Tree Talk: Reduce small rodent damage

If you’re an experienced tree grower, you know about deer damage on new tree plantings. Deer damage led to the invention of tree tubes, which are routinely used for successful hardwood plantings.

What is often overlooked is the damage from gnawing rodents on new tree plantings. Rodents come in many shapes and sizes from large, (beaver and nutria) medium (rabbits and hares), to small (mice and voles), but they all have a taste for young seedlings.

This article focuses on smaller rodents — gophers, mice and voles — and ways to limit the big damage they can cause.

Planning and assessment

A simple field survey to spot potential problem critters can help prevent planting failure. Do it well before breaking ground. Study your planting site. Does the planting area have heavy grass that provides thick cover to conceal mice and voles? Are gopher mounds visible in and around your proposed site? If your answer is yes to one or both of these questions, read on before you grab that shovel.

Gophers

Photo courtesy of Planta, Inc.

Gopher mound

Pocket gophers are a threat to new seedlings below and above ground, but they also contribute to a healthy, functioning ecosystem by relentlessly turning over vast amounts of soil important for nutrient cycling. Many studies indicate gophers, though weighing only few ounces, routinely turn over about 1 to 2 tons of soil annually, with some estimates as high 3 tons or more. Mineral soil is rotated to the surface, offering an excellent seed bed for acorns, nuts and other seeds. Soil mixed by gopher activity improves plant root growth and rainwater percolation and retention, all of which can reduce run-off and erosion.

Gopher burrows provide homes for a host of other wildlife including salamanders, toads, snakes and lizards. The good news is gophers contribute to a healthy ecosystem. The not-so-good-news is gophers routinely feed on the roots and shoots of newly planted tree and shrub seedlings.

Mice and voles

Mice (genus Peromyscus) and voles (genus Microtus) are also part of a healthy ecosystem but can cause headaches for tree and shrub growers, especially during winter months when forage is scarce. When food supplies dwindle, these critters often resort to stripping the bark from small seedlings. Many plantings have suffered the fate of girdling by these animals.

The most successful small rodent management program relies on combination of population control, exclusion (very cost effective with a high probability of success) rather than eradication (expensive with a low probability of success) and vegetation management.

Photo courtesy of Planta, Inc.

Owl in flight

Kestrels, owls and snakes! Oh my!

Gophers, mice and voles can be partially controlled by attracting natural predators such as raptors and snakes. Kestrels and screech owls are excellent mouse predators, and the barn owl is without equal in its appetite for gophers. It is commonly reported that an average barn owl family (two adults and three young) easily consumes 700 to 1,000 or more gophers in a year. Attract winged rodent predators to your site with the help of nest boxes suited to each species. Rock piles and snake boards (wide pieces of wood supported slightly above ground level) provide excellent habitat for gopher and mouse eating snakes.

Keep the biters at bay

On a micro level, protecting individual seedlings below ground with wire mesh gopher baskets is an excellent strategy. In many regions, a newly planted tree without a gopher basket (much like a hardwood seedling in deer country without a tall tree tube) is a waste of time, money and effort. Gopher baskets are simple devices that keep tunneling gophers at bay by allowing root growth, yet creating a barrier to keep gophers out of the main root area near the stem. Above ground, consider using tree tubes for hardwood trees to prevent stem damage from girdling and bark stripping, especially by mice and voles during the winter months. A taller tree tube (5 feet or more) will prevent deer browse. For problem gophers, trapping can be effective on a small scale.

Level the playing field

In addition to protecting the individual seedling, another excellent strategy involves managing the vegetation near the plantings. Mowing tall grass at the planting site and eliminating weeds from the area nearest the seedlings removes cover for small rodents and makes them vulnerable to predators. — Steve Tillmann, Research and Development, Plantra, Inc.