Spotted owls and forest fire: Comment

Abstract

Western North American forest ecosystems are experiencing rapid changes in disturbance regimes because of climate change and land use legacies (Littell et al. 2018). In many of these forests, the accumulation of surface and ladder fuels from a century of fire suppression, coupled with a warming and drying climate, has led to increases in the number of large fires (Westerling 2016) and the proportion of areas burning at higher severity (Safford and Stevens 2017, Singleton et al. 2018). While the annual area burned by fire is still below historical levels (Taylor et al. 2016), some forest types in the west are burning at higher severities when compared to pre-European settlement periods (Mallek et al. 2013, Safford and Stevens 2017). As such, they face an increased risk of conversion to non-forest ecosystems (e.g., shrublands, non-native grasslands) following large, severe fires because of compromised seed sources, post-fire soil erosion and loss, high-severity re-burn, and climatic thresholds (Coppoletta et al. 2016, Stevens et al. 2017, Rissman et al. 2018, Shive et al. 2018, Wood and Jones 2019). Restoration methods such as mechanical thinning and prescribed and managed wildland fire that reduce accumulated surface and ladder fuels (e.g., removal of small- and medium-sized trees, especially non-fire adapted species) may reduce the spatial extent of severe fires and increase forest resilience to fire in a changing climate (Agee and Skinner 2005, Stephens et al. 2013, Hessburg et al. 2016, Tubbesing et al. 2019) and, in doing so, promote key ecosystem services (Hurteau et al. 2014, Kelsey et al. 2017, Wood and Jones 2019). Proposals to increase the pace and scale of fuel reduction in frequent-fire forests, however, have been controversial for three main reasons. First, some stakeholders view such “forest restoration” activities as a euphemism for logging remnant large trees (Gutiérrez et al. 2015), and decades of logging throughout western forests have already created a deficit of large, old trees with undesirable ecological consequences (Safford and Stevens 2017, Jones et al. 2018). Second, some stakeholders have expressed concern that scientific or ecological justification for management activities intended to reduce fuel buildup is limited, stating that (1) current wildfire activity (including the patch size and proportional composition of high-severity fire) in frequent-fire forests is within the natural range of variation (Baker 2015) and (2) fuel treatments will be ineffective in reducing severe fire extent in a warming/drying climate (Schoennagel et al. 2017). Third, landscape-level fuel reduction projects have the potential to remove key habitat elements required by old-forest associated species (e.g., spotted owl Strix occidentalis) and thus exacerbate ongoing and long-term population declines (Stephens et al. 2014). The strength of this final argument against increasing the pace and scale of restoration hinges on what scientific research can tell us about which factor poses a greater relative threat to old-forest species: fuel reduction activities or changing climate and wildfire characteristics. To better understand effects of wildfire on spotted owls, Lee (2018) conducted a quantitative meta-analysis synthesizing 50 empirical effects from 15 published studies investigating various responses (occupancy, demography, foraging habitat use) by spotted owls to wildfire. He concluded that wildfire—regardless of severity—did not adversely affect spotted owls and thus does not pose a threat to any of the three subspecies. Moreover, based on these results, Lee (2018) asserts that fuel reduction activities are unnecessary and that planning documents (USFWS 2011, 2012, 2017, Gutiérrez et al. 2017, USDA 2019) claiming that forest fires are a primary threat to owls are no longer relevant. We appreciate the attempt made by Lee (2018) to provide a quantitative synthesis of fire effects on spotted owls, which until this time had been lacking. However, as a group representing authors from many of the spotted owl studies included in the Lee (2018) meta-analysis, as well as forest and fire scientists with extensive research experience in western forest ecosystems, we disagree with its central conclusions that high-severity (or stand-replacing) fire does not affect or threaten spotted owls. We also disagree with the assertion that the meta-analysis supersedes previous spotted owl-fire research and planning documents, and we argue below that it therefore is an improper challenge to previous work and conservation efforts. Rather, our interpretation of the scientific research to date is that the way spotted owls respond to fire is highly variable and context specific. Depending on the extent of and severity of wildfire, studies have shown negative fire effects on California (S. o. occidentalis) and northern (S. o. caurina) spotted owls (Rockweit et al. 2017, Jones et al. 2016, 2020), positive effects on the California and Mexican (S. o. lucida) subspecies (Bond et al. 2009, Ganey et al. 2014), or neutral effects on California spotted owls (Roberts et al. 2011, Lee et al. 2012). To distill this variability down to a conclusion of “no effect” vastly oversimplifies the complex demographic responses of the species (and potentially varied responses by each subspecies) to habitat disturbance. As we describe throughout this comment, a more ecologically relevant interpretation of the meta-analysis by Lee (2018) is that fire appears to have neutral or positive effects on owls in some contexts and at certain scales, but that fire can also pose serious threats to owls. We suggest that Lee (2018) arrived at the conclusions he did because a series of ecological, statistical/technical, and inferential issues that we detail below (Table 1). Ecological issues include an overgeneralization of the historical fire regimes of forests inhabited by spotted owls Statistical/technical issues include a focus on the summary (mean) effects in the presence of high among-study variation, data selected for analyses and representations of high-severity fire and its ecological effects, inaccuracies in reported effect sizes of fires, transparency with reporting and treatment of studies with confounded effects, the use of identical data from multiple studies (“duplicate study effects”), and use of data from several studies that underestimated or miscalculated the potential effects of fire. Inferential issues include the lack of recognition of changing wildfire trends and contention that meta-analyses necessarily solve complex conservation issues and supersedes existing and widely accepted understanding based on studies examining specific mechanisms. Lee (2018:1–2) provided the following statement about natural fire regimes within the range of the spotted owl: “Western forest fires typically burn as mixed-severity fires with each fire resulting in a mosaic of different vegetation burn severities, including substantial patches (range, 5–70% of burned area; mean, 22%) of high-severity fire (Beaty and Taylor 2001, Hessburg et al. 2007, Whitlock et al. 2008, Williams and Baker 2012, et al. 2014, Baker While this statement may be when to the range of the spotted it does not that the natural range of variability in fire regimes variation to forest and climate and Stephens et al. 2019). the to such a range of fire effects that it does not describe ecologically variation in fire regimes et al. 2017). of spotted owls range in the western in and and the California forests experience natural to fire are at the of (2018) of in area burned at high severity and in area burned at high-severity in frequent-fire forests, however, which throughout a large of the range of the spotted as in the in the in and and of the in and at the of the range provided by Lee (2018) to extensive published research and Skinner Skinner and and and and 2007, et al. 2009, 2012, et al. for area burned at high severity in the forest types by the California spotted owl in the is in and in with patches of (Safford and Stevens 2017). While Lee (2018) several studies that in high-severity burned area is greater for frequent-fire forests, the data and analyses in these studies have been and conclusions are not widely accepted by the scientific et al. 2008, Safford et al. 2008, et 2014, et al. Stephens et al. Stevens et 2016, et al. 2017, 2018, et al. 2017, and Safford 2017). We to Safford and Stevens for an extensive of in the about of fire regimes in forests in which is a of to the of fire effects on spotted owls. The overgeneralization of the proportion of high-severity fire within the range of the spotted owl to a of the types of post-fire effects to which spotted owls for frequent-fire forests are to be adapted (or not to historical fire regimes within the frequent-fire forests that of the range of the California spotted owl is as the of studies of and specific effects of in the Lee (2018) meta-analysis conducted in this area burned at high-severity has been increasing with such as the in the central that burned at high-severity et al. 2016) within frequent-fire forest as a of fuels climate and legacies et al. 2009, et al. Safford and Stevens 2017, Stevens et al. 2017, and 2019). As such, spotted owls in some frequent-fire forests to be experiencing post-fire forest by high-severity patches that forests for and habitat to foraging habitat or vegetation types that are for these of spotted owl et al. 2017, et al. Jones et al. 2016, forests provide and thresholds in area burned at which high-severity fire that adversely affect spotted owl demographic et al. 2016, et al. 2017). The of effects is on a of the and of (1) high-severity patches that in a and (2) and foraging habitat within a post-fire et al. 2016, The of effects of severe fire also on is Lee (2018) that is that some owl experiencing high-severity fire of area can However, severe fire is typically as that some patches of trees can for and in such and In experiencing it is that a species the spotted owl will be to the et al. when owls in burned in the can be such that population declines may the longer (Rockweit et al. 2017). of and habitat following a fire can from decades to a and the potential conversion to foraging habitat does not for long-term of habitat et al. 2017, et al. 2019). of and habitat is to more in of of increases in severe fire within forests and the climate and et al. a factor not by Lee key conclusion by Lee that not by mixed-severity and studies no of fire on owl Lee (2018) this because effects not at the this is as an on which to and 2016, et al. 2018, et al. 2019). In conservation a can be with negative consequences for species and et al. is the of effects are ecologically As an the for the effect size for the (and therefore not to be Lee (2018) does on to its potential ecological but that the effect size for the is because it is annual declines in forest reported by Jones et al. We this interpretation is for reasons. First, the effect size for the as Lee (2018) annual declines in In it three the annual in from Jones et al. of annual changes in that the ecologically Lee (2018) the annual declines in in forest as the of changes in for with a negative a of however, the by Lee (2018) be to in an that does not the changes in from with positive and negative annual changes be in population a of is the effect of fire on owl from the Lee (2018) meta-analysis of annual declines in forest that the negative effect of fire on Second, the effect because of high among-study meta-analyses that focus on summary (mean) effects and among-study variability to conclusions that are et al. in Lee (2018) variability in positive and negative effect sizes that to a neutral or to neutral As by et al. among-study variability in the effect size of fire by Lee (2018) demography, high by as by the which is a of among-study et al. The in Lee (2018) for each of foraging suggest that be when and et al. et al. is substantial the focus from the summary effect to the a summary effect and are the of the synthesis Moreover, variability in fire effects studies greater at burned which about owls respond to fire The reduction in in burned coupled with the high of variability in effect sizes the conclusion that fire does not threaten owl these the conclusion that wildfire effects on spotted owls can be or negative on the specific to patch size and spatial of severe fire et al. 2017, et al. 2017, et al. Jones et al. 2016, In the of the Lee (2018) high-severity burned area within have some of this variation and a negative effects but did not or the potential of this Rather, Lee (2018) the of high-severity fire effects (occupancy, demography, and to sizes that to and The effect to high-severity fire a positive effect on which a data 2018, three are because of the data are of identical data in multiple studies potential issues with sizes multiple 2018, and The in had a size and to be negative but at However, as we describe this data that be to the effect and therefore to the Lee (2018) reported the of high-severity fire in burned in for each of the 50 effects from the 15 studies in the reported to the of high-severity fire in the fire within the owl areas for the group representing the a group the reported in to the high severity the not reported in the the of the fire area high-severity fire data as to the in which Lee (2018) the potential for high-severity fire to variability in We are at with this that and that the conclusion from the meta-analysis that severe fire does not threaten spotted owls is not First, and of severe burn extent is because have the potential to the extent of severe fire by this from Jones et al. Lee (2018) the high-severity to be for a group of burned The from an from Jones et al. that the of the study area by high-severity fire. The in this group by Kelsey with and severe fire. severe fire extent within this group of the on Lee a may high-severity fire extent by spotted owl burn at higher severities the Second, a of high-severity fire extent variation in severe fire effects that spotted owl within a fire has a positive or negative effect on a (e.g., will on variation in the of severe fire that within and such an effect is to include thresholds may be a of variation in fire within study areas and study this variation a that to to a of about the of severe fire spotted owls in an ecologically for meta-analysis is the to and effect sizes from different studies on the scale et al. We several effect sizes group sizes reported by Lee (2018) or the study group from the et al. 2016), Lee (2018) reported a effect size of that or proportion of in the burned group the group Lee However, Lee (2018) the of as the he the of from the study area (including burned and the to the fire as the group when he have the reported of from the burned group Jones et al. He underestimated the effect which we have as not a In we not in 2018). the effect with et al. of Lee (2018) the group of However, et al. (2018) reported this from of which fire (Table from et al. 2018). it is from the group reported in of Lee (2018) for this study and a size of large size more from this study in the from of Lee (2018) a effect of fire on from Lee and this positive effect also the effect from any as shown in of Lee However, this effect not reported in the of Lee and and we to the any within that The effects of fire on reported by Lee and neutral or no positive effects reported in Moreover, for this specific Lee (2018) reported a size for of in included in Lee and which its positive effect in the the negative and neutral effects of fire on reported from this study and Lee (2018) for the and burned in the The of a large positive effect of fire on spotted owl that not be and appears to have been with group sizes for effects from Lee and the made in the Lee (2018) Lee (2018) in effect sizes for logging in studies it to and wildfire In the final of the Lee that logging had negative effects on in of the that this disturbance and effects from fire and post-fire logging be with large effect sizes However, the not and we therefore to the effect size of logging on the data from studies in for based on a more reporting the methods in the logging the lack of in the of logging with fire effects from different studies and As an studies in the meta-analysis et al. 2012, et al. to the effects of logging and wildfire the effects on this in the of each However, in the meta-analysis the effect of on from et al. to logging and from analyses of wildfire the effect from Lee et al. to fire and included the effect in the of wildfire effects Lee and and To in the treatment of effects be included or from wildfire the effect from Lee et al. and the effect from et al. be to the effect of fire on Lee and and potentially made from the Lee meta-analysis is that effects from studies are of the can a on the effect that is and of study effects in meta-analyses when data are from the or from the such that effects may be more within can be for in a effects and but potentially more serious when the data are in multiple and effects from are as different effects in a meta-analysis (“duplicate study Wood for with data in meta-analyses include of effects or effects from the meta-analysis The Lee (2018) meta-analysis included effect sizes from multiple studies the but no of the 15 studies from which Lee (2018) data for the meta-analysis data that from study in the The of from identical by a of studies et al. 2016, et al. to et al. 2013, Lee and First, et al. (2018) data from of the by Jones et al. to the effects of severe fire on spotted owl Second, Lee and a of the by Lee et al. but the a and the a study effects have made by Lee (2018) about the effects of fire on the Lee (2018) meta-analysis, three studies published from some by Lee (2018) that led to the or of the effect of fire on spotted owl First, et al. that to for of spotted owls the a high-severity may have underestimated the effect of this fire on by and Second, Jones and that Lee and the negative effect of fire on for owls and for owls in the effect the for the of a increased by a factor of for following fire. The conclusion by Lee and based on a of effects in a Third, et al. (2018) and from of severe fire effects on the that high-severity fire (and thus to an effect of high-severity fire) et al. which be to potential negative severe fire we that the of these and data not published until Lee in the meta-analysis the meta-analysis of variation and the that no effects of fire in and severe fire on (2018) of the effects of fire on spotted owl in burned area burned at high-severity fire) within the by Jones et al. also may have to that fire did not affect spotted owls. Lee a of for this that fire owls at these While it is that increased in this group of the increase because some of these the (and thus by that from experiencing more extensive severe fire area burned at high-severity from Jones et al. the increase in at experiencing a of severe fire Lee that these a of severe fire) to the positive effects of fire does not the ecological by which fire and its effects on a positive effect of fire to at these may have the of fire effects on in a positive in the Moreover, this key about fire on by the study of a population of spotted owls in Jones et al. and that not to in many of the studies of owls in Lee Lee that “forest fire does not to be a serious threat to owl and more for In of this Lee (2018) studies that mixed-severity fire typically of spotted owl and habitat We that severe fire has not in substantial declines in spotted owl at or subspecies and that declines et al. 2016, et al. 2016, et al. 2016) have for including with owls et al. 2016, et al. 2016, et al. potentially the of large trees and old-forest habitat et al. and potentially in et al. 2019). severe fire has declines in spotted owl at more (e.g., of Jones et al. 2016) and in an of and but fire has not been an of long-term spotted owl population However, the conclusion that wildfire does not pose a threat to spotted owls does not that will and more severe in warming and drying forest ecosystems (Westerling and 2008, Stephens et al. 2013, et al. 2013, and and Williams 2016, et al. 2017, Stevens et al. 2017, et al. 2018, et al. with Lee (2018) no of climate change or its potential effects on wildfire activity or spotted owls. Moreover, the conclusion that can be from the meta-analysis the of fire on owls a positive effect to Lee and However, as any potential increase in foraging habitat resulting from mixed-severity fire will not for a of and which is to be a key factor spotted owl throughout range et al. 2017). fire effects the range of three subspecies of spotted owls are to increase the decades et al. and in some it has been shown that habitat area that will experience area from wildfire the may the existing habitat for California spotted owls (Stephens et al. the range of the northern spotted fire regimes are to to more frequent-fire and higher of large forest as climate changes the century et al. 2017). it that in old-forest species and ecosystems the consequences of changing disturbance is a of conservation which is with the long-term of To that the types of fires that threaten spotted owls are the types of fires that are to more in the (e.g., large, severe et al. 2018, et al. 2019) does not the by wildfire to this the meta-analysis and therefore necessarily on owl responses to fire and the threat of fire. However, Lee (2018) that meta-analysis has existing planning documents (USFWS 2011, 2012, 2017, Gutiérrez et al. 2017, USDA 2019). the we have several of the planning documents to which Lee (2018) in climate change is to increase severe fire activity and by affect spotted owls. As such, we not to be and, We final the in Lee (2018) that the meta-analysis that forest fires pose risk to spotted owls. First, is meta-analysis to complex conservation While meta-analysis has to scientific understanding a range of by for synthesis et al. its to to understanding is by the data and made by the Moreover, we suggest that meta-analyses are not for ecological In the of spotted owls, long-term studies of that owls can be by severe fire et al. 2016) and that severe fire can (Rockweit et al. that are within a meta-analyses and to (2018) conclusion that severe fire does not adversely affect spotted owls. because meta-analyses are as a of meta-analyses that are to already complex conservation issues and have the potential to to negative conservation As we have throughout this Lee (2018) issues that have created more and thus it did not the complex of spotted owls in Second, the conclusions by Lee (2018) the existing and current understanding of spotted owl responses to Lee (2018) has is that responses of spotted owls to fire is as we a conclusion that is a by previous empirical studies and et al. 2017, et al. 2018, et al. 2018). is no way spotted owls respond to what Lee (2018) to as in or However, fires by burn severities have effects to owls, fires with greater high-severity to demographic responses by owls. to high-severity fire are to on severe fire patch spatial and extent et al. 2017, et al. 2018, Jones et al. 2016, 2020), but as we the Lee (2018) meta-analysis in these studies based on long-term demographic studies of and study have shown that large and patches of high-severity fire have negative effects on owl et al. 2016, et al. 2017). In large but more complex patches of high-severity fire may have negative effects by and Moreover, may be a of high-severity effects within which more et al. Moreover, spotted owls may use burned forest for foraging when patches are (Bond et al. 2009, 2016, Jones et al. but to patches and the of large patches et al. 2017, Jones et al. 2016, to the scale of severe fire effects have not been in the conclusions about severe fire effects on spotted owls from previous studies to be of made by the Lee (2018) meta-analysis and of to and conservation We appreciate the attempt made by Lee (2018) to provide a quantitative synthesis of fire effects on spotted owls, which until this time had been lacking. However, because of the ecological, statistical/technical, and inferential issues we have this attempt did not provide In the conclusions are and not be to or the existing of the highly variable in which spotted owls respond to different types of fire. Moreover, planning documents stating that changing wildfire regimes pose a threat to spotted owls current the assertion of Lee The existing of that spotted owls respond in a neutral or positive to fire and patches of high-severity fire that within the historical range of variability but that spotted owls can respond to patches of high-severity fire. management that can reduce the extent of severe fire within spotted owl habitat in a changing climate may to owl conservation not remove habitat elements associated with spotted owl (e.g., large, old et al. 2016, 2018, Jones 2019). is that analyses examining the effects of fire on spotted owls provide context and to they will be to scientists and to understand to the of owl and habitat to the increasing threat of high-severity fire in a changing The and conclusions in this are of the and not be to any and of or or The use of or in this is for and does not by the of any or

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