Changes in relative abundance of snowshoe hares (Lepus americanus) across a 265-year gradient of boreal forest succession

Abstract

Understory regeneration within canopy gaps in old-growth boreal forests may provide suitable habitat for wildlife typically associated with early-seral stages, leading to an increase in their abundance in late succession. We surveyed a chronosequence of postfire (17-265 years) and postharvest (3-63 years) stands in Canada's eastern boreal forest to determine whether snowshoe hares (Lepus americanus Erxleben, 1777) followed a bimodal abundance distribution with stand age that reflects changes in food and cover during postdisturbance succession. A strong peak in relative hare abundance occurred during the first 80 years of succession, with highest faecal pellet densities observed between 40 and 50 years after disturbance. Changes in hare abundance during this period were similar among fire-and clearcut-origin stands and closely tracked changes in lateral cover and vertical cover. Pellet density increased again in stands >180 years. Variation in hare abundance during late succession was partially mediated by gap dynamics, with highest pellet densities in stands occupied by an intermediate proportion of mortality-origin canopy gaps. Hares thus undergo rapid changes in abundance during early succession followed by a much longer period of subtle changes in density as stands develop old-growth structure. Shifting forest age-class distribution induced by forest management could therefore significantly alter regional spatiotemporal dynamics of snowshoe hares.Résumé : Une régénération arbustive importante à l'intérieur des trouées dans les forêts boréales anciennes peut fournir des conditions d'habitat favorables aux espèces animales typiques des jeunes forêts, menant ainsi à une augmentation de leur abondance en fin de succession. Nous avons échantillonné une chronoséquence de successions après feu (17-265 ans) et après coupe (3-63 ans) dans la forêt boréale de l'est du Canada pour évaluer l'hypothèse selon laquelle l'abondance du liè-vre d'Amérique (Lepus americanus Erxleben, 1777) suit une distribution bimodale en fonction de l'âge des peuplements qui reflèterait les changements de nourriture et de couvert qui ont lieu au cours de la succession. Un fort pic d'abondance relative du lièvre a lieu au cours des 80 premières années de succession, avec les densités de fèces de lièvre les plus élevées dans les peuplements de 40-50 ans après la perturbation. Les changements d'abondance du lièvre pendant cette période sont semblables dans les peuplements issus de coupe et de feu et suivent de près les changements de couvert latéral et vertical. L'abondance relative du lièvre augmente de nouveau dans les peuplements de >180 ans. Les variations d'abondance du lièvre dans les peuplements en fin de succession sont liées à la dynamique de trouées, avec les densités de crottins les plus élevées dans les peuplements ayant une proportion intermédiaire de trouées issues de mortalité. Le lièvre subit donc des changements d'abondance rapides en début de succession, suivis de changements moins prononcés au cours d'une période beaucoup plus ...

Stand-level Attributes of Snowshoe Hare (<em>Lepus americanus</em>) Habitat in a Post-Fire Trembling Aspen (<em>Populus tremuloides</em>) Chronosequence in Central Yukon

“…However, a similar bimodal pattern of pellet densities was reported in eastern Quebec by Hodson et al (2011). Although Hudson et al (2011) did not measure deadfall, its association with more in tensively used canopy gaps in older growth stands seems likely (J.…”

“…For example, de Bellefeuille et al (2001) suggested that peak use of clearcuts in southern Quebec forest was expected when Balsam Fir (Abies balsamea) and Black Spruce (Picea mariana) regeneration was 15-22 and 18-30 years old, respectively. Forest stands >15 years old were more intensively used than younger post-disturbance areas in Quebec (Jacqmain et al 2007;Hodson et al 2011), Labrador (Newbury and Simon 2005), Ontario (Thompson et al 1989), Maine (Monthey 1986), and central Alaska (Paragi et al 1997). Nevertheless, Keith and Surrendi (1971) reported Snowshoe Hare use of 1-year-old burns in central Alberta.…”

“…Minimal shrub content occurs because of forest overstory suppression as part of the ecological succession process, and the general lack of medium-height and tall shrubs such as Beaked Hazelnut (Corylus cornuta), Saskatoon (Amelanchier alnifolia), or Low-bush Cranberry (Viburnum edule) in the vegetation of central Yukon. As a result, stands 21-120 years old were largely unused by Snowshoe Hares in the chronosequence, even though they are important habitats elsewhere (e.g., Monthey 1986;Thompson et al 1989;Paragi et al 1997;Newbury and Simon 2005;Jacqmain et al 2007;Hodson et al 2011).…”

“…The presence of deadfall, however, might encourage early use of post-fire stands if vegetation does not provided sufficient cover (Conroy et al 1979). The fact that a high pellet density occurred in the youngest stand in the chro nosequence (402 pellets/dam 2 , stand 8 years old) suggests that peak Snowshoe Hare abundance may occur within a few years after a fire; this is earlier than reported in other studies (>15 years -e.g., Monthey 1986; Thompson et al 1989;Paragi et al 1997;Newbury and Simon 2005;Jacqmain et al 2007;Hodson et al 2011). In cutblocks with only spruce and Balsam Fir tree regeneration, the delay in Snowshoe Hare reoccupation may be related to the conical physiognomy of the trees, which provide limited horizontal and lateral cover until the trees reach a sufficient height and density (i.e., 15-30 years - Paragi et al 1997;de Bellefeuille et al 2001;Jacqmain et al 2007).…”

Complex effects of site preparation and harvest on snowshoe hare abundance across a patchy forest landscape

“…Thus, specific recommendations will depend on the type of harvest employed and the age class of stands that are likely to be maintained across the landscape. Although mature, unharvested, forest stands had lower pellet counts than two of the mid-successional stand types in our study (stands that were clear-cut with site preparation and stands that were partially harvested without site preparation), we note that other researchers have found conflicting results regarding snowshoe hare abundance in older stands (e.g., Hodson et al, 2011). The relative value of older vs. mid-successional stands to snowshoe hares therefore appears complex and variable, and deserving of more research.…”