METHODS OF STUDYING VEGETATION 



213 



A simple migration circle is located so that a plant or group 

 of plants of the species to be studied forms the center. The size 

 of the circle is largely determined by the nature of the vegetation, 

 and especially by the height of the species, which has much to 

 do with the distance to which seed or fruit is carried. A circle 

 of 1 -meter radius is best for ordinary purposes, though in open 

 vegetation one of 5-meter radius is desirable. The usual quadrat 

 tape is used as a radius. This is fixed in the center and the position 

 of each plant of the species concerned is noted as the tape is carried 



Fig. 7S. A migration circle in a grass formation, used to determine the 

 direction and aniount of movement of the achcncs of Kuhnia glutinosa. 



around the circle. The exact positions are indicated upon a chart 

 circle whose radius is a decimeter. The chart is ruled in such a 

 way that each quarter is divided by five radii, in order to aid in 

 recording the individuals accurately and quickly. After the 

 mapping is completed, a labeled stake is fixed in llie center, thus 

 making the circle permanent. It is often desirable to use a group 

 of individuals of different species as a center, and to recoid Ihe 

 movements of all upon the same chart. 



229. Formation maps. In studying the structure of a foiina- 

 tion, it is imi)ortant to make a graphic record of its princii)al 



