THE QUADRAT METHOD. 429 



rule, this means at least one quadrat in each consocies, with additional ones for 

 important socies. As soon as the quadrat has been mapped and photographed, 

 a labeled stake bearing the number and the date is driven at the upper left- 

 hand corner, and a smaller one is placed at the opposite corner to faciUtate the 

 accurate setting of the tapes in later observations. It is also essential to 

 select and record definite landmarks with care, in order that the location 

 may be readily found again. In forest or scrub this is readily secured by blaz- 

 ing, but in grassland it is necessary to erect an artificial landmark, or to resort 

 to compass and pacing. 



At successive readings of a permanent quadrat, the tapes are placed in exact 

 position by means of the stakes, and chart and photograph are made in the 

 usual manner. To facilitate the study of the charts, four successive readings 

 are recorded on the same sheet, thus greatly reducing the mechanical labor 

 involved in comparing separate sheets. The same advantage is secured where 

 the quadrat is used to show the variations from aspect to aspect of the same 

 year. While the permanent quadrat reveals the actual changes in composition 

 and structure which occur in the course of succession, a large part of its value 

 is lost unless it is made a station for measuring the physical factors involved in 

 ecesis, competition, and reaction. 



Denuded quadrat. — ^A denuded quadrat (Clements, 1905 : 173; 1907 : 209) 

 is a permanent quadrat from which the plant covering has been removed, after 

 having been charted and photographed. Quadrats in bare areas, both 

 primary and secondary, are essentially similar, but they differ in the impossi- 

 bihty of charting the original cover and of controlling the kind and degree of 

 denudation. The denuded quadrat is especially adapted to the analytical 

 study of ecesis and competition in relation to reaction. While denuding is an 

 invaluable aid to the study of succession, it must be recognized that permanent 

 quadrats register the exact course of development, while denuded ones make 

 possible more definite analysis, and throw light upon stages not now available. 



A quadrat which is to be denuded is first mapped, photographed, and 

 labeled as for a permanent quadrat. The vegetation is then destroyed by 

 removal, burning, flooding, or in some other manner. The kind and degree of 

 denudation will be determined by the evidence sought. If it is to throw light 

 upon an area in which denudation has affected the surface alone, the aerial 

 parts may be removed by paring the surface with a spade, or by burning. 

 To trace the effect of a more profound disturbance upon the reaction, the soil 

 may be removed to varying depths, it may be dug up and the underground 

 parts completely removed, or a sterile soU may be used to replace it. For 

 obvious reasons, denuded quadrats are most valuable when used in connection 

 with permanent quadrats, as indicated below. 



Quadrat series and sequences. — In following the sequence of stages, the most 

 valuable method is to use paired quadrats in each associes or consocies. Each 

 pair consists of two permanent quadrats located side by side. After being 

 mapped, one of them is denuded in the manner desired, and the two are then 

 charted annually on the same sheet. If a battery of instruments for recording 

 light, humidity, and temperature is located in the area, and the soil factors 

 are determined for the two quadrats, a complete and acciu-ate picture of suc- 

 cession is obtained. The permanent quadrats link the stages together as they 

 occur; they fix the attention upon the process rather than upon the more 



