Dwarf mistletoes in forest canopies

Dwarf mistletoes (Arceuthobium spp.) are parasitic flowering plants found throughout much of western North America on members of the Pinaceae. Heavy infection by these parasites affects biomass distribution on individual trees, and hence within forest canopies. Most dwarf mistletoes induce the formation of witches' brooms on infected hosts, and these brooms can significantly alter the structure of forest canopies as well. Conversely, forest canopy structure greatly affects horizontal and vertical spread of dwarf mistletoes. Dwarf mistletoes interact with other organisms that also inhabit forest canopies, such as birds, mammals, insects, and fungi. The principal interaction is the mistletoes serving as a food source for these organisms, but birds and mammals also use witches' broom as nesting and foraging sites. Another interaction is long-range dissemination of dwarf mistletoe seeds by animal vectors, primarily birds and squirrels.