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Consequences of pinyon and juniper woodland reduction for wildlife in North America

Bombaci, Sara, Pejchar, Liba
Forest ecology and management 2016 v.365 pp. 34-50
Artemisia, Centrocercus urophasianus, Juniperus, Odocoileus hemionus, Pinus, animal communities, birds, conifers, ecosystems, game animals, grasslands, invertebrates, monitoring, nontarget organisms, pinyon-juniper, reptiles, shrublands, shrubs, small mammals, ungulates, wildlife, wildlife habitats, wildlife management, woodlands, North America
Pinyon and juniper (Pinus spp., Juniperus spp.) woodlands are expanding into shrublands and grasslands throughout much of western North America. Woodland reduction is frequently used to mitigate the effects of conifer encroachment on game species (e.g. mule deer Odocoileus hemionus) and shrub and grassland-obligate species (e.g. sage grouse Centrocercus spp.). Although these practices are widespread, previous studies on the effects of woodland reduction on animal communities have not yet been synthesized, making it difficult to set priorities for future research and practice. To address this gap, we first summarize the history of pinyon and juniper reduction in western North America and characterize known wildlife habitat associations in pinyon and juniper ecosystems. We then review and synthesize evidence from the scientific literature on wildlife responses to pinyon and juniper woodland reduction. We tallied the outcomes of these studies to determine the relative proportions of positive, negative, and non-significant responses by different taxonomic groups and functional groups. The majority (69%) of animal species responses to woodland reduction treatments were non-significant. However, particular groups of species (taxonomic and/or functional) were more likely to respond positively or negatively, depending on the woodland reduction treatment method. Unexpectedly, investigators often found non-significant or negative responses by ungulates to woodland reduction, and non-significant responses by sagebrush obligate species. However, few studies measured effects on sagebrush obligate species, which limits inference for this group. Indeed, our review demonstrates that the effects of woodland reduction are well-understood for only a subset of taxonomic groups (e.g. birds and small mammals); whereas other groups (e.g. reptiles and terrestrial invertebrates) are consistently under-studied. Further, a shortage of large-scale and long-term research limits our ability to fully understand spatial and temporal wildlife responses to woodland reduction. We encourage practitioners to design and implement pinyon and juniper reduction projects to experimentally assess the effects of these practices on both target and non-target species. Adopting consistent monitoring protocols across projects would also facilitate greater understanding of how factors such as treatment type, size, location and duration result in positive or negative impacts to diverse wildlife of conservation concern.