180 



CLASSIFICATION OF SERES. 



life-forms, as this indicates the climatic as well as the genetic relation, when 

 the latter is present. 



Forest climaxes <yr formations: 



1. Boreal forest: Picea-Abies-hylion. 



2. Lacustrian forest: Pinus-hylion. 



3. Deciduous forest: Acer-Fagus-hy- 



lion. 



4. Coastal forest: Pinus-hylion. 



5. Mesa forest: Juniperiis-Pinus-hy- 



lion. 



6. Montane forest :Pm'M«-Psei«iotgtx{/a- 



hylion. 



7. Alpine forest: Picea-Abies-hylion. 



8. Pacific forest: Thuja^Tsuga-hylion. 



9. Insular tropical forest. 



10. Isthmian tropical forest. 

 Scrub climaxes or formations: 



11. Footh}3lcha,pan:al:Ceanothus-Quer- 



12. Desert chaparral: Prosopis-CovUlea- 

 eremion. 



Saryb climaxes or formations — Continued. 



13. Thorn scrub: Cereus-Fovquiera- 



eremion. 



14. Desert scrub: Atriplex-Artemisia- 



fuilion. 



15. Arctalpine scrub: BetulonSalix-hel- 



ion. 



16. Heath: Led/wm-Vaccinium-oxyon. 

 Grassland climaxes or formations: 



17. Prairie: Stipa-Agropyrurrirpoion. 



18. Plains: BvlbUis-Boutelowarpoion. 



19. Alpine grassland: FestucorCarex- 



poion. 

 Tundra climax or formation: 



20. Moss-Uchen tundra: Polytrichuntf 



CladoniorCTymion. 



Subclimaxes. — It is not improbable that several of the above climaxes 

 are actually subclimaxes. This may be true of the prairie, heath, and 

 lacustrian forest, and it may hold also for arctalpine scrub, and for some 

 tundra and chaparral. No certain disposition can be made of these at 

 present, though it is clear that every one of them may be an actual subclimax 

 stage of the adjacent forest formation. Whether there is also a distinct area 

 outside the forest region, in which any one of them persists as an actual 

 climatic climax, is stiU to be demonstrated. In alpine regions scrub, heath, 

 and tundra persist for so long a period that it seems necessary to regard them 

 as climaxes, and this would seem to be even truer for arctic regions, where 

 the climatic zones are much broader. Chaparral affords almost certain 

 evidence of being a climax over much of the Rocky Mountain region, while, 

 in southern California at least, it is often an artificial subclimax due to fire. 

 The case of the prairie is even more puzzling. In the fragmented condition 

 in which it exists east of the Mississippi, it seems to be merely a local subcli- 

 max of the deciduous forest. The nucleus of the prairie as seen in eastern 

 Nebraska and the Dakotas gives much evidence of being a real climax as it 

 passes into the plains on the west. Since this transition is an extremely 

 gradual one, it seems best to regard the prairie as a subchmax and the plains 

 as the real grassland climax.^ The effects of fire, grazing, and cultivation, 

 however, have converted the prairie into an artificial subclimax, which will 

 persist until the prairie disappears as a consequence of man's activities. 



Eelationslup of climaxes. — ^It is evident that the boreal and mountain forests 

 of North America show certain degrees of relationship. The boreal forest of 



'During the summer of 1915 a successional study was made of the transitions between prairie 

 and plains in South Dakota, Nebraska, Kansas, Oklahoma, and Texas, and between the Bouteloua 

 and the Arislida plains in Texas and New Mexico. The developmental correlation of the associa- 

 tions and consociations was greatly promoted by the exceptional rainfall of the seaoon. This 

 brought the successional sequences out in clear relief, and gave a quasi-experimental value to the 

 results. As a consequence, the conclusion that prairie and plains belong to the same climax 

 formation became unavoidable. The prairie-plains climax, or BoiUeUrua-poioa, would thus con- 

 sist of three associations, namely, (1) Slipa^Agropyrum prairie, (2) BulbUis-Boutdmta plains, and 

 (3) Ariatida-Bouteloua desert plains. 



