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Northern Limit . Many species with an essentially southern distribution 



extend into the Bay region; e.g. cypress ( Taxodium distichum) and live oak 



( Quercus virginiana ) . 



Northern Outlier . Some southern species have disjunct populations, often just 



a few individuals, well north of the contiguous populations : e.g. water hickory, 



( Carya aquatica ) . 



Southern Limit . Essentially northern species whose southern-most 



distribution extends into the Bay region: e.g. black ash, (Fraxinus nigra). 

 Southern Outlier . Disjunct populations in the Bay region apart from the 

 southern continguous populations: e.g. balsam poplar, (Populus balsamif era) . 

 Eastern Limit . Species whose distribution is mid-western occasionally 

 extend east to the Atlantic coast: e.g. chinkapin oak, ( Quercus 

 muehlenbergii) . 



Eastern Outlier . Scattered populations of a few basically mid-western 

 species are found in the Bay region ; e.g. bur oak, ( Quercus macrocarpa) . 

 Coastal Plain Outlier . Upland species characteristic of the Appalachians 

 are occasionally found in small colonies deep in the coastal plain over 

 a hundred miles from the nearest upland population: e.g. white pine 

 ( Pinus strobus ) , and hemlock ( Tsuga canadensis ) . 



Regardless of their nature these distrubutions are of far greater 

 importance than as mere geographical curiosities. Any organism living 

 on the edge of its range is operating on the edge of its adaptation 

 to its environment as well and it may be particularly sensitive to en- 

 vironmental stresses with which it can cope in the center of the range. 

 If we are to understand the ecological amplitude of any species it must 

 be studied under extreme conditions as well as optimal ones. For this 

 reason a few acres of scraggly hemlocks on the eastern shore may be worth 

 a hundred acres on the Blue Ridge. These range phenomena have been 

 located as precisely as records allow and they enter importantly into the 

 natural area selection process. 



