THE QUADRAT METHOD. 



425 



differ in form and to some degree in purpose, they are alike in being based upon 

 the eniuneration or charting of the individuals of a community within a cir- 

 cxnnscribed area, and in disclosing as well as registering the changes in popula- 

 tion and structure which are the record of development. 



The use of squares for pmposes of eniuneration or of determining the amount 

 of plant material produced has occurred occasionally for a century or more 

 (Sinclair, 1826; Darwin, 1859; Hanstein, 1859; Blomquist, 1879; Stebler and 

 Schroter, 1883-1892; etc.; c/. Schroter, 1910 : 117). It was organized into a 

 definite system for the study of the structure and development of vegetation 

 by Pound and Clements (1898^ : 19; 1900 : 61) and Clements (1904; 1905 : 161; 

 1907 : 202; 1910 : 45; c/. also, Thomber, 1901 : 29). It has since been used by 

 Sernander (1901), Jaccard (1901), OUver and Tansley (1905), Shantz (1906, 

 1911), Young (1907), Sampson (1908, 1915), Spalding (1909), Raunkiaer 

 (1909), Gleason (1910), Howe (1910), Tansley (1911), PaUis (1911), Adamson 

 (1912), Cooper (1913), Priestley (1913), Kearney (1914), Pool (1914), Weaver 

 (1914, 1915), Hofmann (1916), Bergman and Stallard (1916), and others. 

 With the rapid increase in the number of successional studies, the use of the 

 quadrat and its modifications may be expected to become as universal as it is 

 fundamental. 



Kinds of quadrats. — Quadrats are distinguished with respect to their 

 purpose, location, or size. From the standpoint of purpose and use, they are 

 divided into list, chart, permanent, and denuded quadrats. As to their 

 location in a commimity or kind of community, they are known as layer, soil, 

 water, Hchen, moss quadrats, etc. The unit quadrat is taken as 1 meter 

 square. This may be divided into subquadrats of a decimeter or a centimeter 

 square, or grouped into perquadrats up to 100 or even 1,000 meters square. 

 The meter quadrat is the unit for herbland, herbaceous layers, and grassland, 

 the 10-meter for scrub, and the 100-meter for forest. List quadrats are chiefly 

 useful for taking a census of individuals, species, or life-forms, and making 

 floristic comparisons. Chart quadrats are primarily to record composition 

 and structm-e, while permanent and denuded quadrats are especially designed 

 for the study of succession by the methods of sequence and experiment. 



list quadrat. — The list quadrat is of slight value for the study of succession, 

 since the latter demands the actual study and record of a definite area from 

 year to year. It serves for the superficial values of reconnaissance, but is of 

 small use for intensive investigation. Its chief interest lies in the fact that it 

 was the pioneer quadrat method, and that it has given rise to two appHcations, 

 which have met with some favor. These are the methods of Jaccard and 

 of Raunkiaer, both designed to permit a more exact comparison of localities, 

 communities or regions upon the basis of floristic, and of physiognomy also, 

 to a certain extent. Jaccard (1901, 1902, 1908, 1912, 1914) has made use of 

 the Ust quadrat to estabhsh a statistical method for floristic, with especial 

 reference to the origin of the flora of a region. His method is based upon: 

 (1) the coefficient of community, or the degree of similarity of composition 

 between the different portions of the same region; (2) the degree of frequence 

 of each species; and (3) the generic coefficient, or the percentage relation of the 

 number of genera to the number of species (c/. Drude, 1895 : 17; Pound and 

 Clements, 1900 : 59, 63). The appUcation of Jaccard's principles to present- 

 day succession is difficult if not impossible, but it will perhaps serve as a valu- 



