Rocky's Riparian Rehabilitation

A clear line exists between the willows inside and outside of the rehabilitation fence along the Fall River in RMNP.

Photo by Barb Boyer Buck

By Jason Van Tatenhove

We see them growing along the creeks and rivers of the Colorado mountains. Their red and yellow hues dot the landscapes of Rocky Mountain National Park, adding beauty to the picturesque views. But their importance to the Park's ecosystem is not just one of beauty. The willow has become a critical resource that is becoming more scarce, and this is having far-reaching impacts across the Park.

Willows are a crucial part of the ecosystem which the rising elk and moose populations have impacted. So much so that steps are being taken to try and measure and mitigate those effects. It all comes down to the beavers, more specifically, the lack thereof. Beaver populations have been declining due to growing numbers of elk and moose. All three animals feed on the Park's willows, and without as many natural predators (wolves were extirpated from RMNP before 1915), these populations have exploded, taxing the supply of willow.

According to the National Park Service (NPS), beavers are considered "nature's engineers" because of their dam-building activities. Shrubs and trees (especially willow) become building material. They use their long, front incisors to gnaw down trunks and branches. Dams can reach heights of seven feet and lengths of 1000 yards.

Healthy winter willows in RMNP

Photo by Dave Rusk

The pond created by the beaver dam protects the colony from predators and provides suitable habitat for a wide variety of other plants and animals. When there isn't enough building material left, the beaver colony moves to a different location.

Scientists regard the beaver as a keystone species, which modifies the environment in such a way that benefits the ecosystem and encourages the presence of other species. Building dams and creating or expanding wetlands alters the landscape, providing a habitat for many other species.

Healthy riparian habitat inside the rehabilitation enclosure in Moraine Park.

Photo by Barb Boyer Buck

Beaver populations have declined in many areas of Rocky Mountain National Park since the 1940s. Beaver surveys in the past ten years indicate that beavers are rare. Recent park surveys suggest that beaver occupy only 10 percent of the most suitable streamside habitat in the Park.

There have been some very creative attempts to restore beaver populations, including a program in Idaho in the 1950s that involved parachuting beavers into rural areas where populations had dwindled.

A healthy riparian habitat inside the enclosure in Endovalley last summer.

Photo by Barb Boyer Buck

But a new project (without the use of parachutes) aims to counteract some of the issues that have come up due to the lack of beavers and willow.

According to an article by Jeremy Sueltenfuss and Alex Brooks of CSU in the latest Rocky Mountain Conservancy Newsletter (see next below for an excerpt), there is now a collaboration between Rocky Mountain National Park, the National Park Service Inventory and Monitoring Network, and Colorado State University with support from Rocky Mountain Conservancy, to address these issues.

By building a series of simulated beaver structures (SBS) they will test the effects of these issues, including lower water levels due to a lack of natural beaver dams. The SBS act like real beaver dams, raising the waterways and groundwater levels in the adjacent floodplain.

Before installing the SBS, the project team monitored water levels within the channel and underground in the floodplain and water movement between the channel and the floodplain, plant species composition within the floodplain, and annual willow growth. These measurements will continue to be collected for the years following the SBS installation to see if water levels and willow growth increase.

Five simulated beaver structures were built in 2019 and 2020. The project team was ecstatic to see immediate increases in the water levels behind the structures and continue collecting data on water and willows. There has been preliminary evidence of success; they also know that beavers are much better at maintaining real beaver dams than are humans. With this in mind, the team's immediate goal is to figure out how to restore a sustainable willow community to maintain a healthy population of beavers. The long-term goal is that the beavers will ultimately finish the restoration of Rocky's meadows to the magical mosaics that sustain a healthy riparian ecosystem.

A willow cone in Moraine Park last summer.

Photo by Barb Boyer Buck

The following is reprinted with permission from Rocky Mountain Conservancy, an excerpt from:

Simulated beaver structures may help restore riparian communities in Rocky

photos and excerpt by Jeremy Sueltenfuss and Alex Brooks, Colorado State University

A team of volunteers and RMNP staff construct a simulated beaver dam (SBS) in Rocky.

Uncertainties about restoring RMNP Willow Floodplains

Planting new willows and building fences to keep out hungry elk and moose has been an effective strategy to preserve and restore some of the willow communities within the park, but it’s become clear that the historically shortened willows in some areas are not growing back to their previous height. And without that growth, there are too little food and building supplies for the beavers.

A willow is tagged to monitor its growth.

Digging deeper, what is it, then, that is limiting willow growth? How can we help these systems to increase that growth, potentially leading to beavers in the future?

An SBS in action

Based on previous studies of meadow soils in Rocky Mountain National Park, we know that beaver dams and ponds, prior to European settlement, kept meadow groundwater levels high, providing easily-accessible water to willows throughout the summer. In many of these same areas today, the streambed is eroded by more than three feet below the riverbank, and groundwater is rarely observed near the ground surface, especially later in the summer when willows need water most. Is the lack of beaver dams causing low groundwater levels? Could this lack of high groundwater be limiting willow growth? Is it possible to mimic beaver dams?

This project, and many others, are funded by the Rocky Mountain Conservancy, the fundraising branch of Rocky. Please consider becoming a member.

https://rmconservancy.org/join-or-give/

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