Invasive exotic plant monitoring at Black Canyon of the Gunnison National Park, 2003–2017

Washuta, Amy; Perkins, Dustin; Gommermann, Luke

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. This report documents and maps invasive exotic plant infestations detected at Black Canyon of the Gunnison National Park (NP) during 2017. It also summarizes all NPCN work completed in the park in 2003–2015. In 2017, a total of 115.5 kilometers (71.8 mi) were monitored, covering 65.7 hectares (162.3 acres) at Black Canyon of the Gunnison NP. A total of 1,441 patches of 15 priority IEP species were detected on monitoring routes and transects. Yellow sweetclover (Melilotus of-ficinale), musk thistle (Carduus nutans), reed canarygrass (Phalaroides arundinacea), woolly mullein (Verbascum thapsus), Canada thistle (Breea arvensis), and spotted knapweed (Acosta maculosa) were the most commonly detected priority IEPs. Routes with the highest density of invasive plant patches were the Gunnison River 6–right (51.7/km), Red Rock Canyon (34.2/km), East Portal Road (33/km), and Gunnison River 1 (30/km). Infestation rates were much lower on trails than on riparian and road routes. Most (80.8%) of the IEP patches recorded were 4–400 m2 in size. Of the six recorded tree patches, four were sapling-stage Siberian elm (Ulmus pumila), and two were patches of seedling-stage tamarisk (Tamarix sp.). A total of nine IEP species were detected in 220 transects in 2017. Cheatgrass (Anisantha tectorum), reed canarygrass, and yellow sweetclover were the most common IEP species in transects. Cheatgrass was found in similar prevalence across roads and drainages but declined in both presence and percent cover since 2015. Reed canarygrass remained relatively constant in transect cover along the Gunnison River since 2015, but increased in cover in Red Rock Canyon. Yellow sweetclover was most common along roadways, where it remained relatively constant since 2015. From 2003 to 2017, six IEP species were consistently detected along common monitoring routes in the park. Bull thistle (Cirsium vulgare), common burdock (Arctium minus), Canada thistle, and woolly mullein patch numbers have generally declined since the 2003–2004 or 2010–2012 surveys. Only two patches of Russian thistle (Salsola sp.) were recorded along common routes in 2017, the fewest since surveys began. Russian knapweed (Acroptilon repens) has declined across the three common road routes, with only one patch detected in 2017. Since it was added to the IEP list in 2010–2012, the number of patches of reed canarygrass increased considerably between 2010–2012 and 2015 along the Gunnison River 5 route but decreased considerably along the Gunnison River 6 and Red Rock Canyon routes over the same time period. Yellow sweetclover, one of the most widespread IEP species in the park, increased in patch number over most of the routes from 2015 to 2017. Spotted knapweed has increased in the number of patches during each sampling year on the North Rim Roads. Russian knapweed was detected for the first time on the South Rim Road in 2017.

Invasive exotic plant monitoring at Black Canyon of the Gunnison National Park, 2003–2017

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