Our Living Resources — Interior West 



Ml 



fish species are considered vulnerable, 

 including 9 federally listed and 7 li\ing in sky 

 island drainages (Table 3). Within this national 

 forest, there are 1 1 amphibians whose popula- 

 tion viability is of concern, though none is on 

 the federal list; 8 dwell in the valleys or lower 

 drainages of the sky islands. They are sensitive 

 to upstream watershed alterations. Fourteen sky 

 island reptiles are considered sensitive but not 

 federally listed. There are about 55 bird species 

 of concern. 5 federally listed, and about 20 

 whose population viability is of significant con- 

 cern (Table 3). About 30 mammals are of con- 

 cern, 4 federally listed. The grizzly bear, jaguar, 

 ocelot. Tarahumara frog, and gray wolf have 

 been extirpated from the sky island archipelago. 

 Not counting the extirpated species and the 1 1 

 bats of concern, there are 1 3 mammal species 

 and subspecies dwelling on the sky islands that 

 have low populations of concern (Table 3). 



Distribution 



Some of the most interesting aspects of sky 

 island ecosystems and history are why some 

 mountains lack a particular species ("holes"), 

 why some species skip mountain ranges or 

 appear as an exception in an otherwise species- 

 poor flora or fauna ("outliers"), and why some 

 species, even mobile animals such as birds, end 

 their distribution on a particular sky island 

 (Warshall 1986). For example, why are there no 

 chipmunks on the Huachucas? Why does the 

 Mexican chickadee i Pants scUiteri) stop on the 

 Chiricahuas. but only 35 mi away the mountain 

 chickadee {P. gambeli) inhabits the Pinalenos? 

 Why are there no voles on the Catalinas? 



Colonization of the sky islands by exotic 

 species is increasing with over 60 non-native 

 plants having established regenerative popula- 

 tions in the Arizona sky islands. Major issues 

 include limiting introductions of buffel grass 

 (Penuisetwu cilaris) and exotic lovegrasses 

 (Eragrostis spp.) by the U.S. Department of 

 Agriculture, as well as controlling and restoring 

 habitats swamped by exotic forbs such as 

 Euryops mithifida on the Pinalenos and 

 Catalinas. Fifteen non-native fish species have 

 been added to the five or six native freshwater 

 fish families, with consequent hybridization, 

 predation. and competition throughout springs 

 and drainages. The Central Arizona Project has 

 become a new corridor for exotic fish, some of 

 which are invading the last strongholds of 

 natives. 



Three feral exotic mammals may have colo- 

 nized the sky island complex. The opossum 

 (Didelphis spp.) colonization is believed to be a 

 mix of released Virginia opposum (D. virgini- 

 mui and range-expanding Mexican opossum {D. 

 marsiipialis). It has been reported but not con- 

 firmed that the European ferret (Mitstela piito- 



rlits) has become feral in the Huachucas. Over 

 the last 50 years, about 12 birds and mammals 

 of southern origin have been recorded coloniz- 

 ing more northern sky islands. No animal 

 species is known to have retreated south except 

 the extiipated jaguar, ocelot, and thick-billed 

 paiTot. A few species such as the Abert's squir- 

 rel iSciuris aberti) have been introduced for 

 hunting and have then expanded their range. 

 The monitoring of these changes will be an 

 important barometer to how habitat changes, 

 species introductions, and climate interact with 

 ecosystem management practices. 



Vertical Migration 



Each sky island has a unique ecosystem with 

 a stack of life zones ranging from arid to boreal 

 (Fig. 2). Many species migrate vertically to feed 

 and breed at various elevations. The Pinalenos 

 contain the most stacked life zones in the short- 

 est vertical distance of any mountain in North 

 America. By traversing five biotic communities 

 in a few hours, bears can feed on Opiintia 

 (prickly pear cactus) fruit in the morning and 

 grass roots growing in semi-alpine meadows in 

 the afternoon. Assuring minimal viable habitat 

 size and the appropriate forest age-class struc- 

 ture to support animal populations with vertical 

 migration is an unstudied aspect of forest 

 ecosystem management. 



In addition, various biotic communities are 

 remnants of colder climates with small relict 

 acreage. For instance, only about 243 ha (600 

 acres) of spruce-fir (Picea engelimiimii-Abies 

 lasiocarpa) forest are left within the sky island 

 complex. This forest type, found only on the 

 Pinalenos, is critical habitat for the endemic and 

 federally listed endangered Mt. Graham red 

 squiiTcl, which also inhabits the transition to 

 mixed conifer forests (Douglas fir- white fir; 

 Pseiidotsuga menziesii-Abies ctmcolor) at lower 

 elevations. These two plant associations, heavi- 

 ly logged and cleared, will not become mature 

 enough to supply the minimum viable habitat to 

 ensure the squirrel population's survival for 2 

 centuries. Annual growth rates, seeding rates, 

 and regeneration cycles have become less pre- 

 dictable with the unknown effect of global 

 warming and fire risk, requiring rethinking of 

 the minimum size required for viable habitats. 



Special Habitats 



Special habitats and plant associations (e.g., 

 high-elevation cienagas, limestone outcrops, 

 perennial streams, talus slopes) create islands of 

 habitat within the sky island ecosystem, 

 increasing biological richness. For instance, 

 talus slopes support a series of endemic land 

 snails; the rock cliffs and outcrops support plant 

 species such as the fleabanes Erigeron lem- 

 numii, E. heliographis. and E. pringlei. found 



^1 Coronado d] Kaibab 

 I I Apache-Sitgreav ^H Lincoln, NM 

 H Carson. NM ^| Prescott 

 i I Cibola. NM ■ Santa Fe, NM 

 ^1 Coconino ^1 Tonto 

 Mi Gila, NM 



Threatened, endangered, and sensitive 

 plants in southwestern national forests 

 60 



50 j 

 |4o] 



.30 

 °20J 



^iit 



Threatened, endangered, and sensitive 

 plant species/ 1 0^ acres/ forest 



No. of tfireatened, endangered, and 

 sensitive wildlife species/ 10 acres/ forest 



^ 6 

 oS 5 



Q. 



03 ^ 



«D 3 

 Q. 

 « p 



"o 



d 1 

 ^0 



Threatened, endangered, and sensitive 

 wildlife on southwestern national forests 



SHb 



Fig. 3. Compurison of the 

 Coronado National Forest, which 

 administers all or part of 16 sky 

 islands, with national forests with 

 no sky island flora and fauna. 



