CLIMAX COMMUNITIES : SHIFTS WITH TIME 301 



areas is undoubtedly true. With climatic change, vegetational 

 change is to be expected. Some modern changes are easily recog- 

 nized, as indicated above. In highly populated areas, the changes 

 may be much less obvious because natural vegetation has been 

 disturbed by man. 



PALEO-ECOLOGY 



This phase of ecology deals with the history of vegetation, es- 

 pecially the reconstruction of past climaxes and climates, their 

 rise, decline, and migration over long periods of geological time. 

 Its basic source materials are derived from paleontology and geol- 

 ogy and must be interpreted in terms of what is known of the 

 ecology of modern organisms. 



Tracing changes in modern climax vegetation is a complex proc- 

 ess involving the use of every kind of evidence available. E B. 

 Sears' 218 reconstruction of the natural vegetation of Ohio and its 

 prehistoric development 221 illustrates how historical records and 

 pollen statistics may contribute evidence. A. M. Raup's 203 study of 

 New England climate and vegetation utilizes still other sources of 

 evidence. Archaeology, zoology, botany, and geology all were 

 drawn upon in a variety of ways before he concluded that New 

 England had had a warmer climate within recent years— probably 

 no more than a thousand years— and that the trend has since been 

 to the cooler and moister, with parallel vegetational changes. 



Knowing that climates have changed, one may be equally cer- 

 tain that vegetation has varied accordingly. Major alterations in 

 vegetation may likewise be assumed to indicate modification of 

 climate. In some instances, however, such shifts have been inter- 

 preted as purely successional in nature, a point not to be ignored 

 since succession has gone on in the past as it does today. Change 

 within historical time, if still in progress, may be observed, or may 

 become apparent from detailed quantitative and qualitative studies 

 of transition areas. 39 A less reliable source of information is the 

 historical literature not always dependable, unfortunately, because 

 of the limited knowledge of the early writers. It is, nevertheless, 

 a source from which much of value can be learned, 36 ' 203 particu- 

 larly when the information is drawn from several sources and is 

 correlated with other kinds of evidence. 



The difficulties of reconstructing the vegetational picture dur- 



