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UW Study Finds That Beavers Help Keep Riparian Systems Healthy

February 21, 2014
Beaver building a dam
Matt Hayes, a spatial analyst with the Wyoming Cooperative Fish and Wildlife Research Unit, wrote his master’s thesis on his research that shows beavers can be used as managers to ensure healthy riparian systems. (Stock Photo)

In some circles, beavers have long been considered pests that damage trees, clog up culverts, and build dams that inhibit or alter the natural flow of waterways. But, to two University of Wyoming researchers, the crafty critters are viewed as natural allies that actually can help keep riparian systems healthy in the short and long term.

Results of a recent study of the Pole Mountain Recreation Area in the Medicine Bow National Forest reveal that beavers can be helpful managers of ecological and hydrological systems.

“The goal of this project was to better understand how beavers impact riparian systems and gain an understanding for how managers might be able to use beavers to enact desired habitat/hydrology management strategies,” says Matthew Hayes, a spatial analyst with the Wyoming Cooperative Fish and Wildlife Research Unit at UW.

Hayes, a native of Hastings, Mich., was a UW graduate student who presented his master’s thesis on the subject during November 2012. Scott Miller, associate professor in the Department of Ecosystem Science and Management, served as Hayes’ faculty mentor.

“Historical momentum has been that they are viewed as pests,” Miller says of beavers. “Maybe their positive environmental benefits are being overlooked.”

Management of riparian systems provides water for plants, animals and people -- livestock operations and erosion control. Riparian systems are particularly important in the Mountain West. Such systems occupy less than 2 percent of land area while providing forage and habitat for more than 80 percent of the region’s wildlife species, Hayes says.

Leave it to the beavers

The study determined that, when beaver numbers increase in a habitat and trapping of the animal stops, willow counts improve while aspen and conifer numbers decrease. Beavers forage on aspen and use it to build dams.

As a result of the beavers’ action, trout, amphibian, songbird and moose habitat is increased, and foraging for winter ungulate (hooved animals such as deer, elk and moose) improves. This is because, when beavers build dams, the local water table rises.

More water becomes available and accessible to plants which, in turn, increases the width of the riparian system and provides more food for animals and aquatic life. The increased water table can be crucial to these species, especially if rainfall levels are limited in arid systems like Wyoming.

Beaver ponds store water from snowmelt and rainfall runoff events, and slowly release water over time as damming slows water movement. Beavers provide optimal brook trout habitat in southeastern Wyoming and other places in the West, and can be viewed positively by sportsmen, Miller says.

This riparian area within Pole Mountain includes a mixture of uplands, rock outcroppings, aspen, willows and conifer forest. (Matt Hayes Photo)While riparian systems benefit in from the presence of beavers, there also is a positive cycle when beavers leave an area, Hayes says.

When beaver ponds disappear due to beaver trappings or relocation of the animals, aspen and conifer numbers increase while willow numbers dwindle. Lowered water tables and reduced pressure from beavers are likely reasons aspen bounced back or were converted to conifer, according to the study. Thermal cover increases; nutrient and vegetation cycling go up; and there is regrowth of mature, woody vegetation, with aspen being a notable beneficiary.

The study surprisingly revealed that the vegetation composition in areas influenced by beavers can be altered in as little as eight years.

“This relatively short length required for vegetation to change will allow managers to alter beaver management strategies for desired vegetation outcomes,” says Hayes, who also received his bachelor’s degree, in wildlife fisheries biology and management, from UW. “This same technique can be applied statewide.”

“Beavers are perceived as taking away from riparian areas,” Miller says. “But what Matt’s study shows is that when beavers move out of an area and the dam fails, you can have a desirable vegetative community become established fairly quickly.”

Hayes and Miller say they do not have an accurate count of how many beavers currently inhabit the Pole Mountain area. A 1974 survey, the last time a beaver count was taken there, estimated 272 beavers lived in the area.

Going high tech

Hayes and Miller examined riparian vegetation composition within 100 meters of beaver ponds that were gained or lost between 2001 and 2009, as well as areas, between 1994 and 2009, that were never ponded. This provided the research team two snapshots in time of the area’s land cover. These two periods -- using photos from the very high-resolution National Agriculture Imagery Program (NAIP) -- were compared to determine changes to vegetation over time.

That process could have been laborious and incredibly time intensive, as Hayes' analysis covered a 56,000-acre study area and focused on nine primary stream channels within the recreation area.

But Hayes developed a remote sensing system -- using a laser range finder that communicates wirelessly with a hand-held GPS system. The laser range finder obtained the training data needed to map vegetation at a 1-meter spatial scale. Using Random Forests (a machine-learning algorithm), with the aid of NAIP and ancillary data, Hayes developed a model that was able to map vegetation at a 1-meter spatial scale.

“This is important because most of the data that we have for land cover is 30-meter spatial scale. A large contribution of our work was developing the methods to accurately map vegetation at a 1-meter spatial resolution,” Hayes says. “NAIP data is generally poor for remote sensing application such as this but, using Random Forests, we were able to create a technique to model vegetation.”

To do this, a data management system was set up within the GPS device to collect field data. The system was created so that every collected point was associated with a certain type of vegetation the team researched. These included conifer, aspen, willow, grass, beaver ponds, rock outcrop and uplands.

Total time spent in the field to compile this data was less than eight days, Hayes says.

“These are important tools, but fairly new to the management community,” Hayes says. “One of the major reasons to do this work is to minimize field work and get accurate answers you need for future mapping efforts.”

Hayes has made his models available to the Wyoming Game and Fish Department Aquatic Habitat Division, which funded the research. The organization is interested in the feasibility of using beavers to enhance ecological services and assist managers in watershed restoration efforts.

The research described in his master’s thesis can be used as a baseline for further studies in this area to assist in understanding riparian nutrient cycling and alterations to hydrologic regimes, Hayes says. He adds that Colorado, Idaho and western portions of Montana -- states with riparian habitat at elevation -- also may benefit from his work.

Miller views the interdisciplinary research as unique, as it combined ecology, hydrology and high technology.

“This research merged my interests in wildlife and management tools to find different ways to manage wildlife problems,” Hayes says.

The research Hayes conducted to develop his remote imaging system was published in Remote Sensing Letters earlier this year. He currently is prepping his beaver findings with plans to submit a paper to the Journal of Wildlife Management for possible publication.

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