Review of the Science Directly Related to the Effects of Fire on Spotted Owls and their Habitat
Spotted owls are emblematic of controversies that surround management and protection of wildlife in commercially valuable forests. The spotted owl (Strix occidentalis) has three recognized subspecies: northern (S. o. caurina), California (S. o. occidentalis) and Mexican (S. o. lucida). Each subspecies uses a diversity of forest structures throughout their lifecycle: from large, late-seral trees with dense-canopy cover for nesting and roosting to forests with low-to-moderate canopy cover for foraging (Forsman et al. 1984, Gutiérrez and Carey 1985, Verner 1992, Franklin et al. 2000). The diversity of spotted owl habitat requirements reflect pre-European forest heterogeneity which was maintained through disturbances such as fire, insects, and disease (Collins et al. 2011, Barth et al. 2015). Over a century of clear-cutting and fire suppression practices has resulted in landscapes less resilient to disturbances, putting at risk the vestiges of old growth forests spotted owls rely upon. Restoring the resilience of western forests to maintain ecological function in-light of climate change, insects, disease, and increased frequency and extent of high-severity fire represent contemporary objectives of public land agencies (Stephens 2014). As such, integrating the habitat requirements of spotted owls into forest restoration practices presents managers with many daunting decisions – many of which involve questions of fire and its effects on spotted owls.
Accounting for fire regimes
The frequency and severity of wildfire has historically varied across the range of the spotted owl. For example, in mesic and high elevation forests within the western range of the northern spotted owl it has been suggested that mixed-severity fires were relatively more common than low-and-moderate severity fires, and occurred at return intervals between 50-200 years (Spies et al. 2006). Conversely, in drier mixed conifer/evergreen forests and adjacent forests dominated by Ponderosa Pine (habitats frequented by California spotted owls and within the eastern range of the northern spotted owl) natural fire exhibited return intervals of 6-24 and 4-11 years, respectively, and were of low severity (Spies et al. 2006; Fig 1).
Figure 1. Map of Northwest Forest Plan area with physiographic provinces identified throughout part of the range of the northern spotted owl: 1, Washington Olympic Peninsula; 2, Washington Western Lowlands; 3, Washington western Cascades; 4, Washington eastern Cascades; 5, Oregon western Cascades; 6, Oregon eastern Cascades; 7, Oregon Coast Range; 8, Oregon Willamette Valley; 9, Oregon Klamath; 10, California Klamath; 11, California Coast Range; 12, California Cascades. Taken from Spies et al. (2006).
Historic fire suppression and clear-cutting practices in forests with dynamic fire regimes and fast-fire return intervals have potentially altered the behavior of wildfire. Fuel treatments and other management prescriptions are often necessary to restore forest resiliency to fire. However, the long-term conservation of northern spotted owls in forests exhibiting dynamic fire regimes may be confounded where the Northwest Forest Plan’s guiding vision was based on setting aside habitat as Late Successional Reserves (LSR) with minimal management activity (Feinstein et al. 2010). Without fuel treatments, LSRs in the eastern range of the northern spotted owl have become more at risk of high-severity fire (Agee 2002). Hence, the “hands-off” reserve approach is emblematic of tradeoffs between the deleterious effects of fuel treatments on spotted owls and habitat loss through increased risk of high-severity fire. Conflicts between the “hands-off” approach and risk of high-severity fire prompted researchers at the USFS to develop candidate fuel treatments in LSRs to restore forest resiliency in spotted owl habitat – at larger spatial scales – across the eastern cascades (Feinstein et al. 2010; Fig 3). The recent change in management philosophy in eastern Washington and Oregon is concordant with current research suggesting that judicial fuel treatments within territories of California spotted owls may be appropriate (Tempel et al. 2016), especially when considering tradeoffs with risk of high-severity wildfire (Tempel et al. 2015; Fig 2). Less attention has been given to tradeoffs between fuel management, forest restoration, and spotted owls in the more mesic forests of the western cascades and coastal regions of California. The mixed-severity fires in these regions historically occurred at longer time-intervals (e.g. 50-200 years) which was thought to maintain landscape heterogeneity to which spotted owls are adapted (Franklin and Dyrness 1973). The loss of old, fire tolerant trees is of particular concern in mesic forests with mixed-severity fires. Dense stands of trees on relatively dry sites increase water use and subsequent drought and insect outbreaks, exacerbating a trend of increasing regional drying, and severity and extent of wildfire (Perry et al. 2011).
Fig 2. Average territory fitness potential and standard errors at four California Spotted Owl (Strix occidentalis occidentalis) territories on a 13,482-ha study area in the Sierra Nevada under four scenarios: (1) no fuel treatments and no wildfire; (2) fuel treatments and no wildfire; (3) no fuel treatments and wildfire; and (4) fuel treatments and wildfire. Simulated fires occurred in year 0 for both the ‘‘no treatment’’ and ‘‘treatment’’ scenarios, and post-fire effects were first assessed in year 10. Taken from Tempel et al. (2015).
Preferred spotted owl habitat often reflect those conditions that promote wildfire. For example, northern spotted owls use forest with large proportions of downed woody debris and snags, high canopy closure, and high structural diversity (Hershey et al. 1998, North et al. 1999, Irwin et al. 2000). These features not only provide habitat for spotted owls, but also serve as ladder fuels that increase the likelihood of high-severity fire (Clark et al. 2012). Numerous studies found that spotted owl population viability is closely tied to late-successional forest within the core of their territory (Forsman et al. 1984, Gutiérrez and Carey 1985, Verner 1992, Franklin et al. 2000). Thus, the proximity of ladder fuels and late-successional forests within spotted owl territories inherently increases the risk of late-successional forest being lost due to high-severity fire. Mitigating such risks through strategic fuel reductions reflects the evolving face of spotted owl management (Fig 3). In addition to balancing tradeoffs between fuels management and spotted owl habitat loss due to fire, identifying the effects of post-fire management – salvage logging – on spotted owls is another reoccurring topic of interest among managers.
Figure 3. An example of optimal allocation of fuel reduction treatments around northern spotted owl locations on the Mission Creek Drainage, Okanogan-Wenatchee National Forest, Washington. To arrive at this solution, PNW researchers simultaneously considered the dual goals of minimizing potential fire behavior and maximizing the maintenance of spotted owl habitat. The open round circles are protected habitat around owl nest sites; the black patches are treated stands. Taken from Feinstein et al. (2010).
Understanding effects of salvage logging on spotted owls requires an appreciation of spotted owl ecology and behavior. Spotted owls are long-lived and use different forest types for various aspects of their natural history (e.g. breeding, foraging, and wintering). In fact, spotted owls have been shown to use habitats subject to high-severity fires where no salvage logging has occurred (Bond et al. 2008). Additionally, occupancy, nest success and survival of spotted owls decreased as the amount of salvage logging increased (Thraillkill et al. 1998, Clark et al. 2011, Lee et al. 2012, Lee et al. 2013). Among the few studies that measured the effects of fire and post-fire salvage logging on spotted owls, there is general consensus that salvage logging negatively affected spotted owl occupancy and habitat use by further degrading the value of habitats within burned landscapes (Clark et al. 2007, Lee et al. 2012, Lee et al. 2013; Figure 4). Importantly, many studies that examined the response of spotted owls to fire may have been confounded by an inability to separate effects of salvage logging from fire on owls – whereby the negative response of owls to fire was exacerbated by salvage logging activities (Clark et al. 2011, Lee et al. 2013). Nonetheless, it has been suggested that managers forgo salvage logging – even after high-severity fires – within the vicinity of spotted owl territories until dynamics between logging, prey-base and the subsequent response of owls are better understood (Bond et al. 2008). To date no study has implemented an experimental design to measure the effects of salvage logging late-seral forest on spotted owls after high-severity fire, or examined the long-term effects of salvage logging on owl populations.
Figure 4. Extinction probability estimates from a study examining the effects of fire and salvage logging on the occupancy dynamics of California spotted owls in the San Bernardino and San Jacinto Mountains of Southern California, from 2003 to 2011. Note the additive effects of salvage logging on the extinction probability of spotted owls post-fire. Figure taken from Lee et al. (2013).
Gradients of spotted owl response to fire There exist striking contradictions in the response of spotted owls to fire within the published literature (Table 1). For instance, Ganey et al. (2014) found that wintering Mexican spotted owls moved to burned areas where prey abundance was higher than unburned areas. Conversely, Clark et al. (2011) found that 22% of radio-marked northern spotted owls within and adjacent to burned areas died from apparent starvation. Even within subspecies the varying response of spotted owls is noticeable. For example, in the Sierra Nevada, Lee et al. (2012) found no significant effect of fire on California spotted owl occupancy despite on average 32% owl habitat within a 200-ha circle around core areas being burned at high severity. Conversely, in the San Bernardino and San Jacinto Mountains of southern California, Lee et al. (2013) found a negative effect of fire on California spotted owl occupancy where on average 23% of owl habitat in a 203-ha circle burned severely. Differences in pre-existing vegetative structure, plant communities, and the subsequent response of prey to fire may be responsible for such differences (Lee et al. 2012, 2013). Several other factors may also be responsible for the seemingly confusing response of spotted owls to fire, including: (1) neglecting the importance of fire severity in analyses (e.g. using overly simplistic categories such as burned vs. unburned); (2) lacking the inability to separate effects of fire and salvage logging; (3) measuring owl responses over short time scales; and (4) variation in local adaptation of owls (e.g. California spotted owls in southern California are substantially smaller than California spotted owls in the Sierra Nevada) (Gutiérrez and Pritchard 1990; LaHaye et al. 1994, 2001).
Table 1. Effects of fire on different estimates of spotted owl demography. Fire severity used in each study is denoted by low(low), moderate(mod), severe(sev) and all (low, moderate and severe pooled). Studies cited are as follows: (1) Jenness et al. 2004 (2) Lee et al. 2012 (3) Roberts et al. 2011 (4) Clark 2007 (5) Gaines et al. 1997 (6) Tempel et al. 2015 (7) Bond et al. 2008 (8) Baker 2015 (9) Lee et al. 2013 (10) Lee and Bond 2014 (11). Bond et al. 2016 (12) Clark et al. 2012 (13) Ganey et al. 2014 (14) Bond et al. 2002 (15) Jenness 2000 (16) Wolfe et al. 2016 (17) Tempel et al. 2016.
The response of spotted owls to fire is dependent on what aspect of their natural history is being measured: survival, productivity, occupancy or habitat use. For example, Wolfe et al. (2016) found that California spotted owls in the northern Sierra Nevada exhibited lower survival when small portions of their territories were burned at high severity, while at the same time California spotted owls in the southern Sierra Nevada exhibited higher productivity when small portions of their territories were burned at high severity. Similarly, Clark (2007) found no difference in northern spotted owl productivity pre-and-post fire, but did find that occupancy and survival were negatively associated with fire, while owls selectively foraged in areas subject to low-severity fire. Such differences probably reflect interactions between habitat requirements during discrete phases of their lifecycle (e.g. breeding, wintering, and molt) and fire-induced changes to those habitats. It’s also important to recognize that interactions between fire and lifecycle probably vary across the landscape. Presumably, as one moves from mesic habitats (e.g. western cascades) to drier habitats (e.g. eastern cascades with more dynamic fire regimes), the response of the vegetative community and prey-base respond differently which can have varying emergent effects on spotted owl demography during different phases of their lifecycle (e.g. breeding, molt, and wintering). Given the diversity of documented responses of spotted owls to wildfire across their range, we suggest prioritizing studies that examine the capacity of local owl populations to withstand fires of different severities, ages, extents, and distances to nesting and roosting habitat.
Barred owls and fire
The arrival of invasive barred owls (Strix varia) represent another emergent and significant challenge for spotted owl management. Native to eastern North America, barred owls are large forest-dwelling owls that were first detected in British Columbia in 1943 and Washington state by 1965 (Grant 1966). Barred owls remained in small numbers throughout the Pacific Northwest until the 1980s, when their populations quickly grew and were first detected in California (Evens and LeValley 1982). Barred owls directly compete with spotted owls by displacing them from territories and currently represent a significant threat to the viability of northern spotted owls (Dugger et al. 2015). Barred owls have expanded into the northern vicinity of California spotted owls and continue to move southward (North 2012). Barred owl diet and habitat use is more varied than spotted owl (Mazur and James 2000), although barred owls have been documented to select strikingly similar habitats as the northern spotted owl in the eastern cascades (Singleton et al. 2010). In the eastern cascades, Singleton et al. (2010) found barred owl habitat use was most concentrated in moist, valley-bottom forest often associated with fire refugia – similar refugia has been elicited as quality habitat for spotted owls (Gaines et al. 1997). In addition to similar habitat preferences between barred and spotted owls, extinction probability increases for each species when the other is present; however, the effect of barred owls on spotted owls is greater (Yackulic et al. 2014). Given the propensity of barred owls to use a wider-breadth of habitats and foods, we speculate that barred owls can probably tolerate the loss of forest cover due to high-severity fire more so than spotted owls. If this conjecture is true, then fire may complicate the preliminary success of barred owl removal experiments. For example, spotted owls displaced by barred owls may be less likely to return to former territories after wildfire and barred owl removal. To our knowledge, the interactive effects of fire and barred owls on spotted owls has not been measured.
Important information gaps
1. Long-term response of spotted owls to wildfire. Most studies occurred over short time scales. Post-fire succession presumably changes the foraging, roosting, and breeding opportunities for spotted owls over longer time periods than those currently being measured. Understanding how the ecological value of burned forests change over time is an important and unknown facet of spotted owl ecology.
2. Interactive effects of fire extent, severity, and distance to territory core on spotted owls. Spotted owls are complex creatures and fire is a dynamic process making it difficult to ascertain how variation in fire extent and severity affect spotted owls across their range. New opportunities to measure and compare localized responses are beginning to emerge as monitored populations of spotted owls are repeatedly subjected to wildfire throughout the west.
3. Late-seral forest salvage logging. No information is available from landscape experiments that remove and leave burned late-seral stage forest in spotted owl territories.
4. Interactive effects of barred owls and fire on spotted owls. Barred owls can use a wider range of habitats and food resources than spotted owls. Such behavioral flexibility may make barred owls relatively more successful in burned landscapes than spotted owls. To our knowledge this conjecture remains unverified.
Annotated Bibliography of Pertinent Literature
Ager, A. A., Finney, M. A., Kerns, B. K., & Maffei, H. (2007). Modeling wildfire risk to northern spotted owl (Strix occidentalis caurina) habitat in Central Oregon, USA. Forest Ecology and Management, 246(1), 45-56.
Simulations of northern spotted owl habitat loss with and without fuel treatments in the Five Buttes Interface planning area, central Oregon. The authors observed a non-linear decrease in the probability of habitat loss with increasing fuel treatment area. Fuels treatments on a relatively minor percentage of the forested landscape (20%) resulted in a 44% decrease in the probability of spotted owl habitat loss averaged over all habitat stands.
Baker, W. L. (2015). Historical Northern spotted owl habitat and old-growth dry forests maintained by mixed-severity wildfires. Landscape Ecology, 30(4), 655-666.
The author was able to reconstruct historic forest conditions and likely northern spotted owl nest trees, nest stands, and foraging and roosting habitat, based in-part on modern habitat studies of northern spotted owls from the eastern Cascades of Oregon. Various stages of post-fire succession provided NSO foraging, roosting and nesting habitat and were historically common; study serves as a counterpoint to the idea of historic reliance on fire refugia.
Bond, M. L., Bradley, C., & Lee, D. E. (2016). Foraging habitat selection by California spotted owls after fire. The Journal of Wildlife Management.
The authors examined habitat use of California spotted owls following fire in the San Bernardino Mountains of southern California. At all extents of available habitat, spotted owls strongly selected foraging sites close to their territory center, and close to riparian areas. Resource selection functions suggested forest burn severity was not significantly associated with probability of use, meaning burned forests were generally used in proportion to availability, with the exception of selection for moderate-severity burned forests farther from the territory center at the largest available habitat extent.
Bond, M. L., Gutiérrez, R. J., Franklin, A. B., LaHaye, W. S., May, C. A., & Seamans, M. E. (2002). Short-term effects of wildfires on spotted owl survival, site fidelity, mate fidelity, and reproductive success. Wildlife Society Bulletin, 1022-1028.
Authors examined minimum survival, site fidelity (if it survived), and mate fidelity (if both members survived) following fires for individual northern, California and Mexican spotted owls. The authors found that 86% of the individual owls affected by fires were resighted at least one year after the fires, and 89% of the resighted owls were located in the same territories in the breeding season after the fire. Among seven owl pairs in which both members were resighted after a fire, all were site- and mate-faithful. Four of seven surviving owl pairs (57%) produced 7 fledglings the year following fire. Minimum survival of spotted owls experiencing fires was similar to overall annual survival rates reported for the 3 subspecies.
Bond, M. L., Lee, D. E., Siegel, R. B., & Ward, J. P. (2009). Habitat use and selection by California spotted owls in a postfire landscape. The Journal of Wildlife Management, 73(7), 1116-1124.
Authors used radio telemetry to examine effects of a burned landscape on habitat use of California spotted owls in the central and southern Sierras relative to foraging, roosting and nesting behaviors. Spotted owls were found to preferentially roost in low-severity burned forest, avoided high-severity, and used unburned in proportion to availability. Conversely, owls selectively foraged in high severity burns over unburned forest. Four spotted owl nests were documented: one in unburned mixed conifer–hardwood, one in conifer forest burned at low severity, and two in conifer forest burned at moderate severity. One pair, nesting in a stand burned at moderate severity, produced the only fledgling of the 4 nesting attempts.
Clark, D. A., Anthony, R. G., & Andrews, L. S. (2011). Survival rates of northern spotted owls in post-fire landscapes of southwest Oregon. Journal of Raptor Research, 45(1), 38-47.
Examined the known-fate survival (using radio telemetry) of northern spotted owls in southwest Oregon. Four of 23 radio-marked owls (22%) within and adjacent to the Timbered Rock and Quartz burns died. All four owls were severely emaciated and likely died of starvation. Model averaged estimates of annual survival for owls inside the burns (S= 0.69 +/- 0.12) and displaced by the burns (S= 0.66 +/- 0.14) were similar but were substantially lower than owls outside burned areas (S= 0.85 +/- 0.06).
Clark, D. A., Anthony, R. G., & Andrews, L. S. (2013). Relationship between wildfire, salvage logging, and occupancy of nesting territories by northern spotted owls. The Journal of Wildlife Management, 77(4), 672-688.
Authors investigated effects of fire and salvage logging on the occupancy dynamics of northern spotted owls in southwest Oregon. Extinction probabilities increased at the Timbered Rock study area following wildfire and subsequent salvage logging, which combined with the lesser colonization rates at this site contributed to greater declines in site occupancy than were observed in recently unburned landscapes at the South Cascades. The Timbered Rock study area had an approximately 64% reduction in site occupancy following wildfire, whereas the South Cascades (control) study area had a roughly 25% reduction in site occupancy during the same time period. The authors found some evidence that colonization probabilities in their study were positively associated with increased amounts of older forest that burned with a low severity within the core area. Their analysis provided weak support that colonization probabilities were positively associated with increased amounts of older forest that burned with a moderate severity.
Clark, D. A. (2007). Demography and habitat selection of northern spotted owls in post-fire landscapes of southwestern Oregon (Masters Thesis).
Thesis examining northern spotted owl occupancy, productivity, survival, home range size and habitat use in pre-and-post fire treatments, and in-and-outside of burned areas in southwestern Oregon. Extinction rates increased following wildfire (stand-replacing wildfire and subsequent salvage logging). However, Colonization rates in the study were constant over time after fire and between study areas but were positively associated with increased amounts of nesting, roosting and foraging habitat with low severity burn in the core area. Owls preferred to forage in unburned-to-low severity burn areas. Estimates of productivity did not differ pre-and-post fire while fire negatively affected survival of owls displaced by fire, or within burned areas. Lastly, home range did not vary as a function of burned area.
Elliott, B. (1985). Changes in distribution of owl species subsequent to habitat alteration by fire. Western Birds, 16(1), 25-28.
California spotted owls in the Los Padres National Forest were not detected post-burn but were detected three years later in an adjacent unburned site.
Ganey, J. L., Kyle, S. C., Rawlinson, T. A., Apprill, D. L., & Ward Jr, J. P. (2014). Relative abundance of small mammals in nest core areas and burned wintering areas of Mexican Spotted Owls in the Sacramento Mountains, New Mexico. The Wilson Journal of Ornithology, 126(1), 47-52.
Authors used telemetry to follow Mexican spotted owls to their winter grounds in the Sacramento Mountains of New Mexico, where they also conducted small mammal trapping. Wintering areas of these owls occurred within the perimeters of two wildfires. The authors estimated relative prey abundance and biomass within paired burned wintering areas and nest core areas used by these owls. Species richness and relative abundance of small mammals were greater in the burned wintering areas than in the associated nest core areas for all four owls, and estimated prey biomass ranged from 2–6 times greater in burned wintering areas relative to the paired nest core areas.
Gaines, W. L., Strand, R. A., & Piper, S. D. (1997). Effects of the Hatchery Complex Fires on northern spotted owls in the eastern Washington Cascades. In Proceedings of the First Conference on Fire Effects on Rare and Endangered Species and Habitats. International Association of Wildland Fire, Coeur d’Alene, Idaho (pp. 123-129).
Largely anecdotal account suggesting that productivity and occupancy of northern spotted owls were lower following fire in the eastern cascades of Washington. Additionally, the authors suggest that riparian areas were less likely to burn and may serve as refugia for northern spotted owls.
Jenness, J. S., Beier, P., & Ganey, J. L. (2004). Associations between forest fire and Mexican spotted owls. Forest Science, 50(6), 765-772.
The authors measured effects of forest composition and percent area burned on the occupancy and productivity of Mexican spotted owls. Estimates of effect size are suggestive of a biologically significant impact where occupancy was 14% higher and probability of successful reproduction 7% higher in unburned sites.
Jenness, J. S. (2000). The effects of fire on Mexican spotted owls in Arizona and New Mexico (Doctoral dissertation, Northern Arizona University).
Examined presence and productivity of Mexican spotted owls in unburned-and-burned areas in New Mexico and Arizona. Unburned territories had slightly more cases of “Pairs” and “Reproduction” than burned territories while burned territories had twice as many cases of “No Owls” and slightly more cases of “Single Owls” than unburned territories. Territories with high percentages of unburned area would most likely be classified at either the “Pair” or the “No Owls” response level which did not make biological sense.
Lee, D. E., Bond, M. L., Borchert, M. I., & Tanner, R. (2013). Influence of fire and salvage logging on site occupancy of spotted owls in the San Bernardino and San Jacinto Mountains of southern California. The Journal of Wildlife Management, 77(7), 1327-1341.
Estimated occupancy dynamics of California spotted owls in southern California relative to burned areas and salvage logging. Fire negatively affected occupancy dynamics and salvage logging exacerbated such effects. Interesting results that are contrary to studies from the Sierra Nevada where owl territories had more trees in core areas relative to southern California sites.
Lee, D. E., & Bond, M. L. (2015). Occupancy of California Spotted Owl sites following a large fire in the Sierra Nevada, California. The Condor, 117(2), 228-236.
Examined occupancy dynamics of California spotted owls before and immediately following the Rim Fire in the central Sierras. The amount of high-severity fire in owl territories did not affect pair occupancy. However, occupancy probability of single birds was negatively correlated with the amount of high severity fire in territories.
Lee, D. E., & Bond, M. L. (2015). Previous year's reproductive state affects Spotted Owl site occupancy and reproduction responses to natural and anthropogenic disturbances. The Condor, 117(3), 307-319.
Investigated multi-state occupancy dynamics of California Spotted Owls in southern California relative to fire, salvage logging and the previous year’s occupation of the site by breeding owls. Both occupancy and reproduction probabilities were much greater at sites that were occupied by breeding owls in the previous year. High-severity fire and postfire logging were correlated with a significant reduction in site occupancy, but the negative effects were small in sites that supported reproductive owls the previous year and pronounced in sites that were occupied by nonreproductive owls the previous year.
Lee, D. E., Bond, M. L., & Siegel, R. B. (2012). Dynamics of breeding-season site occupancy of the California spotted owl in burned forests. The Condor, 114(4), 792-802.
Used 11 years of survey data throughout the Sierra Nevada to examine effects of burned and unburned forest on the occupancy dynamics of California spotted owls. No significant effect of high-severity fire was found to influence occupancy. Post-fire salvage logging may have affected rates of occupancy of the burned sites. The authors did not have spatially explicit data on post-fire logging, but it occurred within 2 years after the fire near at least eight of the 41 burned sites. Seven of the eight sites that were later logged were occupied by California Spotted Owls after the fire but none of the eight sites were occupied after logging.
Lee, D. C., & Irwin, L. L. (2005). Assessing risks to spotted owls from forest thinning in fire-adapted forests of the western United States. Forest Ecology and Management, 211(1), 191-209.
Used a combination of population data, canopy cover measurements, and forest simulation models, the authors examined tradeoffs between fuel treatments and habitat availability for California spotted owls in the Sierra Nevada. Results suggest that modest fuels treatments in the Sierra Nevada are not expected to reduce canopy cover sufficiently to have measurable effects on owl reproduction.
Roberts, S. L., van Wagtendonk, J. W., Miles, A. K., & Kelt, D. A. (2011). Effects of fire on spotted owl site occupancy in a late-successional forest. Biological Conservation, 144(1), 610-619.
Examined effects of burned and unburned habitats on occupancy dynamics of California spotted owls in Yosemite. Owl detection and occupancy rates were similar between burned and unburned sites. Nest and roost site occupancy was best explained by a model that combined total tree basal area (positive effect) with cover by coarse woody debris (negative effect).
Roloff, G. J., Mealey, S. P., Clay, C., Barry, J., Yanish, C., & Neuenschwander, L. (2005). A process for modeling short-and long-term risk in the southern Oregon Cascades. Forest Ecology and Management, 211(1), 166-190.
Simulated amount of northern spotted owl foraging habitat given different management and fire scenarios in the southern Cascades of Oregon. Simulations suggested that, as time progressed, the management scenario that emphasized managing for owl foraging habitat resulted in increasingly greater areas of surface and crown burns.
Tempel, D. J., et al. (2015). Evaluating short‐and long‐term impacts of fuels treatments and simulated wildfire on an old‐forest species. Ecosphere, 6(12), 1-18.
Simulated effects of fuel treatments, fire and forest growth on California spotted owl habitat, occupancy and population growth. Tradeoffs were documented were fuel treatments had a positive effect on owl habitat and demographics up to 30 years after simulated fire, but they had a persistently negative effect throughout the 30-year period in the absence of fire.
Tempel, D. J., et al. (2016). Meta-analysis of California spotted owl (strix occidentalis occidentalis) territory occupancy in the Sierra Nevada: habitat associations and their implicat
ions for forest management. In review.
Authors measured the occupancy dynamics of California spotted owls in the northern, central and southern Sierra Nevada relative to forest structure, climate, logging and fire. Fire was found to increase extinction probability, yet non-significantly, at Sequoia-Kings Canyon.
Wolfe, J. D., et al. (2016). Effects of variation in canopy cover habitat perturbations and climate on California Spotted Owl (Strix occidentalis occidentalis) demography. In review.
Authors measured the survival, productivity and recruitment of California spotted owls in the northern, central and southern Sierra Nevada relative to forest structure, climate, logging and fire. Fire was found to negatively affect survival in the northern and positively affect productivity in the southern reaches of the study area. Results suggest that the response of owls to fire may vary on a latitudinal gradient across the Sierra Nevada.
Barth, M. A., Larson, A. J., & Lutz, J. A. (2015). A forest reconstruction model to assess changes to Sierra Nevada mixed-conifer forest during the fire suppression era. Forest Ecology and Management, 354, 104-118.
Collins, B. M., Everett, R. G., & Stephens, S. L. (2011). Impacts of fire exclusion and recent managed fire on forest structure in old growth Sierra Nevada mixed‐conifer forests. Ecosphere, 2(4), 1-14.
Dugger, K. M., Forsman, E. D., Franklin, A. B., Davis, R. J., White, G. C., Schwarz, C. J., ... & Doherty Jr, P. F. (2015). The effects of habitat, climate, and Barred Owls on long-term demography of Northern Spotted Owls. The Condor, 118(1), 57-116.
Evens, J. and R. LeValley. 1982. Middle Coast region. American Birds 36:890
Feinstein, M., Lehmkuhl, J., & Hessburg, P. (2010). An evolving process: protecting spotted owl habitat through landscape management.
Forsman, E. D., Meslow, E. C., & Wight, H. M. (1984). Distribution and biology of the spotted owl in Oregon. Wildlife Monographs, 3-64.
Franklin, A. B., Anderson, D. R., Gutiérrez, R. J., & Burnham, K. P. (2000). Climate, habitat quality, and fitness in northern spotted owl populations in northwestern California. Ecological Monographs, 70(4), 539-590.
Franklin, J. F., & Dyrness,
C. T. (1973). Natural vegetation of Oregon and Washington. USDA Forest Service General Technical Report, Pacific Northwest Forest and Range Experiment Station, (PNW-8).
Grant, J. 1966. The Barred Owl in British Columbia. Murrelet 47:39-45.
Gutiérrez, R. J., & Carey, A. B. (1985). Ecology and management of the spotted owl in northwest California. US For. Serv. Gen. Tech. Rep. PNW-185. 119pp.
Gutiérrez, R. J., & Pritchard, J. (1990). Distribution, density, and age structure of spotted owls on two southern California habitat islands. Condor, 491-495.
Hershey, K. T., Meslow, E. C., & Ramsey, F. L. (1998). Characteristics of forests at spotted owl nest sites in the Pacific Northwest. The Journal of wildlife management, 1398-1410.
Irwin, L. L., Rock, D. F., & Miller, G. P. (2000). Stand structures used by northern spotted owls in managed forests. Journal of Raptor Research, 34(3), 175-186.
LaHaye, W. S., Gutiérrez, R. J., & Dunk, J. R. (2001). Natal dispersal of the spotted owl in southern California: dispersal profile of an insular population.The Condor, 103(4), 691-700.
LaHaye, W. S., Gutiérrez, R. J., & Akcakaya, H. R. (1994). Spotted owl metapopulation dynamics in southern California. Journal of Animal Ecology, 775-785.
Mazur, K. M., & James, P. C. (2000). Barred Owl (Strix varia) The Birds of North America Online.
North, M. (2012). Managing Sierra Nevada forests. Gen. Tech. Rep. PSW-GTR-237. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station.
North, M. P., Franklin, J. F., Carey, A. B., Forsman, E. D., & Hamer, T. (1999). Forest stand structure of the northern spotted owl's foraging habitat. Forest Science, 45(4), 520-527.
Perry, D. A., et al. (2011). The ecology of mixed severity fire regimes in Washington, Oregon, and Northern Cali
fornia. Forest Ecology and Management, 262(5), 703-717.
Singleton, P. H., Lehmku
hl, J. F., Gaines, W. L., & Graham, S. A. (2010). Barred owl space use and habitat selection in the eastern Cascades, Washington. The Journal of Wildlife Management, 74(2), 285-294.
Spies, T. A., Hemstrom, M.
A., Youngblood, A., & Hummel, S. (2006). Conserving old‐growth forest diversity in disturbance‐prone landscapes.Conservation Biology, 20(2), 351-362.
Stephens, S. L. (2014). Increasing resiliency in frequent fire forests: Lessons from the Sierra Nevada and western Australia. In: Sample, V. Alaric; Bixler, R. Patrick, eds. Forest conservation and management in the Anthropocene: Conference proceedings. Proceedings. RMRS-P-71. Fort Collins, CO: US Department of Agriculture, F
orest Service. Rocky Mountain Research Station. p. 123-132.
Thrailkill, J. A., Anthony, R. G., Meslow, E. C., Perkins, J. P., & Steidl, R. J. (1998). Demography and habitat associations of the spotted owl on the Eugene District Bureau of Land Management, Central Oregon Coast Ranges. Oregon Cooperative Wildlife Research Unit, Department of Fisheries and Wildlife, Oregon State University, Corvallis, OR.
Verner, J. (1992). The California spotted owl: a technical assessment of its current status (Vol. 133). DIANE Publishing.
Yackulic, C. B., Reid, J., Nichols, J. D., Hines, J. E., Davis, R., & Forsman, E. (2014). The roles of competition and habitat in the dynamics of populations and species distributions. Ecology, 95(2), 155-279.