Effects of Precommercial Thinning on Snowshoe Hares in Maine

Abstract

Snowshoe hares (Lepus americanus) are an important prey species and a dominant herbivore across much of their North American range, and researchers have questioned the influences of forestry practices that alter habitat for hares and the potential community‐level effects on carnivores. We examined the effects of precommercial thinning (PCT) from 1 to 11 years posttreatment on snowshoe hares. In the commercial forests of northern Maine, USA, we counted and cleared hare pellets twice a year during 2001 and 2002 on >46 km of pellet transects across 30 regenerating conifer stands (17 treated with PCT) previously treated with an aerial application of herbicide. We compared densities of snowshoe hare pellets among 3 development classes with (1 yr after thinning, 6 yr after thinning, and 11 yr after thinning) and without thinning (stands with a similar history of clearcut and herbicide treatment but no thinning). During both years, densities of hares were lower in stands treated with PCT than in similar unthinned stands across the 3 development classes and during both leaf‐off and leaf‐on seasons (P < 0.001). Within both thinned and unthinned stands, hare density was greatest in stands in the 1‐year development class when compared to the 6‐year and 11‐year development classes, but a statistical difference (P = 0.048) among classes was evident only during leaf‐off seasons. Precommercial thinning was associated with densities of snowshoe hares that were approximately half of those in similar unthinned stands up to at least 11 years posttreatment; however, thinned stands may retain densities of hares greater than stands managed using other forest harvesting regimes. Our results apply to core portions of stands with crop trees spaced at 1.8–2.4‐m intervals following complete overstory removal and herbicide treatment. We advocate caution when applying our results to other thinning regimes or across broader spatial scales.

Long-term effects of precommercial thinning on small mammals in northern Maine

“…Although densities of adult female deer mice were similar between thinned (averaged 2.3/trapping grid) and unthinned conifer (averaged 1.7/trapping grid) stands, a companion study on the same 37 forest stands examined in this study reported a greater proportion of adult female deer mice were lactating in unthinned stands compared to similar PCT-treated stands (Homyack, 2003). Reproductive output of deer mice may have been affected by treatment; deer mice often have aggressive intra-specific interactions (Martell, 1983b), which may lead to subordinate, non-reproductive individuals occupying areas with lower habitat quality (Van Horne, 1983).…”

“…We recorded species, sex and age (adult or juvenile) of each individual (Homyack, 2003). Traps were checked from 0600 to 1300 h, and after processing, animals were released at the trap site.…”

“…Increased rates of stand development associated with PCT may help compensate for the short rotations (<60 years) commonly applied to intensively managed stands in the Acadian forest (Seymour and Hunter, 1992). Maintaining a significant portion of the landscape in PCT, however, may involve trade-offs for earlysuccessional dependent forest mammals such as snowshoe hares (Sullivan and Sullivan, 1988;Homyack, 2003) and their predators. Although this study evaluated stand-scale effects of PCT, broader landscape-scale evaluations of PCT are needed to reconcile silvicultural objectives with desired balances between conflicting habitat needs of early (e.g., snowshoe hares) and mid-successional (e.g., redbacked voles, masked shrews) wildlife species.…”

“…Without mortality of large diameter trees, however, recruitment of coarse woody debris (CWD) may be reduced (Carey and Johnson, 1995;Hayes et al, 1997;Homyack et al, 2004). These structural changes associated with PCT within forest stands could potentially influence, either positively or negatively, a variety of forest mammals dependent on overstory or understory structure, such as snowshoe hares (Lepus americanus) (Sullivan and Sullivan, 1988;Homyack, 2003) and various species of small rodents (Yahner, 1986;Nordyke and Buskirk, 1991;Witt and Huntly, 2001;Mengak and Guynn, 2003) and shrews (Yahner, 1986;Mengak and Guynn, 2003). However, studies in the Pacific Northwest have indicated that thinning of second-growth forests may diversify the landscape and increase richness of wildlife species by accelerating stand succession (Carey and Johnson, 1995;Hayes et al, 1997;Sullivan et al, 2001).…”

Inclusion of forest harvest legacies, forest type, and regeneration spatial patterns in updated forest maps: A comparison of mapping results

“…Conversely, under-representation and misclassification of regenerating stands could significantly affect the reliability of habitat assessments for species that depend on regenerating forest, such as Canada lynx (Lynx canadensis). Snowshoe hares (Lepus americanus) are the primary prey for lynx (O'Donoghue et al, 1997) and high snowshoe hare densities in Maine are associated with coniferregenerating clearcuts (Homyack et al, 2007;Fuller et al, 2007;Hoving et al, 2004). The GAP update methodology provides both the forest regeneration cover type and stand age information (time since harvest) required for applications such as spatially-explicit wildlife habitat modeling.…”