Forest Management and Conservation of Boreal Owls in North America

j. RaptorRes. 31(2):114-124 ¸ 1997 The Raptor ResearchFoundation, Inc.

FOREST MANAGEMENT AND CONSERVATION OF BOREAL OWLS IN NORTH AMERICA

GREGORY D. I-M•WU•D Departmentof Zoolo• and Physiolo•,University of Wyoming,Laramie, WY 82071 U.S.A.

ABSTP,ACT.--Boreal Owls (Aegoliusfunereus) in North America occur throughout the boreal forests of Canada and Alaska and in subalpineforests of the Rocky Mountains north of central New Mexico. A recent assessmentof Boreal Owl conservation statusin the western mountains of North America sug- gested that Boreal Owls were not in immediate peril. However,in the long-term and in selectedlocal areas,Boreal Owls likely face conservationproblems. This conclusionreflects the hypothesizedresponse of Boreal Owls to the type and pattern of forest harvestthat occurred in the past and may occur in the future. Over the last 40 yr, a majority of timber harvestoccurred asclear-cutting that removed the older, more diverseforest stands.Forest structure influences the availabilityof suitable cavities,the quality of roost sites,the foraging movementsof individual owlsand prey availability.Components of mature and older forestsare especiallyimportant to Boreal Owl habitat quality;the owlsnest in large tree cavities and prey populationsare most abundant in older forest stands.Clear-cut sites will remain unsuitable for roosting or foraging for a century or more and new nest trees will not develop in some situations for two centuriesor longer.Timber harvestwhich maintainscomponents of mature forestwell dispersed acrossthe landscapemay be compatiblewith conservationof Boreal Owls.In particular,forest manage- ment must considerthe consequencesof management decisionsacross broad spatial scalesand over a long-term horizon. Metapopulationmodeling and experimentationthrough adaptivemanagement will be necessaryto developtimber harvestpractices compatible with conservationof Boreal Owls. KEyWorn)s: forestmanagement, Boreal Owk Aegolius funereus; wvodpec•, small mamma& adaptive management.

Administraci6n Forestalesy Conservaci6nde Bfihos Boreal en Norte America RESUMEN.---E1Bfiho Boreal Aegoliusfunereus en norte americaocurre en todaspartes de bosquesboreal en Canad/ty Alaskayen bosquessub-alpino en las montafiasRocosas norte de centro Nuevo M•xico. Una evaluaci6n reciente del estado de conservaci6n del Bfiho Boreal en las montafias del oeste en norte america sugieraque el Bfiho Boreal no est• en peligro inmediato. Sin embargo,en la larga duraci6n,y en •eas seleccionadasen el local, Bfiho Boreal pueden encontrarsecon problemasde conservaci6n.Esta conclusi6nreflecta la respuestahipotesisada del bfiho borealpara el tipo y ejemplode cosechasde bosque que ocurri6 en el pasadoy puede ocurrir en el futuro. En los filtimos40 aftosuna mayoria de cosechas de madera ocurri6 en el corte-completoque quito fireasde bosquemaduros y de mas diversidad.La estructurade bosqueinfluencia la disponibilidadde parcelassuficiente, la calidadde perchas,los movi- mientos de forraje de bfihos solitarios,y la disponibilidadde cazar.Componente de bosquesmaduros y viejos son especialmenteimportante al h/tbitat del Bfiho Boreal: Los bfihos hacen nidos en cavidades grandesde los firbolesy poblacionesde cazar son mas abundanteen parcelasde bosqueviejas. Sitios cortados-completose quedaraninconveniente para perchaso forraje para un siglo o m• y •boles con nidos nuevosno se desarrollanen unos situacionespor dos sigloso mas. Cosechade maderasque man- tienen componentede bosquesmaduros bien dispersosa travis el paisajepuede estarcompatible con la conservaci6nde BfihosBoreal. En particular la administraci6nde bosquesnecesita considerar las conse- cuenciasde las decisionesque hace a travis de la escalade espacioamplio y sobresuficiente tiempo con perspectiva.Modelos de meta-poblaci6ny experimentaci6na travis de administraci6nadoptivo va ser necesariopara desarrollarcostumbres compatible de cosechasde madera con conservaci6nde Bfihos Boreal. [Traducci6n de Rafil De La Garza,Jr.]

The North American distribution for Boreal coasts in the boreal forests of Alaska and Canada Owls (Aegoliusfunereus) forms a relatively continu- (Godfrey 1986). South of the continuoustranscon- ous band extending from the Pacific to Atlantic tinental band, disjunct populations occur in the

114 JUNE1997 FORESTMANAGEMENT AND BOREAL OWLS 115

Rocky Mountains extending from Canada to north- brate. The Boreal Owl in North America repre- ern New Mexico (Palmer and Ryder 1984, Hay- sents a classicexample of uncertainty in wildlife ward et al. 1987, Whelton 1989, Stahlecker and Ra- management. winski 1990). Throughout this broad distribution Over 14 yr ago, Romesburg (1981) admonished the owl occursin a variety of boreal and subalpine wildlife managersfor the development of manage- forests: conifer and mixed forests in Canada (Bon- ment plans built upon unreliable knowledge.Man- drup-Nielsen1978), transitionforests in Minnesota agement built on poor science leads to a loss of (Lane 1988) and subalpine forestsin the Rockies credibility and poor resource management. Cur- (Hayward et al. 1993). Boreal Owl populationsare rent understanding of Boreal Owl ecologyand bi- intimatelylinked to the composition,structure and ology is poor. Management built on this founda- dynamics of these forests (Hayward and Hayward tion alone will invite criticism and loss of credibil- 1993, Hayward and Verner 1994). Therefore, the ity. Recently though, Murphy and Noon (1991) dis- distribution and abundance of Boreal Owls may be cussed an approach to deal with the inherent stronglyinfluenced by forestmanagement practices. uncertainty associatedwith management of a forest How do populations of Boreal Owls respond to raptor, the Spotted Owl (Strixocddentalis). They ad- alternative approachesin forest management?In vocate applying the hypothetico-deductive ap- this paper I provide a perspectiveon the potential proach to management. Through a rigorous as- impacts of forest management on the owl. Forest sessmentof the assumptionsthat form the basisof management represents the human activity most management, they reduce the uncertainty cloud- likely to influence the long-term distribution and ing an evaluation of the efficacy of various man- abundance of Boreal Owls. Among Holarctic rap- agement options. Walters' (1986) adaptive man- tors, Boreal Owls, at least in the North American agementconcepts are another attempt to deal with Rockies,may represent the specieswhose ecology the uncertainty that accompanieswildlife manage- is most universallytied to the forest system.An un- ment. derstanding of the potential response of Boreal My perspectiveson forest management for Bo- Owls to various changesin forest structure and dy- real Owls is guided by a philosophythat combines namics is a critical step in designingmanagement. the conceptsof the hypothetico-deductivemethod In the U.S., managementof Boreal Owls has be- and Walters' adaptive management to develop come an important task on public lands. Four Na- management in the face of poor knowledge. tional Forest Regions and the Superior National Therefore the statementsI make regarding the po- Forest which represent most of the species'range tential responseof Boreal Owls to forest manage- south of Canada have designatedthe Boreal Owl ment, must be regarded as hypotheses.I would ad- as a "sensitivespecies." Within the National Forest vocate the testing of these hypotheses through System, sensitive speciesare plants and animals multi-scale experiments in the spirit of adaptive whose population viability is identified as a con- management. cern by a Regional Forester. Sensitivespecies re- To provide a perspectiveon forest management quire special management and programs are un- and Boreal Owls, I will review the conservation sta- derway to develop management plans for Boreal tus of Boreal Owls in North America including a Owls (J. Friedlander pers. comm.). discussionof trends in forest management, exam- Unfortunately, the knowledge needed to devel- ine our understanding of the ecology of Boreal op a sound management strategymay be lacking Owls as it relates to the owl's potential responseto (Hayward 1994a). To date, only four major pub- forest management, present some hypothesescon- lished investigationsfrom North America provide cerning how different forest management ap- the ecological basis for management planning proaches may influence Boreal Owls on different (Bondrup-Nielsen1978, Palmer 1986, Haywardet geographic and temporal scalesand provide some al. 1999, Hayward et al. 1993). None of these in- ideas concerning strategies to approach forest vestigationsrepresent experimental approaches to management for Boreal Owls. ecological questions,none of these was designed The perspectiveI present is biased by the geo- to directly addressforest management issuesand graphic limits of my field experience with Boreal all extended for 4 yr or less--a temporal scalein- Owls--I have worked in the Rocky Mountains. sufficient to address important issues in forest More important, the literature on Boreal Owl ecol- management or the ecologyof a long-livedverte- ogy in North America is limited. Literature from 116 HAVWAR• VOL. 31, NO. 2

Europe significantly broadens our understanding northern New Mexico (Stahlecker and Rawinski of the species.However, the ecologyof Boreal Owls 1990, Stahlecker and Duncan 1996). Do these re- differs geographicallywithin Europe (KorpimSki cords indicate an extensionof the speciesrange? 1986) and within North America (Hayward et al. I suggestthat the actual distribution of Boreal 1993). I suspectthat the responseof Boreal Owls Owls has not changed recently,but our knowledge to forest management differs between the Old and of distribution has increased because of an in- New Worlds and geographicallywithin both. creasein surveyeffort. Historical records indicate Although our understandingof Boreal Owl ecol- that Boreal Owls were recorded in the western ogy in North America is limited to three forest sys- United Statesbut not recognized as breeding. A tems (one in each of northcentral Canada, central closer look at the literature indicates that Boreal Idaho and northern Colorado), the BorealOwl ap- Owls were documentedin Colorado for nearly 100 pears to occupya variety of forest types.These for- yr (Ryder et al. 1987). Despite the occurrenceof ests range from deciduous and mixed forests to Boreal Owls in the western U.S., checklists and subalpine conifer forests (Meehan and Ritchie field guides did not list the specieseven after 1982, Palmer 1986, Lane 1988). The dynamicsof breeding populationswere documented in 1983. these forests differ substantiallydue to differing Biologistsin Europe alsolocated new populations patterns of forest growth and different disturbance of Boreal Owls during the past three decadesand regimes (Knight 1994). Likewise,Boreal Owl pop- attributed theseto increasedinterest in the species ulation dynamics,relationships with primary cavity (Cramp 1977). nestersand relationshipswith prey populationsdif- Direct evidence concerning trends in Boreal fer among these forest types (Hayward 1994b). Owl abundance is completely lacking for North Therefore, the responseof the owl to alternative America. Breeding populations of Boreal Owls forest management patterns almost certainly dif- were only recently documented throughout most fers geographically. Any forest management of the species'range in the U.S. Studiesin North scheme must be cognizant of the differences America generally have not focused on demogra- among the forest systems. phy, precluding any assessmentsof trend in the near future. I am aware of only two populations STATUS OF BOREAL OWLS IN NORTH AMERICA (one in Idaho and one in Montana) that have been Trends in population abundance or trends in sampledusing methods that will facilitaterigorous habitat conditions are often used to assess status assessmentof trends within the next 5 yr (Hayward (Anderson 1991). In 1994, the U.S. Forest Service et al. 1992). The prospectsfor assessingtrends in publishedan assessmentof Boreal Owl status(Hay- the near future appear bleak. ward and Verner 1994). That document concluded Abundance and Distribution of Important Hab- that Boreal Owls were not in immediate peril itats. Information on trends in condition of forest throughout their range but that over the long-term habitats used by Boreal Owls offers an indirect and in local areas over the short-term, Boreal Owls method to infer population trends. Gathering and likely face significantconservation problems in the summarizing the necessaryinformation at a broad absence of conservation planning. To reach this geographicscale is not feasiblefor this paper. Fur- conclusion the assessment examined evidence con- thermore, most statistics on timber harvest do not cerning trends in the distribution and abundance include the information necessaryto evaluatethe of the owl and the habitatrelationships of the owl. pattern in distribution and abundance of impor- Distribution and Abundance of Boreal Owls. I,it- tant forest types. For instance, stand-replacement fie evidence exists to assesschanges in the distri- harvests (clear-cuts) create stands without habitat bution of Boreal Owls in North America. Prior to value for Boreal Owlsfor a century or more, while 1979the owlwas not recognizedas a breedingbird parti'd cutting may leave standswith high habitat south of Canada (Eckert and Savaloja1979). Since value if dominant trees are not removed. An ob- then numerous published reports have extended jective evaluationof habitat trends relies not only the recognized range of Boreal Owls in North on knowledge concerning recent timber harvest America (Palmer and Ryder 1984, Hayward et al. but knowledgeon successionof lands that experi- 1987, Whelton 1989). Today, evidenceexists for enced large disturbanceevents 100-150 yr ago. breeding populations throughout the Rocky Maybe more important than the problems with Mountains south to southwestern Colorado and describingimpacts from past harvest are the diffi- JUNE1997 FORESTMANAGEMENT AND BOREAL OWLS 117 culties in predicting future harvest. As the avail- characteristics. I also consider nesting, roosting ability of timber has declined on lower elevation and foraging habitat separately because each of forest lands in western North America, focus is these may be limiting in different managementset- shifting to high elevation spruce-firforests used by tings. I will review the evidence describing the link Boreal Owls. Furthermore, the rules regulating between forest conditions and Boreal Owl popu- timber harvest in the U.S. have changed recently lations. In my reviewI move from fine scalehabitat regarding salvageafter fire (U.S. Public Law 104- characteristicsto more broad scale relationships. 19). The consequencesof these changesare diffi- Fine Scale Habitat Relationships. Nestinghabitat. cult to predict. As they might sayin a prospectus, The requirement for a large tree cavityconstrains the extent of future harvest and therefore impact the range of sites used by Boreal Owl for nesting on Boreal Owl habitat may not be related to past habitat. As secondarycavity nesters, boreals are in- trends. timately linked with the organismsand processes Summary. There is little direct evidence con- associatedwith formation of large tree cavities.An cerning trends in North American Boreal Owl pop- envirogram (Andrewartha and Birch 1984) empha- ulations. In a Boreal Owl conservation assessment sizes the linkage between forest structural condi- (Hayward 1994c), evaluation of habitat use pat- tions, primary cavity nester populations (wood- terns, life history and trends in habitat condition peckers), forest insects and pathogens (Fig. 1). were used to infer owl trends. The elements of the centrum relate directly to the

HABITAT RELATIONSHIPS OF BOREAL OWLS owl while the web depicts components of the sys- tem important to maintaining the centrum. Ele- I review the habitat relationshipsof Boreal Owls. ments of this envirogram are forest characteristics My goal is to establishthe relationshipbetween the associatedmainly with the presence/absence of owl and the forest to form hypothesesconcerning suitable nesting cavities. the potential response of Boreal Owls to forest Beyond cavity availability, observations in the management. Rocky Mountains suggest that forest structural Habitat relationshipsof Boreal Owls and habitat characteristicsare important in nest-siteselection. relationshipsof principal prey specieswill, in large In Idaho, comparisons of forest structure at nest part, dictate the potential responseof Boreal Owls sites and random sites indicated use of stands with to timber management. The realized impact of for- mature and older forest structure. Forest structure est management in a particular situation will be at nest sitesdiffered from the random sample (101 determined by the interaction of habitat relation- sites) of available forest. Used sites occurred in shipsof the owl and prey populationsmediated by more complex forest, with higher basal area, more those factors currently limiting population growth. large trees and less understory development than Nesting habitat conditions (especiallycavity avail- ability), prey availability(winter and summer) and availablesites (Hayward et al. 1993). Also in Idaho, microclimatic conditions related to owl thermoreg- a small nest-box experiment evaluated whether ulation likely limit the distribution and abundance choice of nest sites is driven solely by cavity avail- of Boreal Owls in different populations (Hayward ability or if forest structure per se is important 1994b). Management that focuseson these limit- when a range of alternatives are available (Hay- ing factors, after examining evidence suggesting ward et al. 1993). In this experiment nest boxes which factor may be most critical in a particular were hung in three forest types that differed sig- setting,will most effectivelytarget managementac- nificantly in structural characteristics.Owls used tions. boxes in two forest types with complex structure As I have emphasized, the ecology of Boreal (e.g., multiple canopy layers, many tree size class- Owls varies geographically.For instance,daily and es) but did not use boxes in the forest type with a annual movement patterns, relationship with prin- more simple structure (e.g., single canopy layer, cipal prey populations, population stability and more uniform tree diameters). Based on our ob- limiting factorsvary from the boreal forestsof Can- servationsI hypothesizethat forest structure is im- ada to southern New Mexico (Hayward et al. portant in an indirect way.Owls first searchfor nest 1993). Despite this variation, Boreal Owls are forest sitesin forestsof a particular structure becausethe owls throughout their range and their ecology is probability of finding cavitiesis highest in those linked to forest habitats with particular structural types. So selection of old forest for nesting may be 118 HAXSVARD VOL. 31, NO. 2

WEB CENTRUM

MATES

mature forest __ insectsand other • primarycavity nesting, ,_snags with cavities __ nest site: largetree cavity (suitablenest; as a foods birds H • token) water __ largelivetrees I•,•ghSroO•I Llarge cavitiestrees(asp. with aspen) •

topographyand micro,-•mature aspen stand • sitecønditiøns H / weather fire or other I Lstand with moderate .•1 site with structure __ nest site: majordisturbance to largetrees associatedwith foreststand (recognized as highprobability of potentialbreeding habitat; as haviingsuitable cavities a token) Boreal Owl

water • mature and older

forestforestrodent stands Ilandscape of suitable.•

matureforest __ insectsand other • primarycavity __ intactpopulation foods nestingbirds

water__ largelive trees __ dispersedpopulationslarge snags _landscapeforaginghabitatwith • • or trees with rot dispersedsuitable nestinghabitat

water mature forest __

F•gure 1. Envirogram (Andrewartha and Birch 1984) illustrating the relationship between Boreal Owls and specific componentsof the forest system.This portion of a larger envirogram (Hayward 1994b) focuseson Boreal Owl nesting ecology. based more on efficiency in finding a cavity than tures and the availability of cool microsites for increasedsurvival after locating a nest. roosting. Forest structure, then, may influence the The same studiesin idaho suggestthat patch distribution of Boreal Owls through an interaction size may not be an important characteristicof nest with limitation by heat stress. stands.Nest standsranged in size from 0.8 to 14.6 Foraginghabitat. A variety of evidence suggests ha and averaged7.6 ha. that Boreal Owls in the Rockiesforage principally Roostinghabitat. Patterns of roosting habitat use in mature and older forest,especially spruce-fir for- also suggestthese owls choose forestswith partic- ests (Hayward 1987). These observationsare cor- ular structural features during certain times of the roborated by evidencethat red-backedvoles (Cleth- year. In Idaho, forest structure at summer roost rionomysgapperi) represent a dominant prey for Bo- sites differed substantiallyfrom paired random real Owls throughout their range in North Amer- sites. Roost sites had higher canopy cover, basal ica (Bondrup-Nielsen1978, Palmer 1986, Hayward area, and maybemost important, were significantly and Garton 1988, Hayward et al. 1993). Red- cooler microsites(Hotelling's T 2, P < 0.001) (Hay- backed voles are principallyforest voles (Hayward ward et al. 1993). In summer,and particularlyin and Hayward 1995). Our studiesof small mammals the southern portion of their range, Boreal Owls in Idaho found redbacks were up to nine times find roost sites to minimize heat stress. We wit- more abundant in mature spruce-fir forest than nessed owls gular fluttering and other behaviors other forest habitats (Hayward et al. 1993). The associatedwith heat stresswhen the temperature argument for the importance of mature forest for was as mild as 18øC.I hypothesizethat the eleva- foraging stems also from observations of snow tional distribution of Boreal Owls in the Rockies characteristicsin openings, young forest and ma- may be determined, in part, by summer tempera- ture forests.Snow crusting is significantlyreduced JUNE1997 FORESTMANAGEMENT AND BORF•XL OWLS 119

in mature forests facilitating accessto small mam- .,• •Subolpine-firForest mals during critical winter periods (Sonerud 1986, '•'r/,• •S.E. I)ougles-firWoodlend Sonerud et al. 1986). In Idaho, mortality and sig- nificant movement events most often occurred during warm winter periods when snow crusting OtherMonteneForest became severe. An envirogram further emphasizesthe link be- tween Boreal Owl foraging habitat and particular features of the forest, especially features linked with mature forests (see Hayward 1994b). The en- virogram illustratesthe indirect tie betweenBoreal Owl fitness and abundance of lichen, fungi and Vacciniumground cover all of which can be influ- enced by various forest management practices. The evidence regarding habitat use for nesting, roosting and foraging in the Rockiessuggests that at a fine scale,Boreal Owls rely on particular char- acteristics of mature and older forests. This rela- Figure 2. Pattern of potential Boreal Owl habitat in Ida- tionship suggeststhat forest management at the ho suggestingthe distribution of a portion of the meta- level of standswill likely influence abundance of population extending along the RockyMountains. Poten- Boreal Owls. tial habitat is defined as forested sitesin the subalpine- Landscape Scale Habitat Relationships.Analysis fir zone throughout the state and Douglas-firwoodland of patterns of Boreal Owl abundance in relation to in southeastern Idaho. Other montane forests are not landscapepatterns is not availablefor North Amer- consideredpotential habitat (adapted with permissionof ica. Indirect evidence from Europe and North WildL Monogzfrom Hayward et al. 1993). America suggeststhat Boreal Owls differentiate among forest habitats at the landscapescale. Our for management. In portions of the boreal forest, observationsof owls in Idaho suggestthat land- distributions of Boreal Owls may be quite contin- scapesdominated by mature spruce-fir forest or uous. Along the southern and northern borders of those with mature spruce-fir juxtaposed with ma- the boreal forest and in the Rockies, the owl may ture larch (Larix sp.), ponderosa pine (Pinuspon- occur in an interesting geographic pattern which derosa)or aspen (Populustremuloides) sites will have likely results in a strong metapopulation structure the greatestabundance of boreals (Hayward et al. (Hayward et al. 1993). In Idaho, patchesof suitable 1992, 1993). In other words, an interspersion of habitat occur throughout the mountainous land- foreststhat generally support high densityof cavi- scapesin a wide range of patch sizes (Fig. 2). As- ties in mature spruce-firforest will provide quality suming that subpopulationsof owls occupyhabitat habitat. as hypothesizedin Figure 2, the metapopulation More direct evidencefrom Europe supportsthe structure of the owl in the region is a complex mix notion that landscapescale forest cover influences of subpopulations.Because of this structure, man- Boreal Owl density and productivity.As the pro- agement of forest at the scaleof individual national portion of Scotch pine (Pinus sylvestris)forest de- forestsmay have important implications for neigh- creasedand the proportion of Norway spruce for- boring national forestsover a broad geographicre- est (Picea abies)and agricultural land increased, gion. quality of territories (those with more frequent nesting) increased (Korpimfiki 1988). The conclu- HYPOTHESES: BOREAL OWL RESPONSE TO sion that territories with spruce forest and agricul- FOREST MANAGEMENT tural land (in small patches)were the highestqual- Stand-ReplacementHarvest. The importance of ity habitat was corroborated by evidence on breed- mature forest to Boreal Owls for nesting, roosting ing frequencyand clutch sizes. and foraging suggeststhat the short-term impact Regional Scale Habitat Relationships. At very of stand-replacement harvest (clear-cut) will be broad geographic scales,distribution patterns of negative. Open habitats as well as young, even-age Boreal Owls may also have important implications forestsprovide few resourcesfor Boreal Owls. Fur- 120 HAYWARD VOL. 31, No. 2 thermore, these habitats generally do not enhance and patches of forest remaining within the cut habitat for woodpeckersor small mammals.Large unit, will have fewer negative impacts than large clear-cutsappear to provide no resourcevalues for rectangular or circular cuts. This hypothesisstems Boreal Owls except along edges where owls may from the pattern of habitat use by Boreal Owl prey capture prey (Hayward 1994b). However, impacts species(Williams 1955, Merritt 1981,Wells-Gosling will depend upon the size and spacingof cutsand and Heaney 1984) and observationsthat Boreal the fbrest type being harvested. Furthermore, Owls will nest in small patches of forest (G. Hay- long-term impactsmay not parallel short term re- ward unpubl. data). sponse. Basedon the same arguments,sloppy clear-cuts I hypothesizethat small, patch clear-cutsimple- (clear-cuts with residual standing dead and live mented with long rotations may not negativelyim- trees, especiallyaspen and patchy slash),and cuts pact Boreal Owl habitat over the short- or long- that retain standing and downed wood on the site, term. Boreal Owls generally attack prey within 30 will have fewer negativeimpacts, especially over the m of a perch (Hayward et al. 1993), so most of a long-term. The mitigating qualities of retaining 1-3 ha patch cut will be accessiblefor foraging. patchesof live trees and shrubs,snags and woody Furthermore, in small patch cuts, ground cover, debris arise from several factors. These elements which could reduceprey availability,often doesnot will accelerate the rate at which the future stand change significantlyfrom that found under the for- attains mature and older forest characteristics est, snow crusting affectsonly a small proportion (Knight 1994). In particular,recovery of fungi and of a small forest opening and small patch cutsem- lichen populationsmay be acceleratedby mainte- ulate, to some extent, the landscape structure of nance of residuals (Ure and Maser 1982, Hansen mature spruce-fir forests (Knight 1994). In cases et al. 1991). where small patch cutting is employed, I hypothe- Partial Cutting and Uneven-Age Management. sizethat potential negativeimpacts will be reduced Discussionof sloppyclear-cuts or irregular shelter- if the patch cutting is concentratedin a portion of wood prescriptionsleads logicallyto discussionof each watershedrather than dispersedthroughout entire watersheds and mature forest remains in the partial cutting and uneven-ageregeneration pre- matrix between cuts. scriptions.I hypothesizethat group selection (har- vest of small groups of trees in an uneven-age Larger clear-cutsin conifer forest most often will stand,maintaining the uneven-ageproperties) may reduce habitat quality for 100 to 200 yr. However, not significantlyreduce Boreal Owl habitat quality clear-cuttingof aspen may be important in main- in many situations if, over the long-term, mature taining the long-termavailability of cavitiesin some and old forest qualities are maintained and tree systems.In many forest systemsaspen is a pioneer speciescomposition does not exclude important speciesthat is lost through succession(DeByle and Winokur 1985). Restoration of aspen forests cavity trees. Timber harvest prescriptionssuch as through silviculturemay be an important manage- group selectionand single tree selection(harvest ment tool to maintain Boreal Owl habitat in forest of individual trees from an uneven-agestand in a systemswhere aspen provides a majority of the pattern that maintains the size structure of the nesting habitat. Through coordinated timber har- original stand) that retain forest structure, are vest, large aspenwhich provide cavitiesfor nesting compatible with developing owl nesting habitat. may be maintained over the long-term, at the land- Thinning from below (harvest which removes in- scapescale, despite loss from individual stands.Fo- dividuals smaller than the dominant size class) and cus on aspen management may even be more im- single tree selection that reduces competition portant in systemswhere aspen occupiesa small among dominant trees and increasestree growth, proportion (<1%) of the landscapeand occursin could acceleratethe processof developingsuitable small patchesassociated with particular microsites. nest structures.While clear-cuttingeliminates red- The shape of clear-cutswill likely influence both backedvoles in RockyMountain forests(Campbell the short- and long-term impact on Boreal Owls. and Clark 1980, Scrivner and Smith 1984, Ramirez Although no direct evidenceis available,I hypoth- and Hornocker 1981), preliminary resultsof an ex- esize that more complex shaped cutting units, es- periment examiningclear-cuts and group selection pecially those with stringers of forest extending harvests indicate that red-backed voles remain into cutting units in upland areas,riparian buffers abundant in partial cut standswhen many large JUNE1997 FORESTMANAGEMENT AND BORFAt, OWLS 121 trees are retained and ground disturbance is min- neighboring regions.These subpopulationswould imal (G. Hayward unpubl. data). receive special attention to assure that manage- Broad ScalePredictions. Predicting the response ment actionseither favored the owl or did not neg- of Boreal Owls to differing landscapescale patterns ativelyimpact the subpopulation.Spatial modeling is more difficult. The lack of information on pat- and good information on dispersalwill be neces- terns of Boreal Owl abundance at the landscape sary to make sound management predictions at and broader scalesprecludes extensive predictions this scale. at broad scales.I would argue that a primary focus of adaptivemanagement approaches should be at STRATEGIES TO APPROACH FOREST MANAGEMENT FOR BOREAL OWLS this scale. The issue of fragmentation seems to dominate I began this discussionby emphasizingthe ex- much of the discussionof landscapescale impacts, tent of uncertainty in our understanding of Boreal so preliminary predictions regarding fragmenta- Owls and noted the substantialgeographic varia- tion may be useful in stimulating inquiry. In refer- tion in Boreal Owl ecology acrossNorth America. ring to potential responseto fragmentation,I ex- In combination, these factors produce a discour- plicitly separatethe influence of habitat lossfrom aging management environment where predic- the influence of increasedlandscape heterogene- tions must be made tentatively.Therefore, the re- ity. Fragmentationeffects result from the process sponseof Boreal Owls to forest management was of changing the characteristicsof the landscape framed as a seriesof hypothesesto be tested and mosaic and must be considered after eliminating likely only testablethrough adaptivemanagement. the direct influence of reducing habitat area. Despite the degree of uncertainty and the extent The high mobility and the extensiveareas used of geographicvariation, I believe some general on a daily basisby Boreal Owls suggeststhey may points can be made concerningapproaches to for- react to fragmentation differently from passerines. est management and planning for Boreal Owls. For instance, timber harvest of 30% of a basin Limiting Factors. Site-specific forest manage- through clear-cuttingmature lodgepole pine (Pi- ment for Boreal Owls must consider the factors nus contorta)in 1-5 ha patchesdispersed through- most likely limiting the population in a particular out the area may not significantlyreduce habitat setting. Thermal stresslikely limits the elevation quality if the remaining forest is dominated by ma- distribution of Boreal Owls in the central and ture and older spruce-fir forest. The forestsused southern Rocky Mountains. Therefore, availability by Boreal Owls exhibit a patchy mosaicunder nat- of cool microsites, which often occur in mature ural disturbance (Knight 1994). In a natural forest and older forests, may be important in many mosaic, owls move between distant patches on a regions. daily basis (Hayward et al. 1993). This hypothesis The availabilityof nest cavitiesand prey likely assumesthat timber harvestwould not significantly limit populations of Boreal Owls in different situ- reduce small mammal populations in the unhar- ations. In regions with few or no Pileated Wood- vested stands. pecker (Dryocopuspileatus) or Northern Flicker (Co- Asidefrom fragmentation,it is important to con- lapresauratus) cavities, nest-site availability will limit sider the impact of harvestschemes that target dif- Boreal Owl abundance.Even within the geograph- ferent forest types: aspen, lodgepole pine or old ic range of Pileated Woodpeckers,the absenceof spruce-firforests. I hypothesizethat the negative these woodpeckersat higher elevationsmay limxt impacts of any stand replacement harvest scheme Boreal Owl abundance (Hayward et al. 1993). If will be decreased if stands of mature and older cavity availability limits Boreal Owl populations, spruce-fir or aspen forest remain dispersed management of primary cavityexcavators as well as throughout the landscape. the forest processesthat support large snagswill Predicting the consequencesof management at influence Boreal Owls. the broadest spatial scalesis challenging. Conser- In some forests,cavities are abundant and prey vation strategiesat the regional scaleshould focus availability may play a strong role in Boreal Owl on maintaining the continuity of Boreal Owl me- population dynamics.It is unclear whether abso- tapopulations.This involvesidentifying subpopu- lute abundanceor variation in prey populationsis lations and landscapesthat likely play key roles in more important in owl population regulation. the persistenceof owls within the region and However, small mammal populationsappear to be 122 HAYWARD VO•.. 31, NO. 2 linked to forest conditions (Hayward and Hayward velopment of old forest conditionsfollowing stand 1995) and forest management will influence the replacement disturbanceproceeds slowly; succes- abundance of potential prey, and in turn, affect sion to mature forest conditions takes >150 yr. owl population persistence.Forest structurewill However,old forest standsrepresent a mosaicre- also influence the availabilityof prey by changing suiting from the frequent action of small scale dis- owl accessto prey. For instance,forests with dense turbance. Partial cutting emulates (to some extent) ground cover or a high density of small trees will insect mortality and windthrow, two common dis- reduce the efficiency of foraging Boreal Owls. Fur- turbancesintegral to the formation of old spruce- thermore, forest structure affects snow conditions fir forest structure. Alexander (1987:59) indicated which influence prey availability(Sonerud 1986). that "uneven-aged cutting methods--individual Cavity availabilityand prey availabilitylikely in- tree and group selection--haveseldom been used teract to influence Boreal Owl population growth. in spruce-fir forests, they appear to simulate the Tree cavitiesoccur nonrandomly acrossthe land- natural dynamicsof theseforests." Therefore, care- scapeas do smallmammal populations.The spatial ful harvest of trees from spruce-firforest may not arrangement of cavitiesand prey (relative to one be incompatiblewith maintaining important ele- another) are important in determining Boreal Owl ments of old forest and habitat characteristics abundance. The conservation status of Boreal Owls linked with Boreal Owls. will be intimately tied to the interaction of these The paucity of information availableon the re- resources. sponseof Boreal Owls to specificforest manage- While cavitiesand prey likely limit Boreal Owl ment actionspresents an obstacleto the formula- populations in most landscapes,predation and tion of management within an ecosystemframe- competition may influence populationsin certain work. A strong conservation strategy for Boreal circumstances. In local situations, mustelids de- Owls cannot be produced without new knowledge stroya high proportion of owl nestsin someyears on Boreal Owl ecology.Management basedon cur- (Sonerud 1985). The influence of these losseson rent knowledgemust contendwith uncertaintyand population abundanceis unknown. Evidencealso be devisedspecifically to deal with this uncertainty. indicates that interactionswith other owls may in- Adaptivemanagement (Walters 1986), then, must fluence the distribution of Boreal Owls suggesting be built into any approachto manage the species, that competitionmay be an important limiting fac- particularlyan ecosystemmanagement strategy. tor in some situations (Hakkarainen and Korpi- CONCLUSIONS miiki 1996). Boreal Owl ManagementWithin EcosystemMan- Based on my review of the habitat relationships agement.In westernNorth America the ecologyof of Boreal Owls and management considerations,I Boreal Owls is linked with many characteristicsof offer the followingconclusions: (1) MaintainingBo- mature and older spruce-fir forests (Hayward real Owls on a local scaleis not incompatiblewith 1994b). Management which facilitates the long- timber harvestbut is incompatiblewith extensive, term maintenance of a landscapewith significant stand replacement silvicultureimplemented over representation of mature and older forest habitat entire watersheds,employing large cutting units; will provide quality Boreal Owl habitat. Therefore, (2) Forestswith high habitat value for Boreal Owls managementschemes which promote the process- develop through long successionaltrajectories. es that maintain productive spruce-firforests, and Therefore forest management must consider long- managementwhich facilitatesthe stand dynamics term forest patterns on broad spatial scales;(3) necessaryto produce old spruce-firforest, will pro- The hypothesizedmetapopulation structure of Bo- vide the habitat characteristicsnecessary for Boreal real Owls in North America suggeststhat forest Owls.As indicated earlier, this is not incompatible management must be coordinated at a regional with timber harvest. scale; (4) Adaptive managementwhich links man- Most applications of ecosystemmanagement agers and research ecologistsis necessaryto pro- strive to manage systemsto emulate natural distur- duce the knowledge needed to understand the re- bance patterns and processes.As reviewed by sponseof Boreal Owls to alternativemanagement Knight (1994), spruce-fir forests experience a va- approachesat a variety of spatial scales;(5) As a riety of disturbanceagents that act at scalesrang- top carnivorethat preysupon the dominant small ing from single trees to hundreds of hectares.De- mammal speciesin subalpineforests and nestsin JuNv.1997 FORESTMANAGEMENT AND BOt•V•L OWLS 123 large tree cavities,the Boreal Owl integratesinto ern Palearctic. Volume IV. Oxford Univ. Press, Ox- its ecology many aspectsof forest dynamics. As ford, U.K. such, the owl may represent a good model to aid DEBYLE,N.V. AND R.P. WINOKUR[EDS.]. 1985. Aspen: in developing ecosystemmanagement; (6) At all ecology and management in the western United States.USDA For. Serv. Gen. Tech. Rep. RM-119, Fort spatial scales,an eye to restoration management Collins, CO U.S.A. mustbe taken in landscapesthat haveexperienced ECKERT,K.R. ANDT.L. SAVALOJA.1979. First documented intensive harvest in the past. Restoration may be nestingof the Boreal Owl south of Canada.Am. Birds particularly appropriate in aspen forests of the 33:135-137. Rocky Mountains. GODFREY,W.E. 1986. The birds of Canada. National Mu- Forest management which sustainsmature sub- seum of Natural Sciences, Ottawa, Ontario, Canada. alpine and boreal forestslikely will conserveBoreal HAKKARAINEN,H. AND E. KORPIMAKI.1996. Competitive Owls. Such management, however,must consider and predatory interactionsamong raptors: an obser- (among other things) the successionaldynamics of vational and experimental study. Ecology77:1134- 1142. spruce-firforests including the detritusfood chain, HANSEN,AJ., T.A. SPIES,FJ. SWANSONAND J.L. OHMANN. the consequencesof variousdisturbances and the 1991. Conservingbiodiversity in managedforests: les- long-term (post-glacial)trends in these forests. sons from natural forests. BioScience 41:382-392. Management must focusas much on the long-term HAYWARD,G.D. 1987. Betalights:an aid in the nocturnal condition of the plant communitiesused by Boreal study of owl foraging habitat and behavionJ. Raptor Owls as on the population dynamicsof the owl. Res. 21:98-102. 1994a. Information needs: Boreal Owls. Pages ACKNOWLEDGMENTS 148-153 in G.D. Hayward andJ. Verner lEDs.], Flam- I sincerelythank Gerald Niemi and JoAnn Hanowski mulated, Boreal, and Great Gray Owls in the United for organizing the symposiumthat led to the develop- States: a technical conservation assessment. USDA ment of this paper. Erin O'Doherty, Edward (Oz) Gatton, For. Serv. Gen. Tech. Rep. RM-253, Fort Collins, CO Ronald Ryder, Gerald Niemi and Daniel Vatland re- U.S.A. viewed an earlier draft of this paper; their comments 1994b. Review of technical knowledge: Boreal were very helpful. The ideas presented here would not Owl. Pages92-127 in G.D. Hayward and J. Verner be possiblewithout the dedicatedfieldwork of manyper- lEDs.], Flammulated, Boreal, and Great Gray Owls in sonsincluding folks who have aided in my field studies. the United States: a technical conservation assess- Discussionswith Pat Hayward, Floyd Gordon, Edward (Oz) Carton and Joan Friedlanderhave been influential ment. USDA For. Serv.Gen. Tech. Rep. 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