Protecting Trees

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Protecting Trees from Beaver Damage 

by Steve Materkowski, EIT, Engineering Inspector, South Platte River Program

An integral part of re-vegetation along the South Platte River has been the planting of Plains Cottonwoods and other native tree species. Unfortunately, many of these trees have been damaged or killed by beavers. Given the time, difficulty and expense of growing trees to maturity, these losses, in the limited areas of riparian growth in an urban environment, are not tolerable. 

Originally we tried to protect trees using "chicken wire" cages. These proved to be mostly ineffective. Beavers can rip down this light wire or bite through it. The more recent practice suggests using a welded wire cage. Although this system works, it is unsightly. 

In 2002, we became aware of the idea of painting trees to protect them from beaver damage. This "Beaver Paint" consists of a combination of latex paint and sand. Two areas along the South Platte River with active beaver populations were chosen for initial testing. Working closely with our routine maintenance contractor, we selected the type and color of paint to use and the proportions of sand to add to the paint. We found that using approximately 20 ounces of sand per gallon of exterior latex paint worked well. We painted a total of 100 trees at the two locations. The trees ranged from 2- to 24-inches in diameter. Some of them had recent beaver damage, which meant that the paint was applied not only to outer bark but to live inner fibers as well. So far the beavers have not damaged any more trees at these two sites. Secondly, after two growing seasons all trees in the test areas appear to be in good health.

Last summer, we had our contractor paint approximately 100 trees in South Platte Park. As of this writing, there has been no further beaver damage in those areas of the park. The Denver Parks Department is also experimenting with this method.

Based on our experience so far, we recommend the following paint-sand mix for beaver protection: 

  • 1 gal. exterior grade latex paint (match paint color to color of tree bark) 
  • 20 oz. playground sand 
  • Mix in sand thoroughly.

It is very important to remove dirt from around the base of the tree and to paint, starting at the ground line, 3 feet up the tree. Apply a thick coat to all areas being painted. We suggest you experiment with the proportions and the color to get the best results. To match the color to the tree bark, get paint swatches from a supplier or have the supplier mix the color that you need.

Each application is unique but with proper mixing, only the beavers will know the paint is there. We do expect the trees will need to be repainted every few years. The exact maintenance cycle for this has yet to be determined.

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