Ecological Applicationns. 2(1), 1992, pp. 3-17 ($3 1992 by the Ecological Society of America

INTEGRATING SCIENTIFIC METHODS WITH HABITAT CONSERVATION PLANNING: RESERVE DESIGN FOR NORTHERN SPOTTED OWLS1

DENNIS D. MURPHY Center for Biology, Department of Biological Sciences, Stanford Stanford, California 94305 USA

U.S.D.A. Forest Service, Redwood Sciences Laboratory, I700 Bayview Drive, Arcata, California 95521 USA

Abstract. To meet the requirements of Congressional legislation mandating the pro- duction of a “scientifically credible” conservation strategy for the threatened Northern Spotted Owl (Strix occidentalis caurina), the Interagency Spotted Owl Scientific Committee employed scientific methods to design a habitat reserve system. Information on the current and historical distributions of the owl and its habitats was reviewed in light of economic, political, and legal constraints; results were used to develop a preliminary reserve system of habitat “polygons.” A map representing these polygons and their attendant properties served as a set of hypotheses that were tested. Statistical analyses of empirical data, pre- dictions from ecological theory, predictions from population dynamics models, and infer- ences drawn from studies of related species were used to test properties of the preliminary map, including the number and sizes of habitat conservation areas (HCAs), their distri- bution, configuration, and spacing, and the nature of the landscape matrix between HCAs. Conclusions that failed to confirm specific map properties were used to refine the reserve system, a process that continued iteratively until all relevant data had been examined and all map properties had been tested. This conservation planning process has proven to be credible, repeatable, and scientifically defendable, and should serve as a model for wildlife management, endangered species recovery, and national forest planning. Key words: habitat conservation planning; habitat fragmentatian; Northern Spotted Owl: old- growth forests; population models; scientific method.

INTRODUCTION Faced with this mandate, the Committee looked to More than anv threatened or endangered species be- emulate previous attempts at conservation planning fore it, the northern Spotted Owl (Strix occidentalis under the federal Endangered Species Act of 1973. Sec- caurina) has become a cause c&!bre in the struggle tion 10(a) of the Act, which authorizes the develop- between groups representing disparate value svstems ment of so-called “Habitat Conservation Plans” to in a land of dwindling resources. The media portray “enhance the propagation or survival of the affected the choice as simple - a choice between resource uti- species” and “to the maximum extent practical, min- lization, emplovment, and economic vitality on the one imize and mitigate” the impacts of actions prohibited hand and rich, healthy ecosystems and security for the under the Act, provided little guidance. Indeed, no reg- species and populations that they support on the other. ulations, no standards, and no guidelines exist to direct The Northern Spotted Owl thus has become a symbol the application of biological data to the design of re- of the philosophical, moral, and social dilemma for serves or reserve systems for imperiled species. While our times. This dilemma, in the case of the owl, has a number of studies have brought substantial quanti- provoked lawsuits, intense public and scientific dis- tative information to conservation planning processes agreement, and rapidly diminishing options, and led (see Gilpin 1989, Givnich et al. 1989, Souli 1989, the United States Congress to judge the situation a Menges et al. 1990, Murphy et al. 1990), none has conflict to be resolved. In an amendment to an appro- offered a step-by-step application of biological data to priations bill, Congress directed the United States Fish the development of a reserve design. and Wildlife Service, United States Forest Service. Na- Without a model appropriate to its complex task, tional Park Service, and Bureau of Land Management the ISC struggled to develop a scientific protocol that to convene an Interagency Spotted Owl Scientific Com- would allow consideration of nonbiological factors in mittee (hereafter TSC) to “develop a scientifically cred- the development of a habitat conservation plan that ible conservation strategy for the Northern Spotted would have the rigor of strong inference. Here we offer Owl.” such a protocol, showing how the ISC incorporated hypothesis testing and iterative map revision in the 1 Manuscript received 28 November 1990; revised 15 Feb- development of a conservation strategy - a reserve de- ruary 1991; accepted 25 February 199 sign-for the Northern Spotted Owl. In this paper we 4 DENNIS D. MURPHY AND BARRY R. NOON Ecological Applications Vol. 2, No. 1 attempt to generalize in order to enhance the value of and reproduction), and adult (>2 yr of age). A key this exercise as an example, and we hope that this aspect of the species’ life history is that juvenile birds presentation proves valuable in the development of are forced to disperse from their natal area, sometimes conservation strategies for other species. However, we over long distances, in search of suitable territories and underscore that habitat conservation planning cannot mates (Forsman et al. 1984, Allen and Brewer 1985a, be approached from a recipe: rather, each plan is a b, Guti&rez 1985, Gutierrez et al. 1985, Meslow 1985, unique combination of an understanding of the target Miller 1989). First reproduction usually occurs at 2 yr species and its habitats and of the scientific framework of age, but this is also variable (Franklin et al. 1990). presented here. The stage-structured simulation models employed in conservation planning for the Northern Spotted Owl were designed to parallel its three discrete life-history PLANNING CONSIDERATIONS AND CONSTRAINTS stages. The Northern Spotted Owl, one of three subspecies These demographic considerations and several cru- of Strix occidentalis, ranges from southwestern British cial “sideboards" directed the structure of the habitat Columbia south through the Coast Ranges and Cascade conservation planning process for the Northern Spot- Range of Oregon and Washington and into the Klam- ted Owl. First was the ISC’s acknowledgment that more ath Mountains Physiographic Province, which includes considerations were involved in the planning process southwestern Oregon and the coastal mountains of than the biological factors that affect the fate of the northwestern California. In Oregon and Washington owl. The very demand for conservation planning ac- the species is found on both west and east slopes of knowledges conflicting interests and diverse values. The the Cascade Mountains but is rarely found in moun- products of conservation planning, be they reserve de- tains to the east. signs, in situ management plans, or ex situ propagation While the species has been found to reside and breed activities, are prescriptions resulting from, or are ad- in forests of diverse composition and structure and to juncts to, activities that place species at risk of extinc- show geographic variation in patterns of habitat use tion. At the outset of the process, planners must ex- throughout its range, the Northern Spotted Owl is gen- plicitly address competing interests or constraints. erally associated with extensive forest stands that pro- Nonbiological considerations that bear on the avail- vide forage, cover, and suitable nest sites. Nearly all ability of habitat for reserve status- lands owned or observations of successful nesting, breeding, and fledg- managed by different jurisdictions, lands of varying ing of young are from “old-growth” (i.e., mature or monetary value, or lands having other distinguishing “ancient”) forests, or from those younger forests that nonbiological qualities -must be integrated into the include the structural characteristics of old-growth for- planning process before ecological data are used to pro- ests (Thomas et al. 1990). Timber harvest, fire, and duce the initial reserve design. clearing for agricultural and urban land use have re- For the Northern Spotted Owl on public lands in the duced these habitats, once widespread across south- Pacific Northwest, a conservation strategy that would western Canada and northwestern United States, to set aside all suitable habitat was viewed as biologically < 10% of their original area. This broad regional de- preferable, but not legally or politically viable. National cline in the extent of habitat and associated decline in Forest lands, for example, are managed under the 1976 Northern Spotted Owl numbers prompted a petition National Forest Management Act, which requires that for federal intervention under the Endangered Species land management meet multiple-use objectives. Land Act. After legal chalIenges and protracted review of management plans for national forests must “provide biological information, the United States Fish and for diversity of plant and animal communities” and Wildlife Service announced conferral of threatened sta- must “provide for outdoor recreation, range, timber, tus to the subspecies (Federal Register 55[123]:26114- watershed, wildlife and fish.” No available data sup- 26194, 26 June 1990). ported the notion that lands subject to current standard Demographic analyses of Northern Spotted Owl modes of timber harvest could also support stable pop- populations suggest that age-specific survival rates, and, ulations of Northern Spotted Owls. The ISC therefore in particular, variation in adult survival, strongly affect acknowledged that significant amounts of public: land population dynamics (Lande 1988. Noon and Biles must be separately allocated both for commodity pro- 1990). Reproductive success in the Northern Spotted duction and for owl habitat. Furthermore, the laws Owl can vary greatly from year to year. In some years pertaining to the management of private timber lands most pairs nest and produce offspring; in other years were not considered to be conducive to comprehensive, few pairs even attempt to nest. This variation may be biologically based habitat conservation planning. The reIated to fluctuations in abundance of the owl’s pri- ISC therefore made a crucial decision to exclude pri- mary prey, small mammals. For demographic analysis vate lands from conservation planning considerations and conservation planning, three distinct life-history (a decision that. all else being equal, increased the re- stages are recognized-juvenile (0 to 1 yr of age), sub- quired contribution of public lands to the ultimate con- adult (1 to 2 yr of age, the period between dispersal servation strategy). February 1992 CONSERVATION PLANNING FOR SPOTTED OWLS 5

Second, the application of biological information to A conservation strategy that adequately mitigates the conservation planning is a process that, like any pure likelihood of species extinction due to these potential or applied scientific endeavor, requires strict adherence threats must state conservation goals in terms of Ievels to scientific methods (Murphy 1990). As Hairston of certainty of population persistence for specified pe- (1989:2) has warned, ecologists (and, implicitly, their riods of time. (Such a statement must recognize that colleagues in wildlife biology and related fields) com- the current state of the art in population viability the- monty appeal “to the complexity of nature, apparently ory and application does not allow a precise, quanti- in the hope of avoiding the rigorous thought that is tative evaluation of persistence likelihood for any spe- required to formulate clear hypotheses, and to avoid cies.) For any real population, it is currently impossible devising proper tests to permit choices among com- and certainly misleading to assign a numerical value peting hypotheses.” Like the products of ecological ex- to "high likelihood”; therefore, “high likelihood” is perimentation, scientifically credible conservation used qualitatively throughout this paper. For the strategies must be derived from procedures that yield Northern Spotted Owl the ISC’s goal was to develop strong inference (see Platt 1964). In the conservation a conservation strategy that would provide a high like- planning process the ISC constructed alternative hy- lihood of population stability and persistence through- potheses related to reserve design, considered empir- out the species’ range for = 100 yr. ical data and theoretical models as tests to exclude Two additional factors are important for conserva- hypotheses, and, using additional data and models, tion planning. First, stochastic phenomena differently formulated and excluded further hypotheses. For pur- impact populations of different sizes and distributions. poses of habitat conservation planning hypotheses were While only the smallest demographic units are subject represented on maps and included map properties that to the deleterious effects of genetic inbreeding, even delineated management units. This provocative ap- large populations may be negatively impacted by cat- piication of the scientific method to conservation plan- astrophic environmental events or by disruption of ning added critical structure, repeatability, and credi- dispersal dynamics. Conservation planning, therefore, bility to the process and product as discussed below. should first address stochastic phenomena that affect As a third consideration the ISC acknowledged that populations at their largest sizes - i.e., phenomena that nonbiological constraints tend to drive conservation are most inclusive in their impacts on species persis- planners to the identification of as few “viable” pop- tence. Planning should then sequentially address phe- ufations as are considered necessary to ensure species nomena that act to reduce incrementally the likelihood persistence. Toward the design of a reserve system ad- of species persistence at diminishing population sizes. equate to the goal of species persistence, conservation Distributional phenomena and environmental varia- planning must address two sources of threat to a target tion should be addressed first, followed by demograph- species. First, systematic pressures associated with hu- ic stochasticity, and then deleterious genetic phenom- man activities that act to threaten target species (in- ena as required. cluding habitat destruction, overharvest of individuals, Second, stochastic perturbations that can put pop- and toxic pollution) must be eliminated or controlled. ulations at risk can act synergistically to reduce the size The decision to exclude commercial timber harvest of populations, thus reducing species persistence times. from areas allocated as habitat for the Northern Spot- Gilpin and Soule (1986) have described the interac- ted Owl eliminated the most significant systematic tions among stochastic phenomena as feedback loops threat to the species. Second, natural stochastic phe- between “extinction vortices” that determine popu- nomena-that is, expected normal, random pertur- lation vulnerability. A population subject to multiyear bations to populations and their habitats-also affect drought, for example, may be reduced in size to a level population persistence. Population viability analysis, at which stochastic demographic events may push it as it has been described, is used to determine reserve to extinction before favorable environmental condi- design characteristics, such as the number of habitat tions again prevail. Northern Spotted Owl populations, patches, their sizes, and their geographic distribution, although demonstrably declining, are still relatively that would reduce the chances of population extinction large and widespread; therefore the conservation strat- from natural stochastic phenomena. These phenomena egy focused on distributional phenomena, likely en- include: (1) loss of genetic diversity, including such vironmental perturbations, and local demographic factors as inbreeding depression and founder effects; considerations. Because the loss of genetic diversity (2) demographic stochasticity-chance events that affect does not appear to be an immediate threat to this spe- reproduction or survival of individuals, such as biased cies, genetic considerations for long-term population age structures or skewed sex ratios; (3) environmental survival were not central to conservation planning for uncertainty, including temporal variation in habitat the owl. quality and the impacts of natural catastrophes; and (4) distribution phenomena, particularly disruption of OVERVIEW OF THE PROCESS landscape areas between habitat patches that mav affect The ultimate measure of success of a conservation dispersal and extinction-recolonization dynamics. strategy or habitat conservation plan is the long-term 6 DENNIS D. MURPHY AND BARRY R, NOON Ecological Applications Vol, 2, No. 1 persistence of populations in natural habitats. None- habitat. The intersection of the species range (map lay- theless, the immediate products of conservation plan- er 1) with currently and potentially suitable habitat ning normally are not populations of specific target (map layer 2) provides an initial outline of habitat sizes, but habitat reserves, conservation easements, or conservation areas (HCAs), habitat “polygons” that other set-aside lands that are designed to assure species are candidates for inclusion in the reserve network. For persistence. These entities normally are represented on the Northern Spotted Owl the ISC had extensive in- maps and by the information that maps convey, in- formation on habitat-use patterns from radio-tracking cluding political boundaries, topographic features, studies. Characterizing occupied habitats in terms of dominant vegetation? and elevation demarcations. The timber type categories used by the United States Forest most basic information on the natural history and ecol- Service and Bureau of Land Management allowed the ogy of a target species is used to produce a preliminary use of maps from those agencies to plot the distribution map (or maps), the boundaries of which delineate the of extant and potential habitat on public lands. The location, size, shape, and spacing of habitat patches finer scale of resolution of habitat distribution provid- planned for incIusion in a reserve or reserve system. ed by these maps (1:24000) allowed the detail essential For the purposes of scientific planning, a preliminary to begin to delimit potential HCAs. reserve design map can be considered to have prop- Available survey or census information from the erties that serve as falsifiable hypotheses. In the con- range of the species provides the third map layer. Even servation planning process a hypothesis can be defined limited information from highly localized habitat areas as an assertion of a map property that is subject to may be useful to identify known population centers, tests with existing empirical information and theoret- and, importantly, to determine quantifiable environ- ical predictions (from population viability analyses). mental correlates of habitat quality that may then be Tests of these hvpotheses may be based on natural- mapped. The association of survey data with specific history observations, analyses of empirical data, pre- habitat types allows projections of species occurrences dictions from theoretical models, or predictions based from unsurveyed areas of similar habitat type. Density on studies of related species. When test conclusions fail estimates of the target species from specific habitat to confirm one or more properties of the preliminary types are particularly valuable, as they allow initial reserve design, the proposed reserve system is adjusted. projections of potential population sizes for individual Successive map iterations are sequentially tested with habitat polygons. available information. The final product, a conserva- Extensive, but incomplete, survey data were avail- tion strategy or habitat conservation plan, is then por- able for the Northern Spotted Owl. Although most of trayed as a map. A given map-based solution to a those data did not allow reliable estimates of popula- conservation challenge is not necessarily unique. It is, tion density, the data did allow prediction of the pres- however, a solution that is fuIly supported by available ence of owls within similar habitat types and at specific empirical data and theoretical model predictions, locations. The survey data also proved particularly The conservation planning process is dependent upon valuable in documenting extensive geographic varia- spatially explicit information relevant to the species’ tion in the owl’s abundance. Density estimates were ecology - particularly the distributions of populations, available from three intensive study areas (> 250 km2 habitats, and resources. That information is best por- in size) located across the distribution of the Northern trayed on independent map layers that, when overlaid Spotted Owl. The restricted nature of density studies to form a composite map, collectively provide the ini- precluded any but very localized density estimates; tial hypotheses for the conservation strategy. The first however, the ISC was able to extrapolate these esti- map layer should outline the current and historical mates to neighboring areas of similar habitat type and geographic distribution of the target species. The scale quality. of the first map layer is often dependent upon the extent A fourth map layer depicts land ownership and use of the target species’ distribution, the scale at which patterns? including areas currently set aside for the spe- the species responds to environmental variation, and cies and areas in permanent reserve status (such as the spatial extent of environmental disturbances that wilderness areas, parks, etc.). At this initial stage of the threaten the species. For example, Northern Spotted process, lands available for conservation planning must Owls have large annual home ranges (500-2000 ha), be carefully distinguished from lands not available for are widely distributed across Washington, Oregon, and planning. Significant subsequent changes in land avail- northern California, and are threatened by extensive ability would likely force a repeat of the entire planning areas of habitat loss. The resolution provided by process. 1:250000 scale maps was sufficient for initial mapping The combined intersection of the four map layers- of the owl’s distributional range. the geographic range of the target species, the distri- The second map layer should portray the current bution of suitable and potentially suitabIe habitat, pop- and historic distributions of suitable habitats, includ- ulation density information, and land-use patterns- ing disturbed areas with potential to recover to suitable yields a first iteration of the conservation strategy (or February 1992 CONSERVATION PLANN ING FOR SPOTTED OWLS 7 reserve design), represented as a map. Polygons formed empirically. Appropriate confirmation entails tests, us- by the intersection of map data from each of the four ing relevant population data, of the null hypothesis that map layers represent potential HCAs. The initial map populations are stable or increasing. These tests ne- of these polygons clearly indicated that the strategy for cessitate accurate demographic information from as persistence of the Northern Spotted Owl would need many locations as possible over as long a period as to be evaluated in the context of a “metapopulation,” possible. Estimates of the finite rate of population or a population of populations (see Levins 1970, Shaf- change (l ) were available from three geographically fer 1985). The distribution of polygons was discontin- distinct areas within the range of the Northern Spotted uous across the Iandscape. HCAs were, for the most Owl, two of which, northern California and the Oregon part, rather small (< 30 000 ha), irregu lar in shape, and Coast Ranges, had sequences of data longer than 3 yr. geographically relatively widely separated (mean near- From both areas, detailed knowledge of the fates and est-neighbor distance > 13 km). The landscape be- reproductive status of banded owls provided estimates tween HCAs (the landscape matrix) varied extensively of survival and fecundity rates and, in turn, estimates in its suitability as habitat for the owl. The patchy of l. If l > 1.0, vital rates suggest that the population distribution of HCAs reflected natural discontinuities is increasing; if l = 1.0, the popuiation is stable; and in vegetation structure and composition, in topograph- if l < 1.0, the population is declining. We tested the ical conditions, and in constraints resulting from hu- following null hypothesis: man-induced habitat disturbance and land-ownership H : The finite rate of population change (l ) patterns. Additionally, substantial amounts of habitat 0 is > 1.0. that appeared suitable for the owl were treated as un- (1) available for conservation planning because of the de- The estimate of l was < 1.0 at both sites, and the null cision to limit the initial reserve system to public lands. hypothesis was rejected. (An estimate of l from the Typically, few empirical data will have been used to Olym pic Peninsula was < 1.O. The test, however, had construct the initial conservation map representing the low power since just 3 yr of data were available from proposed habitat-reserve system. That map represents this study area. Details of these and other tests of this the maximum size and number of HCAs available for hypothesis are found in Thomas et al. [ 1990: Appendix planning purposes. Within the confines set by the initial L].) map may be a large number of possible “solutions” Given evidence of declining Northern Spotted Owl that reflect different sets of constraints, each described populations in two geographically separated portions by a unique set of reserve properties. It is at this point of their range, and without clear evidence of other caus- in the process that the initial map (and its attendant al factors (e.g., hunting, interspecific competition, pre- properties) is considered as a set of falsifiable hypoth- dation), a logical explanation was to attribute the de- eses. cline to habitat loss. However, tests of a habitat-loss For the No rthern Spotted Owl we used data from hypothesis required evidence of habitat selection by all pertinent biological studies and inferences drawn the owl as well as documentation that selected habi- from those data to test the properties of the map- tat(s) had become reduced in extent prior to owl pop- including the number and sizes of HCAs, their distri- ulation declines. A preliminary habitat-selection hy- bution, configuration, and spacing, and the nature of pothesis was stated as: the landscape between the HCAs. Valid tests included H : Northern Spotted Owls do not differentiate statistical analyses of empirical data, predictions from o among habitats on the basis of forest age or ecological theory, predictions from population dynam- forest structure. ics models, and inferences drawn from studies of re- (2) lated species. Not all hypotheses could be tested di- All Northern Spotted Owl habitat studies rejected this rectly with empirical data and statistical models; null hypothesis and provided evidence in favor of hab- however, all assertions were subjected to some sort of itat selection (these studies are too numerous to review falsification procedure. If one or more properties of the here; a detailed summary is provided in Thomas et al. map were falsified, conclusions drawn from tests that [1990: Appendix F]). In general, in Oregon and Wash- failed to confirm specific map properties were used to ington, old-growth forest was the only habitat in which refine the map. The new map then became the new set owls consistently nested and reproduced in greater of falsifiable hypotheses. This process continued iter- numbers than would be expected from the proportional atively until all relevant data had been examined and occurrence of that habitat type across the forested land- all map properties had been tested. scape. Only in the coastal redwood forests of northern California were Northern Spotted Owls also found to THE NORTHERN SPOTTED OWL EXAMPLE use younger forests disproportionately. At a relatively A habitat conservation planning process is initiated early stage (60-80 yr) these fast-growing forests exhibit on the presumption that a target species is declining- stand characteristics similar to those of old-growth for- a presumption that often will not have been confirmed ests elsewhere. DENNIS D. MURPHY AND BARRY R. NOON Ecological Applications Vol. 2, No. I 1) Species that are well distributed across their his- torical geographic ranges tend to be less prone to extinction than species confined to small portions of their historical geographic ranges. A hypothesis that logically follows from this concept is:

H0: The probability of species persistence is not related to the extent of its geographic dis- tribution. (4)

Indeed, this concept is rather resistant to empirical testing for most species. Only a species that is essen- tially “extinction-proof’ in portions of its range would 0 provide data that might falsify this hypothesis. Because FIG. 1. Estimated trend in the areal extent of suitable Northern Spotted Owl habitat on NationaI Forest lands in the frequency, intensity, and locations of catastrophic Oregon and Washington for 1930-20 10. Estimates for 1990- events that would eliminate entire owl populations are 20 10 are projections. unknown, direct tests of this hypothesis with Northern Spotted Owl data were not possible. Instead we used an indirect test based on inductive arguments from extinction theory and studies of species whose extinc- The rejection of hypothesis (2) allowed a test of a tion has been documented. For example, the mathe- habitat-loss hypothesis, stated as: matical model of Nisbet and Gurney (1982) suggests that time to metapopulation extinction increases ex- H : No decline has occurred in the area1 extent of 0 ponentially with the number of local populations. As habitat types selected by Northern Spotted Owls a consequence, a moderate degree of subdivision into for foraging, roosting, or nesting. (3) local populations may increase overall persistence tie- The ISC explicitly tested this hypothesis based on data lihood (Quinn and Hastings 1987). These arguments from National Forest lands in Oregon and Washington usually reference the concept of “risk spreading” (Den (national forests provide >70% of the remaining owl Boer 1981). Specifically, advantages are gained by spe- habitat). The analysis documented significant declines cies that are distributed widely across an extensive geo- in the extent of suitable owl habitat, a trend that is graphical area-the degree of environmental correla- projected to continue into the future (Fig. 1). tion among reserve areas is reduced, as is the likelihood Given evidence of habitat specialization by the owl, of simultaneous extinction of populations. Several the- declines in owl populations, and projected continua- oretical studies have demonstrated that correlation in tion of significant losses of suitable habitat, conserva- the probabilities of experiencing major environmental tion planning for the species appeared justified- Rejec- perturbations among populations reduces the effective tion of hypotheses (1) - (3) provided the empirical number of populations in a metapopulation (Goodman support that contributed to the recommended listing 1987, Harrison and Quinn 1989). In this context it is of the Northern Spotted Owl as a threatened species important to recognize that timber harvest throughout under the Endangered Species Act (USDI 1990). the range of the subspecies may act as a correlated For the Northern Spotted Owl, the return to popu- environmental disturbance and may contribute to de- lation stability is contingent upon first achieving a con- stabilization of the Northern Spotted Owl metapopu- dition of no net loss of habitat and, second, providing lation. sufficient habitat in a spatial configuration that allows Empirical studies of endangered species are few and for a balance between local extinction and recoloni- rarely distinguish between the deleterious effects of re- zation events. The map resulting from the overlay pro- duced risk-spreading and the effects of reduced pop- cess described above (see Overview of the process) por- ulation size. One of the best examples is that of the trayed the essential spatia1 information as HCA heath hen (Tympanuchus cupido), a once rather wide- polygons with varying sizes, shapes, and spacing. The spread species that became confined to a single island task was to test and refine that map until the arrange- off the coast of Massachusetts. The extinction of the ment of HCAs described a reserve system sufficient to species was, at least in a proximal sense, the result of allow the Northern Spotted Owl a high likelihood of successive local environmental perturbations that would persistence for 100 years. To do this, the ISC tested have been unlikely to extirpate a more widely distrib- map-generated hypotheses in the context of five gen- uted species (Simberloff 1986; see also Thomas et al. erally accepted concepts of reserve design (Diamond 1990: Appendix N). Based on inferences from such 1975, 1976, Den Boer I981). empirical and theoretical studies, we rejected hypoth- The first reserve design concept was: esis 4. Implications of this rejection were straightfor- February 1992 CONSERVATION PLANNING FOR SPOTTED OWLS 9

ward. Constrained to a system of HCAs that would Improvement of the regression models was needed allow Iand management agencies to meet other legal to predict more precisely the sizes of populations that obligations (e.g., the “viable popuIations” regulation would occupy HCAs in a final reserve system. The in the I976 National Forest Management Act), we chose ability to predict the carrying capacities of HCAs was at this juncture to distribute HCAs widely across the important because many habitat polygons identified in entirety of the Northern Spotted Owl distribution on the earliest map iteration were poorly surveyed. The public lands (rather than concentrate effort on a portion regression models were used to identify HCAs that of that distribution). This decision had substantial im- exhibited large differences between their predicted car- pact on all further reserve design analysis. rying capacities and observed population sizes (i.e., The second basic reserve design concept was: “outliers”). The ISC generated improved estimates of carrying capacities for these outliers by using province- 2) Large habitat patches that support large popu- specific estimates of pair home-range sizes, corrected lations of a target species will tend to support that for the observed overlap between adjacent pairs species for longer periods of time than will small (Thomas et al. 1990: Appendix 1). Regression models patches that support fewer individuals. were then recomputed, and the process continued until Concept 2 suggests a relationship between habitat area only anomalous observations remained as outliers. and population size. For the Northern Spotted Owl, These HCAs deviated from the predicted size-popu- tests of hypotheses (l) - (3) indicate that the owl is lim- Iation retationship due to, for example, unusual local ited by habitat area and predict some relationship be- vegetation patterns or topography, past disturbance tween the size of an HCA and its carrying capacity. history, or the condition of adjacent lands. The lack of Estimates of carrying capacity were made indepen- fit for each unique HCA was formally justified by bi- dently for each habitat polygon, were adjusted for the ologists familiar with the individual HCA and was doc- current amount of suitable habitat, and were based on umented in the conservation plan. existing survey data and the expert opinion of field This procedure established a predictive relationship biologists familiar with individual polygons. A hy- between HCA size and carrying capacity for Northern pothesis then was stated in null form as: Spotted Owls. To address the goal of population per- sistence, however, required insights into the relation- H : No relationship exists between the size of an o ship between carrying capacity (thus HCA size) and HCA and its carrying capacity for Northern local population stability. Specifically, the ISC asked Spotted Owls. (5) how many owl pairs an individual HCA must support The hypothesis was tested by regressing estimated car- in order to have a high likelihood of local population rying capacity on HCA size. A significant regression stability in the face of demographic and mild environ- would lead to rejection of the null hypothesis. Since mental uncertainty. This question, stated as a null hy- key aspects of the ecology of Northern Spotted Owls pothesis, was: (e.g., population sizes, distributions, home range, prey H : No relationship exists between HCA size (or selection, etc.) vary across the range of the subspecies, o carrying capacity) and population stability (that analyses were conducted separately by physiographic is, the likelihood of population persistence). province (i.e., by widely recognized landscape units). (6) The ISC found that across provinces a significant relationship existed between HCA size and carrying InitiaI. information to reject this hypothesis was avail- capacity. Furthermore, habitat polygons of the same able from empirical studies of bird species occupying size on the Olympic Peninsula and in the Klamath islands off the coast of Britain (e.g., Jones and Diamond Mountains in northern California differed in the num- 1976, Diamond and May 1977, Diamond 1984, and ber of owls they could support. The null hypothesis Pimm et al, 1988) and from population dynamics the- thus was rejected. Rejection of hypothesis (5) was not ory (e.g., Richter-Dyn and Goel 1972, Leigh 1981, surprising; however, these tests provided additional Goodman 1987). Estimates of the relationships be- support for habitat limitation, and allowed the incor- tween population size and persistence time of large- poration of geographic variation in home-range size bodied, nonmigrant birds from combined British is- into population projections. land data provided valuable insights into minimum Additional confirmation of a relationship between HCA sizes for Spotted Owls. Estimates indicated an habitat area and carrying capacity was provided by a average persistence time of 2 yr for populations with number of landscape-level studies, all of which con- < 2 pairs, =;25 yr for populations of 10 pairs, and z 50 cluded that the removal of old-growth forests results yr for a single population of 20 pairs (Thomas et al. in a decrease in the regional abundance of Northern 1990:288-289). Further empirical support for an effect Spotted Owls (reviewed in Thomas et al. [1990: Ap- of population size on persistence is provided by census pendix H]). The size of HCAs appeared to be critical data from isolated populations of the Middle Spotted to habitat conservation planning for the Northern Woodpecker and Socorro Red-tailed Hawk (Pettersson Spotted Owl. 1985, Waiter 1991) For example, during the period of 10 DENNIS D. MURPHY AND BARRY R. NOON Ecological Applications Vol. 2, No. 1 Sites/cluster (number) HCA was equal to the number of suitable pair sites. The population size of an HCA was equal to the num- 10 o” 0.8 ber of sites occupied by pairs. The model was an all- E female, stage-projection model, with the stages being 5 0.6 juveniles, subadults. and adults. This structure was similar to those previously presented by Boyce (1987) and Lande (1987, 1988). All juvenile owls were as- sumed to disperse from their natal territory in search of suitable, unoccupied sites- In the model the birds first search within the natal HCA; those that do not find suitable sites attempt to cross the matrix to search 0 20 40 60 80 100 in adjacent HCAs. Demographic stochasticity was sim- Years ulated by variation in survival rates and by variation FIG. 2. Mean pair-occupancy proportion for the Northern associated with dispersal between HCAs. Low-inten- Spotted Owl, plotted against time for a 100-yr simulation. sity environmental variation (or uncertainty) was ex- Cluster size (number of pair-sites per nesting-site cluster) was pressed by variation in fecundity to represent good and varied from 5 to 25. All pair sites were assumed to be com- bad years for reproduction. Parameterization of this pletely suitable habitat. territory-cluster model was based primarily on the studies of Franklin et al. (1990). study (1967-1983) the woodpecker population reached The number of pair sites per HCA was systematically a high of 25 individuals (z 8-l0 pairs). By 1983, how- varied to simulate variation in HCA size. A simulated ever, the population had gone extinct, presumably due network of HCAs would persist where the average pair to deleterious demographic or genetic effects associated turnover rate at a site (due to mortality) and the average with small population size. recolonization rate of unoccupied sites were in long- Additionally, the ISC sought to test hypothesis (6) term balance. Persistence likelihood was estimated by with a dynamic metapopulation model developed spe- plotting 100-yr trends in mean pair occupancy (number cifically for the Northern Spotted Owl. This model of occupied sites per HCA, averaged over all HCAs) allowed the carrying capacity of simulated HCAs to be for HCAs of different sizes. Two basic scenarios were systematically varied in order to evaluate the effect of simulated: the first assumed that all sites within an population size on population stability (Thomas et al. HCA were currently suitable, the second assumed that 1990: Appendix M, Lamberson et al., in press). 60% of the sites within an HCA were currently suitable The basis of the dynamic metapopulation model was (the latter value was similar to forest conditions in the a continuous rectangular array of HCAs that collec- Pacific Northwest). Given the assumption of 100% tively occupied 35% of the forested landscape. HCAs suitability, we did not predict stabilization at high mean were assumed to be circular, and owl pair-territories occupancy levels unless HCAs were sufficiently large within an HCA were assumed to be of equa1 size. The to support at least 15 pairs of Northern Spotted Owls HCAs were assumed to be either totally or partially (Fig. 2). Based on the more realistic assumption of 60% suitable habitat, and the landscape matrix between suitability, mean occupancy did not stabilize at high HCAs was assumed to be entirely unsuitable, except levels until HCAs were large enough to support at least for purposes of dispersal. The carrying capacity of an 20 pairs of owls (Fig. 3). Details on additional infer- ences drawn from the metapopulation model are found in Thomas et al. (1990: Appendix M). 1 Based on evidence from empirical studies and theory and the predictions of the metapopulation model, the 0.8 null hypothesis of no relationship between HCA size 0" C 0 (carrying capacity) and population stability (the like- 2 0.6 lihood of persistence) was rejected. The model results t: provided additional insights into a minimum target * 0.4 c HCA size with a high likelihood of local population ii persistence, contingent upon some level of dispersal 2 0.2 among HCAs. Model predictions, theory, and empir- ical studies were consistent, suggesting that, to be sta- ble, a local population must consist of =: 15 or more pairs. However, for HCAs not composed of uniformly Years suitable habitat, population stability required 220 pairs FIG. 3. Mean pair-occupancy proportion for the Northern of owls (Fig. 3). The ISC used 20 pairs as a minimum Spotted Owl, plotted against time for a l00-yr simulation. target population to select HCAs from Cluster size (number of pair-sites per nesting-site cluster) was available habitat varied from 5 to 25. Only 60% of the pair-sites were assumed polygons on the iterated map and to refine HCA to be suitable habitat. boundaries. February 1992 CONSERVATION PLANNING FOR SPOTTED OWLS 11

The third reserve design concept invoked was: Unfortunately, the specific effects of fragmentation within HCAs are difficult to separate from those of 3) Habitat patches that are continuous (less inter- concomitant reduction in suitable habitat. To further nally fragmented) in configuration tend to support test hypothesis (7), the dynamic metapopulation model species for longer periods than patches that are ir- was used. For these simulations all HCAs were as- regular in configuration (more fragmented). sumed to be equal in size with potential carrying ca- pacities of 25 pairs. Increasing fragmentation was sim- An hypothesis that logically follows from this concept ulated by varying the actual number of suitable sites is: within these HCAs from 25 down to 5. The fewer suitable sites within the HCA, the greater the likelihood H0: Given a set of habitat patches that vary in their that a dispersing juvenile owl would search unsuitable degree of fragmentation. no relationship exists sites within its natal HCA. Given these assumptions, between the extent of fragmentation within a mean pair occupancy did not stabilize, over 100 yr, patch and the persistence likelihood of species until ~60% (15 of 25) of the sites within HCAs were that occupy those patches. (7) suitable. Based on the results from both modeling and empirical studies conducted at the landscape scale, null Little published information exists to document a re- hypothesis (7) was rejected. The ISC concluded that lationship between population persistence likelihoods populations in HCAs with contiguous suitable habitat and degrees of fragmentation within individual habitat exhibit a higher likelihood of persistence than those in reserves. Pickett and Thompson (1978) discussed the HCAs in which habitat is more fragmented. At this dynamics of vegetation patches within habitat islands point in the process, most HCA polygons that showed or reserves. They argue that patterns of vegetation dis- little potential to recover to contiguous blocks of suit- turbance and subsequent succession can profoundly able habitat even in the absence of timber harvest (that affect extinction dynamics of animal populations with- is, HCAs that had substantial natural irregularities, in a reserve. Many proposed HCAs currently have such as poor soils) were deleted from the reserve sys- abrupt edges created by clearcuts adjacent to old-growth tern. Exceptions were made to retain small HCAs in forest. Disturbances at these edges, such as windthrow portions of the species’ range where no large HCAs in forest patches, are likely to reduce the amount of with the potential for contiguous habitat existed. suitable owl habitat. This effect, coupled with the ob- The fourth basic reserve design concept invoked was: servation that Northern Spotted Owls increase their home-range size in response to fragmentation (Fors- 4) Habitat patches that are sufficiently close together man et al. 1984, Carey et al. 1990), suggests that frag- to allow dispersal tend to support target populations mented HCAs will have lower carrying capacities for for longer periods than habitat patches that are far owls. apart. At the landscape scale, in contrast, there has been extensive discussion of fragmentation effects (e.g., Fah- This concept embraces the so-called “rescue effect” rig et al. 1983, Harris 1484, Fahrig and Merriam 1985, (Brown and Kodric-Brown 1977) that suggests that Burley 1989, Harris and Gallagher 1989) and an ex- population stability in a habitat patch is contingent tensive literature based on a wide array of species. For upon a balance between local population extinction example, studies of many forest-dwelling bird species and recolonization from neighboring populations. have found that an increased ratio of forest edge to Considerable evidence from bird studies shows the im- forest interior, the inevitable consequence of forest portance of distance from mainland sources of mi- fragmentation, can have strong negative consequences grants as a determinant of local species richness on (Whitcomb et al. 1976, Wilcove et al. 1986, Temple continental shelf islands (Case 1975, Diamond 1975, and Cary 1988, Yahner 1988). The species affected, Terborgh 1975, Soul6 et al. 1979) and within recently mostly forest-interior songbirds, experienced increased isolated forest fragments (Burgess and Sharpe 1981, levels of predation and brood parasitism (Whitcomb Whitcomb et al. 1981, Lynch and Whigham 1984; Wil- et al. 1981, Brittingham and Temple 1983, Wilcove cove et al. 1986). Particularly strong empirical support 1935). Two indirect, but valuable, tests of this hy- for concept 4 is provided by research on insular pop- pothesis at the geographic scale appropriate for Spotted ulations of pikas (Ochotona princeps) (Smith 1974, Owl planning were available. Meyer et al. (1990) found 1980). Smith demonstrated a dynamic equilibrium be- that landscape samples centered on Spotted Owl nest tween extinction (inversely related to patch size) and sites contained a significantly higher percentage of old- recolonization (inversely related to inter-patch dis- growth forest and significantly larger average sizes of tance), as well as an increase in turnover rate with old-growth patches than similar areas at randomly se- degree of isolation. lected sites. Bart and Forsman (1992) also found a Consideration of (and empirical support for) the res- significant relationship at a landscape scale between cue effect argues that conservation planners should space the amount of old-growth forest and the occurrence HCAs to facilitate demographic interaction among and productivity of Northern Spotted Owls. them. The metapopulation model assumed that when 12 DENNIS D. MURPHY AND BARRY R. NOON Ecological Applications Vol. 2, No. 1 O- - Dispersal coefficient 8- . . . . . 3h 6- .-c \ -‘= 0.6-j 4 n 2 4- 0 0.4 ii 4 2- 0.2 00 0 20 40 60 80 IO0 n i vi T 1% 1 1 1 I , I f Years 0 IO 20 30 40 50 FIG. 5. Mean pair-occupancy by Northern Spotted Owls, Distance (km) plotted against time for a 100-yr simulation. The dispersal FIG. 4. Probability of successful dispersal by Northern coefficient was varied from 1.0 (high environmental resistance Spotted Owls, plotted against distance. Figure is read as the to dispersal) to 0.03 (low resistance to dispersal). Cluster size probability of dispersing >x kiIometres. was five pair-sites per cluster, all stocked with suitable habitat.

the null hypothesis. The data fit a negative exponential a juvenile owl failed to find a vacant suitable site and/ model (R2 =0.97 P < .OO1; Fig. 4), suggesting that or a mate within its natal HCA, it had some likeiihood dispersal capability declines with increasing distance of successfully dispersing to a vacant site in a neigh- from the natal area. Null hypothesis (8) thus was not boring HCA. This assumption requires presence of supported by the data; hence, not only the sizes of HCAs within acceptable distances for dispersing owls. HCAs but the distances between HCAs had to be viewed Without adequate dispersal routes, populations must as critical elements in the reserve system design. be self-sustaining- an unlikely event in aIl but excep- No data were available to test hypothesis (9) directly. tionally large HCAs capable of sustaining very large The simulation model, however, allowed the system- populations. The putative importance of HCA spacing atic variation of risks associated with inter-HCA dis- was addressed by testing two null hypotheses: persal and estimates of its effects on mean pair occu- Ho: No relationship exists between the likelihood of pancy of HCAs. The objective was to simulate the a juvenile owl successfully dispersing and the environmental resistance to dispersal that an owl could distance dispersed. (8) experience when traveling through the forest matrix, Two sources of mortality could result from dispersal H,: No relationship exists between the persistence between HCAs--(1) a juvenile could disperse in a di- likelihood of an HCA and the spacing among rection that would not intercept an adjacent HCA, or HCAs, (9) (2) it could select an appropriate direction. The like- To test the first of these hypotheses, dispersal was de- lihood of successful dispersal between HCAs was mod- fined as the permanent movement of juvenile owls eled as a decaying exponential, from one location to another. The distribution of dis- Pr(success) = exp[ - k . (distance between HCAs)]. persal distances from 56 radio-tracked juvenile birds was estimated, based on maximum dispersal distance The effect of varying environmental resistance was computed as the greatest straight-line distance traveled evaluated by estimating the sensitivity of mean pair by an individual from its natal site during the period occupancy to variation in the dispersal coefficient k of tracking, Only one bird was documented to have (preliminary estimates of k were provided by analysis found a suitable nesting site and a mate. The remaining of data on juvenile dispersal). For HCAs of size suf- birds either died (68%), were subject to transmitter ficient to hold five pairs, variation in the dispersal co- failure (27%), or simply disappeared (5%). Because of efficient strongly affected mean occupancy (Fig. 5). The a possible relationship between dispersal distance and model assumed high resistance to dispersal across un- number of days of transmitter exposure, analyses were suitable habitat (the landscape matrix), and mean oc- first conducted to determine if transmitters had any cupancy did not reach equilibrium. Simulated popu- effect on maximum dispersal distance (Thomas et al. lations went to extinction. In contrast, the effects of 1990:306). Given an apparent lack of a relationship varying the dispersal coefficient were much less pro- between dispersal distance and the length of transmit- nounced in HCAs supporting at least 20 pairs (Fig. 6). ter exposure, null hypothesis (8) was not rejected. All coefficients provided for long-term equilibrium; Based on the cumulative distribution of dispersal however, higher resistance provided by the landscape distances, the estimated probability of dispersing x ki- matrix resulted in significantly lower mean occupancy lometres, or farther, was regressed on distance (x). Lack rates. Empirical and model-based results led to the of a significant regression would provide support for rejection of hypothesis (9). February 1992 CONSERVATION PLANNING FOR SPOTTED OWLS 13

Collectively, the results of these two tests indicated that spacing between HCAs should be within the dis- persal capabilities of juvenile owls. The ISC was un- able, however, to bring empirical data directly to bear on the question of the exact spacing required among HCAs. After lengthy discussion following a Delphi ap- proach (e.g., Soul6 1989), the ISC concluded that HCAs should be within the dispersal capability of approxi- mately two-thirds of dispersing juveniles-about 20 00 TT II II II IIIIII 1111 11 km (12 miles). Comparison of the distributions of dis- 00 20 40 60 80 100 persal distances and nearest-neighbor distances among Years HCAs showed that nearly all HCAs described on pre- FIG. 6. Mean pair-occupancy proportion for Northern vious map iterations were within the dispersal capa- Spotted OwIs, plotted against time for a 100-y simulation. The dispersal coefficient was varied from 0.3 (moderate en= bilities of two-thirds of radio-tracked juvenile owls vironmental resistance to dispersal) to 0.03 (low resistance to (Thomas et al. 1990: Appendix P). dispersal). Cluster size was 20 pair-sites per cluster, of which The final reserve concept invoked was: 50% were stocked with suitable habitat. 5) Habitat patches that are connected by habitat cor- ridors, or that are set in a landscape matrix of similar INTEGRATING THE RESULT’S OF HYPOTHESIS structure to the habitat patches, will allow a target species to disperse freely among patches and will As presented in the previous section, sequential tests tend to support a species for longer periods than of map properties, stated as null hypotheses, provided habitats not so situated. the guidelines for interim drafts of the conservation We were aware of few published accounts to confirm plan. For the Nor-them Spotted Owl, test results in- the corridor concept (for example, see Fahrig and Mer- dicated a positive relationship between HCA size and riam 1985, Henderson et al. 1985). Preliminary results carrying capacity, a positive relationship between HCA from Brazilian rainforests suggest that corridors may size and population stability (persistence likelihood), be effective in facilitating the recolonization of isolated a negative relationship between juvenile dispersal ca- forest fragments by ant birds (Lovejoy et al, 1986). pabilities and distance, and an inverse relationship be- Anecdotal evidence suggests that corridors may permit tween HCA spacing and population persistence. These dispersal between patches for chaparral-requiring birds reserve design guidelines, inferred from tests of explicit in California (Soule et al. 1988). However, no direct hypotheses, provided a basis for eliminating some empirical tests of this concept were possible for Spotted HCAs from the conservation strategy, thereby offering Owls. Biological intuition, however, suggests that the opportunities for compromise involving legal consid- presence of vegetation structure or other habitat fea- erations and economic concerns. Test results suggest tures between HCAs that reduce the risk of mortality that smaller HCAs. particularly those that are more to dispersers should promote population stability. The isolated (all else being equal), would contribute less to results of modeling also suggest that factors that reduce the long-term conservation of the Northern Spotted the resistance to movement among HCAs will enhance Owl than larger, less isolated HCAs. As a result, a population persistence (Fig. 6). number of small, isolated HCAs, even those currently To address this concept in the conservation strategy, supporting owls, were removed from the reserve sys- the ISC reviewed the character of landscapes through tem and became candidate areas for timber harvest. which radio-tagged owls had successfully dispersed. This occurred. presumably, with acceptable cost to the There was no evidence of directional movement along likelihood of species persistence. In addition, the re- “corridors.” Nearly all such landscapes, however, con- lease of these potential HCAs represented a significant tained forested areas with canopy closure exceeding compromise and hopefully increases the likelihood of 40% and trees of moderate size. Therefore, standards plan adoption. and guidelines for forest management of the landscape The ISC thus used the results of hypothesis to matrix were proposed to ensure a high likelihood of edit the original map of HCA polygons into a, sub- movement of owls among HCAs. The conservation stantially smaller subset. One final task remained: to strategy specified that at least 50% of the forest land- test the overall map for consistency between the pro- scape between HCAs consist of forest stands with a jected number of owls per HCA, and HCA size and mean diameter at breast height 2 11 inches (28 cm) shape. A good relationship was expected since the pro- and canopy closure ~40% (the 50-1l-40 rule; Thomas jected carrying capacities of manv HCAs were adjusted et al. 1990:327). The adequacy of this management bv location-specific home-range and densitv data. Some standard to provide for connectivity among HCAs can d;gree of deviation from a best-fit regression was ex- only be determined by future long-term monitoring of pected because of geographic variation in key biological the HCAs. parameters (e.g., home-range size, habitat-use patterns, 14 DENNIS D. MURPHY AND BARRY R. NOON Ecological Applications Vol. 2, No. 1

0 100 200 | kilometres

FIG. 8. Map showing the overall conservation strategy (distribution ofhabitat conservation areas, HCAs) for Oregon, FIG. 7. Close-up of land allocations within a portion of USA. The darkest shaded areas are HCAs and Wilderness the Mount Hood National Forest, Washington (state), USA. Areas; all light-shaded areas are other public lands. The map shows areas not appropriate for timber harvest (il- lustrated as hatching), demonstrating habitat connectivity along riparian and scenic corridors and between adjacent habitat Therefore, null hypothesis (10) was rejected and the conservation areas (HCAs) that facilitates Spotted Owl dis- ISC concluded that the conservation map was logically 2 persal. Solid black areas represent 0.3-km (80 acre) “reten- consistent. As before, regression diagnostics were used tion areas,” in which an active owl nest is located and timber harvest is not permitted. to identify “outlier HCAs,” with final adjustments based on empirical data. The final product was a conservation strategy for the Northern Spotted Owl expressed in the form of maps of HCAs (Figs. 7 and 8). etc.). For example, in the initial tests of hypotheses (5) and (7) a tendency for irregularly shaped HCAs to have projected populations smaller than predicted from area DISCUSSION alone was observed. Therefore, the ISC used as data An extensive literature addresses the philosophy, independent variables both the area and perimeter of merits, and implications of the hypothetico-deductive each HCA to test the following null hypothesis: process in scientific injury (e.g., Popper 1959, Platt

H0: No relationship exists between HCA size and 1964) and in wildlife biology in particular (Romesburg configuration and HCA carrying capacity. 1981). Fundamental issues that have generated the most (10) controversy, such as the appropriate role of prior in- formation in hypothesis formation, seem to call into Based on the penultimate conservation map of the en- question the very application of hypothesis testing in tire range of the Northern Spotted Owl, a significant applied sciences. Suffice it to say, the process of hy- regression of carrying capacity on HCA area and pe- pothesis development and subsequent testing is pred- rimeter (an edge effect) was found. The best-fit regres- icated-even dependent- on some amount of prior in- sion model had the form: formation. Assumptions about the degree of threat to ln(projected population) a population, species, or ecological community moti- vates the habitat conservation planning process. = b0 + b1 ln(HCA area) + b2 ln(HCA perimeter). With February 1992 CONSERVATION PLANNING FOR SPOTTED OWLS 15

that in mind, the values of the hypothetico-deductive involved. In our opinion, the public has a pervasive method in habitat conservation planning are several. misunderstanding of the scientific process. In general, First, although there is rarely a unique solution to a the public fails to recognize that scientists conduct tests reserve design problem, the formation of demonstrably of hypotheses to disprove assertions about how the falsifiable hypotheses serves to exclude at least some natural world functions. As a consequence, scientists potential conservation responses. Wiens (1984) sug- cannot prove the truth of an assertion; rather, ulti- gested that field experiments in community ecology mately they fail to disprove hypotheses. This is the should emphasize “refutation of untenable hypotheses, accepted norm to render conclusions “scientifically rather than . . . vain verifications of favored hypoth- credible.” An essential aspect of the habitat conser- eses.” Similarly, hypotheses that truly discriminate be- vation planning process developed here is that the tween empirically refutable reserve design alternatives process of sequential map revision does not depend should facilitate the dismissal of untenable habitat con- upon the ultimate truth of one or more specific em- servation plan options. Moreover, the falsification pro- pirical, model-based, or theoretical research results. cess assists in the development of alternative hypoth- Rather, the process follows inferences drawn from re- eses, the subsequent testing of which focuses planning search results and hypotheses not falsified by specific from conceptual issues to specific design options. For tests. If one or more tests performed during the habitat the Northern Spotted Owl, the process of testing the conservation planning process are later shown to be almost mundane null hypothesis-no relationship ex- flawed (for example, because of an error in a calculation ists between HCA size and its carrying capacity-led or because of new information), the strategy is not to the recognition that the area necessary should vary undermined. On the contrary, the plan is appropriately across physiographic provinces. viewed as having been exposed to one fewer valid test Second, hypothesis testing in habitat conservation than planners had intended (see a full discussion in planning offers a useful framework for the timely con- Murphy and Noon 1991). sideration of extrinsic (nonbiological) constraints in the A huge gap exists between the theory and empirical decision process. Since economic. legal, and social con- data that is available in biology and their application siderations motivate habitat conservation planning, in efforts to conserve our wild. disturbed, and imperiled many politicians and planners, not illogically, seek to landscapes. The habitat conservation planning process resolve such issues with compelling biological data. is a credible vehicle for the resolution of conflicts that However, biological data inevitably provide little help- result from the intersection of a burgeoning human ful information that bears on the salient philosophical population, resource-hungry technologies, and a finite questions that drive habitat conservation planning- natural. world. The testing of map-based hypotheses is at what cost should species be protected and what level the fundamental means of applying data to, and ac- of certainty of population persistence is acceptable? knowledging and addressing uncertainty in, the con- Certainly biological data cannot resolve the hard prac- servation planning process. The conservation planner, tical decisions concerning the intrinsic worth of pop- nonetheless, must remain aware that habitat conser- ulations, species, and ecological communities. No ex- vation planning is driven by, and must be resolved to act population size of a certain species in a specific satisfy, diverse and often conflicting obligations. habitat can justify a single given land cost. In this arena, Finally, we have emphasized five reserve design con- data and dollars simply do not equate. For that reason, cepts that we perceive as universally crucial for con- we prescribe treatment of intransigent. extrinsic con- sideration in species conservation efforts. Clearly, many straints as an initial step in the process. Extrinsic con- species thrive in circumstances that do not meet the straints thus define the available landscape for habitat design criteria invoked here; however, such species-, conservation planning but are not otherwise involved including edge-adapted, generalist, introduced, and/or in the application of biological data to the process. weedy organisms -are rarely the targets of conserva- Third, the framework that allows both biological and tion efforts. But, for those species that are both adapted nonbiological contributions to the reserve design pro- to early habitat successional stages and, in fact, are cess logically orders that process so that it is easily threatened or endangered, these reserve design con- repeatable. Since conservation strategies and habitat cepts must be addressed with generous concomitant conservation plans are rarely unique solutions, and so consideration ofhabitat management regimes to assure much is virtually always at stake, the availability of a species persistence. In general, habitats set aside in the step-by-step schedule allows planners to document, absence of intensive management may not be adequate justify, and defend their products. Conservation strat- to meet conservation goals over the long term. For egies and plans are commonly’subject to litigation upon those many species that are now solely restricted to completion, and the conservation biologists involved remnant natural habitats (those species for which re- often experience extensive efforts to discredit their ef- serve design is a limited option), we suggest the ap- forts (Murphy and Noon 1991). Antagonists normally plication of the map-based scientific method presented exaggerate areas of uncertainty in the scientific process here to the development of appropriate habitat man- in an attempt to dismiss the importance of the habitats agement plans. Explicit, falsifiable hypotheses-and 16 DENNIS D. MURPHY AND BARRY R. NOUN Ecological Applications Vol. 2, No. 1 their rigorous testing with data from research and mon- Diamond, J. M., and R. M. May. 1977. Species turnover itoring-can be as important to habitat management rates on islands: dependence on census interval. Science 197:266-270. as the testing of such hypotheses has been to planning Fahrig, L., L. Lefkovitch, and G. Merriam. 1983. Popula- reserve design for the Northern Spotted Owl. tion stability in a patch environment. Pages 61-67 in W, K. Lavenroth, G. V. Skogergoe, and M. Rug, editors. Anal- ACKNOWLEDGMENTS ysis of ecological systems, state-of-the-art in ecological We dedicate this paper to the dozens of field biologists modelling. Elsevier, New York, New York USA. whose extraordinary efforts provided the knowledge of dis- Fahrig, L., and G. Merriam. 1985. Habitat patch connec- tribution and habitat associations of Northern Spotted Owls tivity and population survival. Ecology 66:1762-l768. that made this analysis possible. We greatly appreciate the Forsman, E. D., E. C. Meslow, and H. M. Wight. 1984. efforts of our good friends and colleagues on the Interagency Distribution and biology of the Spotted Owl in Oregon. Spotted Owl Scientific Committee, in particular our fearless Wildlife Monograph 84:l-64. leader, Jack Ward Thomas. Jerry Vemer, David Wilcove, Franklin, A. B., J. A. Blakesley, and R. J. Guti&ez. 1990. Reid Noss, Barry Mulder, Paul Ehr1ich, and Mike O’Connell Population ecology of the Northern Spotted Owl (Strix oc- savaged early drafts of this. much to the betterment of the cidentalis caurina) in northern California: preliminary re- final product. Kathy Switky in particular brought order and suits, 1989. Technical Report 1990-9. California Depart- improved syntax to the endeavor. And, to our colleagues at ment of Fish and Game, Sacramento, California, USA. the Center for Conservation Biology and the Redwood Sci- Gilpin, M. E. 1989. A comment on Quinn and Hastings: ences Laboratory, our special thanks. Grants from the Wil- extinction in subdivided habitats. Conservation Biology liam and FIora Hewlett Foundation, the New Land Foun- 2:290-292. dation, and the National Science Foundation made this work Gilpin, M. E., and M. E. Souli. 1986. Population vulner- possible. ability analysis. Pages 19-34 in M. E. Soul& editor. Con- servation biology. Sinauer, Sunderland, Massachusetts, LITERATURE CITED USA. Allen, H., and L. Brewer. 1985a. A progress report for the Givnich, T. J., E. S. Menges, and D. F. Schweitzer. 1989. cooperative administrative study to monitor Spotted Owl Minimum area requirements for long-term conservation of management areas in National Forests in Washington. the Albany Pine Bush and Karner Blue Butterfly: an as- Washington Department of Fish and Game, Olympia, sessment. Environmental Impact Report on the Rapp Road Washington, USA. Sanitary Landfill Expansion. City of Albany, Albany, New Allen, H., and L. Brewer. l985b. A review of current North- York, USA. em Spotted Owl (Strix occidentalis caurina) research in Goodman, D. 1987. The demography of chance extinction. Washington state. Pages 55-57 in R. J. Guti&ez and A. Pages 1l-34 in M. E. Soul&, editor. Viable populations for B. Carey, editors. Ecology and management of the Spotted conservation. 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