Neighborhood Salad Bar - How Mule Deer Can Impact Your Landscape

 By Lauren Vanier

Mule deer, like this doe in Yellowstone National Park, are iconic wildlife throughout the western US.

The penstemons in my front yard were developing flower buds, thrown up on stalks two feet tall. I was anticipating watching bees disappear into their cavernous flowers and hummingbirds bury their long beaks deep into the blossoms. Instead, on one recent morning, I found them chewed off so cleanly, they appeared to have been cauterized. The deer had made their round in the neighborhood. Sheltered amongst our homes from threats, they consume at-will, unbothered and unrepentant.

The chewed remnants of Penstemon stems, with a hastily assembled deer cage protecting plants in the background. Photo by Lauren Vanier

While they are beloved wildlife and generate significant revenue for the state via hunting tags, deer can be absolute menaces to gardeners and farmers. Ask anyone who has invested a pretty penny and hours of labor in gardens or fields, only to have them decimated overnight.

White-tailed deer dominate the eastern United States, while mule deer are the primary western species. Deer are selective browsers, meaning they consume only the most nutritious and palatable forage. They browse leaves, buds, fruits, and stems of both herbaceous and woody plants. In high numbers, deer can severely limit growth and recruitment of their preferred plants, reducing plant diversity across landscapes. There is consensus that white-tailed deer have reached unsustainable numbers in the east, greatly suppressing forest understory plants.

This brazen gal was munching on the shrub behind her in broad daylight!  Photo by Lauren Vanier

A mule deer uses the Rio de Flag as a corridor through the neighborhoods of Flagstaff. Photo by Lauren Vanier

Mule deer are highly conspicuous around Flagstaff; one recent day, I saw three separate groups of more than seven deer each within two miles of each other. This led me to wonder about the population here and their possible ecological effects.

Mule deer populations in the west have complex dynamics dependent on ecoregion-specific conditions. Harsh winters, droughts, and forage availability constrain mule deer numbers. Forage can be limited in a number of ways. Invasive plants outcompete native species; overgrazing depletes plant regrowth and reproduction, and leads to degraded soils; and the exclusion of disturbance events such as a natural fire regime leads to canopy closure, which shades out understory plants. Populations of mule deer can be increasing in one region while another experiences decline.

The Kaibab Plateau Deer Drive (aka Disaster) is an infamous example of a drastic explosion, then crash, in a mule deer population. After Theodore Roosevelt established the Grand Canyon National Game Preserve in 1906, rangers systematically annihilated thousands of predators. The local herd of 3,000 mule deer exploded to 100,000. Forage was virtually eliminated by the swollen population and they began to starve. In 1924, Arizona’s governor proposed herding the deer from the North Rim to the South Rim through the Grand Canyon. The 150 hired men managed to round up around 200 deer, a feat unto itself, just to have them flee in every direction at the sight of a corral. It became evident that a deer round-up was impossible, and the drive was abandoned. By 1939, the population had crashed by an estimated 60%. This event is now an important case study about the unintended impacts of human intervention on ecosystems.

Mule deer are often attracted to the nutritious forage in our gardens. There are several methods that the gardener can implement to deter deer. First, plant deer-resistant plants. The distinction between ‘-resistant’ versus ‘-proof’ is important, as nothing is deer-proof if forage is scarce. The University of Arizona Cooperative Extension publishes an online deer resistance rating plant list that rates percent probability of damage, which I have found to be accurate thus far based on anecdotal evidence. You may decide that you can deal with feeding deer from time to time - if your garden is diverse, you will have remaining species that they ignore.

The difference between penstemon growth in and outside the exclosure illustrates the effect of deer and elk herbivory. Photo by Lauren Vanier

While there are some products and home remedies that claim to repel deer, the only way to ensure that plants are protected from herbivory is to exclude deer from the area with a fence or barrier. The Cooperative Extension suggests installing deer fencing at least eight feet in height, using a double fence, or placing wire cages around individual plants. Deer have poor depth perception and can jump high and wide, but not both at the same time, so double fences use a bit of psychological trickery.

Mule deer are an iconic western species, but can be a nuisance for gardeners. We don’t have the same overpopulation issues as our friends in the east, but we also may not enjoy seeing our plants mowed to stubs, either. You may be a person that would happily give your flora up as forage, and for that, I salute you. For the rest of us, the right combination of deterrents can keep the peace between gardener and deer.

Gardening Etcetera is written for the community by certified Master Gardeners of the University of Arizona's Coconino County Cooperative Extension Master Gardener Program. To learn more, visit extension.arizona.edu/programs/coconino-county-master-gardener.