212 PLANT PHYSIOLOGY AND ECOLOGY 



decimeter wide. The distance between them is checked here and 

 there by a decimeter rule, and they are fixed firmly in place by 

 quadrat stakes. The plants are recorded as for the line transect, 

 except that the record is for a decimeter strip, and occupies the 

 width of a centimeter on the plotting paper. An interval of a 

 centimeter is left between the successive portions of the strip, in 

 order that they may be copied readily upon the topographic 

 outline. The latter is traced on the plotting paper as indicated 

 for the transect, except that it consists of two lines a centimeter 

 apart. The outline and the field record of the plants of the tran- 

 sect are combined upon a common scale, as in the line transect. 

 Because of their value and the labor involved in making them, belt 



Fig. 77. A belt transect through the Fruyuria society of a spruce forest. 



transects are regularly made permanent by placing a labeled stake 

 at each end. 



The limits of zones are shown on charts of belt transects by 

 single cross-lines, and those of alternating areas by parallel cross- 

 lines. Whenever possible, the physical factors should be deter- 

 mined for the various areas through which the transect runs. 



228. The migration circle. This is the method employed to 

 show the movement or migration of plants outward from a 

 parent individual or group. Such a movement usually takes 

 place in all directions, and a circle is hence better to record it than 

 a quadrat. Migration circles are regularly permanent in order 

 that the yearly spread of the plants may be accurately followed. 

 Circles of this sort are of great value in the study of competition 

 and invasion. The actual movement of the migrants is often 

 seen to the best advantage in denuded circles, but these are scarcely 

 feasible except for protracted investigation. 



