Landscape‐Scale Forest Habitat Relationships to Tassel‐Eared Squirrel Populations: Implications for Ponderosa Pine Forest Restoration

Abstract

Pinus ponderosa (ponderosa pine) forest ecosystem restoration is a growing emphasis in the southwestern United States to address over 120 years of forest structure change, decreased forest health, and increased potential for disease and wildfire. Restoration treatments replicating presettlement conditions may reduce tree density by 98%, are detrimental to canopy-dependent wildlife such as tasseleared squirrel (Sciurus aberti), particularly at the patch scale, and are of concern when applied at the landscape scale. We examined S. aberti population dynamics in north-central Arizona, U.S.A., from 1999 to 2002 at nine 280-ha sites oriented along a landscape gradient of varying proportions (4.6-99.2%) of unlogged, high-quality (HQ) habitats within a matrix of intensively thinned low-quality habitat. Our objectives were to estimate S. aberti density, juvenile recruitment, and survival across this gradient; quantify patch-and landscape-scale habitat relationships to populations; evaluate possible habitat thresholds in squirrel population response; and develop forest management recommendations. In regression models, both patch-scale and landscape-scale parameters influenced squirrel populations. At the patch scale, number of interlocking canopy trees was added most frequently, whereas the proportion of HQ habitat was the landscape-scale variable added in five of seven models. Recruitment and survival at dense, HQ plots were inversely related to number of small, saplingsized trees. Nonlinear thresholds in density and recruitment occurred when the proportion of HQ habitat at study sites was between 24 and 42%. Our study points to the importance of maintaining HQ habitat in mesoreserves on the landscape at or above this threshold range, as well as pursing a mix of forest management prescriptions in the matrix surrounding mesoreserves to achieve wildlife, forest restoration, and fire risk reduction objectives.

Small mammal community maintains stability through compensatory dynamics after restoration of a ponderosa pine forest

“…Two species responded negatively to thinning, including woodrats, which probably experienced a lack of cover at the thinned sites, and pocket gophers, which may have been negatively affected by the soil compaction associated with thinning. Tasseleared squirrel densities remained fairly constant following thinning, which was contrary to past v www.esajournals.org research suggesting that restoration treatments will have negative consequences (Dodd et al 2003, Dodd et al 2006; however, tassel-eared squirrels might be more closely linked to largediameter trees (Patton 1977, Kalies et al 2012 which are retained in thinning treatments and do not change in density or size in the short term. Thus, species densities fluctuated in response to various habitat elements, but total community density remained constant following disturbance, indicating that the community remained stable through compensation.…”

Wildlife responses to thinning and burning treatments in southwestern conifer forests: A meta-analysis

“…Only animal density could be compared in treatments versus controls across different taxa, which eliminated studies that examined other responses such as home range size, diet, or habitat use. Since fitness is often viewed as the best indicator of population performance (Bock and Jones, 2004), we compared density and reproductive output results and found that both were consistent in treatments versus controls (either both positive or both negative) for the plumbeous vireo and western tanager (Battin and Sisk, 2003), western bluebird (Germaine and Germaine, 2002;Wightman and Germaine, 2006;Hurteau et al, in press), and tassel-eared squirrel (Dodd et al, 2006). However, black bear had similar densities pre-and post-fire, and in burned areas versus control, but lower reproductive output in the burned areas (Cunningham et al, 2003).…”

“…owls, based on sighting of young outside the nest, was higher in unburned versus burned treatments within 4 years of treatment, but the relationship was weak and possibly confounded by the large range in burn severity in the burned sites. Dodd et al (2006) found that density, adult survival, and juvenile recruitment, in terms of juveniles/ha, of tassel-eared squirrels was lower in shelterwood treatments versus controls approximately 10 years after treatment. In a 4-year study beginning 1 year after a high-severity wildfire, Cunningham et al (2003) demonstrated that bear densities remained the same before and after fire, and in the burned area versus control; however, the sex ratio in the burned area was skewed towards males compared to the same area prior to fire or the control.…”

Restoring fire-prone Inland Pacific landscapes: seven core principles

“…10) show that patches in fire-prone dry and mesic mixed-conifer forests comprised fine-scale mosaics of individual trees, and tree clumps and openings (gaps) of various sizes. These spatial patterns influence patch-level resilience to disturbances, rates of succession and stand dynamics processes (Sánchez Meador et al 2009;Stephens et al 2008;Dodson et al 2008;Fettig et al 2007), and wildlife habitat characteristics (Kotliar and Wiens 1990;Dodd et al 2006;Wiens and Milne 1989).…”