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Small-scale Beaver Management Methods: A Review

Introduction

The North American beaver, Castor canadensis, is a native species with building and feeding habits that

cause variations to the water level and local tree growth (Campbell et al., 2015; Johnston et al., 2015).

Beavers consume aspen, poplar, ash, maple, and hickory trees, chewing at the base of the tree to reach the

plant sugars. They use the waste to create dams or lodges. Additionally, beavers engineer lakes to hold

enough water so that during the winter the water does not fully freeze, thereby protecting access to their

lodges (Collen et al., 2001).

Beaver presence has a complex role in the ecosystem. By consuming the cambium layer under the bark of

woody plants, they cause constant destruction of trees along shorelines. They also increase wetlands and

riparian vegetation (McKinstry et al., 1999). Beaver cause hydrologic, chemical and temperature changes

to a location. Introducing beaver can cause sediment deposits, which may alter habitats and improve

species diversity. For instance, researchers in Newfoundland discovered that beaver presence creates

habitats for larger fish and prevents bank erosion (Collen et al., 2001).

Beaver activity sometimes alters ecosystems in unwanted directions. Beaver-induced flooding causes

damage to root systems of seedlings and suppresses overall height growth of trees (Campbell et al., 2015).

They consume threatened species such as the trembling aspen (Populus tremuloides) and the willow

(Salix spp.) (Gallant et al., 2004). Researchers found that the beaver modify habitats by selecting

deciduous trees for food and building material, causing gradual change to tree species composition. Also,

flooding alters nitrogen content in soil and kills most trees within a few years (Hyvönen et al., 2008).

Beavers can also cause residential flooding, which makes them unpopular. Human engineers build

spillways to control the flow of water during flood events, and beavers occasionally dam them. This can

flood neighboring residential areas. Aside from the mess, this imposes a financial burden. New York

State Department of Environmental Conservation has ruled that the State is not responsible for property

damage from wildlife (DEC: Nuisance Beaver), including beaver-caused floods.

Wildlife managers seek to control beaver populations in order to minimize unwanted flooding and

environmental damage. Several types of management techniques exist, including flow devices, fencing,

human pathways, and baiting and trapping. I consider only the first three options here, excluding trapping

because when rangers remove beaver populations, foreign beaver migrate and fill old habitats. I've also

excluded baiting because most stakeholders morally object to killing beavers.

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Over the summer, I engaged in an ongoing project to that used innovative ways to keep the spillways free

of beaver dams and protect the local vegetation surrounding the three lakes at Teatown Lake Reservation

in Westchester, NY. This paper reviews our techniques and compares them to alternatives in order to

suggest a best management practice suitable for Teatown Preserve.

Materials and Methods

Teatown Lake Reservation has developed reliable techniques to observe the complex beaver issue.

Teatown interns and volunteers used Garmen Etrex 10 GPS units to map beaver lodges, dams, and entry

points onto Wildflower Island. (See Figure 1). Staff uploaded data from the GPS units into Google Earth

to create user-friendly maps of beaver habitat. Additionally, staff attached Reconyx Hyperfire camera

traps to trees and posts in order to observe beavers as they rebuild dams and remove trees. The staff at

Voyageurs National Park in Minnesota collect similar data via aerial photography (Johnston et al., 2015).

Figure 1. Trailmap of Teatown Lake Reservation

One of the major goals of Teatown Lake Reserve concerns keeping spillways free of beaver litter. The

New York State Department of Environmental Conservation classifies its spillways according to the

hazard level associated with their failure during a flood. Floods of Class B spillways pose a danger to

homes, main highways, and minor railroads. Floods of Class B spillways may also interrupt relatively

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important public utilities or services (DEC: Guidelines). Landowners need a state-issued permit to

remove a beaver dam; however, if beaver debris blocks structures such as “culvert pipes, water level

control structures and drainage ditches,” people may remove it without a permit (DEC: Permitting).

Flow Devices

Teatown uses three types of beaver management strategies. The first, pipe flow devices, provide a passive

form of management. At Shadow Lake, pipe flow devices are currently in use. This system consists of

pipes of various diameters placed inside a spillway opening, allowing water to flow out of the lake and

into the chute. This device enables beavers to build dams on top of the device without obstructing water

flow through the spillway. Flow devices such as these are considered a cost-effective alternative to

clearing dams or trapping; additionally, they do not require a high level of maintenance (Taylor et al.,

2013). However, if a flood were to occur, the pipes would not control overflow as well as a beaver-free

spillway because even with this devise in place, beavers still manage to place mud and vegetation inside

the chutes. Volunteers at Teatown use plumbing snakes to remove the buildup.

Beaver Peavers

Beaver peavers are experimental structures used in conjunction with flow devices to deter beaver activity.

This passive method of exclusion uses rods covered with thin metal spikes. The beaver peavers make dam

construction difficult for beavers without posing a hazard to wildlife. Teatown uses beaver peavers inside

all spillways in the park.

Fencing

Fencing provides a second method of beaver control. Teatown staff uses it not on spillways, but on

Wildflower Island. Teatown volunteers restored Wildflower Island with rare native plants, and aims to

protect the vegetation from a booming deer population and the destructive nature of beavers.

A wire and electric fence surround the island, but this does not protect the vegetation. Beavers regularly

bypassed the barrier by pushing and bending the plastic fence. Occasionally, they create tunnels under the

fence. In response, Teatown volunteers cut sheets of metal wire to create patches for the pre-existing

fence. They pushing the fencing teeth into the mud and fastening them to existing fence with plastic zip

ties. They also used plastic flexible fencing to wrap the trunks of trees favored by beavers, in accordance

with NYSDEC recommendations (DEC: Nuisance Beaver). Other wildlife managers have had more

success with different types of fencing. Park staff in Washington found that small diameter Vexar mesh

successfully protected seedlings from beavers (Campbell et al., 2015).

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Human Pathways

Human pathways provide the fourth tool for beaver management. Trailways passively deter beavers

because they avoid the odors of pedestrians. A trail along the edge of a lake could serve as a barrier

protecting trees and shrubs from beaver girdling. Trails constructed with wood chips, macadam, and

wood boards have been found to be the most effective by researchers in Tennessee. However, long

periods of rain would wash away human scent and beavers would return (Loeb et al., 2014).

Human pathways exist along all of Teatown Lake, most of Vernay Lake and very little of Shadow Lake.

Figure 2 shows the Lakeside Loop trail, which runs around the entire circumference of Teatown Lake.

This trail is constructed with a floating bridge of wood boards (shown), a wood chip and a natural trail.

We don’t know if this trail deters beavers, but if it does, Teatown might consider installing more of them

in key locations.

Figure 2. Human Pathway at Teatown Lake

Results and Discussion

The managers at Teatown Lake Reservation seek to protect native vegetation and local properties from

beavers. I volunteered with Teatown during the summer of 2016, giving me first-hand experience with the

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damage caused by beavers and the methods that wildlife managers use to control them. After my time as a

volunteer, I reviewed the published literature to create an overview of methods used by other parks and

preserves. My recommendations come from my experience in combination with a literature review.

My first recommendation concerns Teatown’s observation methods. At present, camera traps provide the

main source of observational data related to beaver structures, as shown in Figure 3. However, camera

traps are expensive, and their data require large segments of time for staff to analyze.

Perhaps volunteers and interns could identify trees in the field that are a preferred food source to beaver

using software applications such as iNaturalist. This app collects spatial data on vegetation from people

using smartphones and provides much needed observational data to staff. Additionally, it provides an

inexpensive way to educate the general public and foster a participation in ecological restoration.

Researchers found success using this program while studying endangered palm species in New Guinea,

Madagascar and Singapore (Gardiner et al., 2016). The submitted user observations helped to assess the

extinction risk of palm species worldwide. This method could easily be implemented by individuals in

Teatown’s task groups and has potential applications beyond the scope of the beaver mitigation issue.

Figure 3. Camera Trap

Early intervention techniques might also prove effective (Kristensen et al., 2012). For example, staff

could place protective equipment on tree trunks at risk for being used at structure materials or food for

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beaver. This practice is used sparingly at Teatown but is an effective way to protect lakeside trees from

becoming part of a dam structure.

Lakeside trails could be reworked to serve as human barriers to deter beaver damming and lodging. This

method would benefit the visitors who use the lakes for recreation. On the other hand, the trails may

erode the lakeside and it would require many hours of staff time to fortify them. Also, more access to the

lake would lead to increased amounts of litter from park visitors. Researchers who have used this method

have faced problems when there are rain events, which are common at Teatown (Loeb et al., 2014).

In my opinion, upgrading flow devices used at spillway locations is the most realistic solution for beaver

management. It is a financially feasible method that park staff could easily implement at Teatown. They

could install culvert guards could into the lake bottom and surrounding the spillway in order to block

access to dam locations. Park staff could install additional pipes at Teatown Lake spillway to allow flow

underneath the rain guard when the beaver impoundments prevent water flow (Figure 4). Beavers built

dams as an instinctual response to the sound and movement of water, which cues damming behavior.

Staff could also install perforated pipes in addition to existing pipes, which filter out debris and allow

water flow without the audible cues for damming behavior (Taylor, et al., 2013).

For my last recommendation, I suggest that the people of Teatown consider making peace with the

beaver. Beaver presence may help to improve conditions at Teatown due to their ecological impact.

Teatown Lake is rapidly returning to swamp due to the natural processes involved with the succession of

ponds over time (Sayer et al., 2012). Teatown directors and trustees have been repeatedly faced with the

costly decision to dredge the lake to return its recreational value, or to allow it to become a marsh.

Instead, existing beaver will cause the lake level to rise, potentially serving as restoration stimulus

(McKinstry, et al., 1999).

In eastern Scotland, scientists introduced beavers to an agricultural stream to assess their ability to

promote wetland creation. Researchers tested total suspended solids (TSS), color, extractable P, nitrate,

chloride and sulphate samples collected upstream and downstream a strip of 500 meters that held four

beaver dam structures. They also collected and tested substrata for percentge of organic material. They

found that the presence of beaver reduced nutrient loading and could aid wetlands restoration efforts (Law

et al., 2016).

Similar studies could be conducted at Teatown. Students of the Teatown Environmental Science

Academy (TESA) could monitor changes in water quality. Ecological experiments would provide a great

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opportunity for park representatives to involve the public community with the restoration process. Data

and public support might persuade the directors to allocate funds towards managing a beneficial beaver

population.

Figure 4. Teatown Lake Spillway

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Conclusion

After reviewing current literature, I’ve determined that methods used by staff at Teatown have potential

for improvement that would both alleviate the consequences of a growing beaver population and reduce

the amount of work for staff members. The four methods of management reviewed in this paper are flow

devices, fencing, beaver peavers, and human pathways. Flow devices allow for water to travel under

beaver dams which means that dams do not need to be manually removed. Interns could install non-

corrosive pipes which would have to be regularly cleared of mud, which is a much easier task than total

dam removal. Also, fully submerged pipes would reduce the sound of running water. Flow devices could

be installed at Vernay Lake and updated at Shadow Lake. Pipes of smaller diameters would be ideal for

Shadow Lake because the water level is lower than the spillway level due to evaporation in the summer

months.

Fencing techniques could be improved if visitors participated in data collection. If volunteers identified

trees commonly used for building and eating such as the maple and ash species, it would enable a more

efficient use of time and fencing materials for Teatown staff. Small diameter Vexar mesh would be a

better alternative to the currently used large diameter metal sheets.

The scent of visitors serve as a predator warning for the beaver. Teatown staff could build trailways fully

circling Shadow and Vernay Lakes. They should be built with wood chips to avoid erosion. Human

pathways do not obstruct the visual aesthetic of the preserve as do the fences and flow systems; however,

this method could disturb other native species.

Trapping was not an option I explored because the preserve manager would need to obtain a permit to

trap beaver; additionally, it is illegal to relocate the animal off of the property. (DEC: Remove)

While working on this project, I often questioned whether it was logical to intervene with the ecosystem.

Teatown Lake is gradually returning to a wetland and must be dredged regularly to avoid this. Since the

beaver structures cause the water level to rise, I felt that their presence was more helpful than hurtful. It

became clear that we are intervening purely to prevent damage to the property from flooding and to align

with NYS laws regarding spillways. These have little to do with the ecosystem’s equilibrium and more to

do with human uses of the land. If this was not the case, I would prefer to not interfere with the beaver

and leave the land untouched. On the other hand, Teatown educates the public through summer camps,

festivals, guided hikes, and volunteer programs. It is difficult to assign monetary value to stewardship and

awareness, but my personal belief is that the preserve’s educational capacity is more valuable than the

cost of maintaining the beaver population.

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References

Campbell, D. L.; Engeman, R.M.; Farley, J.P. Effects of Mountain Beaver Management and Thinning on

15-year-old Douglas Fir Growth and Survival. Environmental Science and Pollution Research.

2015, 22, 10824-10829.

Collen, P.; Gibson, R. J. The General Ecology of Beavers (Castor spp.), as Related to Their Influence on

Stream Ecosystems and Riparian Habitats, and the Subsequent Effects of Fish – a Review.

Reviews in Fish Biology and Fisheries. 2001, 10, 429-461.

Hyvönen, T.; Nummi, P. Habitat Dynamics of Beaver Castor Canadensis at Two Spatial Scales. Wildlife

Biology. 2008, 22, 302-308.

Gardiner, L.M.; Bachman, S.P. The Role of Citizens in a Global Assessment of Extinction Risk in Palms

(Arecaceae). Botanical Journal of the Linnean Society. 2016, 182, 543-550.

Guidelines for Design of Dams. Department of Environmental Conservation. Retrieved from

http://www.dec.ny.gov/docs/water_pdf/damguideli.pdf

Johnston, C.A.; Windels, S.K. Using Beaver Works to Estimate Colony Activity in Boreal Landscapes.

Wildlife Management. 2015, 79, 1072-1080.

Kristensen, E.A.; Baattrup-Pedersen, A.; Jensen, P.N. Selection, Implementation and Cost of Restorations

in Lowland Streams: A Basis for Identifying Restoration Priorities. Environ. Science & Policy.

2012, 23, 1-11.

Law, A.; McLean, F.; Willby, N.J. Habitat Engineering by Beaver Benefits Aquatic Biodiversity and

Ecosystem Processes in Agricultural Streams. Freshwater Biology. 2016, 61, 486-499.

Loeb, R.E.; King, S.; Helton, J. Human Pathways are Barriers to Beavers Damaging Trees and Saplings

in Urban Forests. Urban Forestry & Urban Greening. 2014, 13, 290-294.

McKinstry, M.C.; Anderson, S.H. Attitudes of Private- and Public-Land Managers in Wyoming, USA,

Towards Beaver. Environmental Management. 1999, 23, 95-101.

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Nuisance Beaver. Department of Environmental Conservation. Retrieved from

http://www.dec.ny.gov/animals/6992.html

Permitting Guidelines for Breach and Removal of Nuisance Beaver Dams. Department of Environmental

Conservation. Retrieved from http://www.dec.ny.gov/docs/wildlife_pdf/beaverdamguide.pdf

Remove or “Take” Nuisance Animals Legally. Department of Environmental Conservation. Retrieved

from http://www.dec.ny.gov/animals/81531.html

Sayer, C.; Andrews, K.; Shilland, E., et al. The Role of Pond Management for Biodiversity Conservation

in an Agricultural Landscape. Aquatic Conserv: Mar. and Freshw. Ecosyst. 2012, 22, 626-638.

Taylor, J.D.; Singleton, R.D. The Evolution of Flow Devices Used to Reduce Flooding by Beavers: A

Review. Wildlife Society Bulletin. 2013, 38, 127-133.

Acknowledgements

Dr. Sharon Pochron, Research Supervisor

Leigh Draper, Preserve Manager and Trail Steward at Teatown Lake Reservation

Rebecca Policello and Amber Goodman, Interns

Diane Uhle, Head Gardener