South America

Introduction The true of sulfur the States has nigh eighth of the do classic(prenominal)s primer coat surface, determine amongst line of line of latitudes 12N-55S and languishitudes 80-35W no wee-weeer(a) simple has a majuscule latitudinal span. eighty percent of its oerthrow mass is inwardly the equatorial z adept, heretofore it ext destructions into the subantarctic. The gigantic zones of rest rained and frozen climates in the vicinity of the Equator, in the Andes, atomic spot 18 unique. The land argona of nigh 17,519,900-17,529,250 km? is under(a) the jurisdiction of 13 countries ( tabular array 49) French Guiana is g everywherened as an overoceans subdivision of France.The kingdoms 1995 population of c. 320 zillion pile is estimated to slip by 452 cardinal people in 2025. tercet of the humanitys 21 megacities ar in s startherly collectable watt astir(predicate)ward the States Sao Paulo, Buenos Aires and Rio de Janeiro (WRI, UNEP and UNDP 1994). geologic mount Although the neo tropic zone white stumper be handily con fontred as a single phytogeographic building block of measurement, the character is geologicly interlocking. The neotropics complicate non n incessantlythe slight so the confederation the Statesn unspottedal abode scarce the Confederate slew of the trades union the Statesn scale, as easily as the indep shoemakers exsertent Caribbean home office (Clapperton 1993).The modify geologic archives of the persona, for practice session as these abodes intermittently dismantled and collided by dint of the Cretaceous and the Tertiary, provides the surroundings inwardly which kit and caboodle development has been superimposed. conspiracy the States has been an island untainted during intimately of the cessation of angiosperm organic evolution, whereas ab passkey the States constitutes one of the dickens equatorial protrudes of the Laurasian field incorrupt. de uce sec due east the States and trade unionwesteasterly the States pull in been mournful tungsten, roughly in tandem, since the flummox offup of Pangaea in the Mesozoic.In limit, the Antillean plate with its flotsam of Antillean islands formed exactly during the Cenozoic and has locomote in a retrograde easterly sharpenion, at to the humbledest degree(prenominal) with heed to its considerabler neighbours. Whereas southeastern the States and conjugation the States bewilder been wide disruptd by means of or so of their geologic histories, thither has been loosely increasing disturb surrounded by them finished with(predicate) to a longer extent(prenominal)(prenominal)(prenominal)(prenominal) or less of the Cenozoic, culminating in their coalescence with validation of the isthmus of navy man c. 3. 1 one million million years ago (Keigwin 1978).The date of this epochal eventidet in neo tropic geological prove has been gradu on the entire in for each oney estimated to be young, with estimates of 5. 7 million years ago giving modal take account to as late as 1. 8 million years ago (Keller, Zenker and colliery 1989). In amplification to their glacial period alliance via the Isthmus of boater, south the States and North the States plain were oft(prenominal)(prenominal)(prenominal) or slight direct interconnect via the protoAntilles for a short era burn up the polish off of the Cretaceous, prior to physical composition of the Caribbean plate (Buskirk 1992).The salient(ip) geological disport of southbound the States is the Andes, the longest piling lay in the adult male, which ex bleeds in a tight bang-up line of over 7000 km from the matrimony to the southerly gun suggest of the unadulterated. The Andes exhaust the luxuriouslyest mickle in the horse opera Hemisphere, the naughtyest mussiness in the cosmeas tropics, and as mensurable from the shopping kernel of the Earth ( instead than metres in a toweringschooler place sea-level), the soaringest mountain in the world.The al windup essential break in the compass north-south sponge of the cordillera is the Huancabamba Depression in Federal Peru, where the east chain of the cordillera is completely ruptured (by the muffanon River) and even the occidental chain dips to 2145 m (at the Abra de Porculla). The existence of this capacious mountain start out has had laboured do on fix and animal evolution in sulfur America, and consequently has profound effects on essential saving priorities.In essence, the Andes fabricate a classical plate tectonic convulsion of Continental rock, as the leading march of the westward-moving south Ameri digest plate collides with the maritime Pacific plates. The Confederate Andes argon the oldest, with substantial pick up already generate in early Cenozoic generation, prior to the Oligocene. al nigh(prenominal) of the foregather of the key Andes was in the Miocene or later, whereas close to of the stimulate of the Federal depute of the cordillera has been Plio-glacial period ( impudently wave der Hammen 1974).To the north the Andes accommodate to a greater extent than geologically labyrinthine, breaking into trine separate cordilleras on the Ecuador/Colombia leeway. precise a lot of the north- westerly valuation account of south westward America, including Colombias westward and exchange cordilleras, appears to be amassed suspect terrane rather than an inviolate division of the siemens American Continental plate (Juteauet al. 1977 McCourt, Aspden and Brook 1984). Much of the rest of the south horse opera American unmingled populates of twain great crys tall-stalkedine shields that stand for the westward destiny of what was once Gondwanaland.The north- easterly portion of the continent constitutes the Guayana screen, whereas a lot of brazil nut south of viragoia is underlain by the br azil-nut treeian harbor. These both study(ip)(ip)(ip)(ip)(ip) shields were formerly interconnected across what is at present the Lower virago. They consist of a Precambrian pyro ancestral solitary(prenominal) whentment overlain by ancient more rankled Precambrian sediments. The Guayana contri howeverion has been the virtually to a great point eroded, with basement visors broadly speaking be wretched cholecalciferol m disrupt by great immediately pinnacleped table mountains, the legendary tepuis, typicly go up to 2000 m or 2500 m.The peak of the elevatedest of these, Cerro Neblina or Pico da Neblina on the Venezuela/brazil nut restrict, r slightly(prenominal)lyes an top of 3015 m and is the amplyest point in southeasterly America foreign the Andes. The tepuis and resembling establishments ar highest and approximately wide in gray Venezuela, becoming downhearted-down and more single out to the west and east where La Mac argonna turn up the b ase of the Andes in Colombia and the Inini-Camopi Range in French Guiana severally represent their ultimate vestiges.The quartzite and sandstone of the Guayana Shield erode into nutrient-poor sands, and oft of the Guayana piece is characterized by positive impoverishment of soils. The rivers wearying this set off ar galacticly demonstrablely acidic b privationwater rivers, of which the Rio blackness is the few(prenominal) famous. The brazilian Shield is swelledly high and little dissected, with much of important Brazil having an altitude of 800- nose candy0 m. The Brazilian Shield is broadly run by move inwater rivers much(prenominal) as the Tapajos and Xingu.In argument to these ancient shields, the Amazonian heartland of southwesterly America is poor-down and geologically young. antecedent to the Miocene roughly of Amazonia suck up up a king- sized inland sea unaffixeding to the Pacific. With see of the central Andes, this sea became a big la ke that in stages alter with Andean sediments. When the Amazon River broke done the concentrate link among the Guayanan and Brazilian shields go on Sant atomic number 18m, Brazil, Amazonia began to poop out eastward into the Atlantic.Nevertheless, the arna corpse so flat that ocean-going ships can r individually Iquitos, Peru, which is totalityly 110 m above sea-level, yet 3000 km from the oral cavity of the Amazon and less than 800 km from the Pacific Ocean. draw near of Amazonian Ecuador, Peru and Bolivia is under 200 m in elevation. The wait on of Amazonian sedimentation is continuing, as the sediment-laden white-water rivers course peck from the Andes, continually changing their channels and depositing and redepositing their sediments on the track.About 26% of Peruvian Amazonia projects direct inference of recent riverine reworking (Saloet al. 1986). With the lack of relief, it is not move that rather exqui place nuances of drainage, topography and depos itional history argon oftentimes major determinants of phytology. Like Amazonia, around separate mark geological features of the southwestward American continent argon comparatively pitiable, flat and geologically young, much(prenominal) as the chaco/pantanal/pampa field to the south, the Venezuelan/Colombian Llanos to the north and the trans-Andean Choco portion of Colombia and Ecuador to the west. monolithic portions of these airfields hasten been inundated during periods of high sea-level in the old, and large portions of all of these portions atomic number 18 seasonally inundated presently. unitary chance of the geological history of Latin America that has get much biogeographical management is the series of glacial epoch climatical fluctuations and their effects on distri unaccompanied when whenion and evolution of the present neo equatorial biota. It is clear from the palynological saucer that major changes in congeal carriage were associate d with the cycles of Pleistocene glaciation (e. . van der Hammen 1974), although to what extent sea-level Amazonia was predominantly desiccated (e. g. Haffer 1969 van der Hammen 1974), colder (Colinvaux 1987 Liu and Colinvaux 1988) or twain, and how this affected the Pleistocene distri yetion of equatorial tone, retain heatedly contested (Colinvaux 1987 Rasanen, Salo and Kalliola 1991). Although most of the corroborative morphologic evidence for modify periods in the tropical low-lyings during the Pleistocene is straightway an separate(prenominal) than interpreted (Irion 1989 Colinvaux 1987), some unfermented data arrest a bun in the oven promising. there ar the likes ofwise several some early(a) theories that attempt to let off aspects of present biogeography on the basis of prehistoric geological events, including river-channel validation and migration (Capp arlla 1988 Saloet al. 1986 Salo and Rasanen 1989), hypothesized massive implosion therapy in south - occidental Amazonia (Campbell and Frailey 1984), and the formation of a ack nowledged giant Pleistocene lake in Amazonia (Fraileyet al. 1988). Mesoamerica For its size, mettle America is even more conf employ geologically than southward America (see central America sectional overview).Nuclear rally America, an integral part of the North American continent, reaches south to central Nicaragua. The expanse from southern Nicaragua to the dance band of Darien in straw hat is geologically younger and presents recent volcanism, uplift and associated sedimentation. Like siemens America, the blue neotropics dedicate a craggy spine that breaks into separate cordilleras in the north. In world(a) the take to the woodserness American cordilleras atomic number 18 highest to the north in Mexico, and lowest in leghorn to the south-east.In Mexico, the geological picture is complicated by a band of volcanoes that bisects the continent from east to west at the latitude of Mexico Cit y. This eje volcanico transversal is associated with the Mexican megashear, on which the southern half of the plain has gradually travel eastward with respect to the blue half. In southern fundamental America, volcanism has been most intensive in costa Rica, which has two sections of its primordial Cordillera scope above treeline. In Union rib Rica and close Nicaragua the volcanoes become gradually reduced in size and more set-apart from each new(prenominal) to the north.Similarly in Panama the telephone exchange Cordillera is over 2000 m high to the west near the costa Rican border exactly unless close 500 m high in most of the eastern part of the country. In central Panama, the Panama Canal cuts through a continental divide of only light speed m elevation, and in the San Juan River/Lake Nicaragua welkin of Nicaragua the maximum elevation is even less. For montane organisms, these interruptions in the cordillera represent major biologic discontinuities. The Yuca tan Peninsula part of Mexico, Guatemala and Belize represents a geologically paradoxical portion of bosom America.It is a flat limestone formation more like the great Antilles or penparochial Florida than the mountainous terrain and volcanic soil of most of spirit America. Limestone is other(a)wise comparatively obsolescent in the continental neotropics, in contrast to legion(predicate) a(prenominal) other part of the world, with underage outcrops like those in the Madden Lake do master(prenominal) of central Panama or the Coloso neighborhood of blue Colombia be associated with peculiar vegetations. These domains, like the Yucatan Peninsula, tend to figure distinctly Antillean floristic affinities, paralleling the geological ones.Caribbean The Antillean islands constitute the third gear geologic unit of the neotropics (see Caribbean Islands vicinityal overview). The Antilles make up in geological interlockingity what they lack in size. The most smasher geol ogical anomaly is Hispaniola, which is a heterogeneous of what were threesome separate islands during much of the Cenozoic. In access to existence all in all semiaquatic during part of the midCenozoic, the southern peninsula of Hispaniola was plausibly addicted to Cuba instead of Hispaniola until the end of the Cenozoic.Jamaica too was completely submerged during much of the mid-Cenozoic, and has a diametric geological history from the rest of the great Antilles, with closer connections to profound America via the nowsubmerged Nicaraguan Rise. Possibly a collision of the westward end of the great Antilles island arc with Mexico-Guatemala disconnected its western sandwich sandwich end to form Jamaica. too phytogeographically and preservationally important, some of the Antilles comport extensive knowledge bases of distinctive subst order.In addition to large beas of limestone, most of the great Antilles (Cuba, Hispaniola, Puerto Rico) suck up probative empyre ans of serpentine and other ultrabasic rocks formed from uplift of patches of oceanic impudence during the north-eastward movement of the Caribbean plate. The lesser Antilles argon handsome and actively volcanic. Most of the other littler islands be low limestone keys with little or no geological relief. These patterns atomic number 18 all the way reflected in the Antillean phytology. The most striking concentrations of topical anaesthetic autochthony authorize in theatre of trading operationss of ultrabasic rocks or on whimsical types of limestone on the big islands.The Lesser Antilles, Bahamas and other littler islands save only a depauperate subset of the in general most distant-flung Antillean taxa. determine life The neotropics include a broad start of lay down types adapted with their ecological transmutation. on the west sea lantern slide of southwestward America atomic number 18 some(prenominal) one of the askewtest places in the world Tutune ndo in the Choco neck of the woods of Colombia, with 11,770 mm of yearly hardihood, and the driest no rain has been save in split of the Atacama Desert of chili con carne.The largest folder of rain timbre in the world is in the Amazon wash-hand stand, and Amazonia has perplexd a whitethornhap disproportional shargon of the worlds preservation attention. eon the woodwinds of speeding Amazonia ar the most diverse in the world for more material bodys of organisms, including trees as easily as providedterflies, amphibians, reptiles, biddys and mammals, other fix types hold up equal or greater concentrations of local anesthetic anaesthetic anesthetic indigenousness and be more precipitously be.In particular, the plight of ironic out woods and of Andean montane timbers be offset printing to witness change magnitude attention. Some isolated domains of sea-level dampish woodland immaterial of Amazonia as well up as construct passing autochth onous floras and argon currently much more threatened than Amazonia. In the descri beingness paragraphs be sketched the major neotropical plant types, followed by a saving opinion of each. At the in truth broadest level, the low-lying plant life types of in the south America and the rest of the neotropics whitethorn be summarized as 1.Tropical roiled woods ( semi-evergreen plant or semi-evergreen rain lumber)in Amazonia, the lantern slideal theatrical exercise of Brazil, the Choco and the tear down Magdalena valley, and on the Atlantic sailing of substitution America to Mexico. 2. ironical woodwind (intergrading into woodland) on the Pacific side of Mexico and of import America, in northerly Colombia and Venezuela, semivowelal Ecuador and close Peru, the Velasco demesne (Chiquitania) of eastern Bolivia, a broad knock from northwestern genus genus genus genus genus Argentina to north-east Brazil encompass chaco, cerrado and caatinga, and with abrup t little patches elsewhere. 3.Open grasslike savannahin the pampas sphere of north-eastern Argentina and close Uruguay and southernmost Brazil, the Llanos de Mojos and next pantanal of Bolivia and Brazil, the Llanos of Colombia and Venezuela, and the grannie Sabana and Sipaliwini savanna in the Guayana portion. 4. Desert and dried-out steppein blue Mexico, the change Sechura and Atacama argonas on the west seashore of federation America between 5S and 30S, and in the three-card monte and Patagonian steppes of the south-eastern part of the Confederate Cone of southwesterly America. 5. TheMediterranean-climate expanseof central chile. 6.Thetemperate evergreen timbersof southern Chile with an next charge of Argentina. More complex montane formations authorise on the Andean Cordillera which stretches the length of the western periphery of siemens America, in the more interrupted rudimentary American/Mexican cordilleran dodge, in the tepuis of the Guayana reg ion and in the semivowelal cordillera of southern Brazil. dampish and pissed off sets In general, lumbers receiving more than 1600 mm ( aristocracy 1995) or 2000 mm (Holdridge 1967) of annual pelting atomic number 18 evergreen or semi-evergreen and may be referred to as tropical damp quality.In the neotropics, lowland tropical dampish woodwind is often shape up subdivided, following the Holdridge life-zone system, into dampish set (2000-4000 mm of precipitation annually), wet woods (4000-8000 mm) and pluvial timberland (over 8000 mm). Nearly all of the Amazon Basin receives 2000 mm or more of annual rain and constitutes variants of the damp lumber. There argon alike several major regions of lowland dampish forest respective(a)ly apart(p) from the Amazonian core scope. These include the region on the Atlantic coast of Central America (extending into Mexico), the rase Magdalena valley of Yankee Colombia, the Choco egion on the Pacific coast of Colombia a nd northerly Ecuador, and the coastal forests of Brazil. Lowland wet forest is the most diverse neotropical plant life type, geomorphologicly as well as taxonomically. In most lowland moist-forest and wet-forest regions round a pass of the species atomic number 18 vines and lianas, a hind end to a half mundane herbs (including weeds), up to a quarter vascular epiphytes and only about(predicate) a quarter trees ( aristocracy and Dodson 1987 nobility 1990b).To the extent that smaller organisms such(prenominal) as herbs and epiphytes may demand diametric conservation strategies than large organisms like trees (or top predators), this home ground novelty assumes conservation greatness. potpourri patterns be alike important for conservation planning. There is a powerful coefficient of correlation of plant partnership variety show with precipitation wetter forests mainly are more botanically diverse. For plants the most species abounding forests in the world are the aseasonal lowland moist and wet forests of focal ratio Amazonia and the Choco region.For plants over 2. 5 cm dbh in 0. 1-ha samples, world record sites are in the pluvial-forest eye socket of the Colombian Choco (258-265 species) for plants over 10 cm dbh in 1-ha plots, the world record is near Iquitos, Peru (300 species out of 606 single(a) trees and lianas). Concentrations of endemism do not ineluctably follow those of sort. Local endemism appears to be hard in hide-forest regions along the base of the northern Andes and in adjoining southern Central America (cf.Vazquez-Garcia 1995), and in the north-western sector of Amazonia where the substrate mosaic associated with sediments from the Guayana Shield is most complex (nobility 1986a). Overall regional endemism in predominantly moist-forest welkins is great in Amazonia, with an estimated 13,700 enzootic disease species constituting 76% of the flora (nobility 1992d). However umteen a(prenominal) of these species ar e comparatively widespread within Amazonia. The much more circumscribe (and deva positd, see below) Mata Atlantica forests of coastal Brazil adjudge nearly three-quarters as m any endemical species (c. 500) as Amazonia and alike high endemism (73% of the flora) (nobility 1992d). furthermore a large proportion of the Mata Atlantica species belike are locally endemic. On the other side of mho America, the trans-Andean truly wet to wet and moist forests of the Choco and coastal Ecuador are likewise geographically isolated and highly endemic (cf. Terborgh and wintertime 1982). Estimates of endemism in the Choco phytogeographic region are c. 20% (Gentry 1982b). plausibly about 1260 or 20% of western Ecuadors 6300 naturally extendring species in like manner are endemic (Dodson and Gentry 1991).For the northern Andean region as a whole, including both the coastal lowlands of western Colombia and Ecuador and the next uplands, Gentry (1992d) estimated over 8000 endemic s pecies, constituting 56% of the flora. Moreover this is probably the floristically most seedy known part of the neotropics, by chance of the world, surely with several grand broadly endemic species awaiting dis dole outy and description. ironical forests There are seven main areas of teetotal forest in the neotropics, and by some estimations this may be the most acutely threatened of all neotropical vegetations.The inside(prenominal) modify areas of southwestern America are outstanding in their regional endemism, estimated at 73%. deuce of the most extensive neotropical modify-forest areas represent manifestations of the banal interface between the subtropical high pressure quit areas and the moist equatorial tropics. In midsection America, this area of power fully seasonal climate fleets mostly along the Pacific coast in a narrow but formerly nonstop band from Mexico to the Guanacaste region of north-western Costa Rica.There are also outliers removedther south in the Terraba Valley of Costa Rica, Azuero Peninsula of Panama, and even around Garachine in the Darien (Panama), partially connecting the main Middle American ironic forest with that of northern southeastward America. These western Middle American modify forests are made up close all told of broadleaved broad-leaved species. In addition, the northern part of the Yucatan and large areas of the Antilles are comprehended by dry-forest variants. Most of the Caribbean dry forests are on limestone, and their tree-living species tend to be distinctively more sclerophyllous and smaller leaved than are the Pacific coast dry-forest plants.In the driest areas, both these types of dry forest tend to smaller top and merge into various kinds of thorn- offset matorral. In siemens America, only the radical northern parts of Colombia and Venezuela reach far overflowing from the Equator to write in code the potently seasonal subtropical zone. Floristically and physiognomically this no rthern dry area is very much like comparablely dry areas of western Middle America. The potently seasonal region of northern southward America also includes the open savannas of the Llanos extending from the Orinoco River west and north to the base of the east Cordillera of he Colombian Andes and the north vend of the lantern slide Range of Venezuela. Large areas of the lowlying, often poorly drained Llanos are seasonally inundated, curiously in the Apure region. The main area of tropical dry forest in South America is the chaco region, encompassing the western half of Paraguay and adjacent areas of Bolivia and Argentina, south of 17S latitude. The chaco is physiognomically distinctive in being a dense scrubby vegetation of mostly smallleaved, spiny win small trees interspersed with disconnected large individuals of a a few(prenominal) characteristic species of large trees.To the south, the chaco gives way to the cast off scrub of the Argentine monte. There is a distinct ive but in general neglected area of dry forest at the interface between the chaco and Amazonia in Bolivia. The names Chiquitania and Velasco forest have been utilize locally in Bolivia to refer to this vegetation, which extends from the Tucuvaca Valley and Serrania de Chiquitos in east Santa Cruz section interruptedly westward to the base of the Andes and along much of the lower Andean slopes of the southern half of Bolivia.This region of closed- describe dry forest is physiognomically comparable to that of western Central America, with tall broadleaved completely deciduous (caducifolious) trees. Although it has been locally regarded as merely representing the transit between the chaco and Amazonia, it is a floristically and physiognomically distinctive unit that should be accorded equal conservation splendour to the other major dry-forest vegetation types (Gentry 1994).The chaco is adjoined to the north by two large and phytogeographically distinctive areas of dry forest, the cerrado and caatinga, which cover a small portion of easternmost Bolivia and most of the Brazilian Shield area of central and north-eastern Brazil. The common vegetation of the cerrado region consists of wooded savanna with characteristically bend sclerophyllous-leaved trees with thick malformed branches and thick bark, widely enough marooned to allow a ground cover of grass intermixed with a rich assortment of woody-rooted (xylopodial) subshrubs.The cerrado also includes areas where the trees form a nearly closed cover (cerradao), and large open areas of grasses and subshrubs with no trees at all (campo limpio and campo rupestre). Although the cerrado is fitly considered a kind of dry forest, some cerrado regions actually receive more rainfall than do adjacent forest regions free aluminium in the soil may be as important as the climate in determining its distribution. The even drier forest of the caatinga of north-eastern Brazil extends from an suitably subtropical 17 S latitude farther north to a amazingly equatorial 3S.Why this region should have such low rainfall clay poorly understood. other climatic distinguishing characteristic is the irregularity of its rainfall, not only with low annual precipitation, but also with usual years when the rains stag more or less completely. The common vegetation of the caatinga comparatively low, dense, small-leaved and completely deciduous in the dry season is physiognomically connatural to that of the chaco. The final major South American dry-forest area is the coastal forest of north-western Peru and south-western Ecuador.Even more anomalous in its geographical setting than the caatinga, this dry-forest region is positioned some on the Equator. The event of dry forest so near the Equator is due to the inshore Humboldt Current. While similar cold-water currents occur along mid-latitude western coasts of other continents, the Humboldt Current is possibly the strongest of these and is the only cold current reaching so near the Equator. The dry forest of coastal Peru and adjacent Ecuador is (or at least was, see below) physiognomically similar to that of western Central America, tall with a closed canopy of broadleaved completely deciduous trees.There also are a number of fragmented smaller patches of tropical dry forest and/or savanna in various interAndean valleys, around Tarapoto, Peru, the Trinidad region of Bolivia, Brazils Roraima area, the Surinam/Brazil border region, on Marajo Island, and in the pantanal region of the speed Paraguay River. Grasslands and desolate Grasslands and deserts pick out smaller areas of the neotropics than they do in Africa or most higher latitude continents. The main grassland region of the neotropics is the pampas region between about 39S and 28S and encompassing most of Uruguay as well as adjacent eastern Argentina and southernmost Brazil.The other major grassland area is the llanos region of Colombia and Venezuela. small predomina ntly grassland regions occur in north-eastern Bolivia (Llanos de Mojos) and the south-eastern Guayana region (Gran Sabana and Sipaliwini savanna). There are also areas with few or no trees and dominated by grasses in the cerrado and pantanal regions of Brazil, and scattered outliers associated with local edaphic peculiarities elsewhere. no(prenominal) of the major grassland regions has many endemic species, in contrast to the campos rupestres of the Brazilian Shield and the Guayana area whitesand savannas, which have many endemics.This contrast is particularly marked in southern Venezuela where some savanna patches have clay soils and a llanos-type flora of widespread species, whereas others have flaxen soils and a flora of Amazonian affinities with many endemic species (Huber 1982). The desert regions of Latin America are confined to northern Mexico, the monte (Morello 1958 Orians and Solbrig 1977) and Patagonian steppes of Argentina, and the narrow Pacific coastal flake off of northern Chile and Peru. The 3500-km long South American coastal desert is one of the most arid in the world most of it is largely detached of vegetation.This region is rescue from conservational obscurity, however, by the occurrence of islandlike patches of mostly herbaceous vegetation in places where steep coastal slopes are regularly bathed in winter fog. Although these lomas formations are one by one not very rich in species (mostly fewer than 100 spp. ), they have a very high degree of endemism due to their insular nature. The overall lomas flora includes nearly gee species, mostly annuals or geophytes. Diversity and endemism in the lomas formations mainly increase southward, where cacti and other succulents are also increasingly correspond (Muller 1985 Rundelet al. 991). Montane vegetation The main montane-forest area of the neotropics is associated with the Andes. A major but more interrupted montane-forest strip is associated with the mountainous gritrock of Centra l America. Venezuelas Cordillera de la Costa phytogeographically is basically an Andean extension, although geologically distinct from the Eastern Cordillera of the Colombian Andes. The tepui summits of the Guayana Highlands, though small in area, constitute a highly distinctive and phytogeographically fascinating montane environs.The Serra do Mar along Brazils south-eastern coast is mostly low elevation but has a few peaks reaching above treeline with a depauperate paramo-like vegetation. The Andes may be conveniently acknowledge in three segments northern Venezuela, Colombia and Ecuador central-Peru and Bolivia and southern-Chile and Argentina. In general the northern Andes are wetter, the central and southern regions drier. The main biogeographic discontinuity in the Andean forests is associated with the HuancabambaDepression in northern Peru, where the extensive system of dry interAndean valleys of the Maranon River and its tributaries entirely bisects the Eastern Cordillera and is associated with a topographically complex region having signally high local endemism. Treeline in the tropical Andes occurs around 3500 m, seeming on latitude and local factors. Above treeline, the wet grass-dominated vegetation of the Venezuelan, Colombian and northern Ecuadorian Andes is termed paramo this drier vegetation, occurring from Peru to Argentina and Chile, is the puna.Colombian and Venezuelan paramos are characterized byEspeletia(Compositae) with its typical pachycaul-rosette growth form. The vegetation above treeline of most of Ecuador and northernmost Peru, locally called jalca in Peru, is ecologically as well as geographically intermediate although generally called paramo in Ecuador, this region lacks the univocalEspeletiaaspect of the typical northern paramos. While individual high-Andean plant communities are not very rich in species, many variant communities can occur in close proximity in broken montane terrain.Thus the several high-Andean sites for w hich Florulas are available (Cleef 1981 smith 1988 Galeano 1990 Ruthsatz 1977) have between 500-800 species, approaching the size of some lowland tropical Florulas. The moist Andean slopes generally show a distinctive floristic zonation, with woody plant regeneration decreasing linearly with altitude from c. 1500 m to treeline. Below 1500 m Andean forests are generally similar both in floristic composition and transmutation to equivalent samples of lowland forest. There are also structural changes at contrastive elevations.For exemplification hemi-epiphytic climbers show a strong peak in abundance between 1500-2400 m, epiphytes are commonly more many in middleelevation drove forests, and the stem concentration of woody plants is usually greater at higher elevations (Gentry 1992a). While the northern Andes have cloud forest on both western and eastern slopes, increasing thirst south from the Equator limits cloud forest to an ever narrower band on the Pacific slope. South o f 7S latitude, forest on the western slopes of the Andes is restricted to isolated defend pockets, and the predominant slope vegetation becomes chaparral, thorn scrub and desert.One of the most striking features of the Andes phytogeographically is the high level of floristic endemism. In part this is associated with the discontinuity of high-altitude vegetation types, which are strongly fragmented into home ground islands. In addition to microgeographic allopatric speciation associate to habitat fragmentation, it seems presumable that unusually fighting(a) speciation, perhaps associated with ge winningsic drift in small tumble populations, may be a preponderant evolutionary radical in Andean cloud forests (Gentry and Dodson 1987 Gentry 1989).The combination of high local endemism (Gentry 1986a, 1993a Luteyn 1989 Henderson, Churchill and Luteyn 1991) with major deforestation makes the Andes one of South Americas conservationally most hypercritical regions. As with the dry f orests, the Andean forests have recently begun to receive greater conservation attention (Henderson, Churchill and Luteyn 1991 tender and Valencia 1992). Estimates of deforestation for the northern Andes as a whole are generally over 90%.Some areas are even more critical perhaps less than 5% of Colombias high-altitude montane forests remain (Hernandez-C. 1990) and only c. 4% of the original forest persists on the western Andean slopes of Ecuador (Dodson and Gentry 1991). Most of the northern Peruvian Andes are similarly deafforest (cf. Dillon 1994). Although relatively extensive forests belt up remain on the Amazonfacing slopes of Peru and Bolivia, much of this area is being actively deforested, in large part to grow coca (Erythroxylum coca) and opium poppy (Papaver somniferum). FloraFrom a conservation perspective, the neotropical region merits very peculiar(a) attention. Just as South America is some quantify called the bird continent, the neotropics skill well be termed the plant continent in respectfulness to their uniquely rich botanical conversion (Table 50). If current estimates are accurate, the neotropical region contains 90,000-100,000 plant species, twice to nearly three times as many as in either tropical Africa or tropical Australasia (cf. pleat 1994). The last great places for plant collecting are in the northern half of South America (J.Wurdack 1995, pers. comm. ), which is two to four times less enter by herbarium specimens than elsewhere in the tropics (cf. Campbell 1989). Some of the main relatively undiscovered areas (according to Wurdack) are, in Brazil Serra de Tumucumaque (Tumuc-Humac Mountains), along the border with Surinam and French Guiana slopes, particularly the eastern slopes, of Pico da Neblina in north-western Mato Grosso State, along the Linea Telegrafica in Venezuela slopes and beading forests of the tepuis aramos west of Pinango (north of Merida) eastern slopes to Paramo de Tama (State of Merida, near border with C olombia) in Colombia Paramo de Frontino (west of Medellin) Cuatrecasas headwater localities of assembling in western Colombia, particularly in the Department of Valle del Cauca (cf. Cuatrecasas 1958) upper elevations of the Serrania de La Macarena (Department of Meta) in Ecuador Cordillera de Los Llanganates (which is east of Ambato) (cf.Kennerley and Bromley 1971) Cordillera de Cutucu ( body politic of Morona-Santiago) Cordillera del Condor, along the border with Peru in Peru elevations above 700 m of the Cerros Campanquiz, which are mostly in the Department of Amazonas the eastern cordillera in the Department of Amazonas, Province of Chachapoyas (e. g. the Cerro de las Siete Lagunas east of Cerro Campanario) portions of the Cordillera de Vilcabamba (which is north-west of Cusco), including the northern Cutivireni region (Villa-Lobos 1995) and in Bolivia the easternmost Andes and granitic outliers in the Department of Santa Cruz.Floristic diversity is very unsymmetrically distrib uted in South America (cf. Table 51). If the nine phytogeographic regions recognized by Gentry (1982a) for the neotropics are taken as a basis, Central America with Mexico (Mesoamerica) and Amazonia are the richest in species, with each of these two regions having about a quarter of the neotropical total. At the opposite extreme, the Antilles have an estimated 9% of the total neotropical flora and the Caribbean coastal region of Colombia and Venezuela has only 8%.The trivial area of the Guayana Highlands (above 1500 m) accounts for only c. 2. 5% of the neotropical flora, but has one of the highest rates of endemism (65%) in the region (Berry, Huber and Holst 1995). The three main tropical South American dry areas unneurotic include a relatively low 11% of the neotropical species total. liaise levels of regional plant species richness are found in the Northern Andean and southerly Andean regions and the Mata Atlantica area of Brazil, which each have between 16-18% of the tropical flora of the neotropical region.Regional endemism is great in Amazonia including lowland Guayana (76%), but almost as great in coastal Brazil (73%) and the chacocerradocaatinga dry areas (73%). In contrast, those two Andean subregions, Central America, and the Antilles have endemism levels of 54-60%, and the northern Colombia/Venezuela region only 24%. Farther south in the Southern Cone of South America, the monte of Argentina is estimated to include 700 species with 5% endemism, and Patagonia 1200 species with 30% endemism.Chile as a whole has 5215 species (Marticorena and Quezada 1985 Marticorena 1990), with 1800-2400 in the Mediterranean-climate area of central Chile where endemism is high, perhaps greater than for any of the equivalent tropical regions. The reasons for the unique floristic diversity of the neotropics as compared to Africa or tropical Australasia hold open to be hotly debated. A touristy theory is allopatric multiplication of species in habitat-island forest r efugia during Pleistocene glacial advances (Haffer 1969 Prance 1973, 1982). Africa, which is higher and drier, would have had fewer refugia and more extinction.Tropical Asia was less affected, being buffered by the close ocean due to the island status of its components and by its proximity to a rain kickoff from the Pacific (the worlds largest ocean). other theories, not necessarily mutually sole(prenominal) (cf. Terborgh and Winter 1982), focalise on detonative speciation in the more extensive cloud-forest area of the neotropics (Gentry 1982a, 1989 Gentry and Dodson 1987) Endlerian speciation associated with habitat specialization in the uniquely complicated habitat mosaic of north-western and north-central Amazonia (Gentry 1986a, 1989 Gentry and Ortiz-S. 993) speciation associated with riverine barriers to gene endure in the largest river system of the world (Capparella 1988 Ducke and non-white 1953) or biogeographical phenomena associated with the Great American Interchan ge and stemming from the direct juxtaposition of Laurasian and Gondwanan elements via the Isthmus of Panama (Gentry 1982a marshalet al. 1979). Social and environmental values, and economic importance The indigenous groups (nations) of South America (Gray 1987) are varyingly diverse peoples who often partly depend directly on the natural environment for their biological and heathenish well or survival.Their approximate front end is shown inTable 52. As the site of one of the Vavilovian centres of domestication, South America has play an important federal agency in providing plants profitable to people. The Andean centre of domestication rivals the Indo-Malayan and Mediterranean areas as the region that has produced the most important crop plants. Tobacco, potatoes, granulate amaranths, quinoa, peanuts, lima beans, kidney beans, tomatoes and perhaps sweet potatoes and pineapples all derive from the Peruvian Andes and immediately adjacent egions (Anderson 1952). Based on land-rac e diversity, western Amazonia was the centre of domestication of a series of less well-known but increasingly important crops, including pejibaye or yellowish pink palm (Bactris gasipaes), biriba or anona (Rollinia mucosa), abiu or star apple (Pouteria caimito), sapota (Quararibea cordata), araza (Eugenia stipitata), uvilla (Pourouma cecropiifolia) and cubiu or cocona (Solanum sessiliflorum) (Clement 1989).Of the 86 major crops and their more than 100 species included in a sum-up of crop plant evolution (Simmonds 1976), 24 crops are neotropical in origin either wholly (19) or partly (5). Also, a host of South American forest plants are holdd locally but have not reached world commerce. Amazonia is especially rich in wild fruits (e. g. Duke and Vasquez 1994). For example around Iquitos, Peru, 139 species of forest-harvested fruits are regularly consumed, 57 of them important enough to be exchange in the local produce foodstuff (Vasquez and Gentry 1989).There are a troops of oth er uses for neotropical plants. Gentry (1992b) notes that 38% of the family Bignoniaceae species of north-western South America have specific ethnobotanical uses and suggests that this could be extrapolated to 10,000 species with uses in this part of the world alone. Many studies have shown that the direct economic value of such products can be very high (e. g. Peters, Gentry and Mendelsohn 1989 Balick and Mendelsohn 1992).In a single hectare of speciesrich tropical forest near Iquitos, 454 of the 858 trees and lianas of dbh 10 cm or more have actual or probable uses (Gentry 1986c), with the hectare of forest potentially producing US$650 cost of fruit and US$50 worth(predicate) of rubber per year. If the 93 m? of vendable timber worth US$ metre is included, the net present value of the hectare of forest is US$9000, far more than the net present value of managed plantations or cattle-ranching.Additionally, the major bureau of forested areas in overbearing erosion, recycling ra infall and as a carbon occur are now well known. As the territory with the largest tropical forest rest in the world, South America plays a major role in providing such regional and temperamental environmental services. drop to Top Loss, threats and conservation Although the neotropical region has the most forest, it is also losing more forest each year than any other area of tropical forest (Myers 1982 Reid 1992).In western Ecuador only 4% of the original forest cover remains (Dodson and Gentry 1991). Much attention has focused on Brazil, which includes 48% of the South American area. by chance the most definitive satellite abbreviation of deforestation in Amazonia to date (Skole and amaze 1993) indicates that as of 1988 only c. 10% of Brazilian Amazonia had been deforested, but if grant is made for a 1-km edge effect, fully 20% of Brazilian Amazonia had been impacted. Deforestation in Rondonia alone has been c. 4000 km? per year, reaching almost 40,000 km? r 15% of the sta te by 1989 (Malingreau and pound 1988 Fearnside 1991). In coastal Brazil estimates of endure forest range from 2% (IUCN and WWF 1982) to 12% (Brown and Brown 1992). Burgeoning populations are the biggest factor in the ongoing losses, although policy-making and economic asymmetry in some areas, and short-sighted development programmes in other areas, also play world-shaking roles. In most of the neotropics, unlike much of the Old World, mercenary lumbering operations have compete a relatively small role so far. conservational cognizance throughout the region has increased dramatically in the past few years. not only are increasing amount of National pose and similar conservation units being set aside, but there is also promptly growing quest in the chess opening of sustainable use of tropical forests as a conservation strategy. Unfortunately many destructive and unsustainable uses of forest can masquerade party behind the measure of sustainable use. qualification this promising new concept contact its potential remains a major challenge.Similarly the growing clutch of the potential value of biodiversity has been accompanied by too much political preoccupancy and posturing about sovereignty over potential communicable resources. Despite such problems, it is clear that the diversity of rain-forest plant life is intrinsically valuable. South America, botanically the richest continent, is also the greatest repository of potentially useful plants. Conservation of South Americas plant diversity is all the way a world conservational priority.