Moles do not typically cause tree death directly, but their tunneling activities can contribute to a tree’s decline. Moles are not seeking out tree roots for food, yet the extensive network of tunnels they construct beneath the soil can inadvertently damage a tree’s support and uptake systems. Understanding the mole’s biological purpose and the mechanics of their burrowing is the first step in protecting trees. The damage homeowners attribute to moles is often the result of other pests or environmental factors exacerbated by the mole’s presence.
Understanding the Mole’s Diet
Moles are insectivores, not herbivores, which is why they are not direct threats to tree health. Their diet consists mainly of invertebrates found in the soil, with earthworms often comprising up to 80% of their intake. Moles also consume insect larvae, such as beetle grubs, centipedes, and slugs.
They have a vigorous appetite, often eating between 70% and 100% of their body weight daily to sustain their high metabolism and constant tunneling. Plant roots are not a source of sustenance for them. When a mole tunnels near a tree, it is simply following the scent of insect prey, which is often abundant in the moist soil near a tree’s root system.
How Mole Tunneling Indirectly Harms Trees
While moles do not consume roots, their tunneling creates significant disruptions that can harm trees, particularly younger ones. Their activity loosens the soil structure, causing fine feeder roots to become suspended in air pockets instead of remaining in contact with soil particles. This condition, known as root desiccation, causes the delicate feeder roots—which absorb water and nutrients—to dry out and die.
The disruption of the soil structure also hinders the tree’s ability to absorb water efficiently. Water drains away quickly through the mole’s tunnels instead of being held in the compact soil around the roots. This is detrimental during periods of drought or for stressed trees. Furthermore, vacated tunnels can act as protected highways for other destructive pests, allowing easy access to the tree’s vulnerable root crown and main roots.
Distinguishing Moles from Root-Eating Pests
Confusion regarding tree damage often stems from misidentifying the pest, which is usually a root-eating rodent like a vole or gopher. Moles are identified by their signature volcano-shaped mounds of soil, pushed up from deep, vertical tunnels, and the raised ridges marking their shallow surface runs. Moles rarely leave an open hole at the surface, as they quickly plug tunnel entrances.
Voles
Voles are small, herbivorous rodents that are the true culprits in root consumption. Vole damage is recognizable by small, circular open holes, typically one to one-and-a-half inches in diameter, and visible above-ground runways in the grass. These rodents gnaw on tree bark at the base and girdle the root system, which fatally halts the flow of nutrients and water.
Gophers
Gophers are also herbivores and cause damage by eating entire roots or taproots, often pulling whole plants down into their burrows. Gopher activity leaves behind fan-shaped or crescent-shaped mounds of soil, which are asymmetrical. The plugged entrance hole is located off to one side of the mound. Correctly identifying the type of mound and the presence of gnaw marks is the first step toward effective mitigation.
Strategies for Protecting Tree Roots
Protecting trees from subterranean pests requires a targeted approach based on the specific pest present. For young, newly planted trees, installing a physical barrier around the root ball is an effective preventative measure against voles and gophers. This barrier should consist of a cylinder made from quarter-inch hardware cloth, buried deep enough to prevent tunneling underneath and extending at least six inches above the soil line.
Habitat Management
Managing the habitat can significantly reduce the attraction for these animals. Keeping grass mowed short around the base of trees and eliminating dense ground cover creates plant-free zones that voles are reluctant to cross. For mole activity, reducing their primary food source by minimizing excessive lawn irrigation can help, as moles are drawn to moist soil where earthworms thrive. Repellents, such as those containing castor oil, can also be applied to the soil to make the tunnel environment unappealing, causing moles to move elsewhere.