Dead and decaying trees are used by a wide range of species and are a foundational structural element of forest ecosystems. The decay process is caused primarily through a combination of senescence and fungal or insect invasion, but many non-human vertebrates also modify trees, which can accelerate this process. While previous research has investigated the economic costs of bear damage or the keystone importance of primary cavity excavators, we are unaware of work to unify this process into a single framework of non-human vertebrate tree modification. To highlight the extent of this key functional role, we conducted a systematic literature review to identify non-human vertebrate tree modifiers. We categorized types and measures of damage across individual, population, and community levels. In North America, we summarized spatial patterns of modifier richness. We found non-human vertebrates that modify trees are found extensively in forests, and that trees are damaged from the roots to the buds, with consequences for other species that rely on damaged trees. While non-human vertebrates that modify trees have often been persecuted for the resulting economic harm, we suggest that these species can play an important role in restoring degraded forests to more structurally complex, and therefore biodiverse, communities.