The Madrean Sky Island Archipelago: A PlanetaryOverview PeterWarshaltl Abstract.-Previouswork on biogeographicisolation hAFoncerned itself with oceanicisland chains, islands associated with continents, fringingarchipelagos, and bodiesof watersuch as the Africanlake system which serue as "aquaticislands". This paper reviewsthe "continentalislands" and comparesthem to the Madreansky island archipelago.The geological,hydrological, and climaticcontext for the Afroalpine,Guyana, Paramo, low and high desert of theGreat Basin, etc. archipelagosare comparedfor source areas, number of islands, isolating mechanisms,interactive ecosystems, and evolutionary history. The history of scientificexploration and fieldworkfor the Madrean Archipelagoand its uniquestatus among the planet'sarchipelagos are summarized. In 1957,Joe Marshall published "Birds of the American Prairies Province of Thkhtajan, 1986) Pine-Oak Woodland in Southern Arizona artd Ad- and western biogeographic provinces, a wealth of jacent Mexico." Never surpassed, this elegant genetically unique cultivars in the Sierra Madre monograph described the stacking of biotic com- Occidental, and a myriad of mysteries concerning munities on each island mountain from the the distribution of disjuncts, species "holes," and Mogollon Rim to the Sierra Madre. He defined the species "outliers" on individual mountains (e.g., Madrean archipelago as those island mountains Ramamoorthy, 7993). The northernmost sky is- with a pine'oak woodland.lnl967, Weldon Heald lands are the only place in North America where (1993), from his home in the Chiricahuas, coined vou can climb from the desert to northern Canada the addictive phrase-"sky islands" for these in- in a matter of hours (Warshall, 1986). The sky is- sular mountains of the North American lands pose numerous puzzles about vertical borderlands. Weldon Heald's catch phrase immor- migration strategies used by plants and animals talized |oe Marshall's meticulous observations. both annually and over glacial time periods. Today's conference is the first solely dedicated to These interests in ecology and evolution mix understanding Madrean sky island biology, with the other citizen interests in skiing, grazing, beauty, and needs for rnanagement and conserva- hunting, fishing, escaping the heat, summer tion. I homes, telescopesand radio towers, bird watch- There are about 40 sky islands (fig. 1) between ing, rock-climbing, military practice maneuvers, the Mogollon Rim and the Sierra Madre Occiden- fuelwood cutting, camping, mining, sacred Native tal (Warshall, in press). Mt. Graham on the American values and ceremonies, archaeological Pinaleno mountains is the tallest peak (10,712 sites,as well as preservation of sky island habitat feet), Relief between valleys and peaks ranges for threatened and endangered species.Underpin- from 1250to 6750f.eet (Mclaughlju;.,7992), bui is ning all these interests is the exceptional beauty of typically between 3000 and 5000 feet. The Ma- the sky islands-their layering of peaks in a dusty drean region has exceptional species richnesi, sunset, lines of vibrant ripariart along arid yellow super-species complexes, unusual neoendemics slopes, the contrast of snow and desert, the baf- and archeoendemics, an exceptional mixture of fling complexity of erratic ridge lines, the power species from the Nearctic and Neotropic regions, of files, and the subtle tones of blue-gray lime- important influences fronn the eastern (North stoner,speckled granite, and pastel volcanics. lOfrice ol Md Lands Study,Colege ol Agiculture, lJnivarsityol Ari- zorlg.,845 N. Park,Iucson, ,Z BS71g. 6 luclon o t :g c :;\ a o C ;it coaitarost forall q. cc 9lna-ool roodlott ctd t ( g.'t Oouolct nolcrrr \ f- ancanol L Alca Pt L,{.C, d-; ll 0 ':D/..:"..i' jt" o :9 t fro!alond o c o data r I Ingr al ."J 'li ' ""tf ilr.. rrL.. .! Arttoa 3 c 6 (' I a t a a a 3 ! .a la \: fi a loclarr0c 9Olrl.! a te ).- Flgun 1.-Thc lltdreen Sky ldrnd lrchlpclego (b...d on llrrrhall' l95f). 7 WHATARE SI(Y ISTANDS? SI(Y ISI.ANDSOF THE PI-ANET Sky islands are a type of continerrtal or inland There are about twenty sky island complexes terrain made up of a sequence of valleys and on the planet (table 1 and fig. 3). Atl the conti- mountains. All skv islands have a stack of biotic nents with, perhaps, the exception of Australia, communities that illo* vertical (as well as aspect) harbor sky island complexes. The information on migration arurually or during one of the planet's the sky island complexes of Eurasia, China, and long-term climatic events. The valleys act as barri southeast Asia remains incomplete becauseof the ers or bridges to the colonization by new species difficulty of obtaining English translations (Sus- that attempt to cross the intervening valley. The lov,1967; Aiken, t992). Most of the literature has vallevs become barriers when thev contain an focused on the mourrtains themselves, not the im- ecology alien to the migrating specie's.By analogy portance of the valleys between them. There has with the saltwater seas betweert oceanic islands, been remarkably lithe work comparing the the higher elevation biotic commurrities of sky is- planefs continental island ecosystems (Carlquist, land mountains are isolated by each valley's "sea" 1963), their palaeogeographic history, floristic and of alien vegetation. The mountains, like the Gala- faunal source areas,and vallev barriers. patos or other oceanic islands, act as isolated By creating a parallel typology with recent cradles of evolution. classifications of oceanic islands such as isolated In the Madrean archipelago, the valleys and island "chains" (Hawaii), "continent associates" motrntains are roughly parallel. The stacked biotic (Madagascar,Philippines), and "f ringing archipel- communities (fig. 2) include: montane coniferous agos" (the southern japanese or Sea of Cortez forests; oak-pine (coniferous) woodlartds; tropical island groups), we can approximate a classifica- deciduous forest; oak savanna (deciduous vs. ev- tion for the continental islands. Thble 1 classifies ergreen oaks predominate); short-grass prairie; continental island clusters on the basis of their subtropical thornscrub; and subtropical desert geographic axis, ladtude, whether they are coastal (Brown, 7982). The "heart" of the Madrean archi- or inland, the number per complex, and the con- pelago (its defining characteristic) is the oak-pine figuration of each grouping. Configurations woodlands (Marshall,795n. The barrier "seas" in- include: stepping stone archipelagos (mountains clude the short-grass prairie, the subtropical and valleys spaced between two cordilleras), iso- thomscrub, and subtropical desert. lated massif(s) with outlier sky islands, linear ioitr <-- SOUrH->> alcaa a.ltl.Id 6a ltti ropoo _- at'.r at,aa aa.aard :- ..*.r.. ... ttaiaarara. ra.rtat,. I,OOO - a,ooo- Jsrt.rrr t.-- WHITg PIIIALENO ltuAcHUcA llcr alt ana t.arr OPOSURA ft.'... .t!.-.n'. Flgule 2.-Ex.mple "ttrcklng" of Dlotlc communlderof thc lledrern rrchlpelrgo (llffrhrtl, 1957). Note the podtlon ot thc ork-plne woodlrndr. chainsof outlier mountains/valleys at one end of Table1.-Sky lsland Tvoer a cordillera, and completely isolated groups of rVpe Examples mountains. A surprisi^gly large number of com- Steppingstone archipelago Madreanarchipelago plexes (e.g., the Adamoua, Baja Peninsula, and between two mountainchains Great Basin archipelago arc) contain both oceanicislands and Altai/TienShan Basin East African Meso-Americanmassifs sky islands with both saltwater and vegetative "seas." Like all typologies, there are ambiguously lsolated massif with oulliers Ethiopianhighlands East African arc categorizedgroupings. Saharan massifs Atlas Mountains Jabal Lubnan Adoumoua Mountains PlanetaryExamples Drakenbergs Central European massifE The four descriptive variables used to classify Caucaso-lranianmaasile sky islands act in ioncert. Compare the Madrean Cordillerawith outliers Chaine Annimatique (Vletnam) stepping stone configuration with the isolated ar- Malay peninsula chipelago of the Western Ghats of India (not Baia Galiforniapeninaula Coastal Cordillera(SA) illustrated), the isolated cluster of the Pantepuisof Southern Andes Brazil, Guyana, and Venezuela (fig. 5) and the East African arc and the Ethiopian massif com- lsolatedsky island chains Western Ghats plexes (fig. 6) . The Western Ghats (Manickam, Pantepuig 1992) comprise a north-south cluster of tropical High aliitude sky islands Punas and paramoe (SA) mountains spanning about six degreesof latitude. Himalayas g H t, 1, rffe|Dt It t2 .tl t 1' I I A E T \ I o I I I ? \ I N TF OI I 0 ----.-1.\ -- -'-.u' cariniFli-- - . ANTARCTI Flgure 3.--.Locrdonr of *y lrlrnd complexe. mentlonedIn text on r m.p ot the Florle$cReelmr of thc phnet Only ttc lhdrcrn .]chlpelrgo ltrrddler two; Florlrdc Rcrlmr. (1) llrdreen; (2) Gr.rt B.3ln; (3) Brle Celllomlr (4) ile.o Amerlcen; (5) Cordrl Cordlller|: (€) Prnt pulr: (7) 8ralllrn rhleld; (t) Srhrnn me$l{r; (9) Ehloplrn Hlghlmd.; (1o) E.tt Afrlcrn rlc; (11) Crmcroon Blght; (12) SouthernAfdcrn compler; (13) Weilem chrtr: (14) Ctucro lrenlan mr.rib; (15) Altllmen Snan; (1O)Tnnr-Brlkrl: (17)ChrlneAnnlmrdque; (1S) Malay peninrulr. High valley "lslendf'can be foundIn the nortrernAndcr rnd Himtlayrr. Thev are isolated from the nearest cordillera, the Himalayas, by over 7,200 miles. The Western Ghats ire funtrer isolated to the south and west by the Laccadive Sea. On the north and east, the $ c valley barriers are, at the present, highly human- ^ ized landscapes with pockets of Deccan NOtrlllERtl-