Demography Of Northern Flying Squirrels Informs Ecosystem Management Of Western Interior Forests

Abstract

We studied northern flying squirrel (Glaucomys sabrinus) demography in the eastern Washington Cascade Range to test hypotheses about regional and local abundance patterns and to inform managers of the possible effects of fire and fuels management on flying squirrels. We quantified habitat characteristics and squirrel density, population trends, and demography in three typical forest cover types over a four-year period. We had 2034 captures of flying squirrels over 41 000 trap nights from 1997 through 2000 and marked 879 squirrels for mark-recapture population analysis. Ponderosa pine (Pinus ponderosa) forest appeared to be poorer habitat for flying squirrels than young or mature mixed-conifer forest. About 35% fewer individuals were captured in open pine forest than in dry mixed-conifer Douglas-fir (Pseudotsuga menziesii) and grand fir (Abies grandis) forests. Home ranges were 85% larger in pine forest (4.6 ha) than in mixed-conifer forests (2.5 ha). Similarly, population density (Huggins estimator) in ponderosa pine forest was half (1.1 squirrels/ha) that of mixed-conifer forest (2.2 squirrels/ha). Tree canopy cover was the single best correlate of squirrel density (r = 0.77), with an apparent threshold of 55% canopy cover separating stands with low- from high-density populations. Pradel estimates of annual recruitment were lower in open pine (0.28) than in young (0.35) and mature (0.37) forest. High recruitment was most strongly associated with high understory plant species richness and truffle biomass. Annual survival rates ranged from 45% to 59% and did not vary among cover types. Survival was most strongly associated with understory species richness and forage lichen biomass. Maximum snow depth had a strong negative effect on survival. Rate of per capita increase showed a density-dependent response. Thinning and prescribed burning in ponderosa pine and dry mixed conifer forests to restore stable fire regimes and forest structure might reduce flying squirrel densities at stand levels by reducing forest canopy, woody debris, and the diversity or biomass of understory plants, truffles, and lichens. Those impacts might be ameliorated by patchy harvesting and the retention of large trees, woody debris, and mistletoe brooms. Negative stand-level impacts would be traded for increased resistance and resilience of dry-forest landscapes to now-common, large-scale stand replacement fires.

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

“…Presumably, the increase in tree diameters and heights, as well as understory coniferous structural diversity, in thinned stands at these densities may have provided sufficient canopy closure and concomitant food and cover (Sullivan et al 2010). Lehmkuhl et al (2006) found that a threshold of 55% canopy cover separated stands with low-and high-density populations of G. sabrinus.…”

“…Although we did not evaluate response of hypogeous fungi to PCT, higher abundance of G. sabrinus in high-density stands might reflect a positive response of hypogeous fungi to thinning. Gomez et al (2005) and Lehmkuhl et al (2006) both concluded that the presence of hypogeous sporocarps may be more important for flying squirrels than forest structure. Rosenberg and Anthony (1992) suggested that food availability, predation, and competition with other species (e.g., Tamiasciurus, Smith 2012) may limit abundance of G. sabrinus more than struc- Fig.…”

Tamm Review: Management of mixed-severity fire regime forests in Oregon, Washington, and Northern California

“…Naturally recovering, structurally and compositionally diverse early successional ecosystems are biologically and functionally rich components of landscapes (Fontaine et al, 2009;Hutto, 1995;Kotliar et al, 2002;Smucker et al, 2005;Swanson et al, 2010), and they provide resources for many associated food webs (e.g., see Lehmkuhl, 2004;Lehmkuhl et al, 2006aLehmkuhl et al, , 2006b). Especially after severe fires, early successional forests are characterized by structural legacies (snags, logs, and remnant, mature live trees) with accompanying grassland, shrubland, woodland, or herbland dominance (Habeck, 1976;Hutto, 1995;Kotliar et al, 2002).…”

Effects of partial harvesting on vertebrate species associated with late-successional forests in Ontario’s boreal region

“…Lehmkuhl et al (2006) hypothesized that silvicultural practices that retain less than 50% canopy cover would only support low-density populations of northern flying squirrels. Likewise, practices that sharply reduce supplies of coarse woody debris, which is associated with hypogeous fungi in northern flying squirrel diets (Carey et al 1999), may prevent this species from reaching the high densities characteristic of old forests (Carey 2000).…”