VEGETATIONAL ANALYSIS 



47 



the average increment. Beyond this point addition of samples will 

 yield progressively less than the average. In the region of point B 

 a sample yields only one-half the information and at point C only 

 one-quarter the information obtained by a sample at point A. 

 Used in combination with the tangent procedure, this should be 

 helpful in interpretation of the species : area curve and the selec- 

 tion of numbers or sizes of plots most suited to a vegetation type. 

 If a series of quadrats of an arbitrarily set size is run in a stand, 

 a species : area curve constructed from the data will indicate how 

 many such quadrats would have been necessary for sampling to 

 achieve a desired accuracy. The most efficient size of plot to be 

 used can likewise be determined from the same preliminary series 



Dune Grassland. N.C 



MINIMUM QUADRAT SIZE IF 25 ARE USED 



SIZE OF QUADRATS SQ.M. 



Dune Grassland, N.C. 



MINIMUM NUMBER OF ^ SQ.M. 

 QUADRATS 



10 15 



NUMBER OF i SQ.M. QUADRATS 



20 



25 



than % sq. m. and (D) a minimum of six such samples. The lines tangent to 

 the curves were put in using Cain's triangle method described on page 000. 

 In (B), point a is equivalent to the average increment per sample, at point b 

 the yield is only one-half this increment, and at point c only one-quarter the 

 increment. 



