ABSTRACT: We identify wetlands, riparian woodlands and shrublands, green ashwoodlands, aspen forests, pinyon-juniper woodlands, and pure and mixed forests ofponderosa pine as important wildlife habitats in the US. Forest Service's Rocky MountainRegion. The relationships of vertebrate species to each ofthese types are discussed relativeto habitat requirements and species conservation. The importance of late-successionallodgepole pine, Douglas-fir, and spruce-fir forests is discussed in the context of regionallandscapes and the maintenance of biological diversity.

INTRODUCTION

Species conservation is integral to both themaintenance of viable plant and animalpopulations and the maintenance of'biodi-versity, Sustaining biological diversity en-tails much more than simply maximizingspecies richness, that is, maximizing thenumbers of different species that occur in alocal area. A broader view is necessary. Theconservation challenge is to ensure that all

j. •• .

species native to an entire region are main-tained as well-distributed, viable popula-tions (Murphy 1989, Knopf 1992). Federallegislation requiring the protection of spe-cies, critical habitats, and biological diver-sity is already in place. The National ForestManagement Act (NFMA) of 1976 andrelated regulatory mandates are designedto (1) provide for the diversity of plant andanimal communities and (2) maintain via-ble populations of native and desirable non-native plants and animals on national forestlands. Also, the Endangered Species Act of1973 established the conservation of indi-vidual threatened and endangered speciesand their critical habitats as national prior-ity. Individual species are one of the funda-mental components of biological diversity.Sustaining biological diversity within aregion requires a comprehensive knowl-edge of regional communities, the biologyof associated species, the interconnectionsof species and ecosystems, and the rolesand human uses of resources other thanwildlife. We hope that the information wepresent here will contribute to efforts tosustain biological diversity in the RockyMountain Region of the US. Forest Ser-vice (Region 2), which encompasses Colo-rado, Wyoming, South Dakota, Nebraska,and Kansas. Some of this material wasoriginally prepared as unpublished back-ground information to support the RockyMountain Region's Biological DiversityAssessment (US. Forest Service 1990).

The Biological Diversity Assessment wasproduced as a supplement to the revisedRocky Mountain Regional Guide, whichprovides land and resource managementplanning direction to the national forestsand grasslands in the region.

The wide variety of plant communities inthe Rocky Mountain Region provides for aregionally diverse fauna (Hoover and Wills1984), and reduction or loss of any partic-ular species or vegetation type would resultin loss of biotic diversity. However, de-clines in wildlife diversity are more likelywhen critical habitats are degraded. Habi-tats that add substantially (more than aver-age) to wildlife diversity can be identifiedas those with (1) high numbers of wildlifespecies; (2) high abundances or biomassesof animals; (3) unique, obligatory faunasor specialized wildlife species; (4) limited,disjunct, or shrinking distributions; and (5)threatened, endangered, or sensitive spe-cies. Finch (l992) evaluated threatened,endangered, and sensitive species in 15major vegetation types in the Rocky Moun-tain Region, concluding that wetlands, ri-parian areas, and various lowlands con-tained higher numbers oflisted vulnerablespecies than upland coniferous and decid-uous forests. Using this information in com-bination with summaries by Hoover andWills (1984) of overall wildlife speciesrichness and abundance in the Rocky Moun-tain region, we identified six general hab-itats that have unusually high overall valueto vertebrate faunas: wetlands, riparianwoodlands and shrublands, green ash wood-lands, aspen forests, pinyon-juniper wood-lands, and pure and mixed forests of ponde-rosa pine. To ensure compatibility withHooverand Wills (1984), we excluded shortgrass and mixed grass prairie from ourconsideration. However, we emphasize thatGreat Plains grasslands are essential habi-tats to many threatened, endangered, and

Volume 13 (3), 1993 Natural Areas Journal 191

This file was created by scanning the printed publication.Errors identified by the software have been corrected;

however, some errors may remain.

sensitive species (for summary, see Finch1992).

In this paper, we discuss why woodland andwetland communities have high biologicaldiversity value and describe human landuses that can sometimes contribute to theirdegradation or loss. In addition, we explainwhy the late-successional stages of otherhabitats (lodgepole pine, subalpine spruce-fir, and Douglas-fir) are also very impor-tant in the maintenance of regional wildlifediversity. Sustaining regional wildlife di-versity will involve management practicesdesigned to conserve and restore all ofthese natural communities.

IMPORTANT HABITATS

Wetlands

Wetlands are areas that are permanentlywet or intermittently covered by water, suchas marshes, swamps, bogs, potholes,muskegs, shallow lakes and ponds, andoverflow land of rivers and streams (Veatchand Humphrys 1966, Schwarz et al. 1976).Freshwater wetlands are valuable for theirfunctions in hydrologic, chemical, and bi-ological cycles; as receivers and transform-ers of natural and human wastes; as protec-tion from floods; as recharge groundwateraquifers; and as unique habitats for a widevariety of plants and animals (Mitsch andGosselink 1986). Over 200 migratory birdspecies visit western wetlands (Capen andLow 1980). Wetlands serve as crucial fly-way stopovers for migratory ducks, geese,and swans. In the U.S. Forest Service RockyMountain Region, 35 species of waterfowluse wetlands regularly or occasionally tobreed, migrate, or winter. Other birds inthe Rocky Mountain Region that almostexclusively use wetlands include terns (5species), gulls (6), sandpipers and plovers(35), cranes (2), rails (4), loons (6), herons(8), grebes (5), pelicans (1), ibises (1), andcormorants (1) (Colorado Field Ornitholo-gists 1978, Oakleaf et al. 1982). Fish-eat-ing predators such as bald eagles, ospreys,mink, and river otters (throughout, see Ta-ble 1 for scientific names) rely on wetlandsfor prey, while big game, upland gamebirds, and numerous nongame species usewetlands for refuge and water duringdrought or fires. Wetlands typically have

higher numbers of species and individualsof small mammals, songbirds, reptiles, andamphibians than surrounding natural com-munities (Johnson and McCormick 1978,Szaro et a1. 1988, Shantz and Gibbons1989).

Seven bird species and subspecies federal-ly listed as threatened or endangered areknown to use wetlands frequently or pe-ripherally in the Rocky Mountain!GreatPlains region: whooping crane, brown pel-ican, bald eagle, least tern, Eskimo curlew,and piping plover. Wetland/prairie speciesidentified by the u.s. Fish and WildlifeService Office of Endangered Species aspotentially threatened or endangered (Cat-egory 2 species) for the Rocky Mountain!Great Plains Region are snowy plover, long-billed curlew, and white-faced ibis. Someresident wetland species are rare and local.For example, Preble's race of the meadowjumping mouse, a candidate subspecies(Category 2) on the federal threatened andendangered species list, occupies easternfoothill marshes of Wyoming's LaramieRange. The Rocky Mountain wood frog, alocal inhabitant of the Medicine Bow andBighorn Mountains, breeds predominatelyin small standing ponds with emergentvegetation along a shallow north bank(Haynes and Aird 1981). Wyoming toad, asubspecies federally listed as endangeredand found in Wyoming's Laramie Basin(Baxter et al. 1982), and western borealtoad, a candidate subspecies (Category 2)for the federal list, inhabit isolated wet-lands and riparian areas.

Prior to recent legislation, wetlands weredestroyed at an alarming rate of about 1%per year in the United States (Mitsch andGosselink 1986). Draining, degradation,and loss of wetlands can severely reduceanimal abundance and species diversity;population sizes of resident threatened,endangered, and sensitive species; water-fowl and furbearer production; harvest quo-tas; and hunter-trapper success. Livestockgrazing, agricultural conversion, tree-cut-ting, industry, energy development, urbanencroachment, water pollution, recreation,and numerous water-control practices candrastically alter wetland environments, re-ducing their value to wildlife (Johnsgard1956, Weller et al. 1968, Christiansen and

Low 1970, Horwitz 1978, Sharitz and Gib-bons 1989). Changes in water levels, live-stock trampling, human disturbance, andnest predation have had disastrous conse-quences for ground-nesting colonial birdssuch as pelicans, gulls, and terns because ofimpacts to whole colonies (Johnson andSloan 1976, Capen and Low 1980). Trophicconcentration of pes tic ide residues and otherenvironmental contaminants have resultedin population declines in numerous fish-eating birds such as bald eagle, osprey,

.western grebe, white-faced ibis, and Arner-ican white pelican (Herman et al. 1969,McCrow 1974, Capen 1977, Henny andAnthony 1989). In summary, wetland eco-systems provide essential habitats for alarge number of vertebrate species, manyof which use them exclusively. Wetlandsare regarded as important, irreplaceableecosystems for their characteristic plantsand animals (Mitsch and Gosselink 1986).

Riparian Woodlands and Shrublands

The term riparian refers to the area border-ing a river, stream, or lake (Schwarz et al.1976). Riparian zones are highly valued asareas of wildlife habitat, recreation, timber,livestock forage, and water; travel passage-ways for animals and humans; buffer zonesbetween managed and natural areas; natu-ral filters of surface runoff and waste; sta-bilizers of shorelines and stream channels;interceptors for precipitation; and insula-tion for streams (Melton et al. 1984). Likewetlands, riparian ecosystems provide wa-ter, food, and shelter to a large number ofgame species, including mule deer, white-tailed deer, moose, elk, waterfowl, and up-land game birds. In the Rocky Mountainregion, several furbearing mammals suchas river otter, mink, opossum, ringtail, rac-coon, beaver, and muskrat depend on ripar-ian areas for survival and reproduction.Hoover and Wills (1984) reported morespecies of amphibians (13), reptiles (33),and birds (177) in cottonwood riparianwoodlands than in eight other forest typesof Colorado, and species richness ofmam-mals (59) was second only to that in pin-yon-juniper woodlands (Table 2). Riparianareas may contain the majority ofa region'samphibians and reptiles (Brode and Bury1984).

192 Natural Areas Journal Volume 13 (3), 1993

In the Great Plains alone, 73% of 325breeding bird species are reported to useriparian woodlands, and 45% (117 species)of 260 regular breeders nest in riparianareas (lohnsgard 1979). Riparian habitatsare valuable in spring and fall as migratorycorridors for songbirds (Rappole and Warn-er 1976, Stevens et a1. 1977) and as stagingareas for whooping cranes and sandhillcranes (Frith 1974,Aronson and Ellis 1979).Many species of small mammals, bats, song-birds, amphibians, and reptiles reside sole-ly in riparian habitats (Armstrong 1972,Seabloom et a1. 1978, Johnsgard 1979,Brode and Bury 1984). Short-tailed shrew,eastern mole, red bat, and river otter arerare Colorado mammals using riparian andwetlands exclusively (BisseI1978). Popu-lation declines in Bell's vireo may be theresult ofloss of riparian areas and increasedcowbird parasitism (Office of MigratoryBird Management 1987).

Cross (1985) found that mammal speciesdiversity in riparian sites exceeded that inconifer sites. Riverbank cottonwood sitesalso have higher densities and species rich-ness of birds than adjacent uplands (Knopf1985), grasslands and sagebrush (Ports1979), conifer forests (Hopkins et a1.1986),or agricultural lands (Hehnke and Stone1978, Ports 1979). In the northern HighPlains, cavity nesters were found to bemore abundant in cottonwood-dominatedvegetation types than in three other vegeta-tion types (Hopkins et a1. 1986). By com-paring the percentages of shared speciesamong nine forest types in Colorado,Raphael (1987) demonstrated that cotton-wood types are least similar in speciescomposition of birds, mammals, amphibi-ans, and reptiles. Also, species diversity ofbirds and mammals varies greatly amongriparian vegetation types in the centralRockies (Olson and Knopf 1988, Finch1989a). A total of 45 bird species werefound nesting in various riparian habitatsabove 1980 m in southeastern Wyoming,but 78% of these species use foothill cot-tonwood woodlands, while only 27% nestin subalpine riparian shrublands (Finch1988, 1989b). In six riparian areas of north-ern Colorado, numbers of small mammalsvary from 2 to 7 species and 17 to 84captures (Olson and Knopf 1988). Olsonand Knopf(1988) revealed that small mam-

mal communities in riparian and uplandareas decrease in similarity at higher eleva-tions, largely owing to increased use ofriparian areas by shrews. In contrast, Knopf(1985) concluded that conservation effortsshould be focused at both lower and upperelevational extremes of a watershed wherehe found that the between-community (beta)diversities of riparian and upland avifaunasof Colorado were greatest.

As much as 100,000 ha of riparian lands arelost annually in the United States (McCor-mick 1978). Damage to riparian ecosys-tems and reductions in biotic diversity haveresulted from livestock overgrazing (Ames1977, Crouch 1978, Boldt et al. 1978, Duff1979), agricultural conversion (Hehnke andStone 1978, Conine et a1. 1978), uplandand floodplain timber-harvesting (Beidle-man 1978, Borden 1978, Cross 1985), nat-uralization of exotic plants (Knopf andOlson 1984, Olson and Knopf 1986), rec-reation (Aitchison 1977, Thomas et al.1979), oil and gas development (Girardand Stotts 1985), sand and gravel mining(Graul and Bissel 1978), water use man-agement (Tubbs 1980), and other humanpractices (Johnson et ai. 1985). In someriparian ecosystems, natural events likeflooding can also affect species composi-tion, abundances, and habitat selection ofground-using vertebrates (Knopf and Sedg-wick 1988, Olson and Knopf 1988). Ripar-ian habitats can deteriorate more rapidlyand more extensively than surrounding ar-eas, and the damage can have far-reachingeffects. As riparian restoration is expen-sive, complex, and time-consuming, landmanagers should take considerable care inplanning and executing management strat-egies (Behnke and Raleigh 1978, Tubbs1980, Knopf et al. 1988).

Green Ash Woodlands

Although green ash and other deciduouswoodlands comprise less than 1% of thenorthern Great Plains (Bjugstad and Sorg1984), they offer valuable cover, forage,and habitat diversity to wildlife, particular-ly because of their floristic and structuralcomposition, limited distribution, and is-land-like dispersion (Boldt et a!. 1978,Faanes 1984). Green ash woodlands arecritical breeding habitats for raptors and

songbirds in North Dakota (Gaines andKohn 1982; Faanes 1983, 1984) and areimportant areas for birds, small mammals,mule deer, and white-tailed deer through-out the Great Plains (Severson and Carter1978, Uresk 1982, Petersen 1984, Hodorffet al. 1988). In winter, green ash woodlandscontain abundant browse and shelter fordeer (Swenson et a1. 1983). Deer, turkey,furbearers, and firewood contribute to thehigh economic value of ash-wooded drawsin the northern High Plains (Bjugstad andSorg 1984,1987).

Bird species richness in green ash wood-lands increases with woodland size (Hop-kins 1980, Fleckenstein 1981). Hopkins etal. (1986) found that, in comparison toconiferous woodlands, ash woodlands sup-ported higher bird abundances; higher den-sities of ground foragers, ground nesters,and shrub-sapling nesters; more bird spe-cies and more foraging guilds; and highernumbers of bark foragers and canopy for-agers. Compared to open, nonregeneratinggroves of green ash, closed ash woodlandswere reported to have higher densities offive mammal species and ten bird species,as well as nearly twice as many birds intotal (Hodorff et al. 1988). Greater abun-dance of animals in closed, regeneratingwoodlands was related to increased verti-callayering of shrubs and saplings (Hodor-fTet al. 1988).

Lack of regeneration is a major problem ingreen ash woodlands (Boldt et a!. 1978).Grass-forb communities are replacingwoodlands in many areas of the northernGreat Plains (Boldt et al. 1978). Forestswith multiple layers of shrubs reproducenaturally, but open woodlands fail to regen-erate (Hodorff et al. 1988). Heavy livestockgrazing is probably most responsible forthe decline of green ash woodlands, thoughinsect and disease damage, fire suppres-sion, and drought may contribute to wood-land deterioration (Severson and Boldt1978, Bjugstad Sind Girard 1984). Wood-land restoration strategies have involvedfencing to exclude cattle, felling of low-vigor trees, and transplanting of nurserystock (Boldt et al. 1978),

Volume 13 (3), 1993 Natural Areas Journal 193

Aspen Forests

Geographic variation in the aspen ecosys-tem and structural and floristic variationam;ng clones, understories, elevations, andseral stages, produces a wide variety ofaspen habitats for wildlife. DeByle (1985)listed 135 bird species and 55 mammalspecies associated with aspen forests ofwestern North America. Aspen groves areoften the primary source of ample forage inwestern coniferous forests and the onlysource of wildlife coverin grasslands (Gul-lion 1977). Elk and moose select aspenover several other available habitats, anddeer favor aspen as a browse species (De-Byle 1985). In many areas, beaver dependsolely on aspen for food and dam construc-tion. Aspen is heavily used by ruffed grousefor food, cover, and nesting in areas of theWest where aspen and grouse ranges over-lap (Phillips 1967, Rusch and Keith 1971).

Aspen forests often have higher densitiesand diversities of birds than are found inother plant communities (Salt 1957, Win-ternitz 1980, Finch and Reynolds 1989). Ina study in northeastern Wyoming, bird bio-mass was at least three times higher inaspen forests than in five other vegetationtypes (Salt 1957). Insect density and diver-sity are about twice as high in aspen com-pared to conifer forests (Schimp: and M~c-Mahon 1985), which may explain the highbiomass and abundance of avian insecti-vores in aspen. In comparing bird commu-nities among aspen sites, Flack (1976) foundthat bird species diversity increased withincreased plant community layering, largertree diameters, and reduced tree densities.The presence of aspen in conifer standsincreases bird species richness (Scott andCrouch 1988a,b), but Joss of aspen due toconifer succession results in populationdeclines and loss of aspen-associated birds(Finch and Reynolds 1989).

About 34 hole-nesting bird species useaspen cavities (DeByle 1985), comprisingas much as 60% of the birds in pure aspenstands (Winternitz 1980). One cavity-nest-ing species, the purple martin, has a limiteddistribution in U.S. Forest Service Region2 (Finch 1992); natural nest sites have onlybeen found in local, disjunct aspen forestsin south-central Colorado (Finch 1992).

Scientific Name

Table 1. Common and scientific names of animal species.

Common Name

AMPHIBIANSRocky Mountain wood frogWyoming toad

REPTILESDesert striped whipsnakeEastern collared lizardLong-nosed leopard lizardMesa Verde night snakeMidget faded rattlesnakeMountain short-horned lizardTexas horned lizardYellow-headed collared lizard

BIRDSAmerican white pelicanBald eagleBarn owlBell's vireoBlack railBrown-headed cowbirdBrown pelicanColumbian sharp-tailed grouse

Eskimo curlewFlammulated owlGray vireoLeast ternLewis' woodpeckerLong-billed curlewLong-eared owlMexican spotted owlNorthern goshawkOspreyPiping ploverPurple martinPygmy nuthatchSandhill craneSnowy ploverWestern bluebirdWestern grebeWhite-breasted nuthatchWhite-faced ibisWhooping crane

Because cavity nesters prefer mature, liveaspens infested with decay fungi for feed-ingand nesting (Crockett and Hadow 1975,Winternitz and Cahn 1983), they may beparticularly sensitive to clear-cutting and

Rana sylvaticaBufo hemiophrys baxteri

Masticophis taeniatusCrotaphytus collaris collarisGambelia wislizeniiHypsiglena torguata lorealaCrotalus viridis con cotorPhrynosoma douglassiiPhrynosoma cornutumCrotaphytus collaris auriceps

Pelecanus erythrorhynchosHaliaeetus /eucocephalusTyto albaVireo belliiLarteral/us janiaicensisMolothrus aterPelecanus occidentalisTympanuchus phasianellus

columbian usNumenius borealisOtus flamnteolusVireo viciniorSterna antillarumMe/anerpes lewisNunienius american usAsio otusStrix occidentalis lucidaAccipiter gentilisPandion haliaetusCharadrius melodusProgne subisSitta pygmaeaGrus canadensisCharadrius alexandrinusSialia niexicanaAechmophorus occidentalisSitta carolinensisPlegadis chihiGrus aniericana

fragmentation of mature or so-called deca-dent aspen forests. As the standing lives ofaspen snags and sun-scalded trees left inclear-cuts are short (DeByle and Winokur1985), retention of snags and live trees

19.t Natural Areas Journal Volume 13 (3), 1993

Table 1, Continued

Common Name Scientific Name

MAMMALSAbert's squirrelApache pocket mouseBeaverBushy-tailed woodratCliff chipmunkDesert woodratEastern moleElkHog-nosed skunk --Kit foxMeadow jumping mouseMinkMooseMule deerMuskratRaccoonRed batRingtailRiver otterShort-tailed shrewVirginia oppossumWhite-footed mouseWhite-tailed antelope squirrelWhite-tailed deerYuma myotis

Sciurus abertiPerognathus apacheCastor canadensisNeotoma cinereaEutamias dorsalisNeotoma lepidaSealopus aquaticusCervus elephusConepatus mesoleucusVulpes macrotisZapus hudson iusMustela visonAlees aleesOdocoileus hemionusOndatra zibethicusProcyon lotorLasiurus borealisBassarisdus astutusLutra canadensisBlarina brevicaudaDidelphis marsupalisPeromyscus leucopusAmmospermophilus leucurusOdocoileus virginianus 'Myotis yumanensis

does not solve the cavity nest shortage incutover aspen. Species that use large, intactforests of mature aspen - for example,hawks, owls, and woodpeckers - are like-ly to be adversely affected by clear-cutting,while birds that prefer early successionalstages of aspen should increase in abun-dance once regeneration is established(Scott and Crouch 1988c). Overgrazingand fire suppression can result in ecosys-tem deterioration, lack of regeneration,conifer succession, and ultimate loss ofaspen forests (DeBy\e and Winokur 1985).

Pinyon-Juniper Woodlands

Hoover and Wills (1984) listed more mam-mal species (62) in pinyon-juniper wood-lands than in other forest types of Colorado(Table 2). Several rare arid-land mammalsof Colorado, including Yuma myotis, cliffchipmunk, white-tailed antelope squirrel,

Apache pocket mouse, desert woodrat, kitfox, ringtail, and hog-nosed skunk are vir-tually absent from forests other than pin-yon-juniper (BisseI1978). Colorado's pin-yon-juniper woodlands are second only tocottonwood riparian woodlands in num-bers of species of amphibians (10) andreptiles (23, Hoover and Wills 1984). Pin-yon-juniper provides habitat for easternand yellow-headed collared lizards, long-nosed leopard lizard, mountain short-horned lizard, Mesa Verde night snake,desert striped whipsnake, and midget fad-ed rattlesnake (Smith et al. 1965, Langlois1978, Hoover and Wills 1984), uncommonspecies more typically associated withdesert and shrublands in other regions.Three candidate species or subspecies (Cat-egory 2) for federal listing as endangeredor threatened by the Office of EndangeredSpecies - Texas horned lizard, hog-nosedskunk, and Columbian sharp-tailed grouse

- occur in pinyon-juniper woodlands. Inaddition, at least 107 bird species use var-ious seral stages of pinyon-juniper for sur-vival and breeding (Table 2; Hoover andWills 1984).

Vertebrate assemblages in Colorado pin-yon-juniper are more similar in speciescomposition to the specialized faunas asso-ciated with cottonwood riparian, pondero-sa pine, and Gamble oak community typesthan to those found in subalpine spruce-fir,Douglas-fir, lodgepole pine, aspen, andhigh-elevation riparian communities(Raphael 1987). In areas with high densi-ties of pinyon pine, cavity nesters comprisealmost half of the breeding bird species(Hering 1957, Masters 1979). In a pinyon-juniper-ponderosa pine ecotone, foliage-feeding birds selected pinyon pine moreoften than predicted by chance (Lauden-slayer and Balda 1976). Thus, bird commu-nities are likely to be seriously impacted byselective removal of pinyon pine (Baldaand Masters 1980). Some foliage-nestingbirds apparently prefer junipers over pin-yons (Hardy 1945, Short and McCulloch1977). Wintering birds depend heavily onjuniper berry crops, and winter speciesdiversity is strongly correlated with berryproduction (Balda and Masters 1980).

In the Badlands of South Dakota, juniperwoodlands harbor 22 bird species not foundin adjacent grasslands (Sieg and Uresk1986) and provide specialized habitat fortwo mammal species - white-footedmouse and bushy-tailed woodrat (Sieg1988). Isolated juniper woodlands mayserve as dispersal sites for woodland mam-mals in the northern Great Plains (Sieg1988). In the High Plains ecoysterns ofSouth Dakota, steep juniper slopes are high-ly important habitats for mule deer (Sever-son and Carter 1978, Severson.l 981) andlong-eared owls (Paulson and Sieg 1984).

Livestock grazing, oil and gas develop-ment, fire suppression, firewood gather-ing, and urban encroachment can reducethe importance of pinyon-juniper wood-lands for wildlife (Uresk 1982, Bjugstadand Girard 1984, Wills 1984, Girard andStotts 1985). Pinyon-juniper woodlandstraditionally have been undervalued be-cause they produce less forage for live-

Volume 13 (3), 1993 Natural Areas Journal19S

stock than grasslands and because the treeshave low commercial value relative to oth-er harvestable trees (Arnold et a1. 1964,Terrel and Spillett 1975). Management ofpinyon-juniper woodlands has largely con-sisted of eradication and type-conversioninto grazing lands (Arnold et a1. 1964,Terrel and Spillett 1975). Because the pin-yon-juniper type is valuable to wildlife andhas a limited distribution in the RockyMountains and northern Great Plains, itshould receive special conservation efforts.

Pure and Mixed Forests of PonderosaPine

The ponderosa pine type offers a broadrange of natural communities for biodiver-sity. First, it has the widest distribution ofany pine forest in North America. Further-more, plant associations encompass savan-nas, mixed broadleaf-conifer forest, mixedconifer forests, and pure yelIow pine for-ests; and local size naturally varies fromsmall, disjunct forest islands to extensive,contiguous forests. FinalIy, timber produc-tion is secondary to noncommercial values(Diem and Zeveloff 1980). Vertebrate fau-nas in ponderosa pine forests differ greatlyin species composition from the sharedcommunities associated with spruce-fir,lodgepole pine, and Douglas-fir forests ofColorado (Raphael 1987). At least 57 mam-mal species use ponderosa pine forests inColorado (Table 2; Hoover and Wills 1984),including rare species like Mexican voleand fringed myotis (Bissell 1978). Abert'ssquirrel is dependent on later seral stages ofponderosa pine forests (Keith 1965, Pattonand Green 1970).

From 113 to 128 bird species reside inponderosa pine forests (Diem and Zeveloff1980, Hoover and Wills 1984). Hoover andWills (1984) identified 7 bird species (6%of 128) that used only mature to old-growthforests of ponderosa pine and 28 bird spe-cies (22 %) that used mid- to late-succes-sional stages (Table 2). Diem and Zeveloff(1980) estimated that 22% of the bird spe-cies in yellow pine forests had decliningpopulations. Barn owl, flammulated owl,spotted owl, Lewis' woodpecker, white-breasted nuthatch, pygmy nuthatch, andwestern bluebird may be especially sensi-tive to timber management practices in

ponderosa pine habitats because of theirdependencies on late seral stages, specificplant communities, and cavity-nest sites(Diem and Zeveloff 1980, Reynolds et a1.1989, Finch 1992). Northern goshawk, anopen-nesting species that requires largeareas of mature forest for breeding, may benegatively affected by harvesting of oldgrowth (Reynolds 1989). The Mexican spot-ted owl, a species whose range barely in-trudes into southern Colorado, was feder-ally listed as a threatened species in 1993.Flammulated owl and northern goshawkare included on the Vertebrate SensitiveSpecies List issued by U.S. Forest ServiceIntermountain Region (Region 4, Spahr eta1. 1991).

Overharvest of old growth, forest fragmen-tation, structural simplification of clear-cut stands, fire suppression, and snag re-moval can reduce the value of ponderosapine forests to wildlife (BulI 1978; SzaroandBalda 1979a, 1979b; Diem and Zeveloff1980). Quality of Abert's squirrel habitat islikely to be negatively impacted by forestfragmentation and reduction of stand het-erogeneity due to commercial logging(States et a1. 1988). Fragmentation or lossof old growth may cause further rangerestrictions in the Mexican spotted owl(Ganey 1988) similar to the pattern detect-ed in the northern race (Forsman andMeslow 1986, Dawson et al. 1987).

LANDSCAPES, SUCCESSION, ANDCONSERVATION

All the natural communities discussed aboveexist in some context, that is, they aresurrounded by dissimilar vegetation andoccur in variable physiographic conditions.Any specific community type together withits context subsumes a broader geographi-cal area and a broader ecological context orscale than the habitat per se. Punctuated bypatterns of habitat patches, this broaderarea can be thought of as a landscape.Landscapes, in turn, can be ordered by theirgeographic scope, natural resource values,and patterns ofland use into various hierar-chical schemes that are of potential interestto researchers and managers. Most conser-vation issues on state and federal lands areultimately addressed at ecosystem, water-shed, or regional levels of landscape orga-

nization because it is at these higher levelsof spatial resolution that multiple uses,land management approaches, and socio-economic factors interact to affect biolog-ical diversity.

Still, land management activities modifyplant communities at all ecological levels.Compositional and structural features ofhomogeneous communities (e.g., forestsor specific rangeland communities) aremodified by management, including man-agement adapted to industrial land use.Similarly, overall patterns of vegetationabundance within landscapes are modi-fied; kinds, amounts, and arrangements ofvegetation communities are altered. And aslandscape- level vegetation mosaics change,so too does wildlife species compositionwithin communities and ecosystems. Mostimportantly, management-induced chang-es usually simplify structural and composi-tional complexity at all levels of ecologicalorganization. An exception is the creationof complex edge areas by logging or fire,but the addition of edge often results inpopulation increases of undesirable wild-life species (e.g., predators, brown-headedcowbirds, competitors) that interfere withsurvival and reproductive success of birdspecies that depend on large intact blocksof an ecosystem or plant community (Finchand Stangel 1993).

Most commodity-oriented vegetation man-agement practices truncate (i.e., shortenthe duration of) vegetative succession. Ac-cordingly, the natural process of vegetationdevelopment is disrupted. In general, natu-ral succession results in vegetation com-munities of increasing complexity as thedevelopmental sere progresses from youngto old (Margalef 1968, Kormandy 1969,Odum 1969, Krebs 1985, Franklin 1988).It follows that management activities thatcurtail succession tend to simplify struc-ture and composition, relative to that whichwould be expected in the late stages ofcommunity development, potentially re-ducing animal species diversity. Hunter(1990) presents an extended discussion anddocumentation of the importance of suchcomplexity (e.g., vertical habitat structure)in maintaining animal diversity in man-aged forests. The reduction of ecologicalcomplexity occurs at multiple ecological

196 Natural Areas Journal Volume 13 (3), 1993

scales via a reduction of the structural andcompositional complexity within plantcommunities and a reduction in the amountof late-successional vegetation in the land-scape. In addition, the context within whichremaining late-successional vegetation ex-ists (i.e., the pattern of older and youngervegetation) is considerably different thanwould be expected under natural condi-tions. All these factors can be expected toinfluence the patterns of abundance of an-imals that are adapted to interior forestconditions or to the conditions oflate-seralforest or rangeland vegetation. In general,populations of such species will becomeless abundant and the species' distribu-tions will become more limited.

Reductions in the populations of late-suc-cessional animals lead to concerns aboutthe maintenance of viable populations and,ultimately, to concerns about species con-servation. Because forest management of-ten results in an abundance of early succes-

sional vegetation, most wildlife conserva-tion issues will revolve around the kinds,amounts, and arrangements oflate-succes-sional forests in managed landscapes. Thus,any discussion of important wildlife habi-tats must consider the late-successionalstages of plant communities and their rela-tionships to native wildlife populations.

LATE-SUCCESSIONAL HABITATS

Table 2 shows the relationship betweenbird and mammal species richness and thestages of development for eight importantRocky Mountain vegetation types (basedon Hoover and Wills 1984). Total numbersof species associated with these types rangefrom 76 to 177 for birds and from 38 to 62for mammals (means of 107 and 47, re-spectively). As a measure of the variabilityin the numbers of species associated witheach type, the coefficient of variation (CV)for birds is 0.30 and for mammals 0.22. Incontrast, when considering only the num-

bers of species associated with the late-successional stage of each type, we findthat the totals range from 5 to 7 for birdsand from 0 to 4 for mammals. Also for late-successional stages for each type, the meanand CV for birds is 5.8 and 0.12, respec-tively, and for mammals 2.1 and 0.59, re-spectively. These statistics, and a visualexamination of the distribution of speciesfrom Table 2, reveal that the numbers ofbird species associated with late-seral veg-etation are significantly less variable thanare the numbers of bird species associatedwith all developmental stages.

This same pattern is found when birds andmammals are combined; the CV for thenumbers of species associated with late-successional vegetation is 0.14 comparedto a CV of 0.26 for the numbers of speciesassociated with all successional stages (Ta-ble 2). Thus there is relatively low among-habitat variation in the numbers of speciesassociated with the late-successional stag-

Table 2. Numbers of bird and mammal species in vegetation types of the Rocky Mountains and Northern Great Plains (after Hoover and Wills 1984).·SF: Subalpine spruce/fir, DF: Douglas-fir, pp: Ponderosa pine, Lp: Lodgepole pine, A: Aspen, PJ: Pinyon-juniper, HER: High elevation riparian,RC : Riparian cottonwood.

SF DF PP LP A PJ HER RC MEAN S.D. CV

BIRDSAll Seral Stages 76 93 128 86 95 107 94 177 107.0 32.19 0.30

Mid and/or Late Seral Stages 22 23 28 24 19 16 17 28 22.1 4.58 0.21

Late Seral Stages Only 6 5 7 6 6 5 5 6 5.8 0.71 0.12

MAMMALSAll Seral Stages 38 41 57 41 39 62 40 59 47.1 10.25 0.22

Mid and/or Late Seral Stages 6 7 6 7 5 7 4 4 5.8 1.28 0.22

Late Seral Stages Only 3 2 3 2 4 2 0 2.1 1.25 0.59

BIRDSANDMAMMALS

All SeraI Stages 114 134 185 127 134 169 134 236 154.1 40A2 0.26

Late Seral Stages Only 7 8 9 9 8 9 7 6 7.9 l.l3 0.14

"Habitat association of American marten was changed from all seral stages to late-sera I stages for SF, DF, and LP.

Volume 13 (3), 1993 Natural Areas Journal 197

es of these communities. Although there isconsiderable difference among communi-ties with regard to their importance j~ pro-viding for overall species richness, It ap-pears that these communities are of rou~h-ly equal importance with regard to meetmgthe habitat needs of birds and mammalsthat are associated with late-successionalvegetation. The only exception to this. maybe for mammals in the late-successionalcottonwood-riparian type. In general,though it follows that the late stages ofdevelo~ment for the communities underconsideration are all especially importantin maintaining regional wildlife diversity.Managers should place special con~erva-tion emphasis on these areas when biolog-ical diversity is one of their objectives.

KEY HABITATS

The spruce-fir, lodgepole pine, and Dou-glas-fir forest habitat types generally maynot support vertebrate assemblages tha~~reas rich as those of some other comrnurunes(e.g., wetlands, riparian cottonwood, orponderosa pine). However, even t~,o~ghriparian cottonwood (RC) areas (the rich-est" community type considered here) hasfour times the number of species associat-ed with it as are associated with spruce-fir(SF), lodgepole pine (LP), and Douglas-f!r(DF), each of these latter fores~ communi-ties supports more late-successional mam-mals than does RC. And SF and LP supportthe same number of late-successional birdspecies that RC does. Considering that SF,LP and DF are among the most widespreadforest types in the western United States(Eyre 1980), their late-successio~al s~a?esare especially important in mamta.Jt1mgregional biological diversity. AccordJt1g.ly,care should be taken to not unnecessarilyfragment existing areas of late-succession-al forest in any of these types. When man-agement is necessary, prescriptions shouldbe applied that minimize the loss ofecolog-ical complexity at both local and lan?scap.escales. To maintain regional biological di-versity across multiple successi.onal stagesand still recover sensitive species that usecritical natural communities, we recom-mend that adaptive management approach-es, like the U.S. Forest Service's "ecosys-.ern management" strategy, be adopted.

ECOSYSTEM MANAGEMENTAPPROACH

For socioeconomic, recreational, and leg-islative reasons, management strategies forsingle species have traditionally taken pre-cedence over management for multiplespecies. Single species are highlighted infederal and state management plans wheno populations of a species need to be re-

covered, in accordance with the Endan-gered Species Act,

o a species has high commerical value (e.g.,waterfowl, big game),

o a species has high recreational or aes-thetic value (e.g., large species like rap-tors and cranes),

o a species is a keystone or critical linkspecies (e.g., woodpeckers ~hat sup~lyhomes for secondary cavity-nestingbirds), and

o a species is an indicator of env!ro~me~-tal problems (e.g., eggshell thinning Jt1waterbirds and raptors indicates the pres-ence of contaminants in the local envi-ronment).

The conservation of biological diversityinvolves keeping common species com-mon (Finch and Stangel 1993) while simul-taneously maintaining or recovering popu-lations of rare or jeopardized species. Tomove beyond traditional single-speciesmethods for managing ecosystems, re-searchers and land managers must expandtheir vision and recognize broader scales ofinteraction, thus accounting for naturalcomplexity, population changes, ~ommu-nity succession, temporal and spatial land-scape dynamics, and shifting pattern~ ofland use. A model program that providesguidance for research, mon.ito:ing, andmanagement of multiple species ~sth~ ne:conservation program, "Partners In Flight."Partners in Flight" is a cooperative, inter-national program to conserve neotropicalmigratory birds, particularly. migr~torysongbird species whose collective regionalpopulations have experienced long-termdeclines (Finch 1991, Finch and Stangel1993).

Biological diversity conservationmu~t fac-tor in the human dimension early In themanagement planning stages. This wi~1as-sure that socioeconomic concerns Gobs,

markets), political issues, environmentalvalues, and multiple uses oflands are inte-grated into plans for biological diversityconservation. To synthesize human con-cerns, single-species needs, and biologi~aJdiversity goals, large-scale cooperativestrategies like the new ecosystem manage-ment approach advocated by the U.S.For-est. Service (Overbay 1992) need to beadopted. Ecosystem management is theuse of an ecological approach to managemultiple uses of national forests and grass-lands; it IS achieved by blending the needsof people and environmental values in sucha way that national forests and grasslandsrepresent diverse, resilient, productive, andsustainable ecosystems. We believe that theecosystem management strategy, if imple-mented as proposed by the Forest Service,can straddle the necessary geography, tem-poral scales, biotic and abiotic intercon-nections, species dependency patterns,monitoring needs, and scientific disciplinesto effectively conserve biological diversity,including the maintenance of viable popu-lations of rare, common, and human-val-ued species (Finch et al. 1993). Ecosystemmanagement is adaptive management. Itrequires that researchers and managers,industry and environmentalists, work asteams to develop suitable techniques and.plans for sustaining commercial and non-commercial natural resources within con-stantly changing environments.

To shift from a single-use, single-speciesapproach to an ecosystem-level, multiple-species approach, we recommend .th~t spe-cies of concern be evaluated within thecontext of regional and global species rich-ness and abundance, and that regional goalsfor species composition be managed at theecosystem level. If needs of threatened orendangered species are ignored, however,these will be the first species to drop out ofecosystems. Their loss will result in thereduction of overall species richness at anyparticular spatial scale. Therefore, they canbe thought of as the weakest link in biol~g-ical diversity conservation. To ensure main-tenance of regional biological diversity, thefollowing steps can be taken by agenciesand their cooperators:

J. Using existing research knowledge, pri-oritize species of concern, i.e., the weak-

198 Natural Areas Journal Volume 13 (3), 1993

est links of biological diversity, using anobjective standardized procedure thataccounts for global species rarity, popu-lation trends over time, demographic pat-terns, rates of habitat loss, and effects ofcurrent management (e.g., Hunter et al.1993).

2. Weigh species of current concern along-side those that may become of concern inthe future if management practices arechanged to favor current high priorityspecies (Finch et al. 1993).

3. Adjust final values to ensure that region-al and global biological diversity, as in-dexed by species richness and composi-tion, does not decline.

4. Determine what future environmentalconditions are necessary to sustain pop-ulations of multiple current and futurespecies of concern, reasoning that thesefuture conditions will favor overall bio-logical diversity.

5. Develop goals and guidelines that inte-grate management of these desired con-ditions with other resource values, in-cluding recreational and socioeconomicvalues. This involves the development ofan interdisciplinary team that includesboth researchers and managers.

6. Establish management direction that isadaptive to shifts in priorities and suc-cessional patterns, managing for a dy-namic ecosystem and allowing for popu-lation changes, critical habitats, old-growth forests, and a full and naturalvariety of successional habitats.

7. Involve all those who affect, manage, orvalue ecosystems early in the planningprocess.

Once the system components, weakest links,and management directions are defined,demonstration projects can be established.We recommend that natural areas be usedto establish model demonstration projects,and that managers of natural areas take anactive interest in sustaining biological di-versity and ecosystem integrity.

ACKNOWLEDGMENTS

We thank members of the BiodiversityAssessment Team for Region 2 of the U.S.Forest Service, especially Dick Linden-muth and Larry Mullen, for guidance onassessing habitat and wildlife needs in theRocky Mountain Region. We thank LarryMullen and Erin O'Doherty formanuscriptreview, Robin Byars for table preparation,and Lori Kelly and Tracey Parrish for for-mat editing.

Deborah M. Finch is a Research WildlifeBiologist with the U.S.Forest Service, RockyMountain Forest and Range ExperimentStation. She received an MiS. in Zoology

from Arizona State University and a Ph.D.in Zoology and Physiology from the Uni-versity of Wyoming. Her interests includeavian reproductive ecology; bird and mam-mal habitat relationships; community ecol-ogy; threatened, endangered, and sensitivespecies; neotropical migratory birds; andtechnology transfer.

Leonard F. Ruggiero is the Project Leaderof a wildlife habitat relationships unit forthe UiS. Forest Service, Rocky MountainForest and Range Experiment Station inLaramie, Wyoming. He has an MiS. in Wild-life Science from Virginia Polytechnic In-stitute and a Ph.D. in Animal Ecology fromUtah State University. His research inter-ests include the behavioral ecology andwildlife habitat relationships offorest car-nivores and other sensitive species.

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