Invasive Plants at Capitol Reef National Park: The 2019 Survey

Capitol Reef National Park. NPS.

Bottom line: the 2019 survey found relatively few invasive exotic plant species and low overall cover — but tamarisk had increased sharply, as known patches grew larger.

Why invasive plants matter

Invasive exotic plants (IEPs) are non-native species that cause, or are likely to cause, economic or environmental harm or harm to human health. They can spread fast, take over new ground and displace native plants, which threatens wildlife, landscapes and recreation. Because they fill different ecological roles than the natives they replace, animals that depended on native plants can lose out, setting off a cascade of effects.

The good news: caught early, IEPs can be eradicated. Small populations are cheaper and easier to control than large ones.

How monitoring works

The Northern Colorado Plateau Network (NCPN) watches for invasive plants in eight National Park Service units:

1. Network and park staff list the priority species for each park.
2. On a rotating schedule, a crew searches for them along set routes, stopping for plots that let ecologists track trends.
3. Each patch gets a Patch Management Index (PMI): patch size × how much of it is covered in weeds, scored from very low to very high.

PMI works together with species and patch counts. Treating very low and low PMI patches can stop small problems from growing — but a species with many small patches may be harder to treat than one with a few large ones.

Capitol Reef, 2019

Capitol Reef's routes — Highway 24, the Pleasant Creek and Oak Creek cattle trails, the Scenic Drive and Cathedral Valley Road — are monitored on a four-year rotation. On May 30–June 1, 2019, NCPN crews surveyed the Scenic Drive and Cathedral Valley Road for the third time.

• 122 patches of 10 invasive species along 34 km (21 mi) of routes and in 66 transects.
• Six priority species made up 119 of the patches; 93.2% of priority patches scored low or very low PMI, so local control or eradication looks feasible.
• Cathedral Valley Road had more priority patches per kilometer than the Scenic Drive.

Tamarisk was the most widespread priority species. Its 72 patches were a marked increase over earlier years, and they had grown: along Cathedral Valley Road, 87% were in the largest size class (1,000–2,000 m2).

Along Cathedral Valley Road, tamarisk made up 80% of invasive plant patches, most in the largest size class. NPS.

Everywhere weeds: cheatgrass and Russian thistle are too widespread to record along routes, so they are tracked in transects. Russian thistle was in 33.3% of transects — more often than since 2012 — though its cover stayed low (0.2%). Cheatgrass was in just 3%.

Tamarisk, also called salt cedar. NPS.

Recommendations

• Prioritize the Scenic Drive and Cathedral Valley Road for control, to stop patches growing and multiplying.
• Treat small patches early to prevent spread and allow eradication. Tamarisk is scattered thinly over a wide area, so controlling it means covering a lot of ground.
• Weigh how fast each species spreads, rainfall and temperature, patch numbers and PMI in setting priorities.

The network planned to return in 2020 to survey Oak and Pleasant creeks, completing the third rotation.

Sources

Based on "Invasive Exotic Plant Monitoring at Capitol Reef National Park, 2019 Field Season," Northern Colorado Plateau Network, National Park Service, summarizing K. Fahey and D. W. Perkins's report; a work of the United States government in the public domain. Its tamarisk photograph, licensed CC BY-NC, is replaced by an NPS one.