Oak mistletoe (Phoradendron villosum) is linked to microhabitat availability and avian diversity in Oregon white oak (Quercus garryana) woodlands

Abstract

Mistletoes are parasitic or hemiparasitic flowering plants that parasitize woody plants around the globe. Important food and cover resources provided by mistletoes have been related to strong patterns of positive association between wildlife diversity and mistletoe density. Mistletoes also create microhabitat features known to be important to wildlife by causing deformations in their host trees. However, links between availability of mistletoe-formed microhabitat and wildlife diversity has not been well-studied. We investigated this relationship by quantifying microhabitat features and avian abundance and diversity related to infection by oak mistletoe (Phoradendron villosum (Nutt.) Nutt. ex Engelm.) in Oregon white oak (Quercus garryana Douglas ex Hook.). Quercus garryana woodlands support several avian species of conservation concern, so understanding the influence of mistletoe on wildlife habitat is critical. Our results suggest that (i) structural heterogeneity within tree crowns is positively associated with mistletoe load; (ii) avian species richness and abundance are positively associated with mistletoe load; and (iii) the fruit of P. villosum is an important food for Western Bluebird (Sialia mexicana) and other wildlife in late autumn and early winter. If a goal of restoration is to maintain habitat for oak-associated bird species, managers should consider the retention of some oaks hosting mistletoe.