QUADRATS I73 



or year, the tapes are placed with reference to the stakes, and a chart and 

 photograph are made in the usual manner. These are labeled and dated like 

 the original ones, but they are numbered to indicate both the quadrat and the 

 series, e. g., 15- indicates the second chart, and photograph made of quadrat 

 15. The date indicates whether the readings are by the aspect or the year, 

 though this may be shown also in the name of the series itself. It is clearly 

 an advantage to have the two successive charts of a quadrat ujwn the same 

 sheet, and to file all the charts and photographs of the same permanent quad- 

 rat together, and in the proper order. 



Since much of the value of a permanent quadrat depends upon its use as a 

 station for observing physical factors, it is unprofitable to establish a large 

 number. The results of invasion and competition can be ascertained by the 

 quadrat alone, but these should be merely preliminary to seeking for their 

 causes. Clearly, a quadrat should be established for each battery of instru- 

 ments, while additional ones should be located only in so far as they can be 

 visited often enough to give an insight into the factors that control them. 

 In view of the fact that the most important factors, water-content and light, 

 are less variable than humidity, temperature, and wind, it will suffice if visits 

 are made once a week. This is especially true when it is possible to refer 

 the more variable factors to the continuous records of a base station. While 

 all the results determined for permanent quadrats are preserved in the field 

 record, a record of them is also kept on the reverse of the chart sheet for 

 convenience in interpreting the different charts. 



The Denuded Quadrat 



213. Description. This is primarily a permanent quadrat from which the 

 plant covering has been removed, after it has been charted and photographed. 

 What is practically the same thing is obtained by establishing a permanent 

 quadrat in a new soil, or in one recently laid bare and not yet reclothed with 

 plants. These, however, are merely permanent quadrats, in which the first 

 chart and photograph furnish a record of the habitat alone. They are of 

 great importance in succession, and will be more fully discussed under ex- 

 perimental vegetation. The denuded quadrat is of the usual size, i meter, 

 though the smaller lichen quadrats are also denuded. The location is sub- 

 ject to the conditions already indicated, especially with reference to physical 

 factors. The denuded quadrat, however, is particularly adapted to the study 

 of invasion and the resulting competition. Consequently, when migration is 

 markedly from one direction, a series of denuded quadrats throws a flood of 

 light upon the actual steps in invasion. Denuding is a valuable aid in suc- 

 cession, but it must be clearly recognized that, while permanent quadrats 



