Revista Chilena de Historia Natural 64: 413-446, 1991 Historical development of temperate vegetation in the Americas

Historia de Ia vegetaci6n templada en Norte y Sudamérica

1 DANIEL I. AXELROD , MARY T. KALIN ARROYO² and PETER H. RAVEN3

1 Department of Botany, University of California, Davis, CA 95616, USA; 2 Departamento de Biologia, Universidad de Chile, Casilla 653, Santiago, Chile; 3 Missouri Botanical Garden, P.O. Box 299, St. Louis, MO 63166, USA

ABSTRACT

North American and South American temperate forests developed independently. These initially different forests, con- tinue to be distinct, not only because of their different histories resulting in their domination by different woody plants, but because of the distinctive climatic regimes under which they presently occur. In North America, modern vegetation types, though much richer in taxa, first appeared in the Paleocene-Eocene, when the region north of Colorado supported rich deciduous hardwood forest and lowland conifers. Cold-loving conifers were associated with deciduous hardwoods in lowlands farther north. Pure montane conifer forest and mixed conifer- hardwood forests were present in upland areas in Nevada-Idaho in the Middle and Late Eocene. The first appearence of nearly pure montane conifer forest in the north (e.g. Alaska Range) was in the Miocene. Essentially pure conifer forests in lowland areas in the Arctic region appear in the Pliocene, although similar forest is reported from Iceland earlier (9-7 m.y .a.). Conifer parkland (semi-taiga) was spreading over the lowlands of northern Alaska by the close of the Mioce- ne. Taiga spread widely only in the Pliocene and subsequently. In the Southern Hemisphere, the geological history of Gondwanaland is consistent with the occurrence of widespread austral forests across Antarctica, Australia and southern South America. Connections between these areas were eventually severed with the opening of Drake's Passage between the Antarctic Peninsula and southern South America in the late Oligocene. Angiosperms first appear in the Cretaceous, with modern forest types present by the Middle Eocene, fairly contemporaneously with the apprearence of modern forests in North America. Mixed with subtropical elements, the South American forests reached their greatest extent in the Early and Middle Miocene, and then moved northward as the climate deteriorated. Antarctica was occupied, starting at least 83 m.y .a., with a mixed forest of Nothofagus, Podo- carpaceae and Araucariaceae. Myrtaceae, Proteaceae and Lauraceae, families typical of the southern forests today occurred there becoming increasingly depauperate in the Neogene. The more diverse, biologically-richer temperate forests that occurred around the Northern Hemisphere and on the fragments of Gondwanaland until the Middle Miocene, have persisted, respectively, in areas of greatest equability: eastern Asia in the north, and Southeast Asia-northeastern Australasia (including New Caledonia) in the south. Just as there are fossil plants in North America now confined to eastern Asia, there are some taxa now restricted to Australasia that oc- curred in the temperate forests of South America prior to the Middle Miocene. The relative degree of Neogene extinc- tion in North American and South American temperate forests is a theme requiring attention. Important clues to in- dependent forest development and earlier richness will be found in disjunct lands that lie in areas of greater equability. Hypotheses on the ecological dynamics of these forest must consider the tendency for greater dominance by gymno- sperms with their given life-history traits in North American forests, versus angiosperms in South America. We hypothesize that: (1) The origin and abundance of the deciduous habit in the Northern Hemisphere, is linked with the restriction of seaways, widespread vulcanism, and development of more continental, cooler climates from the Middle Paleocene onward, rather than the postulated impact of a bolide at the close of the Cretaceous; and (2) The mix- tures of temperate and subtropical elements that characterize many Tertiary sites reflect greater climatic equability at that time, which allowed many taxa to extend far outside what we have come to regard as their "normal" areas of distribution. Key words: Antarctic forests, boreal forests, deciduous vs. evergreen habit, Gondwanaland, mixed paleofloras, tem- perate forests, plate tectonics.

RESUMEN

Las floras templadas de Norte y Sudamérica se desarrollaron en forma independiente. Estas floras, inicialmente distintas, continuan siendolo, no sólo debido a sus diversas historias que tuvieron como resultado el dominio de diferentes especies lefiosas, sino debido también a los regimenes climaticos distintivos bajo los cuales se presentan actualmente. En Norteamerica, los tipos vegetacionales modernos aparecieron por primera vez en Ia transicion Paleoceno-Eoceno, cuando Ia region a! norte de Colorado presentaba bosques ricos en especies arb6reas deciduas y coniferas de tierras bajas. Coniferas con requerimientos de frio estuvieron asociadas a especies arb6reas lefiosas en tierras bajas más bacia el norte.

(Received 30 August 1990.) 414 AXELROD ET AL.

Los bosques montanos puros de coniferas y los bosques mezclados de coniferas y especies arboreas estuvieron presentes en tierras altas en Nevada-Idaho en el Eoceno medio y tardio. El primer surgimiento de bosques montanos puros de coniferas ocurrio en el norte (ejemplo Alaska Range) en el Mioceno. Los bosques de coniferas esencialmente puros de tierras bajas en Ia region ártica aparecieron en el Plioceno; no obstante, un bosque similar más antiguo se ha descrito para Islandia (9-7 m.a.A.P.). A finales del Mioceno se disperso un bosque ralo y abierto de coniferas (semi-taiga) sobre las tierras bajas del norte de Alaska. La taiga se expandi6 ampliamente sólo durante el Plioceno y periodos posteriores. En el hemisferio sur Ia historia geologica de Gondwana es consistente con Ia presencia de bosques australes amplia- mente distribuidos en Antartica, Australia y Sudamerica austral. Las conexiones entre estas áreas fueron eventualmente destruidas con Ia apertura del Paso de Drake entre Ia Península Antártica y Sudamerica austral durante el Oligoceno tar- dio. Durante el Cretacico aparecieron por primera vez angiospermas y durante el Eoceno medio aparecieron por primera vez los tipos forestales modernos, contemporaneamente con Ia aparici6n de los bosques modernos en Norteamerica. Los bosques sudamericanos, mezclados con elementos subtropicales, alcanzaron su maxima distribuci6n en el Mioceno tem- prano y medio, desplazandose luego hacia el norte cuando el clima se deterior6. La Antartica fue ocupada, comenzando desde los 83 m.a.A.P. por una flora mixta de No tho fagus, Podocarpaceae, Araucariaceae y Myrtaceae. Proteaceae y Lau- raceae, familias tipicas de los actuales bosques australes, tambien se presentaron allí. Dichos bosques se tornaron progresi- vamente depauperados durante el Neogeno. Los bosques templados más diversos y biologicamente más ricos que se presentaron en el Hemisferio Norte yen los fragmentos de Gondwana hasta mediados de' Mioceno, persistieron respectivamente en áreas de mayor equitabilidad: en el norte de Asia occidental, y en el sur desde Asia suroccidental hasta Australia noroccidental (incluyendo Nueva Ca- ledonia). Asi como se han encontrado f6siles en Norteamerica de plantas actualmente restringidas a Asia occidental, existen algunos taxa restringidos actualmente a Australasia, que se presentaron en los bosques templados de Sudamé- rica, antes del Mioceno medio. El grado relativo de extinciones en el Neogeno en los bosques templados de Norte y Sudamerica es un tema que requiere atencion. Claves importantes para el desarrollo independiente temprano de los bos- ques y su riqueza podrian encontrarse en las áreas disyuntas que se encuentran en regiones de mayor equitabilidad. Las hip6tesis sobre Ia dinámica ecoi6gica de los bosques templados de Norte y Sudamerica deberian considerar Ia mayor dominancia de gimnospermas en los bosques de Norteamerica en comparacion con los de Sudamerica y diferencias en las caracteristicas de historia de vida de los grupos de plantas dominantes. Nosotros predecimos que: (1) El origen y abundancia del hábito deciduo en el Hemisferio Norte está !igado con Ia restriccion de corrientes marinas, vulcanismo, y desarrollo de climas más continentales y frios a partir del Paleoceno me- dio, y no debido a! impacto de meteorites a fmales del Cretacico como se habia postulado anteriormente; y (2) La mezcla de bosques templados y subtropicales que caracterizaron muchas regiones terciarias, reflejan un clima de mayor equitabilidad en el momento, lo que permitio a muchos taxa extenderse más allá de lo que actualmente consideramos su área "normal" de distribucion. Palabras claves: Bosques antarticos, bosques boreales, habito deciduo vs. siempreverde, Gondwana, paleofloras de mezcla, bosques templados, tectonica de placas.

INTRODUCTION shall not consider the extensive changes that have occurred in both areas during The flora and vegetation of cold temperate Quaternary time, the past two million and temperate regions of North and South years, a topic partly covered by V illagrfm America differ greatly in their composition, (this volume). physiognomy, and general aspect. Judging To set the background for understand- from the fossil record, these differences ing the divergent histories of forests in the extend back into the Middle Cretaceous, North and South America, we recall first well over 100 million years ago. In other the role plate tectonics has had in the words, the temperate forests of North and history of climate and vegetation. South America are not only very different in their floristic composition now, but they have been very different since dis- ROLE OF PLATE TECTONICS tinctive assemblages of seed plants -gym- nosperms, and then angiosperms- first Plate movements have not greatly affected evolved into the zones of cooler climate the latitudinal positions of North and flanking the tropics. Whatever structural South America since the Jurassic (Smith and functional similarities may be discern- et al. 1981, Smith 1981, Krutzsch 1989). ed between these forests must be viewed The appearance of broad areas of temper- against a background of completely se- ate forests of modern aspect, therefore, parate historical development and tax- did not originate because the continents onomic dissimilarity. In this paper, we drifted into zones of cooler climate, but shall review the development of the tem- rather because the world climate gradual- perate forests of North and South America ly changed. The principal changes have during the Cretaceous and Tertiary. We been opening the Atlantic basin by ocean- HISTORY OF TEMPERATE VEGETATION 415 floor spreading from the mid-Atlantic ments, more heat is transported into higher ridge, which rafted the Americas to the latitudes and tropical regions become coo- west (commencing ca. 125 million years ler, although still tropical. This is shown ago); the separation of Africa-South by ocean temperatures reconstructed from America and of Europe-North America oxygen isotope evidence (Shackieton 1979, later in the Cretaceous; and severing the 1984). The data suggest that from the link of South America (southern Chile- Maastrichtian of the Late Cretaceous Argentina) with Antarctica-Australia in the (73-65 m.y .a.) into the Miocene (perhaps UpperOligocene(ca. 29 m.y.a.;Fig. 1). 15 m.y.a.), surface waters in the low la- Plate movements and accompanying titude Pacific Ocean were near 18-200C, tectonism have had a guiding role in cli- rising to 280C only in the later Neogene, matic change (Savin 1977), and in the several million years before present. Fur- history of life (Hallum 1981) As lands thermore, deep waters that reflect high are isolated by ocean-floor spreading and latitude surface temperatures had a tem- seaways spread onto continents more perature of about 1ooc in the Maastrich- moderate climates become widespread, as tian-Lower Paleocene (approximately 73- in the Middle Cretaceous (ca. 100 m.y.a). 50 m.y.a.), decreasing to about soc during Active plate movements may build mo- the Late Eocene ( 42-38 m .y .a.), and to untains and plateaus. These modify older 3-40C in the Oligocene, which began 36 climates and, as new climates appear at million years ago. higher elevations, new opportunities are The reassembly of the fragments of provided for the evolution of plants and Gondwanaland shows that during the later animals. With uplift, more extreme climates Mesozoic they were centered in tropical develop in the lee of mountains or plateaus, latitudes. This is the area that still harbors where drier and/or colder climates appear the greatest concentration of angiosperm that also provide possibilities for new sorts families and also has, in more isolated of adaptations by diverse biota. At times areas (New Caledonia, northeastern Aus- of isolated lands and broad marine embay- tralia, Madagascar, Fiji), some of the most ancient families and genera of angiosperms (Axelrod 1952, 1970, Raven & Axelrod 1974). The present climatic requirements of these ancient taxa, as well as the cycads, tree ferns, araucarias, and podocarps associated with them, shows that they are confined chiefly to areas of ample pre- cipitation and high equability. Such areas have a mean annual temperature near l40C and a low mean annual range of temperature (Bailey 1960, 1964, Axelrod 1965, Fig. 9; 1979, Fig. 10; 199lb). The ideal (theoretical) rating is M ( = modera- tion) 100, and is approached by stations such as. Quito, Ecuador, with M 94. The

__..,.....--- - Outline of present-day most extreme stations have ratings less eo· a----- Lt.nd ma ..a• - Cratacaoua land araaa than M 20, as in eastern Siberia. It is the highly equable climates (> M 60) that Fig. 1: Late Cretaceous-Eocene paleogeography support the more ancient (archaic, or (Zinsmeister 1982). An essentially continous "primitive") groups, such as the magno- land between South America-Antarctica-Australia Iioids, hamamelids, and annonoids, as provided a route for the interchange of biota. well as the surviving members of the more Paleograf{a del Cretacico-Eoceno (Zinsmeister 1982). primitive angiosperm orders. Inasmuch as Un territorio practicamente continuo se extendi6 entre Sudamerica, Antartica y Australia proporcionando una the pre-Cretaceous radiation of angiosperms via para el intercambio de biota. evidently occurred in equable tropical 416 AXELROD ET AL. uplands, in relatively open areas, with 1969b, 1972). Evidence from the Kuk some seasonal drought (Axelrod 1952, River area, on the Arctic Slope of Alaska, 1970, Stebbins 1974), they must have indicates that angiosperms may have appear- entered mesic lowland regions at a later ed there even later, in the Late Cenoma- date, an inference supported by the known nian-Turonian transition (ca. 91 m.y .a., fossil record. Smiley 1966). This megafossil record that As the Americas separated from the indicates the later occurrence of angio- larger land area of Gondwanaland of the sperms in Arctic regions is supported by Jurassic and earlier times, the Atlantic the microfossil record (Stanley 1966, Ocean rapidly widened and seaways com- Brenner 1976). Furthermore, as reviewed menced to flood the continents, reaching by Spicer eta/. (1987), a plot of the dis- maximum extent during the Late Albian tribution of diverse taxa from the Ceno- to Cenomanian (about 100-95 m.y.a.). manian into the Paleocene (i.e., from ca. These changes resulted in a more equable 98-50 m.y .a.) shows that the derived taxa global climate (i.e., a lower range of tem- are found in the north. This applies to perature) and a more nearly aseasonal such divergent alliances as Magnolian- condition. It was this that may have been like, Platanoid, Trochodendralean, Jugland- the principal factor that enabled angio- oid, and Fagoid as well. In general, vegeta- sperms rapidly to invade lowland regions tion was characterized by low diversity, away from their tropical center (Axelrod especially at the family level, with few 1970) where they had presumably originat- genera and species. ed much earlier ( cf. Cornet 198 6, 1991) During the succeeding Cenomanian age (98-91 m.y .a.), dicotyledons were wholly dominant over lowland areas. These were NORTH TEMPERATE VEGETATION chiefly members of now extinct groups, though in leaf form some resemble the The fossil record for North America is leaves of modern general, such as Platanus, rich. Selected localities referred to in this Vitis, Magnolia, Betula, and others. As- paper are shown in Figs. 2, 3. sociated with these early angiosperms, which apparently were largely deciduous, The Cretaceous ( 144-65 m.y.a.) were diverse conifers of genera such as Metasequoia, Sequoia, and Pinus, which The earliest angiosperms first appeared in had now largely replaced the older Jurassic the record in low-middle latitudes (ca. and Lower Cretaceous conifers. 350N) in the Early Cretaceous ( 124 m.y.a.) Crabtree ( 1987) provides an excellent of eastern North America. Then they shift- summary of the sequence of change in ed northward, gradually entering polar vegetation and taxa in the northern Rocky latitudes in the Late Albian age (ca. 100 Mountain region, from Wyoming into m.y .a.), more than 20 millions years later British Columbia, during the Albian age (Axelrod 1959). The lower and Middle (113-98 m.y.a.) and subsequently; more Albian age (113-105 m.y.a.) Alaskan floras than 20 individual floras have been describ- are dominated by ferns, ginkophytes, and ed from this region. During a period of Podozamites species. Among the taxa are about 3 million years, from the Middle to Baiera, Cladophlebis, Coniopteris, Czerka­ Late Albian (ca. 100 m.y .a.), angiosperms nowskia, Ginkgo, Nilssonia, and Sagenop­ displaced ancient gymnosperms as the do- teris, which range up into the Middle Al- minant vegetation over the lowland region, bian age (ca. 105 m.y.a.). The first angio- although gymnosperms were still abundant sperms appear at high latitudes near the in the uplands. The Middle Albian age (ca. close of the Upper Albian age (ca. 98 m.y. 105 m.y .a.) flora is allied to the floras of a.), if not in the earliest Cenomanian age lower latitudes, with the similarity largely (i.e., 1-2 million years later), associated at the generic level. Platanophylls and with pteridophytes, ginkophytes, conifers, Sapindophylls are prominent. Some al- and the last cycadophytes (Smiler 1969a, liances, such as the Cinnamonophylls and HISTORY OF TEMPERATE VEGETATION 417

·· •·II...... - .. - .. 13 '~e-12-• 14rl5 •• 16 18 17

SCALE 0 700 MILES

0 1000 Km NORTH AMERICA

Fig. 2: Selected Paleogene floras in North America referred to. 1. East Greenland, 2. Ellesmere Island, 3. Disko Island, 4. MacKenzie (Yukon), 5. Kushtaka, 6. Angoon, 7. Kootznahoo, 8. Kupreanof, 9. Prin- ceton, 10. Puget, 11. Republic, 12. Fort Union, 13., 14. Thunder Mountain, 15. Germer, 16. Haiwee, 17. Copper Basin, 18. Bull Run, 19. Lo Cedarville, 20. Susanville, 21. Chalk Bluffs, 22. Denver, 23. Florissant, 24. Creede, 25. Raton. Floras fosiles paleogenas de Norteamerica seleccionadas. 1. East Greenland, 2. Ellesmere Island, 3. Disko Island, 4. Mac- Kenzie (Yukon), 5. Kushtaka, 6. Angoon, 7. Kootznahoo, 8. Kupreanof, 9. Princeton, 10. Puget, 11. Republic,12. Fort Union, 13, 14. Thunder Mountain, 15. Germer, 16. Haiwee, 17. Copper Basin, 18. Bull Run,19. Lo Cedarville, 20. Su- sanville, 21. Chalk Bluffs, 22. Denver, 23. Florissant, 24. Creede, 25. Raton. 418 AXELROD ET AL.

•8

'~··- .. - .. -··- ··-··, ..

'·.-.r··,·. \ .. r".·,., -··

SCALE 0 700 MILES

0 1000 Km NORTH AMERICA I I 120° 110° 100° so•

Fig. 3: Neogene fossil floras in North America referred to. 1. Iceland, 2. Banks Island (Beaufort), 3. Lava Camp Mine, 4. Kivalina, 5. Circle, 6. Seldova, 7. Homer, 8. Red Lake, 9. Latah Grande Coulee, 10. Mas- call, 11. Blue Mountains, 12. Thorn Creek, 13. Trapper Creek. Floras fosiles neogenas de Norteamerica.!. Iceland, 2. Banks Island (Beaufort), 3. Lava Camp Mine, 4. Kivalina, 5. Circle, 6. Seldova, 7. Homer, 8. Red Lake, 9. Latah Grande Coulee,lO. Mascall, 11. Blue Mountains,l2. Thorn Creek, 13. Trap- per Creek. HISTORY OF TEMPERATE VEGETATION 419

Pentalobophylls appear earlier as do- exhibit a strong influence from warm minants in this region than elsewhere, temperature-subtropical floras of eastern suggesting that the regional flora constitut- North America. In the west sector (eastern ed a rather distinct subprovince. Early Siberia-northwest North America), boreal members of some recent higher taxonomic (cooler) elements dominate. Similar re- categories existed by the Middle Albian lationships were present during the Tertiary age, and they increased rapidly so that and have persisted to the present day. by the Campanian age (83-73 m.y.a.), numerous modern families and some The Paleocene ( 65-55 m.y.a.) genera were represented in a very diverse flora (Crabtree 1987). By Paleocene time (Fig. 2), floras from the The Early Cretaceous (pre-Cenomanian far north, as in northwest Greenland age; before 98 m y.a.) floras of high (Koch 1963), include conifers and angio- latitudes indicate the existence of a mild, sperms. The latter have an "older" aspect temperate climate. The abundance of de- and chiefly appear to represent extinct ciduous hardwoods with serrate leaves members of the modern alliances to which reflects seasonality, as shown also by fossil they have been referred. Among the woods with regular growth rings (Creber conifers are Ginkgo and Metasequoia. & Chaloner 1984). This was the result of Of the dicotyledons, taxa referred to the tilt of the Earth's axis that imparts a modern genera such as Carpinus, Cercidi­ long period of darkness in winter and light phyllum, Corylopsis, Credneria, Juglans, in summer. The absense of much biological Magnolia, Platanus, Rhododendron, Quer­ degradation of plant material (especially cus, and Vitis mostly need further study, leaves) also implies cool, moist climate as do species referred to fossil genera (Spicer & Parrish 1986). The general therm- such as Dictylophyllum, Lauraeceaephyl­ al conditions suggest a mean annual tem- lum, and the enigmatic Macclintockia. perature near 10-120C, and a very low Whereas some of the fossil members range of mean annual temperature (Ja- of these genera have the aspect of ancient nuary-July, probably near 6-80C, as plants not fully stabilized in terms of implied by the large reptile (dinosaurs, modern genera, the rich Paleocene flora alligators) fauna that occurs with the of the Great Plains and Rocky Mountains, plant fossils. These animals may have distributed from the Canada-United States hibernated during the long, dark period border to New Mexico (Brown 1962) or migrated seasonally into the area. The has a decidedly modern aspect. Among the suggested temperatures imply that the genera represented are many gymno- temperature fell below freezing for scarcely sperms -Fokienia, Glyptostrobus, Meta­ 0.5% of the hours of the year ( 43 hrs.). sequoia, Taxodium, Thuja, and Zamia­ Others have suggested a greater range of and diverse angiosperms, including Acer, temperature (i.e., 25-300C), but this means Bauhinia, Betula, Carya, Castanea, Cerci­ that 20-25 Ofo of the hours of the year diphyllum, Cinnamomum, Cissus, Cornus, (1,752-2,190 hrs, or fully 2.4-3.1 mos) Corylus, Eucommia, Ficus, Fraxinus, would have had temperatures below freez- Magnolia, Menispermum, Nyssa, Persea, ing. Such conditions would not favor large Platanus, Prunus, Pterocarya, Rhamnus, animal migration north of, or to, the Arctic Robinia, Quercus, Saba/, Sapindus, Sassa­ Circle (where they occurred), and doubt- fras, Viburnum, Zelkova, and Zizyphus. fully would have allowed hibernation Brown (1962) pointed out that there is a there. floristic-climatic difference from south to In their review of the Arctic Cretaceous north, for the remains of breadfruit (Arto­ floras, Sveshnikova & Budantsev (1969) carpus), Cinnamomum, Menispermum, and note that floras attained maximum floristic other evergreens, notably palms, are differentiation in the Late Cretaceous generally limited to areas south of central (i.e., 85-65 m.y .a.). Floras in the east Wyoming. On the other hand, Ginkgo, sector (northeast Canada, Greenland) together with Acer, Betula, Corylus, Vi- 420 AXELROD ET AL. burnum, and other genera that occur in were probably related to the high latitudes temperate forests today are found in areas and seasonal darkness at this very high north of the Colorado-Wyoming boundary. latitude. In general, leaves with toothed margins In general, Paleocene floras show a grada- far outnumber those with entire margins, tion to a moist, milder temperate climate implying a generally temperate climate. extending northward from the Gulf region, The flora was certainly mesophytic in a where the climate was tropical -as illustrat- warm temperate to mild temperate envi- ed by the small Midway Flora of Texas ronment that was cooler northward. This (Berry 1916). The floias also indicate a is apparent from the Paleocene flora of trend from relatively modern taxa to more western Alberta (Bell 1949). Notably ancient ones (relicts) in the north, paral- absent are the abundant palms and broad- leling the Middle Cretaceous shift to more leaved evergreens that are so abundant ancient, relict taxa northward. Vegetation in the Raton and Denver floras of Colorado- shows a change from broadleaved rainforest New Mexico, as well as the poor representa- in the Gulf area, to rich warm-temperate tion of entire-margined species that occur broadleaved evergreen forest with few to the south, such as fossils referred to deciduous hardwoods (Raton, Denver, and Cinnamomum, Ficus, Magnolia, and Persea. allied floras), to mesic dominantly deci- The Alberta flora also includes some an- duous forest north of Colorado, to mixed cient conifers that evidently are not in the deciduous-coniferous forests in the north Paleocene to the south notably Andro­ with a few montane conifers. The record vettia, Cryptometites, and Elatocladus. has not yet provided evidence of pure To the north, in the Yukon Territory, montane conifer forest, although it may Rouse & Srivastava (1972) note that there be inferred for areas where the mountains is a marked floristic change across the were high enough to support a cool tem- Cretaceous-Paleocene boundary ( 65 m.y .a.) perate climate. There is no record of taiga in the Bonnet Plume Formation. In addi- or tundra at this early time. tion, there is an marked influx of conifers, The Eocene (55-38 m.y.a.) including Cedrus, Glyptostrobus, Picea, Pinus, Metasequoia, and Taxodium. As- In the far north, floras from Spitzbergen sociated angiosperms include taxa referred (Schloemer-Jager 1958), Ellesmere Island to Alnus, Betula, Corylus, Fraxinus, (Manum 1962, Christie & Rouse 1976), Myrica, and Ulmus. Several genera of northern Canada (Norris 1982, Staplin pollen taxa -Aquilapollenites, Beaupreadi­ 1976, Rouse & Srivastava 1972), and east- tes, Cranwellia, and Mancicorpus- that ern Greenland (Koch 1963, Manum 1962) occur here are generally taken as indicators provide records of rich deciduous hard- of the disappearance of warm temperate wood-conifer forests. Among the conifers conditions. The change that we have just are species of Abies, Glyptostrobus, Larix, described is paralled by that which occurs Metasequoia, Picea, Pinus, and Taxodium. across the Lance-Fort Union transition Angiosperms include species of Alnus, in Montana, the Dakotas, and Wyoming. Betula, Carya, Castanea, Cercidiphyllum, In eastern north Greenland, at a paleo- Fagus, Liriodendron, Nyssa, Platanus, Po­ latitude of 77 -790N, the Thyra 0 flora, pulus, Pterocarya, Quercus, Ulmus, and of Late Paleocene-Early Eocene age, has Zelkova. In this general region, situated recently been studied (Boyd 1990). This for the most part above 600N, the mixed diverse flora records mild temperate clim- hardwood-conifer forest, dominated by atic conditions with little frost, as judged hardwoods, most probably gave way to from the relationships of the taxa present; montane conifer forest at elevations some- among them were Ginkgo, Fokienia, Me­ what above 500 m. The character of the tasequoia, Platanus, and Cercidiphyllum. lowland forest indicates cool temperate The leaf physiognomy of the taxa present climate, with ample rain in the warm at this locality, on the other hand, indicates season. Owing to the lower elevation of cool temperate conditions. These features the continents, to margin seaways, as HISTORY OF TEMPERATE VEGETATION 421 well as to the absence of a polar ice cap, The mixed deciduous hardwood-conifer temperatures were more moderate than forests of higher latitudes extended south those in related montane forests. In general into the northern Rocky Mountains, as aspect, the broadleaved deciduous hard- shown by the Princeton and allied floras wood-conifer forest of the Eocene at of British Columbia (e.g., Penhallow 1908, higher latitudes resembled the forests that Berry 1926, Arnold 1955, Piel 1971). now occur around the Great Lakes, extend- Among the genera recorded are species ing into the northern and central Appala- of Acer, Aesculus, Alnus, Betula, Carya, chians at middle elevations, where Abies, Castanea, Crataegus, Fagus, Fraxinus, Picea, Pinus, and Tsuga mix with deci- Juglans, Liquidambar, Nyssa, Prunus, Pte­ duous hardwoods. Comparable relations- rocaya, Sassafras, Ulmus, and diverse co- ships are also present in Japan (Ito 1961, nifers, notably Abies, Cedrus, Glypto­ Ito et al. 1966) and also in the mountains strobus, Metasequoia, Picea, Pinus, Pseudo­ of Sichuan and Hubei provinces of south- tsuga, and Taxodium. Similar forests rang- ceo tral China (Wang 19 61). ed southward, as shown by the Republic The Middle to Late Eocene Kushtaka flora of northeastern Washington (Wolfe flora from the Gulf of Alaska region & Wehr 1987), the Salmon flora of east- (600N) presents a floristic anomaly. The central Idaho (Brown 1937), and the Cop- florules represent outer tropical rainforest per Basin flora of northeastern Nevada vegetation, as judged from plants identified (Axelrod 1966a). Of these, the Republic as members of the Annonaceae, Diptero- flora has a few broadleaved evergreens, carpaceae, Icacinaceae, Menispermaceae, indicating a somewhat lower elevation and Myristicaceae, and Myrtaceae (Wolfe 1977). warmer climate. In terms of the global symmetry of vegeta- In the Middle Eocene (47-43 m.y.a.), tion-climate, the flora contrasts markedly the central to northern Rocky Mountains with respect to floras of western Europe were a site of extensive vulcanism (Lip- and Greenland that were then at a lower man et al. 1972). Preserved in lake beds latitude (350N) and include temperate associated with the ashflows and welded taxa. In addition, the Eocene floras of tuffs are several floras wholly dominat- northern Japan-Kamchatka are temperate, ed by montane conifers. These assemblages not tropical. These occurrences of temperate are much like the present montane conifer Eocene forests in coastal areas at latitudes forests that now occur above the mixed lower than the Kushtaka support evidence conifer-hardwood forest zone, although that the latter was on a tectonic block they were much more diverse in composi- that has been displaced many kilometers tion. Occupying elevations near 1,250- northward (Jones eta/. 1972, 1977,Packer 1,500 m (north to south) for the most & Stone 1974, Coney et al. 1980, Cowan part, these fossil floras, dated in the range 1982, Jones & Silberling 1982, Plumley of 46-35 m.y.a., occur in northeastern et a/. 1982, Helwig & Emmett 1983, Sa- Nevada (Upper Bull Run flora) and Idaho leeby 1983, Bruns 1983). This is indicated (Haiwee, Thunder Mountain floras). Two also by the Eocene marine microfossil of them record the transition from hard- fauna, which also suggests a considerable wood-conifer forests that lived in slightly degree of latitudinal displacement (Keller warmer conditions. This is shown by the et a/. 1984). Furthermore, the estimated Bull Run sequence. The lower three florules paleotemperature of the Kushtaka flora, show that the deciduous hardwoods with a mean annual temperature of 10- (Acer, Quercus, Ulmus, Zelkova) gradually 200C (average 150C) and a range of decrease as conifers increase at higher le- 10-15 oc (average 1OOC), indicates on the vels. The upper six florules, distributed order of 4'fe of the hours (350 hrs) of the through about 1 ,000 m of continuous year would have had temperatures below section, are wholly dominated by pure freezing, hence prohibiting the existence montane conifer forest species belonging of the lndomalaysian taxa that occur as to the genera Abies, Chamaecyparis, Larix, fossils at this latitude. Picea, Pinus, and Thuja. 422 AXELROD ET AL.

A large flora from Coal Creek, east- subtropical forest/scrub and oak-pinyon central Idaho, is wholly dominated by woodland (MacGinitie 1953). By contrast, montane conifers (85oto of the specimens), at lower elevations to the west, broadleav- and has few deciduous hardwoods, notably ed evergreen forest was represented by the Acer, Betula, Cornus, Crataegus, Sassafras, Comstock flora of western Oregon (San- Sorbus, and Viburnum, as well as several born 19 35), the Susanville flora of eastern broadleaved evergreens that have not yet California (University of California Palen- been identified. Pure montane conifer tology Museum), and floras from the Puget forest no doubt occupied slightly higher group, Washington (U.S. National Museum levels in the area, where it was composed of Natural History). At moderate elevations of most of the Coal Creek taxa, notably inland, temperate rainforest (Chalk Bluffs, Abies, Chamaecyparis, Larix, Picea, Pinus, flora, MacGinitie 1941) and temperate Pseudotsuga, Sequoia, Sequoiadendron, deciduous hardwood forest with a few and Thuja. Associated forest-floor shrubs broadleaved evergreens (Lower Cedarville in the montane conifer forests belonged flora, University of California Paleontology to genera including Alnus, Arctostaphylos, Museum) were present. Comptonia, Mahonia, Prunus, Ribes, and In response to the trend to cooler, drier Vaccinium. Deciduous hardwoods were climate, and also to the building up to the absent from these montane conifer forest, broad volcanic upland of mid-Eocene age apart from an occasional leaf of A /nus, in the northern and central Rocky Mount- Betula, or Populus. ains, areas it is lee show evidence of spread- An essentially contemporaneous flora ing drier climate. This is especially apparent from the Germer Member, Challis Vol- from floras in the Ruby and Beaverhead canics, situated 90 km southeast of the basins, south-western Montana (Becker Thunder Mountain flora and at a some- 1961, 1969). Taxa of drier environments what lower elevation (ca. 600 m), represents are present, notably small-leaved species a deciduous hardwood-conifer forest (Edel- of Amelanchier, Celtis, Cercocarpus, Maho­ man 1975). Hardwoods dominate and nia, Philadelphus, Ribes, and Sapindus. include Aesculus, Alnus, Betula, Carya, The Florissant flora, Colorado, also has Cercidiphyllum, Eucommia, Juglans, and members of this group (MacGinitie 1953), Ostrya. Among the conifers are Metase­ notably a scrub oak (Quercus), Mahonia, quoia (most abundant), Pseudolarix and Rhus, Vaquelinia, and several legumes Sequoia (frequent), and Abies, Chamae­ with small leaflets, notably Prosopis. cyparis, Picea, Pinus, and Tsuga (uncom- These probably occupied drier sites on the mon to rare). Radiometrically dated at andesite tuffs and breccias that rimmed the 47-46 m.y.a., this flora clearly demon- lake in which the flora was preserved. The strates that the Eocene forests of the Florissant flora also has species of Abies, Arctic extended southward along cooler Chamaecyparis, Picea, Pinus, and Sequoia, mountainous uplands at this early date. associated with a rich mixed hardwood It was later, with the cooling cycle of forest at the borders of a sclerophyllous Oligocene-Miocene times, that this mixed woodland. Similar relations are shown by conifer-hardwood forest zone shifted to the Late Oligocene (27 m.y.a.) Creede flora lower levels at middle elevations in western of southwestern Colorado, where a mixed North America. By mid-Eocene time, ve- conifer forest of Abies, Picea, Pinus, and getation east and west of the continental Pseudotsuga is recorded in e..:otone with divide was developing in different ways. sclerophyll woodland (Axelrod 1987). At This was the result of the building up higher levels (ca. 900 m), pure montane of a broad, relatively high topographic conifer forest probably was present. barrier by vulcanism that ranged from Summarizing, by Middle Eocene time northern Nevada into Canada (Lipman ( 4 7-46 m .y .a.), vegetation zones represent- et al. 1972 ). Mid-Eocene floras to the east ing broadleaved deciduous forest, mixed reflect drier climate as seen in the Green deciduous-conifer forest, and pure montane River flora of Colorado-Utah, with its conifer forest were present from the HISTORY OF TEMPERATE VEGETATION 423 central United States northward into the the Blue Mountains flora of eastern Oregon Arctic. These were arranged with respect (in Chaney & Axelrod 1959) and by the to elevation, with montane conifer forests Trapper Creek (Axelrod 1964) and Thorn largely above 1200 m elevation in Nevada- Creek (Smith 1941) floras of southern Idaho (Axelrod 1968), decreasing north- Idaho, with the latter two largely dominat- ward to an elevation near 300 m in the ed by conifers (Abies, Chamaecyparis, Arctic, where they are inferred to have Picea, and Pinus), mixed with some deci- been above mixed conifer-hardwood forest duous hardwoods (Acer, Betula, Quercus, recorded there. Existence in the north Ulmus, and Zelkova). These were situated was favored by mild temperatures result- above the rich mixed hardwood lowland ing from more uniformly distributed conifer (Metasequoia, Taxodium) forests at global temperature with cooler tropical elevations generally below 600 m, where and warmer polar zones. Drier climate species of Ailanthus, Betula, Cedrela, was spreading in the lee of the volcanic Diospyros, Fagus, Hamamelis, !lex, Ptero­ cordilleran axis by the Middle Eocene, carya, Quercus (broadleaved), Sassafras, when zones of drought -deciduous and scle- Ulmus, and Zelkova are recorded, with a rophyll vegetation are recorded. Since few broadleaved evergreens, including then, the differences in temperate vegeta- species of Magnolia, Persea, and Phoebe (in tion east and west of the continental divide Chaney & Axelrod 1959). This mixed have increased, with more mesic forests hardwood forest ranged north to Alaska, and woodland in the west. as seen in the Seldova Point and allied floras (Wolfe & Tanai 1980). The Neogene (25-2 m.y.a.) This is evident from floras in sediments interbedded with dated basalts ( 13-12 During the mid-Tertiary (Fig. 3), major m.y .a.) in south-central British Columbia physical events directly influenced the (Matthews & Rouse 1963). The megafossil flora and vegetation. Australia was rafted flora has species similar to those in the farther north, away from Antarctica; Miocene of Oregon and Alaska. Together early glaciation developed on Antarctica; with pollen, the species include Abies, and Drakes Passage between Antarctica Picea, Pinus, Pseudotsuga, and Tsuga, and the southern tip of South America as well as Cupressaceae and Taxodiaceae opened (during the Middle Oligocene, (pollen genera not identified). Diverse ca. 27 m.y.a.). Cold water now flowed angiosperms are also present, notably north into equatorial latitudes and strength- Alnus, Carya, Corylus, !lex, Juglans, Li­ ened high pressure systems, so that drier quidambar, Pterocarya, Quercus, Salix, climates spread more widely. Sea level Tilia, and Ulmus/Zelkova. Of special was lowered significantly at about 2 7 interest is the dominant coniferous pollen m.y .a., the Mississippi embayment in North (80-90%), as compared with angiosperm America retreated rapidly, and major pollen. This indicates a cooler, more upland volcanic activity is recorded in western environment not far removed from montane North America. Exotic taxa were now conifer forest and grading to lower eleva- being reduced in numbers in response to tion at the Red Lake site, which is situated colder winters and drier summer climate. farther east and includes dominant an- The uplift to mountains favored the giosperm pollen (63"!.). general spread of cold-temperate conifer The Neogene plant record at high latit- forests and their species. In addition, in udes is poorly known, except for that in the lee of these topographic barriers drier Alaska (Wolfe 1966, 1987b, Wolfe & Tanai vegetation types, including conifer wood- 1980, Wolfe et al. 1966). The Early to Mid- land and grassland, commenced to spread. dle Miocene floras include numerous woody During the Miocene (25-5 m.y .a.), dicotyledons, belonging to genera such as conifer-hardwood forests were present at Alnus, Betula, Carpinus, Carya, Cercidi­ moderate elevations over the western phyllum, Cocculus, Corylus, Liquidambar, United States. Examples are provided by Nyssa, Platanus and Tilia. Metasequoia 424 AXELROD ET AL.

is common in these floras, but remains of although floras to the south -in Wash- upland conifers that represent cold tem- ington, Oregon, and Idaho- still have the perate climate are rarely encountered in aspect of older Miocene floras like that lowland areas. However, a flora from the from Seldova Point in Alaska. They are Wrangell Mountains has a number of of mild temperate aspect, as indicated by conifers -Abies, Picea, Pinus, Thuya, members of the families Aceraceae, Faga- Tsuga- together with exotic genera includ- ceae, Juglandaceae, and Ulmaceae. The ing Fagus, Pterocarya, and Ulmus. The shift in composition from the Middle to abundant conifers imply a higher elevation, the Late Miocene evidently disrupted a as compared with the mixed deciduous continuous forest that ranged across Be- hardwood-conifer forest of the Cook ringia to northern Japan, where some of Inlet region. This suggests that conifer the same species are recorded in the Middle forests were present at higher elevations Miocene (Wolfe & Leopold 1967), alth- throughout the higher latitudes. This may ough those forests include more numerous be inferred from the Paleocene records of broadleaved evergreens (Tanai et al. 1963). floras at high latitudes, as well as from the The major floristic changes in Alaska, Miocene record from Iceland, where a as documented by the differences between mixed deciduous forest included Abies, the Middle and Late Miocene floras, oc- Picea, and Sequoia, associated with species curred at ca. 15 m.y.a. (between the Sel- of Acer, Betula, Carya, Comptonia, Fagus, dova Point and Homer floras) and ca. and Sassafras, all now absent from the 7-6 m.y.a. (between the Homer and Clam region (Heer 1868, Schwarzbach & Pflug Gulch floras). These correspond closely 1957, Pflug 1959, Manum 1962, Ah- with comparable floristic changes that matev et al. 1978). occurred in the floras of Nevada-Califor- Conifer forests are not recorded in the nia-Oregon-Washington Axelrod 198 7, far north until the Late Miocene and 1992). Pliocene. This raises the question as to Pollen floras from the Holmatindur whether their taxa were derived from Tuff, eastern Iceland (650N), come from Eocene-Oligocene species at middle sediments between dated basalt flows; latitudes that spread northward with they provide evidence of rapid cooling cooling climate and the uplift of moun- in the Late Miocene (Mudie & Helgason tainous tracts during the Miocene and later. 1983). The lowest sample consists of a Only the discovery of more numerous rich palynoflora that includes Larix, Pi­ floras in the far north can certainly provide cea, Pinus, Sequoia, and Taxodium, together the answer to this question. Nonetheless, with deciduous hardwoods that include current evidence suggests that conifer Carpinus/Ostrya, Carya, Fagus, Juglans, forests spread northward and down in Nyssa, Quercus, and Ulmus. The overly- elevation following the Eocene as a cooler ing sample has a similar flora, but a slightly climate developed. Such a sequence is well higher percentage of Picea and Pinus, and represented in the later Neogene of both a lower percentage of Fagus. Higher samples Alaska and Iceland. contain palynofloras dominated by Picea, By the Late Miocene in Alaska, the Ho- with a strong representation of cold-to- mer and allied floras have relatively few lerant shrubs, including Betula sect. Nanae exotic broadleaved hardwoods, but still and Alnus viridis. The data suggest a floral include Carya and Ulmus; those hardwoods sequence from a temperate Taxodium­ that remain are not common either as hardwood forest, to cool temperate de- megafossils or in the pollen record. Shrubs ciduous hardwood-conifer forest, to micro- such as Rhododendron, Spiraea, and Vac­ thermal spruce forest, and finally to a cinium are locally abundant. Pollen of subarctic Alnus woodland. The sequence Picea and Tsuga is present at most lo- indicates major climatic cooling during calities. The shift from a rich to a poor the dated time, 10.3-9.5 m.y.a. The forest with scarcely any deciduous hard- cooling predates the earliest Iceland woods heralds the spread of colder climate, tillites (6-4.8 m.y.a.), and evidently cor- HISTORY OF TEMPERATE VEGETATION 425 responds in time to the oldest Alaskan Mio-Pliocene rocks of the Alaska Range tillites (Denton & Armstrong 1969). is a record of montane conifer forest The Late Miocene Beaufort Formation including Abies, Larix, Picea, Pinus, and on Banks Islands, Arctic Canada (730N), Tsuga, and with Populus and Salix as- has well-preserved cones of Picea (banksii), sociated in lake border and riparian sites. Pinus banksiana, and P. strobus, as well Thus, even at this late date, pure conifer as megafossil remains of Larix, Metase­ forest was not yet of wide occurrence quoia, Pseudolarix, Alnus, and Juglans over the lowlands of the Arctic. cf cinerea fruits. In addition, there is pol- A Pliocene flora from Lava Camp len of Tsuga cf canadensis, Carya, Corylus, Mine, on the Seward Peninsula in the Be- and others. A pollen profile indicates that ring Strait region (650N), provides a record the area was covered initially with mixed of rich conifer forest (Hopkins et al. 19 71 ). deciduous hardwood forest with abundant Megafossils include species identified as conifers, such as Pinus (dominant) and Picea glauca, P. mariana, P. sitchensis, Picea. This was followed by increased Pinus monticola, and Tsuga heterophylla, Larix and Picea, and the rapid decrease as well as seeds of Symphoricarpos, Vac­ and disappearance of pollen from deciduous cinium, and Cyperaceae (Carex, Cyperus). trees (Hills, 1971 ). Associated pollen includes species of Al­ A small Late Tertiary flora near Circle, nus, Betula, Corylus, Salix, and Sympho­ Alaska, from old terrace deposits of the ricarpos, as well as several ericads, Epilo­ Yukon River, includes 9 cones of Picea bium, and Oenothera. Approximately ten and 3 of Larix. Pollen is represented by species of conifers are represented by Abies, Larix, Picea, Pinus, and Tsuga, as needles, cones, or pollen. Some of these well as these genera of shrubs: Alnus, are now found on the order of 850 kilo- Betula, Diervillea, and Salix, and species meters or more to the south. This is not a of Caprifoliaceae, Caryophyllaceae, Erica- taiga community, but represents vegetation ceae, and Poaceae (Y eend e t al. 19 89). near the northern border of the Coast Most of this assemblage is not found in coniferous forest. the immediate region today. The principal The evidence indicates that a rich Coast- exotics are Diervillea, now in British Co- al conifer forest dominated by Picea and lumbia, and Pterocarya, possibly reworked Pinus, but including Abies, Larix or Pseudo­ from older rocks, which is a native of tsuga, and Tsuga, as well as members of Asia. The conifers are chiefly in more the families Cupressaceae and/or Taxodia- distant areas where the summers are warm- ceae, extended from the Cook Inlet area er. These include Tsuga (now in Alaskan to the Arctic Circle during the Pliocene Coast Ranges), Pinus (banksiana) (800 (5-2 m.y .a.). The authors note that Glyp­ kilometers east) P. contorta (500 kilo- tostrobus, Diervilla, and Ulmus were present meters south), Abies (/asiocarpa) (350 in the Cook Inlet region, but have not kilometers south), and Larix (laricina) been recorded farther north. Pterocarya (150 kilometers east and 200 kilometers was present as a rare tree in the Cook west) (data from Little 1971). The as- Inlet and Nome regions in the Pliocene. semblage represents a rich interior conifer Pollen of Tilia is rare in the Pliocene floras forest, and suggests that tundra was at high- of the Cook Inlet region and in the Nome er levels in the area. Its age is not known area, and the location and abundance of precisely, but it appears to be transitional the trees that shed this pollen is unknown. Mio-Pliocene, or about 5-6 m.y.a. The large insect fauna associated with During the Pliocene, the Cook Inlet the plant megafossils at the Lava Camp region, Alaska, supported Picea and Tsuga, Mine locality includes a number of extinct and a few exotics as megafossils, including species. In discussing the affinities of this Glyptostrobus and Rhus, as well as rare fauna, Hopkins et a/. (1971, p. 119) pollen of Pterocarya and Ulmus, which stated: "It seems clear that a similar as- may have been reworked from older rocks semblage of living insects and mites could (Wolfe & Leopold 1967). In transitional not be collected on the modern tundra of 426 AXELROD ET AL.

the Seward Peninsula, nor in the boreal the Pleistocene. The spread of drier, colder woodland of present-day interior Alaska. climate in the lee of the Alaska Ranges, A comparable assemblage of insects pro- which are relatively young, favored the bably could be collected in southern British taiga and (later) tundra vegetation, es- Columbia or northern Washington." pecially in the Wisconsin glacial and later That the northern limit of the Coast (reviewed by several authors in Hopkins conifer forest was nearer the Arctic Circle et al. 1982). in the Pliocene is suggested by a Pliocene As taxa were eliminated from the tem- pollen flora from Kivalina, 100 km north perate forests of North America under of the Lava Camp Mine assemblage do- the influence of a cooler, drier, and less minated by megafossils. The Kivalina equable climate, they were also being assemblage is dominates by Pinus, Tsuga, eliminated even more rigorously from and Betula, and lacks Abies, Chamaecy­ western Eurasia. In Chile and Japan, where paris, Larix, Tsuga, and Corylus. It more the climate remained more equable and nearly resembles the vegetation of the there was ready access to mountainous Yukon Territory, northwest Canada, than areas to the south, many more elements it does the Lava Camp Mine flora. of the north temperate forest survived. Summarizing, the differences in vegeta- The modern flora of China, which is about tion east and west of the continental the same size as the United States, consists divide that _existed in the Paleogene were of about 30,000 species of angiosperms, accentuated: in the Neogene (i.e., after at least 50% more than are found in the 25 m.y .a.).1 As forests and woodlands United States and Canada combined; retreated in response to drier, cooler cli- and the modern flora of Europe consists mates, grasslands east and west of the of only about 11 ,000 species. The survival divide were being segregated into seral of archaic, temperate forest plants and communities in local open areas, probably animals in eastern Asia, where they persist by the Middle Paleogene (ca. 45 m.y.a.). in conditions of greater equability than Differences between the grass communities have been maintained elsewhere parallels east and west increased as drier climates the survival of south temperate forest spread, especially during the past 15 mil- elements in Southeast Asia, northern Aus- lion years as forests retreated. This is tralia, New Caledonia, and to some extent, inferred from the rapid increase in hyp- New Zealand and Chile (Arroyo et al. sodont equids ( 15 contemporaneous 1991 ). species) in the Late Middle Miocene (ca. 12 m.y.a., MacFadden & Hulbert 1988). With the rise of the cordilleran axis and SOUTHERN TEMPERATE VEGETATION the building of the Cascade-Sierran barrier, especially following during the past 7-6 As compared with the record in the North- million years, grasslands spread more ern Hemisphere, fewer fossil floras dominat- widely in the lee of these barriers and ed by angiosperms are presently known developed into distinct floras (Leopold & from south temperate regions (Figs. 4, 5); Denton 1987). Increasingly drier climate in addition, their precise (radiometric) during the Late Miocene and Pliocene ages have mostly not yet been established (i.e., the last 7-5 million years) on the and there are many difficulties with iden- High Plains and northward into Alberta tifications. For these reasons, an analysis resulted in rapid ("explosive") speciation of the development of vegetation in South of grasses and herbs (Elias 1942). Generally America cannot be as complete as that similar relations are inferred for the much for temperate North America. smaller grasslands (a quarter of the size The general background history of the of the Great Plains) west of the continental region has been reviewed by Plumstead divide, as on the Snake River Plain, and (1962), commencing with the earliest the coastal valleys of California and Ore- land plants (Devonian; 408-360 m.y.a.) gon, where they assumed dominance in and continuing up to the Tertiary. As HISTORY OF TEMPERATE VEGETATION 427

Fig. 4: Selected fossil floras referred to in South America. Paleogene: l. Coronel Lota, 2. Ri'o Pichileu- fU, 3. Rio Turbio, 4. Fuenes, 5. Laguna d'Hunco, 6. Loreto; Neogene: l. Cuenca, 8. Loja, 9. Pisllypampa, 10. Potosi. Floras fosiles de Sudamerica seleccionadas. Paleogeno: 1. Coronel Lata, 2. Rio Pichileufu, 3. Rio Turbio, 4. Fuentes, 5. Laguna d'Hunco, 6. Loreto; Neogeno: 1. Cuencia, 8. Loja, 9. Pisllypampa, 10. Potosi. she noted, the similarity of the pre-Cre- tinents, as judged from the fossil record, taceous floras of South America, Africa, became less common. In this connec- Australia, India, and Antarctica indicates tion, Raven & Axelrod (1974) pointed out that the southern continents were joined that the distributions of numerous conifer into the earliest Cretaceous, following and angiosperm families common to the which floristic links between the con- southern lands demand connections in the 428 AXELROD ET AL.

UPPER EOCENE­ OLIGOCENE

KEY

Fig. 5: Distribution of floras in South America during the Tertiary. 1. floras from tropical to subtropical climates; 2. floras representing mixtures of temperate and warm climates; 3. floras representing temperate and cool-temperate climates; 4. warm climate floras; 5. austral and cool-temperate floras; 6. temperate floras; 7. arid and semi-arid floras (from Menendez 1971 ). Distribucion de floras en Sudamerica durante el Terciario. 1. floras de climas tropicales a tub- tropicales; 2. floras que representan mezclas de climas templados y calidos; 3. floras de clima templado o templado-frfo; 4. floras de clima cilido; 5. floras australes o de clima templado frio; 6. floras templadas; 7. floras de clima arido y semilirido (tornado de Menendez 1971).

Late Cretaceous (i.e. 100-65 m.y.a.). Australia-Tasmania were finally interrupted Links between New Zealand-New Cale- with the opening of the Drake Passage donia and Australia-Antarctica mostly date between South America and Antarctica from 80-60 m.y.a., while those between about 29 million years ago, in the Late southern South America and southeastern Oligocene. HISTORY OF TEMPERATE VEGETATION 429

The vegetation history of southern that Antarctica may have been a center South America has been reviewed compre- for the origin and dispersal of much of the hensively by Menendez ( 1971) and Romero perhumid, evergreen rainforests that are (1986). The present discussion is drawn now disjunct in Chile, Australia-Tasmania, partly from those studies, in which ex- and southern Africa (Dettmann 1989). tensive bibliographical references are in- This view was supported earlier by Darwin, cluded. Hooker, and others, at a time when these lands were considered to have been per- The Cretaceous ( 144-65 m.y.a.) manently separated by long stretches of open ocean, thus requiring long distance The Early Cretaceous palynology of Ar- dispersal to account for the disjuncts. gentina (Archangelsky 1980, Archangelsky Seward (1941, pp. 41-44) was one of et a!. 1984) shows a generally similar flora the first to accept the likelihood that throughout the area, with ferns and gym- continental displacement, as visualized by nosperms dominant and angiosperms ap- Wegener, provided a means for reassembling pearing only late in the sequence. The the now-disjunct fossil and modern forests vegetation was dominated by conifers, of austral lands. with the family Cheirolepidaceae ( Clas­ The problem of the existence of ever- sopollis) conspicuous, along with Podo- green rainforests in polar latitudes may carpaceae (Callialasporites, Microcachrydi­ be explained by photoperiodic ecotypes tes) and Araucariaceae. Angiosperm po- that made all their annual growth during len appears only as a rare element in the the long light period, with cambial activity Aptian (119-113 m.y.a.). At present, concentrated in rapid growth of wood Albian (113-97 .5 m.y .a.) strata have not during the polar summer (Chaloner & Cre- yielded floras. By the Maastrichtian (73- ber 1989). However, this also requires a 65 m.y.a.), the pollen reveals a diversified highly equable (M 65-70) perhumid climate angiosperm and conifer flora that has with an annual range of temperature of continued to exist in the area to the present 5-70C, and hence a nearly frostless envi- time. ronment (Axelrod 1966b, Fig. 2; 1979, Angiosperms are first recorded in the Fig. 10). Albian of Antarctica and gradually increas- Reference to the disjunct occurrence ed during the remainder of the Cretaceous. of evergreen rainforest taxa of southern By Campanian and later times, recognizable South America brings up the occurrence of alliances of gymnosperms and angiosperms Lactoris, the only genus of Lactoridaceae, (Araucariaceae, Podocarpaceae, Casuarina- now confined to the mesic, equable up- ceae, Nothofagus, Myrtaceae, Proteaceae lands of the Juan Fernandez Islands. Its -Macadamia-type, Xylomelium, Sapinda- primitive features indicate that Lactoris ceae) are not only on Antarctica, but is a relict, ancient angiosperm. Lactoris on the adjoining southern continents pollen is now known from Upper Creta- (Dettman 1989, Figs. 3, 6; Askin 1989, ceous (Turonian-Campanian, 88-84 m.y.a.) Dettman & Thomson 1987). The peren- sediments off the southwest coast of Africa nial herb Gunnera appears in the record (Zavada & Benson 198 7). This implies a even earlier, in the Turonian, was wide- former distribution across temperate west- spread in both hemispheres in the later ern Gondwanaland, with the Juan Fernan- Cretaceous and Paleogene, and then became d~ population the only surviving relicts. progressively restricted to the Southern Among the earliest angiosperm leaves Hemisphere as global climates deteriorated from southern South America are a few (Jarzen & Dettmann 1989). The paleogeo- specimens from the Barquero formation graphic distribution of Nothofagus has of Patagonia. They are associated with a been reviewed recently by Dettmann et fossil flora dominated by more than 100 at. (1990). The distribution of the forests species of gymnosperms and pteridophytes. that occurred in Antarctica and neigh- The large, lobate, craspedodromous and boring lands by the Campanian suggests dentate leaves have ramified tertiary veins 430 AXELROD ET AL. and random fourth-order veinlets. In general tion of their leaf sizes and also in the geo- aspect, they are much like those of the graphic restriction of the larger-leaved Potomac Group, ranging in age from the evergreen taxa (see Birkenmajer & Zastaw- areas, especially those from Zone 1 of the niak 1989). Potomac Group, ranging in age from the Barremian through the Aptian age (ca. The Tertiary ( 65-2 m.y.a.) 125-115 m.y.a.; Romero & Archangelsky 1986). Because of the links that were As reviewed by Menendez ( 1971) and Ro- present at the time, it is to be expected mero (1986), two major vegetation zones that the Cretaceous paleofloras of south- were present in southern South America ern South America, when better known, during much of the Tertiary (Fig. 6). will resemble the contemporary ones of Cool temperate forests were in the south, New Zealand, Australia, and Antarctica, extending to Antarctica and, especially and that the earlier ones will exhibit earlier, with links to Australia, whereas similarities with the contemporary floras subtropical to tropical forests ranged from of India and Africa also. near 4QOS into equatorial regions. The Oxygen-isotope studies of marine mega- maximum southern advance of subtropical fossils of Santonian-Campanian age (85- (or warm temperate) elements seems to 70 m.y.a.), James Ross Island, and from have occurred in the Middle Eocene (i.e., the Maastrichtian (70-65 m.y.a.) of Vega about 40 to 45 m.y.a.), following which Island, Antarctica (Pirrie & Marshall elements associated with warmer climate 1990), indicate cool temperate climate retreated and cool temperate forests, during the Late Cretaceous, with cooling dominated by Nothofagus and austral between the Santonian-Campanian and the gymnosperms, spread some lQO northward. Maastrichtian (70-65 m.y .a.). A generally Only late in the period is there clear evi- similar temperature decline in the high dence of the existence of drier climates Arctic is supported by the morphology of on the eastern side of the southern Andes fossil leaves (Parrish & Spicer 1988). Fossil in Argentina-Chile. woods from James Ross Island suggest In southern South America, the oldest unstressed but seasonal conditions during Tertiary deposit includes the small Funes the Campanian (Francis 1986). Large flora of Danian age (65-70 m.y.a.; Berry leaves (> notophyll) from the Late Cre- 1937a, Romero 1978). Taking into account taceous of King George Island (Zastaw- the results of palynological and paleoxy- niak 1990), indicate a perhumid climate logical studies (Petriella 1972, Archan- with little temperature change. By contrast, ge1sky 197 6a, b), a paleoenvironmental Late Maastrichtian-Paleocene woods show a analysis of this flora was made by Petriella marked change in growth patterns, imply- & Archangelsky (197 5). This analysis ing slower tree growth as a result of im­ indicates that in the area of the Golfo de portant climatic cooling. These data are San Jorge (460S), vegetation similar to consistent with evidence for Early Eocene that now found in southern Brazil, some (ca. 50 m.y.a.) glaciation on King George 2,000 km and 200 of latitude to the north, Island (Birkenmajer & Zastawniak 1989). occurred at that time. Represented are We suggest that it probably was the general mangrove communities, swamp forest, tro- trend to lowered temperature that mo- 'pica1 rainforest, and montane rain forest, dernized the ancestral (Cretaceous) ever- all implying the existence of a humid sub- green forests. Particularly interesting in this tropical forest. The presence of crocodiles connection is the evidence for alternating indicates that minimum winter temperatures glacial-interglacial climates on King George (i.e., in July) were not less than lQOC Island, with cool (glacial) periods in the ( cf. Axelrod 19 84); such conditions now Early Eocene and Late Oligocene._ With occur some 1,500 km to the north (Volk- continued climatic fluctuation, species heimer 1971 ). of the fossil forests became increasingly Of interest is the occurrence in thb modernized, as seen in the gradual reduc- flora of a few plant genera that provide HISTORY OF TEMPERATE VEGETATION 431

+2 +1 +4 ... 3 +S-8 o· +9 4-10 t-11 10" i-12 t-13

NE ROPICAL 20" PALEOFLOR

30" Northern

40"

~g(26'JI.) 27 eo· s Maaatrlcttlan t.tile Eocene 1.Q:Ja' Eocene Oligocene

Fig. 6: Shifting areas of the Neotropical and Antarctic Paleofloras during the Tertiary (from Romero 1986). Areas derivadas de paleofloras neotropicales y antarticas durante el Terciario (de Romero 1986).

links to Australasia, includingDracrycarpus, eludes some 25 species (Berry 1925); Dicranocarpus and Gunnera, as well as the names applied to these taxa by Berry Tricolpites fil/ii, which is a pollen fossil are doubtless much in need of revision. that resembles Beauprea (Proteaceae), re- More than two-thirds of them, however, corded in New Zealand in the Cretaceous have leaves with entire margins, indicating (see Fig. 1). Other elements that link New that the forest at the sites W<'" a marginal Zealand and South America are Anacolosa tropical rainforest, perhap consisting and Nypa, although they are not as com- mainly of present-day Neotrupical genera mon as in Australasia. Indications of genera and their relatives. Endemics of the present that appear in the record in South America Australian region, including Gymnostoma for the first time, evidently reaching New (Casuarinaceae), also occurred in this Zealand during the Eocene and Oligocene, flora (Freguelli 1943). Somewhat sur- are provided by pollen similar to that of prisingly, Nothofagus has not yet been Banksia and Weinmannia. found in this flora. Of evolutionary interest is fossil palm Petrified wood from the vicinity of wood (Palmoxylon patagonicum Romero), Chile Chico, XI Region of Chile, located from the Danian age of Chubut Province, directly east of these Argentine localities, Argentina (Romero 1968). The author has been reported from the Paleocene concludes that since the wood has cha- (Nishida et a/. 1990). The three samples racteristics intermediate between those of resemble the wood of Kageneckia or the subfamilies Sabaloideae, Cocoideae, Quillaja (dominant elements in the me- and Bactrioideae, now represented in Chile diterranean-type vegetation of central Chile and Argentina, that this fossil may belong today), Proteaceae, and Lauraceae, res- to an ancestral stock from which these pectively, and clearly reflect a warm- groups subsequently differentiated. temperate to subtropical climate at that The Paleocene flora of Laguna del Hun- time. Notably, the genus Quil/aja and co, northwest Patagonia, dated at 59 mil- other matorral elements are today disjunct lion years old (Archangelsky 1974), in- to southern Brazil (Arroyo et a/. 1991 ). 432 AXELROD ET AL.

The flora from Lota and Coronel in Chile Eocene climate was warmer than that of (370S), from the Early Eocene (ca. 55-50 the later Eocene in these regions. m.y .a.), was described by Berry (1922) Middle Eocene Patagonian fossil floras as including well over 100 species; he occur in the Rio Turbio formation (Hu- compared it with modern species from the nicken 1966). The flora contains a mixture Amazon Basin. Certainly the aspect of of Neotropical and Antarctic genera, the flora suggests that the climate was among which are species of Acmopyle, wet, lacked freezing temperatures, and was Allophyllus, Cissus, Cupania, Drimys, Mes­ considerably warmer than at present, which pilodaphne, Myrica, Nectandra, Nothofa­ agrees with a lack of mountain barriers gus, Notophoebe, Ocotea, Persea, Phoebe, at the time, and the presence of a very Rhamnidium, Styrax, and Zizyphus. Alth- equable climate. This fossil assemblage is ough these determinations should be exa- poorly described, and would repay ad- mined critically, the leaves suggest that ditional study. these plants constituted a moist, warm- Berry (1938) described another Early temperate forest in which elements that Eocene flora from Rio Pichileufu, Ar- currently occur farther north were mixed gentina. He considered that many of the with others that are characteristic of South species were the same as those at Lota and American temperate forest today. The Coronel, Chile, which agrees with the lack leaves are of intermediate size (notophyll, of mountain barriers at that time. Berry microphyll), and many are serrate. interpreted this rich flora as including On Antarctica (Fig. 7) during the Cam- tropical and temperate elements; its varia- panian age to Paleocene (83-55 m.y.a.), bility suggest that it represents an eco- the development of the regional vegetation tonal climate. The absence of Nothofagus has been traced by several authors (Baldo- here implies that the Paleocene-Early ni & Barreda 1987, Dettmann & Thomson

Weddell Sea

+ IEARDIIDRE 80°5 }': &LACIER WEST "'o e ".r0 ANTARCTICA ANTARCTIC~ u "-"o,..

J "" C'_..-c; ~ oJO _.... ;-~- ... -- R03$ Sea

----Edge of 3helf ice 180° + 70

Fig. 7: Fossil floras on Antarctica. F1oras f6siles de la Antartica. HISTORY OF TEMPERATE VEGETATION 433

1987, Romero 1987). The pollen of po- docarps is abundant and diverse (Askin 1988a). Araucarian pollen is also repre- sented, moss and fern spores are common, and all three groups of Nothofagidites (Nothofagus pollen-brassii, fusca, menziesii types) are recorded. Other angiosperm pol- len can be referred to diverse families, notably Proteaceae, Loranthaceae, Myrta- ceae, and Casuarinaceae, and to the orders Ericales and Liliales, although the modern generic affinities have not been established. These fossils represent members of low land forest and moist fluvial-lacustrine-swamp areas mixed with some palynomorphs probably transported from upland com- munities. The dominant podocarp vegeta- 0 tion suggests a cool temperate, moist R climate such as that now in southern Chile, with its podocarps and araucariads growing with Nothofagus. The distinctive pollen of Phyllocladites, common on Sey- mour Island, may be that of the modern genus Dacrydium, which occurs in western Tasmanian rainforests. 0 400 Km I I Compressions of ferns, Nothofagus, and podocarp foliage in the upper Cross Valley Formation represent a cool temperate Fig. 8: Fossil floras on the Antarctic Peninsula. rainforest (Case 1988). Wood from the Floras fosiles de Ia Peninsula Antartica. Cross Valley and Sobral formations have uniform growth rings indicating a "stable" forest environment (Francis 1986). From South American ancestry near Polydolops the Campanian and Maastrichtian ages thomai or P. rothi, similar to that suggest- (83-65 m.y.a.), there is an increased di- ed by the contemporaneous La Meseta versity of angiosperms, with approximately species Antarctodolops dailyi. This suggests 100 pollen and spore taxa represented. a Paleocene age for the origin of the Sey- The pollen sequence provides no evidence mour Island polydolopids, with a likely of a major extinction event at the Creta- time of dispersal from South America ceous-Tertiary boundary in this region about 60-55 million years ago. Isolation (Askin 1988b). apparently accounts for the Seymour taxa In their review of the Nothofagus spe- being differently specialized from each cies described by Dusen, Romero & Dib- other, as well as from their South American bern (1985) point out that the Seymour allies; they differ remarkably from the Island fossils from the Cross Valley Forma- trends exhibited by the South American tion can be compared with four living polydolopids during the Paleocene and South American species, all deciduous Eocene (Case et al. 1988). These authors and including the fusca and menziesii further point out that the land area in pollen types. southern South America-Antarctica, New Of special interest is the finding of a Zealand, and Australia was covered with a polydolopoid marsupial (Eurydolops sey­ relatively dense Nothofagus-dominated mourensis) from the Late Eocene La Me- forest (see Fig. 1). The arboreal marsu- seta Formation of Seymour Island (Case pials would have been at a selective ad- et al. 1988), (Fig. 8). It apparently had a vantage in such forests. Polydolopoids 434 AXELROD ET AL. possibly filled the rodent or primate were recorded. The assemblage resembles adaptive niches in South America and the the contemporary deciduous forest of Antarctic Peninsula prior to the intro- Nothofagus obliquo and N. procera that duction of these groups to South America. is associated with evergreen, laurophyllous Probable microbiotheriid marsupial remains taxa (Hueck 1966). These thrive under a have also been found in Antarctica in mean annual temperature of ll-120C, Paleogene time (Carlini et al. 1990). in a highly equable climate (M 65+ ), Other lines of evidence are not in agree- one with a very low mean annual range of ment with the hypothesis that Antarctica temperature (7-80C), and represent a at this time was covered with temperate warmth (W) of 12.5-l30C, with 138- Nothofagus forest, however. The recent 153 days warmer. discovery of a tardigrade edentate, a pla- A rich pollen flora from Ezcurra Inlet cental mammal, from the Paleogene of is close to the Dufaley Island locality Antarctica rather suggests the existence (Stuchlik 1981 ). Also of Eocene age, it of warm-temperate environments (Carlini includes a rich fern flora with taxa as- et al. 1990). Such mammals were ap- signed to Schizaeaceae, Hymenophyllaceae, parently relictual in northern Antarctica Gleicheniaceae, Cyatheaceae, and Salvinia- at the time, but may have been widespread ceae. Angiosperms include Nothofagus and there earlier. Rhammaceae. The absence of conifers is The occurrence in the La Meseta Forma- noteworthy (also see Barton 1963). In tion of a fossil beak of a two-meter tall any event, the assemblage indicates a canivorous bird in the Late Eocene ( 40 humid, cool temperate forest environment. m.y.a.) of Seymour Island is significant Megafossil plants have been described for both biogeographical and ecological from the Mount Wawel Formation, Upper reasons (Woodburne et al. 1987). It is Oligocene (25 m.y .a.), Admiralty Bay, allied to other predaceous (flightless) King George Island, in the South Shetland birds of the phororhacoid group known also Islands (Zastawniak et al. 1985). Numerous in South America in the Tertiary. The oc- impressions of Nothofagus represent several currence of such a bird on Seymour Island species, and Podocarpaceae are represented indicates that its ancestors made use of by shoot fragments and numerous seeds. the land connection that existed before Dicotyledonous remains also include leaves the opening of the Drake Passage some I 0 resembling those of Cochlospermum and million years later. The bird would have Rhamnaceae, and indicate a diverse tem- inhabited relatively open country, and its perate forest in West Antarctica at the occurrence suggests that such a com- close of the Oligocene. Small leaves (no- munity may have been widespread in greater tophyll and microphyll) dominate the West Antarctica, presumably in large gaps flora and compare well with those that in the Nothofagus-dominated forest. are frequent in recent Australian-New From the Dufayel Island Group, situated Zealand cool temperate rainforests. in a western arm of Admiralty Bay, King From McMurdo Sound, Antarctica (see George Island, numerous plant remains Fig. 7), Mcintyre & Wilson (1966) note that are diverse, but poorly preserved, that the microfloras in erratic boulders were reported by Birkenmajer & Zataw- of Eocene age are dominated by Notho­ niak ( 1986). The beds are dated radiome- fagus, representing all three major groups. trically as transitional Paleocene-Eocene Also recorded are Araucaria, Dacrydium, (57 -5 I m .y .a.) on the basis of associated Phyllocladus, Podocarpus and Myrtaceae, lavas above and below the flora. The plant as well Proteaceae. Nothofagus comprises assemblage is dominated by Nothofagus, some 80% of the pollen, with gymnosperms Myrtaceae, and various taxa that resemble 5-l 0% and angiosperms other than Notho­ Lauraceae. Leaves are of nothophyll size, fagus the remainder. The flora compares implying a cool temperate rainforest en- with that in the cool temperate forests vironment much like that of southern of New Zealand, and indicates ample rain- Chile today. No remains of gymnosperms fall. HISTORY OF TEMPERATE VEGETATION 435

From glacial marine sediments in Prydz of the genus and compared them with the Bay-West Ice Shelf, East Antarctica, Kemp living ones. He divides the extant species (1972) records abundant pollen of Notho­ into five groups, as follows: fagus, as well as that of several species of Proteaceae, Myrtaceae, Microcachrys, Po- Group 1. Five species, South America. docarpaceae, and several families of ferns. Group 2. Two species in South America, Noteworthy is the presence of all three one in Tasmania. groups of Nothofagus. The bulk of the Group 3. Three species on South America. evidence indicates that the assemblage Group 4. Seven species in New Zealand, was derived from eroded Eocene sedimen- Australia, Tasmania. tary rocks and that the flora represents a Group 5. Species of New Caledonia and rich Nothofagus forest filled with ferns New Guinea. and associated gymnosperms and angio- sperms, in an area now under ice. These groups appear to be of funda- Palynological evidence from drilling in mental significance. Nothofagus apparently the Ross Sea by Glomar Challenger sug- originated in the far south in the Middle gests that vegetation persisted in that Cretaceous, migrating northward as the area into the Late Oligocene (Kemp & climate became cooler during the Tertiary; Barrett 1975). The sample occurs with it apparently reached its maximum extent a dated (26 m.y.a.) glauconitic sandstone. during the Miocene. Considering the wide The assemblage is dominated by Nothofa­ distribution of presently Australian-New gus of all three groups, and includes Podo- Zealand-New Guinea gymnosperms in South carpaceae (Dacrydium, Microcachrys) and America during the Early Tertiary, it is pollen assigned to angiosperm families noteworthy that only a single con- including Proteaceae and Myrtaceae, as well temporary group of the genus, group 2, as several families of ferns. Taken as a links these two regions. The much richer whole, the forest here was apparently representation of fundamentally austral less diverse than that from the older Sey- groups in Australasia than in South America mour Island deposits, indicating a some- at present, together with the earlier oc- what cooler climate. The authors suggest currence of additional groups, now res- that forests in the area may have been tricted to the Old World, in South America confined chiefly to the coastal zone, and (Raven and Axelrod 1974), implies much to slopes above the valley glaciers that extinction in South America. debouched into Ross Sea. The Notho­ In northwestern Patagonia, at the ge- fagus flora was still essentially continuous neral latitude of Puerto Montt, are several at sea level from the Palmer Peninsula to florules of Late Miocene age (8-5 m.y.a.) Ross Sea, a distance of some 4,700 kilo- that have yielded some 45 species, many meters, at the close of the Oligocene with Antarctic affinities (Berry 1928). (Mildenhall 198 9), then linking the biotas These florules are dominated by genera of southern Chile with those of south- such as Araucaria and Nothofagus as well eastern Australia/Tasmania. Similar vegeta- as by leaves resembling Proteaceae. The tion persisted in this area until the Middle percentage of species with non-entire Miocene (ca. 14 m.y .a.) although its di- leaf margins has increased from that found versity seems to have decreased progres- in older floras to fully 70.,.; these florules sively as the continental glaciers expand- apparently represent a cool temperate rain ed (Brady & Martin 1979). Fig. 9 illustrates forest. As judged from the small size of the development of the ice sheet on An- the leaves represented (microphyll, nano- tarctica during the past 20 million years phyll), this forest seems to reflect major (Ciesielski eta/. 1982). cooling following the Middle Eocene. A Following the lead of Romero ( 1980) continuation of this trend is shown by a and Romero & Aguirre ( 1982) on the com- number of small floras in southernmost parative architecture of Nothofagus leaves, Chile and Argentina (reviewed by Romero Tanai ( 1986) reviewed the fossil species 1986). These show few species with entire 436 AXELROD ET AL.

a

0 1500

Ice covering land • above sea level [3] Ice shelf !'7/llce grounded ~ below sea level

Fig. 9: Stages in the history of West Antarctica since the Oligo-Miocene. a. An- tarctica archipelago prior to late Miocene; b. showing ice sheets since late Miocene; c. present West Antarctica showing exent of ice shelves and ice sheet grounded below sea level (from Ciesielski et al. 1982). Estados en Ia historia de Ant:irtica occidental desde el Oligoceno-Mioceno. a. antes del Mioceno tardio. b. extension de los casquetes de hielo desde el Mioceno tardio. c. situacion actual in- dicando Ia extension de los casquetes de hielo por debajo del nivel del mar (tornado de Cie- sielski et al. 1982). leaf margins and an increase in the num- as the monte. The uplift occurred in ber of smaller leaves, chiefly nanophylls several phases, as outlined by Van der Ham- and a few microphylls. men (1961), of which those of the Mio- Miocene floras are well known to the cene and Pliocene-Pleistocene account for north -outside of our area of general most of the present relief (Van der Ham- interest- where they have been elevated men 1961, Arroyo et al. 1988). The An- in the Andes to 2,000-3,000 meters above des provided an important corridor for sea level. The elevation of the Andes result- northward migration of southern genera ed in the development of drier climates such as Weinmannia and the north-south along the west coast of South America, migration of temperate elements such as and also southward on the east side of the Escallonia (Arroyo et al. 1988). Although Andes, resulting in the formation of the the identifications should be reviewed, pampas and allied scrub formations, such such genera have been recorded in Mio- HISTORY OF TEMPERATE VEGETATION 437 cene deposits in Bolivia, intermixed with climate. It represents a wet, tropical low- tropical elements (Berry 1917, 1939). land flora of Amazonian character. Mio- At present, however, they are largely absent cene age. Considerable uplift has clearly on the western flanks of the Andes at occurred since the flora was deposited. similar latitudes, presumably because of the Zorritas, Peru. A rich flora from the Late Tertiary development of the Atacama present coastal desert area of Peru. The Desert. Noteworthy is the fact that no leaves are of tropical rainforest plants, cool-temperate tree genus of North America indicating that the Andes had not been has reached the temperate forests of sufficiently elevated by the Middle Mio- southern South America by this route, cene (ca. 12 m.y.a.) to intercept rains despite the elevation of the Isthmus of from the Amazon Basin to the east, and Panama several million years ago. that the Humboldt Current was not suf- In his review of the paleogeography ficiently effective by that time to give and paleoclimatology of South America, the present coastal region a dry climate. Romero ( 1986) synthesized available data Potos(, Bolivia. The flora comes from that show the general trend of paleoenvi- the high altiplano at an elevaton of 4,100 ronment. His graph, reproduced here as meters; it consists of plants now found Fig. 6, illustrates the environmental change. at much lower elevations. It is a dry thorn A Neotropical paleoflora reached south- bush or thorn scrub community that ward to near 450S in the Maastrichtian- includes many small leaves and leaflets. Paleocene (73-55 m.y.a.), with a south- The revision of this flora, and the accurate ern phase represented by numerous (60oto) identification of the elements in it, would entire-margined leaves. This paleoflora was be of great interest in tracing the evolution replaced in the Early to Middle Eocene of the plant communities of South America. (55-45 m.y.a.) by mixed forest in which Psillypampa, Bolivia. This flora is from Notofagus and its associates are mingled the Sierra de Cochabamba at an elevation with those of the "tropical" vegetation. of 3,600 meters. The leaves represented From the Middle Eocene into the Oligo- indicate a diverse, wet tropical forest like cene, the southern province was dominated that now found in the yungas of Bolivia by the Antarctic Paleoflora, with Notho­ below 1 ,500 m elevation. fagus making up to 25-27% of the floras. Considering that the ages of these latter Similar relationships have been analyzed floras need to be determined more accu- among the present-day floras of other rately using radiometric dating whenever Southern Hemisphere areas, as for example possible, they nonetheless document floras along the western side of the South Island wholly different from those that occurred of New Zealand (Haase 1990); they help on Antarctica (and presumably southern greatly to illuminate past conditions. South America) at the same time. All There is little fossil evidence from now occur at elevations much higher than southern South America that documents those at which they were deposited, in- the floristic changes that resulted in the dicating the uplift of the Andes in Late formation of present-day communities over Cenozoic time -initially during the later the past 25 million years, since the close Miocene and Pliocene, and especially of the Oligocene. These changes, however, during the Pleistocene. At these times, the may be inferred from geologic evidence dry climate that now covers the eastern (e.g., Ramos 1989) and floristic informa- side of the southern Andes and supports tion provided by floras from the Andes the Patagonian desert, pampas, and monte to the north, in Ecuador, Peru, Bolivia, developed from forerunners in the border- and northern Chile. The floras, largely ing Tertiary vegetation (Fig. 5). To the described and reviewed by Berry (1938), north, the matorral and vegetation of the and in need of revision, include the follow- Atacama Desert and bordering semidesert ing: spread from small, isolated areas to form Loja, Ecuador. A large flora now at an the present vegetation. Likewise, the elevation of 2.135 meters in temperate vegetation of the high altiplano is clearly 438 AXELROD ET AL. of comparatively recent origin (Arroyo of the forests there (Axelrod 1985, p. et al. 1988). 102; 199la). As these modern vegetation types spread, there were increased opportunities for accelerating the interchange of plants and PROBLEMS FOR CONSIDERATION some animals between comparable com- munities in North and South America I. Origin of evergreen and deciduous habits (Raven 1963, Raven & Axelrod 1974). in temperate forests Such interchange had been occurring be- tween dryland species in local pockets In the far south, land areas were basically of semiarid vegetation in the tropics since under insular climates following the Early at least the Eocene, but it was greatly Cretaceous (Krutzsch 1989): in other accelerated during the past 15 million words, for 125 million years or more. These years, and especially during Quaternary climates, like those that now prevail in time (the past two million years), account- southern Chile and New Zealand are cha- ing for some of the detailed similarities racterized by highly equable conditions, between the dryland -but not, by and with a range of mean annual temperature large, the temperate forest communities of generally less than IQOC. Similar condi- of North and South America. tions are found also in the high mountains The floristic changes and the accompany- of the tropics, as in New Guinea, Kenya, ing (inferred) climatic modifications that and the eastern Himalayas. Genera of we have reviewed are paralleled by changes these austral evergreen forests were derived in the South American mammalian faunas chiefly from evergreen ancestral taxa (Pascual 1984). Pascual notes that there that deployed there from more tropical were contemporaneous changes in global regions during the Cretaceous. marine temperature, sea level variations, By contrast, in north temperate regions and diastrophic events. The marked cooling the broadleaved angiosperms are chiefly following the Early Middle Miocene is re- deciduous. They originated from ancestral flected in the Patagonian Friasian (ca. groups (e.g., Acer, Betula, Carya, Dios­ 16-12 m.y.a.) mammals, the age of which pyros, Magnolia), as they spread north- is charted with radiometric dates by ward and encountered more continental Marshall et al. (1977) and is centered at climates, owing to the larger land masses 15-14 million years ago. This was the there. It is noteworthy that in south- commencement of a major cycle of aridity, western North America, North Africa, cooler climate, and more varied environ- and southwest Asia, woods from the Ju- mental subdivision. Most of the Early rassic and Early Cretaceous show either Miocene Santa Cruzian taxa related to prominent or faint growth rings (Creber subtropical woodlands became extinct or & Chaloner 1985, Table 1, Fig. 2). All of disappeared from Patagonia. The com- these regions are centered in the present mencement of the Friasian Land Mam- deserts, which developed recently. This mal Age correspond to a diastrophic phase record shows that a seasonally dry climate that resulted in the rise of the Patagonian existed in these areas during the Mesozoic. Andean Cordillera leading to the initial The deciduous habit can be related to steps of Patagonian desertification. Very seasonally drier climate, which may have probably there is also a correlation with influenced the early development of this the onset of major continental glaciation habit on the northern margins of the tro- on Antarctica. It is indeed significant pics (Axelrod 1966b). In this regard, it is that this was the first time (15-14 m.y.a.) recalled that even a slight period of drought- major floristic changes occurred in the -say two weeks- in the superhumid Great Basin of the western United States. inner tropics, will bring many forest trees At the time, there was a very rapid disap- into a severe wilting state, and their leaves pearance of broadleaved deciduous hard- may fall. A moderately longer period of woods that previously Wf':re co-dominants drought on its borders would have a similar HISTORY OF TEMPERATE VEGETATION 439 effect on the broadleaved trees ancestral brief period of semi-darkness could have to the present deciduous genera. Actually, affected the genetic makeup of so many much of the so-called rainforest region does divergent families of plants seems unlikely. have a dry season of slight to moderate Seeds in the ground would have been unaf- length. In some areas, it is in the winter fected by the darkness or semidarkness season, in others in the summer (see -they were already under such conditions. precipitation data in Wernstedt 1972). The fossil record shows that the deciduous Inasmuch as most deciduous genera have habit had already developed in the Cre- their roots in tropical families, and a taceous. That deciduous taxa rapidly rose number of them also have evergreen species to dominance in the Paleocene at middle (as in Acer, Alnus, and Magnolia) in the and higher latitudes seems consistent tropical and warm temperate regions today, with. the restriction of seaways at this gradual adaptation to drought on the time (see Krutzsch 1989), widespread drier margins of the wet tropics probably vulcanism, and the development of more accounts for the deciduous habit. It was, continental, cooler climates (see Axelrod in essence, a preadaptation to the develop- 1981, Hallam 1984, Crowley & North ing colder winters and longer dark winter 1988, Officer et al. 1987, Officer & Drake period that angiosperms encountered as 198 5). Since broadleaved evergreens were they migrated northward. less adapted to such conditions than de- In the south, the forests are predomi- ciduous hardwoods, they became less nantly evergreen, as mentioned above, prominent in the vegetation over temperate but with some widespread species of latitudes and soon disappeared from the Nothofagus deciduous. The first evidence forest there. of deciduousness in southernmost South America is from the Eocene, far removed from regions of seasonal darkness (Ro- 2. What accounts for the mixed mero 1988). Clearly, the origin of the paleo floras? deciduous habit in South America is re- lated to the appearance of cool, seasonal Romero ( 1986) reviewed the problem of climates, and not to winter darkness. mixed paleofloras in the austral portion Northern-hemisphere, trees are adapted of South America, where members of the to the periodical occurence of freezing Neotropical Paleoflora mingled with those temperatures, whereas southern-hemisphere of the Antarctic Paleoflora in an inter- ones are not (e.g. Read & Hill 1989). The mediate zone (Fig. 6). Among the expla- deciduous habit in Nothofagus may have nations previously offered are the follow- originated under cool climate on An- ing: tarctica. In this regard, a current detailed Dusen (1899) explained the mixing of study suggests that deciduousness is pri- species on the basis of topography, with mitive in Nothofagus, and that the ever- those of the Antarctic Paleoflora occupy- green habit has arisen more than once ing higher, cooler terrains than those of (Hill & Read, 1991 ). the Tropical Paleoflora in the lowlands. Another view (Wolfe 1987a), considers In the Appalachian region, the mingling that the terminal Cretaceous event (the of temperate deciduous hardwoods with "impact winter") resulted in widespread broadleaved evergreen (Brown 1944) was selection for plants of deciduous habit also explained by transport form distant and diversification of deciduous taxa in montane sites in the Eocene Appalachian the Northern Hemisphere. There is no Range. evidence that the bolide impact affected Romero ( 1988) suggested that these Southern Hemisphere vegetation (see Askin mixtures were the remains of an Eocene 1986b). In the north, the duration of the stable phytogeographic unit, and that light-intercepting bolide impact must have the species had ecologic-climatic requi- been brief, perhaps a few to several months, rements unlike those of present-day plant according to Wolfe's estimate. That such a formations. Kemp ( 1978) also found that 440 AXELROD ET AL.

in the Australian region, there is a mixture Equable climate enabled taxa to extend of pollen representing tropical-subtropical far outside their "normal" ranges of dis- taxa with those of cool temperate rain- tribution as we know them today (Axel- forest communities. This suggested that rod 1984 ). This applies to cycads in South the Early Tertiary vegetation is not re- Africa and Australia that enter wholly presented by a modern forest, and that temperate regions; species of Araucaria the Eocene forest had a climate unlike are distributed from tropical up into any at present. cold temperate climates; and palms in New Another explanation calls on an equable Zealand occur in cool temperate regions. climate, one in which conditions are neither In these examples, distribution is governed too cool for tropical plants nor too warm by a moist climate of high equability for temperate ones (Axelrod 1984). Cli- (temperateness), chiefly with a rating of mates with a low range of temperate are M 60-70. These relations also clarify the closer in elevation. Under a theoretical problem of the mixtures of taxa repre- climate with no annual range of tempe- senting the Antarctic and Neotropical rature (A = 0), tropical and polar climates Paleofloras. As pointed out earlier (Axelrod are only soc apart, or I ,464 meters in ele- 1984, pp. 114-115), a number of basically vation assuming a normal terrestrial lapse tropical genera that range south in eastern rate. Under a regime of IQOC mean annual Australia to 20-300S, occur in New Zea- range of temperature, polar and temperate land at much higher latitudes, chiefly climates are separated by 180C, or 3,294 35-420S. Among these genera are Alec­ meters. Owing to the absence of high tryon, Beilschmeidia, Corynocarpus, Dyso­ mountains and plateaus, seaways on the xylum, Elatostema, Freycinetia, Genios­ continents, and no ice cover, global cli- toma, Litsea, Macro piper, Peperomia, Schef­ mates were much more equable than at flera, Tecomanthe, and Vitex. Most of present. On this basis, the mixtures of them range southward into the north- warm-and cool-adapted taxa were in broad ern half of South Island. In New Zealand, ecotones characterized by a low range of they are in proximity to, and often as- temperature in which species regularly sociated with, Agathis, Nothofagus, Po­ intermingled near sites of deposition. docarpus, and their usual associates -plants The overlapping nature of species distri- of Antarctic affinities. We suggest therefore butions along altitudinal gradients is a that the mixtures of genera representing common feature of present-day North the two major paleofloras in the South- Island forest of New Zealand (e.g., Elder ern Hemisphere was not an unusual re- 1965, Druitt et a/. 1990), with a markedly lationship, but normal and expectable equable climate. Woody vegetation types under the widespread, more equable Ter- in the mediterranean-type climate zone of tiary climate. central Chile, with a fairly equable climate, seem to be less discrete than analogous communities in California, which has a 3. Did the Antarctic Ice Sheet disappear comparatively continental climate com- during the Pliocene? pared with that in Chile. Moreover, in southern South America at the present Recently, a deposit with numerous unalte- time, deciduous species such as Notho­ red leaves of Nothofagus was collected fagus obliqua grow along side evergreen from the Transantarctic Mountains, at a taxa such as the taxonomically isolated site within 400 km of the South Pole and seemingly relictual Aextoxicon punc­ (Peterson 1991, Raymond, 1991). The tatum. Detailed studies of the altitudinal deposit has been considered to be about ranges of contemporary woody species 3 m.y., or middle Pliocene (see Fig. 9). in Chile, as compared with California and This raises the question as to whether the the Pacific Northwest, might shed ad- Antarctic ice sheet melted during (or be- ditional light on the development of this fore) the Pliocene, or whether the deposit hypothesis. is older than now considered by the col- HISTORY OF TEMPERATE VEGETATION 441 lectors. However it is possible that the Antarctica. Memoirs of the Geological Society of America 169: 155-162. deposit is young and the leaves are from ASKIN RA (1989) Endemism and heterochroneity in trees that lived on slopes above valley the Late Cretaceous (Campanian) to Paleocene glaciers, much as illustrated for the Franz palynofloras of Seymour Island, Antarctica: Im- plications for origins, dispersal, and paleoclimates Joseph Glacier in southern New Zealand of southern floras. In: Crame JA (ed.). Origins today (Seward, 1941 -frontispiece). and Evolution of the Antarctic Biota: 107-119. Geological Society of London Special Publication Number 47. AXELROD DI (1952) A theory of angiosperm evolution. Evolution 6: 29-60. ACKNOWLEDGMENTS AXELROD DI (1959) Poleward migration of early angiosperm flora. Science 130: 203-207. We acknowledge support from the U.S. National Science AXELROD DI (1964) The Miocene Trapper Creek flora Foundation to PR and DA, as well as from FONDECYT of southern Idaho. 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