Tree squirrel abundance and demography in managed coniferous forests of British Columbia are within the range of natural fluctuations of old-growth stands

Abstract

Abstract:The American red squirrel (Tamiasciurus hudsonicus Exrleben) and northern flying squirrel (Glaucomys sabrinus Shaw) are important mammal species in coniferous forests that are widely distributed across temperate and boreal ecological zones. Although T. hudsonicus and G. sabrinus apparently prefer late-successional forests, their population dynamics show no clear pattern in young second-growth and old-growth conifer forests. We used a compilation of study results that had standardized methodology and sampling effort to compare tree squirrel responses across a range of forest conditions. We tested the hypotheses (H) that abundance, reproduction, recruitment, and survival would be higher in (H 1 ) old-growth than second-growth stands, (H 2 ) unthinned than thinned second-growth stands, and (H 3 ) lightly than heavily thinned stands. Tree squirrel populations in old-growth stands were considered the "standard" treatment to which other treatments in second-growth stands (unthinned and variously thinned) were compared. Thinned stands were grouped into low, medium, and high densities of trees. Datasets from seven published studies included 2804 Tamiasciurus and 837 G. sabrinus individuals, 25 study years, and 158 trapping periods. Mean abundance of Tamiasciurus was similar among treatment stands, ranging from 0.62 to 1.29·ha −1 . Mean numbers of G. sabrinus were highest in old-growth stands at 0.65·ha −1 , followed by the low-and medium-density stands at 0.50·ha −1 , the high-density stands at 0.25·ha −1 , and finally the unthinned second-growth stands at a low of 0.12·ha −1 . In terms of effect size, mean proportional change in abundance, relative to that within old-growth stands, of both squirrel species in the three thinned stands were within the range of natural fluctuations in old-growth stands. Populations of Tamiasciurus in the unthinned stands were not within the range of fluctuations in the old-growth stands. Mean number of successful pregnancies and total recruits were similar among stands for Tamiasciurus, with variability in female breeding and winter survival. Mean number of recruits of G. sabrinus was highest in old-growth stands with no other differences in demographic attributes among stands. The biological significance of these differences in demographic variables was small in terms of effect sizes. Tamiasciurus and G. sabrinus seem to persist in a relatively broad range of young managed forest habitats, as well as in old-growth stands.Key words: coniferous forests, Glaucomys sabrinus, managed stands, old-growth forest, population dynamics, Tamiasciurus.Résumé : L'écureuil roux américain (Tamiasciurus hudsonicus Exrleben) et le grand polatouche (Glaucomys sabrinus Shaw) sont deux espèces de mammifères d'importance dans les forêts de conifères qui couvrent une grande partie des biomes tempérés et boréaux. Mis à part le fait que T. hudsonicus et G. sabrinus semblent préférer les forêts de fin de succession, leur dynamique des populations ne montre pas de tendances nettes dans les jeunes forêts d...

Acceleration of Forest Structural Development for Large Trees and Mammals: Restoration in Decades or Centuries?

“…The similar mean abundances of T. hudsonicus across this array of treatment stands was also reported in a comprehensive review by [43]. T. hudsonicus is a common inhabitant of a broad range of temperate and boreal coniferous forests [84] and seems to persist in young managed stands.…”

“…Forest-floor small mammals as a group and the arboreal American red squirrel (Tamiasciurus hudsonicus) and northern flying squirrel (Glaucomys sabrinus) may be considered candidate ecological indicators of mature successional coniferous forests across temperate and boreal North America [43]. The abundance and diversity of forest-floor small mammals may serve as ecological indicators of the effect of structural changes resulting from forest restoration via silvicultural practices [44,45].…”

“…The red squirrel and northern flying squirrel occupy older forests with tall trees, complex stand structure, snags, and large-diameter woody debris [48]. However, both sciurids seem to persist in a relatively broad range of young managed forest habitats, as well as in old-growth stands [43]. Functions of these small mammals include prey for many furbearers and raptors [49,50], distribution of beneficial mycorrhizal fungi [51], and consumers of invertebrates, plants and plant products [52].…”

Abundance and ecological associations of small mammals

“…Despite sympatric exposure to spatiotemporal factors, different covariates were most associated with the mean abundance of each target species. This long‐term data provides important baseline estimates of abundances and spatiotemporal associations of small mammals in a late‐successional forest in the PNW, which can inform our understanding of small‐mammal populations in human‐modified forest cover types such as conifer plantations (Sullivan et al ).…”

“…We defined biologically meaningful values as the average site‐level species‐specific temporal change in abundances. The biologically meaningful values were likely conservative because average temporal change in abundance also incorporated variation associated with the considered main effects and the main effects sampled range did not capture the full biological range (Sullivan et al ). We considered main effects strongly associated with mean abundance if the 95% confidence intervals for the estimated change in mean abundance across the sampled range of each covariate did not contain zero and included only values more extreme than the biologically meaningful values.…”