Comparison of dwarf mistletoes (Arceuthobium spp., Viscaceae) in the western United States with mistletoes (Amyema spp., Loranthaceae) in Australia—ecological analogs and reciprocal models for ecosystem management

Abstract

Whereas the biology, physiology and systematics of mistletoes have been explored in considerable detail, their ecology has received less attention and our understanding is highly fragmentary. A conspicuous exception is the dwarf mistletoes (Arceuthobium spp.)—a genus that exclusively parasitises coniferous trees, including many commercially valuable species in the forests of the western United States. Accordingly, these plants have been the subjects of intensive cross-disciplinary research for the past five decades, initially from a control and management perspective but extending into most aspects of their ecology and life history. This review summarises our understanding of dwarf mistletoes, focusing on recent developments in the areas of mistletoe–wildlife interactions, fire, ecosystem ecology and conservation biology. We also compare dwarf mistletoes with Australian mistletoes in the genus Amyema, a diverse suite of species found throughout the continent. Despite fundamental differences in their evolutionary origin and most aspects of their autecology and life history, the genera exhibit many similarities in terms of their ecological role in forests and woodlands, and their influence on stand- and forest-scale dynamics. In particular, both groups provide nesting resources for a range of birds and mammals, and nutritional resources for a diverse assemblage of species. Both also interact with fire, potentially leading to changes in successional dynamics at the stand scale. At an applied level, both groups are widely considered as pests but, as our understanding of these keystone species improves, they have the potential to serve as sensitive ecological indicators for their respective ecosystems. Key research priorities are identified for further research on both groups of mistletoes and more explicit comparative research, with Arceuthobium serving as a valuable template for future work on Amyema and Australian mistletoes in general.

Highly episodic fire and erosion regime over the past 2,000 y in the Siskiyou Mountains, Oregon

“…Pseudotsuga pollen was depressed through the remainder of the record, possibly reflecting suppression of this species by Arceuthobium. If so, the effects of this parasite are not a novel effect caused by fire suppression and possibly were enhanced by patchy fires in the past (35). From A.D. 950-1450, five large charcoal peaks and erosion events suggest fuel continuity was sufficient to support severe events that synchronize disturbances.…”

Mistletoes: Pathology, Systematics, Ecology, and Management

“…In addition to documenting the wide range of opportunistic consumers of mistletoe fruit (in contrast to the prevailing view), this review also highlighted how many folivores and nectarivores feed on mistletoes. The popularity of mistletoes as a nesting substrate was also revealed, with a wide range of species recorded nesting in mistletoes and in the witches'-brooms associated with dwarf mistletoe infections (43,92,136,198). These interactions were suggested to underpin a generalized positive effect of mistletoe occurrence on diversity, and mistletoes have been proposed to function as a keystone resource in many forest ecosystems (219).…”

“…For example, the effects of dwarf mistletoes on the growth of their conifer hosts have been estimated by investigators reporting reductions in radial diameter growth or reduced volume growth for individual trees, stands of trees, or large geographic regions (88,136,198). Economic losses from dwarf mistletoes amount to billions of dollars annually, but no detailed economic analysis has been published recently (72,92).…”

“…In South and North America, animals other than birds have also been implicated in the dispersal of mistletoe seeds. In South America, a marsupial disperses seeds (4), and in North America, squirrels and other mammals have been shown to rarely disperse dwarf mistletoe seeds adhering to their fur (92,136,198).…”

Is crypsis a common defensive strategy in plants? Speculation on signal deception in the New Zealand flora

“…21,22 There are two main phylogenetic lineages of mistletoes: the family Loranthaceae, which evolved in the Southern hemisphere, and the family Viscaceae, which evolved in the northern hemisphere. 23,24 Both lineages have since dispersed out of their native hemispheres and many geographic locales now house members of both families.…”