VEGETATIONAL ANALYSIS 



53 



advisable to do so by blocks. Values for each block may then be 

 conveniently used as quadrat data, an additional means of analysis 

 and expression of results. A variation of the transect is the method 

 of sampling a unit area at regular intervals along a line. These inter- 

 vals may be determined by distance or altitude. Such records 

 taken on several lines are particularly helpful in mapping several 

 vegetation types that intergrade irregularly over an extensive area. 

 In the early land surveys of the northern and midwestern states, it 

 was required that the characteristic trees be listed in the records 

 for definite intervals along the lines run by the surveyors. Since 

 the county and township lines they established still stand, it has 

 been possible to reconstruct with considerable accuracy the com- 

 position of the forests as they then existed as well as the limits of 



FlG. 22. Forest associations of southwestern Michigan as reconstructed from 

 the field notes of the old land survey. Unshaded areas, marked B, beech- 

 maple forest; X = hemlocks, constituting, along lake shore, a codominant 

 with beech and maple; O = white pines (a mark for each locality of occur- 

 rence noted in the survey); horizontally shaded areas, oak-hickory forest; 

 obliquely shaded areas, oak-pine forest; stippled areas, dry prairies; and ver- 

 tically shaded areas, swamp associations.— From Ke?Joyer. i3i) 



