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I 3 sol 6 II} 1300 1250 RARE II MAP B 1550 1500 1450 1400 1350 1600 1650 1700 I 1750 WEST Barrow l~ \ ~~ o I """""".,~' ", " I A\)'~~ J13g Do ", II II ~,s?d~~ - 0 ARc TIC I ~~ rj,./ ~ II I \ Il ~-J -----~~ (~'" ...",.', II / -.., IJ;~~~~-~r-/ ~j;;: ~'5Lf'''(~('' ""~~ II / ' S-z (-/ ~~?f~- '-~~>).-~~...., L'.. -" ~ I \)1 - -, - - :; I o~ JJ-St.2, G o~,~~, ~ _~~'__ J Ii r I )cjvlx;:~ Q --;)) /~c' \ k n -' ~ / ' )(6~~~~~ G(J 0/ ~ \/9 ~~\ y;,; - /71 / "',,(((~)V ~~~ "1",: / () ;VoJ,v )' ~-~',J ~ ~ I k,~ ~'--- ~ \) ,~ L r ~ '0 - #' r'l_.-;::;J~~ Ii , ~\) ! .~~ 1~~~ l~ _/1/ <; ~!Ml ~ f\~1.-..I ~r.~~~~3 !~~/ ....1"-. ~~' ~rI::J'5:~' fW !;; J:r-.. ,,<'~'cli~AiI, IQ .B!i~J: c ",\O~-- C)' ;;;:- . ~"'\ 0 L '1'\ ~~ ~"">:'r/' I) , _""~~~"~-- ao ~0 ~ : J ~ ~~,~ ,VJ ~1i(j ~.J3 2 ~)~ 1~1 1. , , ~ , ~ _--,;c~- "~f:J'J '~~ f\~~ I IfJ tt~' ;'~p: 12 ro~~_ ./1 ----- ,''''''-'' ~~,:l~ - ~~(l j~~Pti ~j-~ v~~~jffi I ,~~y ~t2;' .:~~ :~. : .~ ~ .". ~~~'~~_LJ~' r-- '~\~ \T~" - ~-~,.'!YY- ~}.! .~,~' . 6( .<':()- ~ &al~"1... u ~ :>::J -- _- .l~' : ) '/ ..:.: \~ .. ~~ ~-- _ ~ -' 6 """cQl"/~ - __ 's ,r=:.SJ ~1, rr cP> U'.......~~~, "')~l.~,.. n _u - -- \Y'~rP"" ~v V .-7L:::' (l/ ~.. ~ l'?>, I~"j t:^\\. ~ '/ i:.?:-@5( Q\S:;~~. ~.~ ..; 1- \ o ~ ~ ~'I".;....'~". ,il""~ JY.l-i) ~ 'b:>jyh:J:(~,,:~ ~ /\0 -t~ ./J(j~~"'v ~ ,.~ ~~c['<" ""oD.'e.~o/E' L(j~ ~f~~~\f ;-f1~::f~$,~?~tL ~........ ~ "~~11-' ~~ ~ ' c" ~ ~I Y.:" .,~ v..-s---f J ," ~~A; V 1 ..c. ~ ~', . : 'g I~ r~ 1:-;''---''''' :.c", " " I jj7"'~' (j)1S'I~d~ ""/"- Crr~~'i -3 l:. -~: '~,,' ~ >~ *9~' ':J...' ';J~ (_i'::J'I . ~~.'f~"i >J/~5f"~ ~.~ _~~ ~ I \"-\ ;-07J~~ O~8~~~ fBf_}~~\ if~~Z~'-%X~~ .~~q~~ t. : ~ ~:~t-~~/Nl~.) ~:r6f;p~-U~~J:~', ,~\ ~.^" ~",Zi~ ~",/~~I~{.~ 'it~::S;.,? :y~t!~~;;~~~):':! ~ ~ ~, ...... I,,,.., __ 'lr. ~, - , -.r 6-0/'<"" <' ' f-~"<<\\~..!. {j ~\...g\'k'(.\,~ . _~])~ -, f~ _'<'5.//1' ~~^~"~Wt..- ~"/JIti,...'V;%-, <;-~",>' -/ 1 .. ~'i : l' ~ )//V ~ ~~_ ' 'it ~.I~ ~VM ~ ~ %' '-<<ZlJ'~~;:~ 'J' "', ~~'!.hl,,11 ~~-L J ~ iif:.4 --J'c, cc. ~? ~ , ' K'",,~ 9::r." ,UItII ~ J r~l~& 0il . - ~~~~< ~:t_ ~ ~ Q J/4~~?\'~r-;; O'--{~~J,~~ ; Ap~l~;j!~t~~V1?-~~~Z~~~0t~~1~if? (ki f17 " 'V"'~.,,,~\ 7k cd' I /~~jl ;:<1 ~~ :~ ~. '''-r''';;;A~f1~fi:G",!E1i'f\'<:'-'I'' a ) '. \~~f/(. "~:;+s~ 0 Hom, ~"i'~ ~ "- i-~~~~1u~~~~1!fjJ\t$:TIt\'\\~~ ,- ') '\ U II c.'" r ' ~- in: ",-, ~~~':; ~'r I ,... . . I ..,'" ~.~ IJI ,,~'\.\~ ~~' l\..< ~"\Sli!,~" 6fp II ;; Y'k~~' ~~~"~\ ~~~, y, ( ~:--4?) ~ -'. ~, / .:r ' /..L ~~G~~'-'V ~ 9ru-e, II II ~\: w. Lh~-:i t'~",,' (,.A~~KOd'" 'i II Y;J.~.,~,. B ~j ~~ ~h ~ _ :~""1,J~,-~:'~ ~L\~~ II ALASKA " "'~""''-I'/ o ~~,,-K--<'.;n;~f';~~""'" """ '" :f..rv "::'t-? - 0 ~f ~!"'- 0 Is' ';",- . ~\\::, .RJ ~ ~ '[jfAY. ",,.. ~_--(I ~ A,W.Kuchler ,\Y" ,. rc<~iti5' ~\ hF"J', ~6u~j p" ~ . '. t cP'cb" University of Kansas, 1966 . . ";':{ "-<.,,\ ",0.1S. Qr ~ '':'''_Q:'''V~'' . ~~. f " U. f."i ,'~\) ~ .~~ ~ ~.., ' ;, ~.{ (j II Albers Equal Area Projection If SUI fl. --c;.-,fa, ~ %:J.\~ - t (> II SCALE 1 :7,500,000 II ~., ,,\ $' 0::: 'j 0 -~, ,.1' .no,l r 1650 1600 1550 15'00 b 100 100 ZOOll 300Z00 <00 "::O.::~::ll \l,,,,.,, . " " ~, _JL~'~ , ===--'1 ! " \\ ~, \t \1 \\ \\ 135~ PU RPOSE To date, most work based on the ecosystem concept of resource management is at a detailed level. There are at least two reasons why a regional view of the ecosystem is needed: (I) To permit detailed data to be aggregated into more generalized units for decision making at higher levels, and (2) to provide an integrating frame of reference needed to fully interpret the more detailed information, Other broad-scale classifications have tended toward systems that are biotic on the one hand and abiotic on the other, having such factors as landform as criteria, In trying to use these classifications, it is apparent that they are inadequate because they are not truly holistic, as ecosystem classification requires, The approach here is to reconcile the biotic and abiotic classifications into a single geographical classification that is relatively objective. The scheme is based on a major division of all lands into low- lands and highlands. Within the classification, bio- climatic criteria are used to determine the upper rungs of the hierarchy, and geologic and geomorphic criteria are taken into account mainly at the lower levels, This map shows only the upper levels, II II \, The United States encompasses wide variations in environment, from forest to desert to tundra, Management of such a diverse area must be based on an understanding of the overall structure and functioning of natural ecosystems, from the entire biosphere down to a single plant community on a specific site. Land is recognized as falling into spatial patterns of broad physical and biological similarities, and can be systematically classified, Once an under- standing of relationships and influences of these interrelated areas on each other is reached, an en- compassing framework can be developed. This is essential to allow an inventory of ecosystems at any level, and any scale of intensity appropriate to man- agement needs and objectives, Unfortunately, no agreement has ever been reached on a universal classification system for natural regions, Various systems have been devel- oped and are in use for different purposes. Most of these have tended toward classifications that are either biotic or abiotic. They are largely inadequate because they do not reflect total ecological patterns, For the purposes of RARE II, an ecosystem classification scheme was sought that would be acceptable to the scientific community, understood by the general public, and refined enough to be meaningful but not so much as to be unmanageable, Although many classification systems exist, they all have their weaknesses, Systems based on vegeta- tion seem to be the easiest to grasp but they fail to recognize major variations that result from differ- ences in climate, zonal soils, and other elements of the physical environment. To overcome the deficiencies of systems based on only the biotic or the abiotic, the ecoregion concept of R. G. Bailey was selected as a starting point but strengthened by adding the more de- tailed potential natural vegetation typing of A. W, Kuchler (except for Puerto Rico where the source was Ewel and Whitmore) at the section level of Bailey's hierarchy, The resultant classification defines as an ecosys- tem any potential natural vegetation type within an ecoregion. Two hundred and forty (240) distinct types of major ecosystems are identified in the United States and two (2) in Puerto Rico. Descriptive text for two building blocks of this ecosystem classification scheme follows for back- ground and information purposes. "0CEAN II " , ~~ ,- , "~Ss '1 o"'~,>. II " " :::;==- = : :'" " d' ~ ~ w:~ \: ~ '~' \. ~ (-1> f "" Q OCJ' - .. )~"~ "" 0 fr~5 -:-"'" 'l\ ~~ a ,c> \j ~ \ PNV of Alaska tcs--..---..~~- ..p.., I\" .. Hemlock-spruce forest (Tsuga-Plcea) q ~ Spruce-birch forest 1\ ~ (PfCea-Betuta) 1\ ____ 650 6S0 <1 .~ lJ ~ Black spruce foresl ~(PlCea) ~ Muskeg ~ (Erlophorum-Sphagnum-Belu/a) ~ Alder thickets ~(AJnusJ ; /' ~ h l~ ~I' \ '" ~ ~ \ '~~ 600 ~ Couonsedge lundra ~ (fflophorum) ~ Walersedge tundra L..:...'..:.... (Care,,) ~ Dryas meadows and barren ~ (Dryas-Carex-8ew/a) ~ Aleutian meadows ~ (Ca/amagrostls-Anemone) ~ Aleutian heath and barren L...:...:.:.-J (Empetrum-Vacclnlum) ~1b\-~~ Ice fIelds ,. ,.,.~~ 'V' ~ I' ECOREGIONS OF THE UNITED STATES R.G. Bailey ! INTRODUCTION To manage land as heterogeneous as that with which the Forest Service deals, we must be able to classify it as to its capability and availability to produce different goods and services, To manage forest, range, and related land on a national, regional, and local scale requires a classification system that is objective, that covers the whole country, and that is hierarchical in nature, To be objective, the system should be based on observed properties, The same method of classifying land in California should be used in Maine and in Florida. The system should be hierarchical, allowing for both broad levels of generalization and highly specific levels, to allow for aggregation of data at dif- ferent levels to meet decisionmaking needs at region- al, State, and national levels. The ecoregion approach was developed to reflect total patterns in a hierarchical system of ecosystem regions, called ecoregions, based on several levels of shared characteristics. 550 --....... OJ " n If ...... :;;:; ;:::.==~ II II I~ II P A C I F I C .1 tl II ---===;;. !I!;:; tL. " II . =,.... "-;b.. ' \, ~tl" ::!: tl ;:: ::: :::!;;;:- ~i:\:::: r, ". ~ r. ......; 5S. ~ A 4:) ~ij .~ -1 M1310'. " r. rl III 'I .. L ~c ~ '\! r. 11 II Sf/ i.> o' P o7fl E "u T I N ~ o ~''IJ A D " OCEAN S N L o A 500 ::!! ~ .~. ~~~,-'!.j Q~...~" 0-1>' ~ '~ C> II II Ii 1700 1400 " :! ~ rl ~ I' 1750r<EAST 1800 1750 WEST ECOREGIONS OF ALASKA, HAWAII AND PUERTO RICO 67' 66' 411 0 A TLANl'IC OCEAN ..-. San Juan.., <? M..,.gUaz . .. ~ lS' i; - Ponce CARIBBEAN SEA 65' 1000 POLAR DOMAIN 1200 Tundra Division 1210 Arctic Tundra Province 1220 Bering Tundra Provinr:e Highland Provinces M1210 Brooks Range Province 1300 Subarctic Divsion 1320 Yukon Forest Province Highland Provinces M1Jl0 Ala..ka Rangt" Province PRINCIPLES OF ECOSYSTEM REGIONALlZATION 1550 160' M4220 PNV of Hawaii r;S@ =220 Ii ~ Guava mixed forest ~ (A/t"urjles~H;biscus-Mangj/era-Psjdium-Sch;nusJ ~ Ohia lehua foreH ~ (Metrosideros-Cibotium' ---- ---- 220 ~-~ ~-- '0' ~Q ~ Sclerophyllous forest. shrubland. and grassland ~ (Heteropogon-Opuncia-Prosop;s) ~ Honolulu lS' CD ~ ~~ o Each ecoregion covers a continuous geographical area and is characterized by the occurrence of one or more important ecological associations that differ, at least in proportional area covered, from the asso- ciations of adjacent regions. In general, ecoregions are characterized also by distinctive flora, fauna, climate, landform, soil, vegetation, and ecological climax. Within such a region, ecological relationships between plant species, soil, and climate are essentially similar and similar management treatments give compatible results. Thus they are also considered biological productivity regions of specific potentials. The classification scheme used on this map is an adaptation derived mostly from Crowley (1967) PUERTO RICO 2000 HUMID TEMPERATE DOMAIN Highland Provinces M2410 Pacific Forest Province II ~ lama-man('le forest ~ lDiospyros-Sapindus) ~ Koa f?reSI ~ (AcaCIa' ~ Koa-mam,lni parkland ~ (Acdcid-Deschampsia.Myoporum.Sophor,l) ~ Grassland, microphyllous snrubland. and barren ~ (Deschampsja-5typh{'/ia~Vaccin;um) 4000 HUMID TROPICAL DOMAIN 4100 Savanna Division 4110 Everglades Province HiRhland Provinces M4110 PUf"rto Rico Province 4200 Rainforest Division Highl.lnd Provinces M4220 Hawaiian Islands Province Ewel and Whitmore 1973 SCALE 1:7 ,SOO,OOO 67' 66' 65' ==200 200 Principal Islands of HAWAII A, W. Kuchler University of Kansas, 1966 SCALE 1,7,500,000 155' PNV of Puerto Rico ~ Subtropical dry forest ~ Acrocomia-luniperu5 ~ Subtropical moist forest ~ Surietenia-Brosimum 1600 ECOSYSTEMS OF ALASKA, HAWAII AND PUERTO RICO ECOSYSTEMS OF THE UNITED STATES AND PUERTO RICO and has four levels of generalization, three of which are reflected in the ecoregions depicted on this map. A domain is a subcontinental area of broad climatic similarity, such as lands having the dry (B) climates of Koppen (Trewartha 1943) or Thorn- thwaite (1931). . A division is a subdivision of a domain deter- mined by isolating areas of differing vegetation and regional climates, generally at the level of the basic climatic types of Koppen, Usually, the zonal soils are related, A province is a subdivision that corresponds to a broad vegetation region having a uniform regional climate and the same type or types of zonal soils, For example, the Boreal Forest Province is the ecoregion characterized by the subarctic continental- boreal coniferous forest-podzol ecosystem, Gen- erally, each province is characterized by a single climax association, but two or more climaxes may be represented within a single province. This often happens on mountains where each altitudinal zone may have a different climax. Mountain regions represent special problems, The middle and upper slopes of mountain regions do not have the same climate as the adjacent low- lands, but rather have the same climatic regime as those lowlands. From the climatic regime of a moun- tain area, one may infer (I) what the lower altitudinal zones will be, and (2) the seasonal pattern of precip- itation and temperature in all zones. For example, in a mountain region having a semiarid steppe regime, the steppe zone will occupy the adjacent lowlands and perhaps the lower sunny slopes; then there will be a subhumid prairie of parkland zone; then will fol'ow the montane zone, and so on. By contrast, in a mountain region having a humid cli- matic regime such as the warm-summer continental, the valley bottoms will be humid and the montane zone will be the lowest zone present. A mountain range in a Mediterranean climatic regime will have a maximum of precipitation in winter in all zones, just as do the adjacent windward lowlands, For the purpose of this classification, highland ecoregions such as mountains, plateaus, and high-elevation plains (altiplano), in which a high degree of altitudi- nal zonation occurs, are considered separate prov- inces, They are classified according to the climatic regime of the lowlands in which they occur. A section is a subdivision of a province and is based on local climatic variation, The section is char- acterized by a single climax association and reflects climatic nuances within the broad regional climate, For the purposes of this map, potential vegetation as mapped by Kuchler (1966) is used as the principle indicator of a section, No attenpt was made to identify ecosystems below the level of section on this map, The concept of "ecoregion" differs from that of "biome" (Shelford 1963), for a biome is coincident with its climaxes. Every area having the same climax, however far from the main area of the climax, belongs to the same biome. An ecoregion, on the other hand, is always continuous (except on marine islands). Ecologic communities having characteristics similar to those of a particular region may exist far beyond its boundaries, thus belonging to a different ecoregion. Each ecoregion comprises both the climax com- munities and all the successional stages within its geographical area and so includes the fresh-water communities. However, it does not include marine communities that may lie adjacent to its shores, The boundaries between adjacent ecoregions are usually difficult to locate precisely. Frequently one region merges gradually into another. Any line separating the two must then be drawn more or less arbitrarily, A convenient way of roughly fixing the boundary between two adjacent regions is to draw' the line where the dominant associations of the two> regions cover approximately equal area. As stated, an ecoregion may best be thought of as a geographical area over which the environmentall complex, produced by climate, topography, and soil" is sufficiently uniform to permit development of characteristic types of ecologic associations, Some ecologic communities are able to modify the natural undeveloped habitat and, to a certain extent, manu- facture their own environment. Through ecologic succession, they tend to spread from their place of origin to adjacent areas. Accordingly, we may also think of an ecoregion as a center of ecologic dispersal. The area covered by a particular ecoregion varies from time to time, not only because of the production of new habitats through ecologic succession, but also because of slow but more or less permanent climatic changes, Any major change .in topography will alter the local climate. Other climatic variations of a worldwide nature are believed to be continually in progress, Climatic changes generally affect the geographic distribution of the ecologic units con- cerned. The ecoregions themselves are slowly evolv- ing, and occasionally a new one may appear or an old one become extinct. Consequently, regio,nal boundaries are not stationary. Instead, slowly but constantly they are changing their position, The classification of ecoregions should properly be based upon the distinctiveness and distribution of various ecologic associations, Unfortunately, available data on the associations of the United States that include both plants and animals are inadequate for this purpose, Actually, the classification of eco- regions presented here is based to a large extent on macro-climate as expressed by potential vegetation, Animals are dependent directly or indirectly upon plants for food and often for shelter and breeding places. Even where plants do not control the distri- bution of animals, they often indicate the characters of climate and soil upon which animals are depen- dent. Accordingly, for the present, vegetation offers the most satisfactory basis for distinguishing the major ecologic communities of the country, The geographic distribution of the ecoregions described here is correlated in varying degrees with climatic types, physiographic provinces and agricul- tural regions (Atwood 1940), and also with soil types (Soil Survey Staff 1970), This correlation is not sur- prising when we consider that climate, physiography, and soil all affect one another-and that the distri- bution of plants and animals is dependent upon all these environmental factors, POTENTIAL NATURAL VEGETATION A.W Kuchler INTRODUCTION Vegetation may be defined as the mosaic of plant communities (phytocenoses) in the landscape. It consists of a given combination of life forms (trees, shrubs) and a given combination of taxa (genera, species) with relatively uniform ecological require- ments. Potential natural vegetation is defined as the vegetation that would exist today if man were re- moved from the scene and if the plant succession after his removal were telescoped into a single moment. The time compression eliminates the effects of future climatic fluctuations, while the effects of man's earlier activities are permitted to stand. The potential natural vegetation is a particularly impor- tant object of research because it reveals the biolog- ical potential of all sites. In contrast to the potential vegetation is the actual, or real, vegetation that occurs at the time of observation. It may be natural (not appreciably af- fected by man), seminatural, or cultural vegetation, depending on the degree of human influence. In many parts of the United States vegetation is now natural or is so well known that it is entirely feasible to determine the potential natural vegetation with a high degree of accuracy. In other parts, the potential natural vegetation of this country can be determined only approximately. The identification of the potential natural vege- tation rests on the degree of disturbance, the avail- able amount and detail of information on the vege- tation that was disturbed, and on remnants of the natural vegetation, The history of the United States is short and the botanical exploration began early enough to permit a great deal of insight today into the nature of vegetation in most of the country, THE UNITS OF'VEGETATION It is the presence and the particular proportion of life forms and of taxa that give a plant community its unique and unmistakable character. The life-form pattern gives a plant community its physiognomy and structure, whereas the species pattern accounts for the floristic composition. As these two features of life forms and taxa are basic and applicable without exception anywhere on earth, they have been selected here to serve exclusively as the criteria for establish- ing the units of vegetation, These criteria permit a uniform approach to the vegetation throughout the country and put the various parts of the country on a comparable basis, In addition, a vegetation map based exclusively on life forms and taxa remains open to continual revision, correction, and refine- ment. This is a valuable advantage, The physiognomic types consist of easily recog- nizable categories, Usually, these categories occur over wide areas and are established without any difficulty, Only one, or very few, life forms are ad- mitted in characterizing the physiognomy, If more than one life form is included, however, it may well be that different life forms will dominate in different areas covered by this type. For example, in the South- west there are shrub savannas dominated in one area by shrubs with relatively little grass between densely growing bushes, whereas elsewhere this same type is dominated by grass with shrubs thinly scattered in the landscape. Variations may range from one extreme to the other. The extreme, however, should be an exception. The floristic approach permits a choice among various levels, or ranks, of taxa, At the given map scale, the species level is too low, All vegetation units are here characterized by genera. Their maximum number of dominant genera was arbitrarily set at six. As a result of using genera, units may seem to occur more than once, For example, there are oak forests in the East as well as in the West. The species are different, but this may not be evident on the map, The names of such types are elaborated in the legend to avoid confusion. Compare, for example, Appala- chian oak forest (Quercus; legend item 9S on map) with Oregon oak woods (Quercus; legend item 22), This terminology alerts the reader that the two types of oak forests (Quercus) are unlike, Several dominant genera in a given phytocenose may dominate in varying degrees, Thus, of genera A, B, and C in one phytocenose, it is understood that genus A may be more dominant in one part of an area, genus B may dominate in a second part, and genus C may dominate in a third part. The types of vegetation are, therefore, not uni- form throughout their area and this lack ofuniformity applies to both life forms and taxa. The small scale of maps requires a degree of generalization that does not show local variations of a given vegetation type. In many areas a type occurs in its pure form, but commonly there are variations, inclusions, and com- plexes, These variations make a type more heterog- eneous than appears on the maps, For example, numerous conifer bogs (legend item 85) are scattered as inclusions through much of the areas where types oflegend items 98 and 99 predominate, although they are shown on the map only where their extent justi- fiesit. Inclusions and complexes within a vegetation type are the result of local conditions. As the condi- tions change, so will the vegetation. But another, broader aspect of the variations that is equally im- portant is the fact that a vegetation type extends horizontally (in plains) and vertically (in mountains) from one set of environmental conditions to another. Thus, a type of vegetation may differ markedly at its opposite borders, be these northern and southern, upper and lower, drier and moister, or of some other kind. In view of the degree of generalization on these maps, a given vegetation type may, in fact, consist of several basic plant communities and represent clines of population. For example, the type in legend item 27 consists, at the highest altitudes, of open pine forests with Pinus leiophylla var. chihuahuana and p, cembroides as dominates, But the dominance of these species declines rapidly with decreasing alti- tudes, and they may disappear altogether near the lower altitudinal limits for this type. Such floristic gradients are common. Finally, it happens that two types of vegetation occur together as transitions, or as mosaics, In a tran- sition, the two types have mixed life forms and taxa. They share the available sites, as in legend item 28. The species of one plant community disappear grad- ually-that is, first one, then another-to be replaced little by little by the species of the other community. In contrast, the mosaics are so arranged that each of the two vegetation types involved retains its discrete character. The species of one type are not mixed with those of the other. Usually, islands of one type are embedded in a matrix of the other type; each type may be either matrix or island, depending on the relative extent of each. For example, the bluestem prairie (legend item 66) is treeless and dominated by tall grasses. Through this type, islands of oak-hickory forest (legend item 9) are scattered, Yet, in such a mosaic (legend item 73), each individual island con- sists of pure oak-hickory forest, and there is no blend- ing or merging with the bluestem prairie, This is not a savanna with trees or shrubs scattered loosely over a grassland. Where two types of vegetation form a mo- saic, each type retains its identity, Transitions and mosaics have been kept to a min- imum, Where they are shown, it is largely because not to do so would have seemed too gross a distortion. The fact that transitions and mosaics are shown does not imply a high degree of uniformity in the other types, Lack of uniformity of the individual vegetation types is more pronounced in Eastern United States than in the West. The mountainous terrain west of the 102d meridian causes the usual altitudinal zonation of vegetation, the contrasts between windward and leeward sides, and other features, The phytocenoses stand out more boldly, and vegetational boundaries can be very meaningful. By comparison. the eastern part of this country is characterized by modest relief and few contrasts of any kind. Vegetation types there merge more grad- ually, and the establishment of types is often difficult. Three overprinted symbols show the occurrence of junipers (J), Joshua-trees (Y), and groves of giant sequoias (S), The symbol for junipers refers to the genus Juniperus and implies different species in different regions. The symbol for Joshua-trees, on the other hand, represents an individual species, Yucca brevi/olia, The symbols J and Yare distributed in their respective areas where convenient. Therefore, the location of a given symbol does not mean that the symbolized plants grow only there and not elsewhere, These plants are likely to grow anywhere throughout the area in which such symbols are shown, The symbol S, representing Sequoia wellingtonia, is different. The small groves of these spectacular trees do not form a type of vegetation of sufficient extent to be shown here. They must, therefore, be indicated by symbols that are shown on the map exactly where the groves occur. The dominant genera listed in the title of each legend item are joined by hyphens to indicate that they belong together and form a vegetation type of which each is an important part. The alpine meadows (legend item 45), however, are an exception. All alpine meadows of the high altitudes in the West are here combined into a single type. The genera enu- merated in the title of this legend item do not form a single type and do not necessarily occur together; they do not all belong together. The legend is concise and simple. The name of every item in the legend consists of two parts, The first part of the names is given in English. Names of vegetation types have evolved in various parts of the country, They are not scientific but rather a part of the folklore of their respective areas arising from popular usage as a kind of tradition. Names like chaparral, pocosin, shinnery, or cross timbers enrich our terminology and give their types a regional flavor. Many of these terms are historically interest- ing. In some areas it became desirable to introduce new names. Where this was not feasible and where no local names have evolved, the Latin names of the dominant genera have been translated into English. The second part of names in the legend items consists of the scientific botanical terms for the leading genus or genera, The consistent use of generic names ties the legend together and makes the legend items meaningf\ll for readers everywhere. This, however, does not apply to the English part of the legend items where the use of species names is sometimes desir- able and sometimes inevitable, For example, buffalo grass and creosote bush are the only species of their respective genera in this country, and the English names are the same for genus and species, INTERIOR-GEOLOGICAL SURVEY A ESTON. VIRGINIA-1 978 U.S, DEPARTMENT OF AGRICULTURE FOREST SERVICE