Invasive Exotic Plant Monitoring at Dinosaur National Monument: 2023 and 2024 Field Seasons

View from Ruple Point overlooking Dinosaur National Monument.

NPS/Amy Washuta

Why Monitoring Matters

At a Glance

• 4,683 infestations of 12 priority species recorded in 2023.
• Tamarisk and broad-leaf pepperwort were most widespread.
• Cheatgrass declined across all river segments.
• Infestations were highest along the Green River above the confluence.

Invasive exotic plants (IEPs)—plants that are not native and can quickly spread in new areas—are growing across Dinosaur National Monument (NM). Species like tamarisk and broad-leaf pepperwort can push out native vegetation, harm wildlife habitat, and reduce the quality of visitor experiences. These plants disrupt ecosystems and cause problems such as fewer pollinators or less plant diversity. Monitoring IEPs helps park managers focus control efforts, protect native species, and keep the landscape healthy. This update highlights current trends, high-risk areas, and ongoing challenges.

What We Found

In 2023, crews recorded 4,683 patches of 12 invasive plant species along nearly 35 miles of monitoring routes in the park (Table 1). Tamarisk, broad-leaf pepperwort, yellow sweet-clover, and Russian knapweed were the most widespread species. These plants were often found along riverbanks and in areas that had been disturbed before.

Table 1. Species observed and infestation size class detected along all monitoring routes, Dinosaur NM, August 16–23, 2023 and June 20–26, 2024.

Species	Common Name	Total Infestations	1 to Few Plants	Few Plants–40m2	40–400 m2	400–1000 m2	> 1000 m2
Arctium minus	burdock	4	1	1	2	0	0
Cardaria spp.	whitetop	9	0	6	3	0	0
Carduus nutans	musk thistle	107	16	33	21	6	31
Centaurea repens	Russian knapweed	271	1	61	106	80	23
Cirsium arvense	Canada thistle	261	2	48	141	44	26
Cirsium vulgare	bull thistle	9	3	5	1	0	0
Elaeagnus angustifolia	Russian olive	9	9	0	0	0	0
Euphorbia esula	leafy spurge	159	1	13	84	38	2
Hyoscyamus niger	black henbane	1	1	0	0	0	0
Lepidium latifolium	broad-leaf pepperwort	365	9	74	124	81	77
Melilotus officinalis	yellow sweet clover	319	12	126	99	67	15
Tamarix sp.	tamarisk	3,169	200	545	1,184	979	261
Priority Species, Total	–	4,683	255	912	1,765	1,295	435

Trends varied by species and river section. Yellow sweet clover decreased on all three river reaches. Musk thistle was less common overall but increased along the Green River above the Yampa. Leafy spurge remained steady along the Green River but increased along the Yampa River.

Cheatgrass declined in cover and frequency across all river segments since 2019 (Figure 1). The decrease may be linked to high water events that washed away some of the plants.

Figure 1. Cheatgrass (Bromus tectorum) persisted across uplands on the Yampa Bench despite a decrease in recent surveys. Although cheatgrass is not a park priority species, its widespread presence warranted monitoring via transects.

NPS/Amy Washuta

Infestations have gone down near Gates of Lodore and Deerlodge Park since 2014 (Figure 2). However, the upper Green River still has many invasive plants and remains a priority for future monitoring and control.

Figure 2. Invasive plant detections mapped along monitoring routes near Gates of Lodore, August 2023. This map shows one example from 33 mapped sections included in the full report. Observations from August 16–23, 2023, document detections of 18 invasive species along this segment of the Green River in Dinosaur NM. Infestation sizes throughout monitoring routes ranged from isolated individuals to patches over 2,000 m².

NPS/Aneth Wight, Eliot Rendleman

How We Collected the Data

Crews surveyed 35 monitoring routes from June 20–26, 2023, covering about 60 kilometers (Figure 3). They recorded invasive plant locations, species, and patch size. Most routes were near water sources, including the Green and Yampa Rivers. Teams walked along each route and documented all visible infestations within a 10-meter-wide area. Quadrats (small 1-m² frames) were placed at set distances along survey lines to estimate plant cover and soil characteristics.

Figure 3. Overview of invasive exotic plant monitoring routes and index of corresponding figures in the full science report at Dinosaur NM, August 16–23, 2023 and June 20–26, 2024.

NPS/Aneth Wight, Eliot Rendleman

Consistent methods were used to estimate how likely it was to detect each plant species in the field. This helps ensure accuracy across different routes and survey teams.

What Comes Next

Infestation patterns were not the same across all rivers. The Green River before it joins the Yampa had the most invasive plants, likely due to controlled water flows from a dam upstream. The section of the Green River below the Yampa had fewer invasive plants, and the Yampa River had the lowest numbers overall. This may be because the Yampa flows more naturally, without a dam controlling it.

Park managers can use these findings to better detect, manage, and prevent the spread of invasive plants at Dinosaur National Monument.

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Information in this article was summarized from Invasive exotic plant monitoring at Dinosaur National Monument: 2023 and 2024 field seasons by T. Nash. Content was edited and formatted for the web by E. Rendleman.