Ecosystem Conditions That Influence the Viability of an Old-Forest Species with Limited Vagility: The Red Tree Vole

SIMPLE SUMMARY: Red tree voles (Arborimus longicaudus) occur throughout old forests in the Western United States of America. Ecosystem conditions needed to support the long-term viability of red tree voles have decreased throughout their range. This has primarily resulted from a reduction and modification of their habitats. We evaluated the risk of maintaining viable populations of red tree voles in three ecoregions within their range. We determined that the long-term probability of maintaining viability within these ecoregions ranged from 26% to 52% when compared to historical conditions. The most immediate threats varied from habitat loss due to timber harvest to habitat loss due to wildfires. Reducing the risks to the long-term viability of red tree voles will depend largely on the implementation of conservation practices designed to protect remaining habitat, restore degraded ecosystems, and adapt ecoregions to climate change. ABSTRACT: We evaluated ecosystem conditions known to influence the viability of a strictly arboreal species (the red tree vole, Arborimus longicaudus) endemic and historically distributed in the forests across the Coast Range, Cascades, and Klamath Mountains ecoregions in the Western United States of America. We found widespread reductions in ecosystem conditions needed to support the long-term viability of the red tree vole. This was particularly evident in the Coast Range where the weighted watershed index (WWI) was 26% of its historical value, and the current probability of maintaining viability departed the most from historical viability probabilities in ecoregions that were evaluated. In contrast, in the Cascades and Klamath Mountains, the WWI was 42% and 52% of their respective historical values, and the current probabilities of maintaining viability departed less from historical conditions than in the Coast Range. Habitat loss from timber harvest represented the most immediate threat in the Coast Range, while habitat loss from wildfires represented the most risk to the red tree vole in the Cascades and Klamath Mountains. Reducing the risks to the viability of the red tree vole will depend largely on the implementation of conservation practices designed to protect remaining habitat and restore degraded ecosystems in the Coast Range. However, the risk of large, high-severity wildfires will require the protection and increased resilience of existing ecosystems. Our results indicate that considerable adaptation to climate change will be required to conserve the red tree vole in the long term. Conservation may be accomplished by revising land and resource management plans to include standards and guidelines relevant to red tree vole management and persistence, the identification of priority areas for conservation and restoration, and in assessing how management alternatives influence ecosystem resiliency and red tree vole viability.