Invasive Exotic Plant Monitoring at Capitol Reef National Park: 2025 Field Season

Pleasant Creek in Capitol Reef National Park, one of four routes surveyed in 2025 where tamarisk increased and Russian olive was detected for the first time.

NPS/Amy Washuta

Why Monitoring Matters

Non‑native plants occur in many places without disrupting the ecosystem, but invasive exotic plants (IEP) are different because they spread quickly and can alter ecosystems, strain park and community resources, and reduce the safety and experience of visitors. At Capitol Reef National Park (CARE), this threat is increasing as tamarisk (Tamarix sp.), halogeton (Halogeton glomeratus), and Russian olive (Elaeagnus angustifolia) now make up most priority infestations and are appearing in new areas. As these infestations increase, IEP monitoring helps park staff detect new invasions early, understand where these aggressive species are spreading, and focus control efforts. This update highlights current trends, high‑risk areas, and ongoing challenges.

At-a-Glance

• 727 patches of 10 priority invasive plant species were detected across four monitoring routes.
• Tamarisk, halogeton, and Russian olive made up 90% of all patches.
• IEPs occurred on nearly half of transects, with Highway 24 the most affected.
• Tamarisk increased on Oak and Pleasant Creeks, while Russian olive appeared on Pleasant Creek for the first time..

What We Found

In 2025, monitoring crews documented 727 patches of 10 priority invasive plant species along 87.1 km of the Oak Creek, Pleasant Creek, Highway 24, and Scenic Drive routes. Highway 24 contained by far the largest number of detections (558 patches/km), followed by Pleasant Creek (89 patches/km), Oak Creek (69 patches/km), and Scenic Drive (11 patches/km) (Table 1). Tamarisk made up more than half of all mapped infestations park‑wide, reflecting its broad distribution across multiple routes.

What's a priority "IEP"?

Priority invasive species are those identified by park and NCPN staff as having the greatest potential to harm park ecosystems and are the focus of early detection and control efforts.

Table 1. Total IEP patches and IEP priority patches by route and route type, Capitol Reef NP, June 5–11, 2025.

Route	Route type	Length (m)	Total patches	Total IEP Priority patches	IEP Priority Patches/km
Scenic Drive	Road	19,632	11	11	0.56
State Route 24	Road/Riparian	50,304	558	558	11.09
Oak Creek	Riparian	7,206	69	69	9.58
Pleasant Creek	Riparian	9,918	89	89	8.97

Species trends varied by location. Tamarisk increased along both Oak and Pleasant creeks, contributing to elevated infestation levels on those routes. Russian olive was recorded on Pleasant Creek for the first time, representing a new area of concern (Figure 1). Along Highway 24, both halogeton and Russian thistle remained widespread, with Russian thistle detected in frequencies similar to previous monitoring years. African mustard (Malcolmia africana) was detected in small numbers and, although limited in extent, remains important to watch because small populations of fast‑spreading species can expand quickly if not treated early.

Figure 1. Close‑up of Russian olive (Elaeagnus angustifolia) foliage and flowers.

NPS/Neal Herbert

How We Collected the Data

Crews followed the NCPN’s invasive plant monitoring protocol, which is designed to efficiently locate both new and established infestations along roads, trails, and stream corridors, the places invasive plants most often spread. Before fieldwork began, staff reviewed and updated the park’s list of priority invasive species, and observers were trained to recognize all species on that list.

During the 2025 field season, crews surveyed the Oak Creek, Pleasant Creek, Highway 24, and Scenic Drive monitoring routes (Figure 2). Observers walked each route recording species, patch locations, and patch size classes.

Figure 2. Invasive plant monitoring routes in Capitol Reef National Park during the 2025 field season.

NPS/Joe Brehm

Crews also collected additional information at transects spaced every 500 meters along the routes. At each transect, they sampled vegetation in three 1‑m² quadrats placed at fixed distances from the route. These quadrats were used to estimate percent cover of invasive plants. Together, the route surveys and transect measurements provide reliable information about where priority invasive species are occurring and how their abundance and distribution change from year to year.

What are “transects” and “quadrats”?

A transect is a straight line that researchers follow, stopping at regular points to record observations about plants, soil, wildlife, or other natural features. A quadrat is a small square frame used to closely examine and measure the plants and ground cover in a specific spot.

What Comes Next

Park managers can use the findings described here and in the full report, Invasive Exotic Plant Monitoring at Capitol Reef National Park: 2025 Field Season, to refine detection, management, and prevention across CARE. Tamarisk remains the most widespread priority species and often occurs as mature trees, so sustained, large‑scale control efforts will be important. African mustard, halogeton, and Russian olive are still limited in extent, which makes them good candidates for immediate response before populations expand. Russian thistle remained widespread on Highway 24 and was detected at levels similar to previous monitoring years, highlighting the need for continued attention along major travel corridors. Although patch frequency on State Route 24 has decreased since its 2021 peak, increases on Oak and Pleasant creeks, including the first confirmed detections of Russian olive on Pleasant Creek, emphasize the importance of timely action in high‑risk road and riparian areas.Park managers can use these findings to better detect, manage, and prevent the spread of invasive plants at Golden Spike National Historical Park.

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Information in this article was summarized from Invasive Exotic Plant Monitoring at Capitol Reef National Park: 2025 Field Season by D. Perkins. Content was edited and formatted for the web by E. Rendleman.

Tags: capitol reef national park, ncpn, northern colorado plateau, northern colorado plateau network, monitoring, invasive plants, plants, invasive, invasive species, inventory and monitoring division, invasive plant monitoring,