 monitoring protocols to be implemented as part of its long-term monitoring program. NCPN staff conducted surveys at Zion National Park (NP) from May 30 to June 4, 2018, representing the first component of the third monitoring rotation. Of 382 total IEP patches recorded, 288 patches of seven priority IEP species were detected along 110.4 kilometers (68.6 mi) of monitoring routes at Zion NP. The majority of patches (52.8%) were 40 m2 or smaller, with cover low enough to make management feasible. Little bur-clover (Medicago minima) was the most prevalent IEP priority species, with bulbous bluegrass (Poa bulbosa), Bermudagrass (Cynodon dactylon), and Siberian elm (Ulmus pumila) also common. These four species represented 94.8% of all patches recorded in 2018. On average, roads had more IEP priority patches per kilometer than trails. The roads with highest density of patches were Watchman Campground and Visitor Center (7.09 patches/km) and Oak Creek and Administrative Area (6.78 patches/km). Patches of priority IEPs were detected along all monitored roads. The trails with the highest patch density were the Pa’rus Trail (9.55 patches/km) and Grotto Trail (5.84 patches/km). No priority species were detected along 10 of the trails monitored. IEPs were found on 144 (73.8%) of 195 transects monitored. Almost all of these detections were cheatgrass (Bromus tectorum). Cheatgrass was widespread—present in 71.3% of transects, with an estimated cover of 1.09% across all transects sampled. Across routes monitored in all three rotations (2012–2013, 2015–2016, and 2018), cheatgrass has increased in frequency (including along the East Rim Trail and Zion Scenic Drive, where it was not detected in transects in 2012–2013), though percent cover remained low. Scotch thistle and Johnsongrass have declined. Both bulbous bluegrass and Siberian elm have increased in prevalence since 2015–2016 but remained lower than in 2012–2013. Little bur-clover increased dramatically across the same monitoring routes from 2015–2016 (21 patches) to 2018 (174 patches). NCPN will return to Zion NP in 2020 to complete the third rotation of invasive plant monitoring.

Invasive exotic plant monitoring in Zion National Park: 2018 field season

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