Northern Leopard Frog (photo credit Colorado Parks and Wildlife - Rémi Pattyn [left] and Keith Penner [right])       

West Plum Creek and East Plum Creek present somewhat of an anomaly in this scenario, as both species have coexisted here for at least three decades. Indeed, during the Stream Health Assessment (SHA), both were observed across most of our study area in West Plum Creek, with most reaches favoring bullfrogs and a few favoring leopard frogs. The SHA provided a unique opportunity to get a snapshot of where these species may be found, but did not provide a complete picture of how these species are interacting in the valley.  

American Bullfrog (photo credit Colorado Parks and Wildlife

Our native Northern Leopard Frogs grow up to 3” long, measured from snout to tailbone. They have leopard-like spots along their back and are further distinguished by light colored dorsolateral ridges, aka two lines along their back on either side.  Bullfrogs grow to the size of a dessert platter and have a nasty reputation for eating virtually any animal that can fit in their mouth. Bullfrogs breed in ponds along the Front Range around August. They spend nearly a whole year as tadpoles before metamorphosing into hopping frogs.  In contrast, leopard frogs breed in early April to early May; their eggs quickly develop into tadpoles, and the tadpoles quickly metamorphose into land hopping frogs in a mere one to two months. This means that leopard frogs can breed in wetlands that only have water for a few months, while bullfrog tadpoles need permanent ponds and lakes.

The increase of such permanent water sources along the Front Range in the form of reservoirs and gravel pit ponds has surely aided the bullfrog takeover. Adding to its uniqueness, Plum Creek stands as a shining example proving that with high-quality, relatively unaltered wetland habitat, our native leopard frogs may be able to coexist with non-native bullfrogs. However, at this point we only have a cursory understanding of how these two species are co-existing and if leopard frogs will be able to maintain their presence despite bullfrog populations.   

Plant Watch: Non-Native Species Can Become Invasive

Canada thistle (Cirsium arvense) is a non-native, deep-rooted perennial that spreads by seeds and aggressive creeping, horizontal roots called rhizomes. Canada thistle can grow 2 to 4 feet in height. The leaves are oblong, spiny, bright green, and slightly hairy on the undersurface.

Canada thistle leaves (left) and first year rosettes (right) (photo credit Denver Botanic Gardens)

Unlike other noxious biennial thistles, which have a solitary flower at the end of each stem, Canada thistle flowers occur in small clusters of 1 to 5 flowers. They are about 1 cm in diameter, tubular-shaped, and vary from white to purple in color (Colorado Dept. of Agriculture). It is designated a ‘List B’ species according to the Colorado Noxious Weed Act.

Canada thistle flowers (photo credit Colorado Department of Agriculture [left] and Colorado State University Extension [right])

Due to the extensive root system and perennial nature of Canada thistle, elimination of infestations requires persistent treatment.  The plant must be stressed and drained of energy over time to kill it entirely. If you are interested in treating Canada thistle, options include:

• Biological control-parasites: Specific insects may be applied for general weakening but won’t eliminate the infestation.  These methods typically take 5-7 years to have significant effect, but can be a pervasive, long-term general control method on large acreage over time.   A rust fungus treatment is being developed. 

• Biological control-grazing: Cattle, sheep, and goats will graze the young plants early in the spring.  This method weakens the plant and slows its seasonal growth, but it should be followed up with other treatments later in the season.   

• Mechanical control-mowing: Mowing can drain the plant’s reserves if done every 10-21 days during the growing season.  It can be done one or more times as the plants are setting flower buds to keep it from flowering and subsequently producing seed.

• Chemical control-herbicides: One of the most effective control methods is the application of herbicides.  Instructions vary, but application periods are typically in the spring through bud formation or bloom and again in the fall.  Fall applications are very effective because the plant is reabsorbing its foliage nutrients at this time of year, taking the herbicide deep into its root system.  Only certain herbicides are labeled for use in open water areas.  (Colorado Dept. of Agriculture-Conservation Services, 2015)

Additional information may be found in the Canada Thistle Identification and Management Fact Sheet produced by the Colorado Department of Agriculture: https://drive.google.com/file/d/1VD0akK6512uYeraw77xI7XVKujmUh81u/view.

Russian Olive (Elaeagnus angustifolia) is a nonnative perennial tree native to Europe and Asia. If you’ve spent any time in the West Plum Creek riparian zone, you have no doubt seen it: a short tree with long silvery white leaves, nasty thorns, and reddish bark. As a Colorado List B noxious weed, Russian olive is one of the most problematic invasive plant species we deal with in West Pum Creek (WPC), and it can be seen along the entire length as well as in several of its tributary creeks.

Left to right: Russian olive leaves and fruits, bark, and thorns (photo credit Jefferson County Invasive Species Management)

Russian olive seedling (left) and clump of mature trees (right) (photo credit Jefferson County Invasive Species Management)

Russian Olive trees are capable of damaging riparian ecosystems in several ways:

• Outcompeting and displacing native vegetation

• Reducing net animal and bird habitat

• Taxing water reserves

As a List B species, Russian Olive trees are required to be eradicated, contained, or suppressed. Many landowners have worked consistently to remove Russian Olive in the WPC corridor. In general, the most successful approach has been to cut down medium and large size trees using a chain saw. Immediately treating the cut stump with an herbicide appropriate for use in a riparian zone will greatly reduce the chances of the tree re-sprouting. Smaller trees may be cut with a large tree pruner and require the same immediate treatment with an herbicide. Very small trees in the first year or two may be simply removed by hand, but of course wearing gloves is strongly recommended.

In all cases, cutting or removal leads to the decision of whether to remove the waste from the riparian zone. Larger trees generate a surprisingly large amount of waste due to the dense growth habit of Russian Olives. In the end the decision to remove the waste or not is up to the landowner, but it is better to cut down the Russian Olive whether or not the waste can be extracted from the riparian zone.

More information on Russian Olive tree removal can be found on the Colorado Department of Agriculture Conservation Services website: www.colorado.gov/ag/weeds

Temperature data readings from May 2022 to July 2023 from West Plum Creek.

In this update, learn about the effects of high creek flows on the 2023 field season, what we are learning so far from conversations with landowners, and next steps for the project. In addition, we are excited to share our new Fishes of West Plum Creek information sheet. 

What effects did the high creek flows have on the 2023 field season?

You know it already, but flows in West Plum Creek were above average this year (see the graph below). Safety is our number one priority so we decided to delay some fieldwork until late summer and early fall when flows had decreased and conditions were safer for accessing the creek. We also needed to wait for flows to decrease because high flows cause soil to wash from the banks, making the water cloudy. The cloudiness, or turbidity, makes it difficult to see and net fish during electrofishing.