Multiscale habitat relationships of snowshoe hares (Lepus americanus) in the mixed conifer landscape of the Northern Rockies, USA: Cross-scale effects of horizontal cover with implications for forest management.

Joseph D Holbrook,Rick L Lawrence,Lucretia E Olson,John R Squires,Shannon L Savage

doi:10.1002/ece3.2651

Abstract

Snowshoe hares (Lepus americanus) are an ecologically important herbivore because they modify vegetation through browsing and serve as a prey resource for multiple predators. We implemented a multiscale approach to characterize habitat relationships for snowshoe hares across the mixed conifer landscape of the northern Rocky Mountains, USA. Our objectives were to (1) assess the relationship between horizontal cover and snowshoe hares, (2) estimate how forest metrics vary across the gradient of snowshoe hare use and horizontal cover, and (3) model and map snowshoe hare occupancy and intensity of use. Results indicated that both occupancy and intensity of use by snowshoe hares increased with horizontal cover and that the effect became stronger as intensity of use increased. This underscores the importance of dense horizontal cover to achieve high use, and likely density, of snowshoe hares. Forest structure in areas with high snowshoe hare use and horizontal cover was characterized as multistoried with dense canopy cover and medium‐sized trees (e.g., 12.7–24.4 cm). The abundance of lodgepole pine (Pinus contorta) was associated with snowshoe hare use within a mixed conifer context, and the only species to increase in abundance with horizontal cover was Engelmann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa). Our landscape‐level modeling produced similar patterns in that we observed a positive effect of lodgepole pine and horizontal cover on both occupancy and use by snowshoe hares, but we also observed a positive yet parabolic effect of snow depth on snowshoe hare occupancy. This work is among the first to characterize the multiscale habitat relationships of snowshoe hares across a mixed conifer landscape as well as to map their occupancy and intensity of use. Moreover, our results provide stand‐ and landscape‐level insights that directly relate to management agencies, which aids in conservation efforts of snowshoe hares and their associated predators.

Highlights

The conservation of strong interactions within food webs is important to sustain ecological stability and biological diversity (e.g., McCann, Hastings, & Huxel, 1998)
To address our first objective, we modeled the effect of horizontal cover on snowshoe hare occupancy (n = 1,297 for plots surveyed for snowshoe hares with associated forest structure data) and intensity of use (n = 865 for plots with ≥1 snowshoe hare pellet and associated forest structure data) using logistic and quantile regression (Koenker & Bassett, 1978), respectively
Our logistic model indicated that the odds of snowshoe hare occupancy increased by 20% for every 10% increase in horizontal cover (z-v alue = 7.87, df = 1,295, FIGURE 4 (a) Predicted occupancy (±95% CI) of snowshoe hares (Lepus americanus) as a function of horizontal cover. (b) Relationship between pellet density of snowshoe hares and horizontal cover for five quantiles of the pellet density distribution (τ = 0.35, 0.50, 0.55, 0.75, and 0.95)

Summary

Introduction

The conservation of strong interactions within food webs is important to sustain ecological stability and biological diversity (e.g., McCann, Hastings, & Huxel, 1998). Snowshoe hares represent 48% of the vertebrate biomass and 41% of the mean energy flow in the southwestern Yukon (Krebs, Boutin, & Boonstra, 2001). Predators such as coyotes (Canis latrans), American marten (Martes americana), red fox (Vulpes vulpes), goshawks (Accipiter gentilis), and great-horned owls (Bubo virginianus) interact strongly with snowshoe hares as a prey resource (Feierabend & Kielland, 2015; Krebs, 2011). In order to effectively conserve snowshoe hares, forest managers need a detailed understanding of their habitat relationships across ecologically and management-relevant scales. This is true as the future of northern forests anticipates changes in the form of reduced snow (e.g., Klos, Link, & Abatzoglou, 2014; McKelvey et al, 2011) and increased wildfire (Liu, Goodrick, & Stanturf, 2013; Stavros, Abatzoglou, McKenzie, & Larkin, 2014), both of which significantly influence snowshoe hares (e.g., Cheng, Hodges, & Mills, 2015; Hodson, Fortin, & Bélanger, 2011; Mills et al 2013; Sultaire, Pauli, Martin, Meyer, & Zuckerberg, 2016; Sultaire, Pauli, Martin, Meyer, Notaro, et al, 2016)

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Discussion

Conclusion