QUADRATS 175 



secondary succession, the denuding cause is made use of in a fashion as 

 nearly natural as possible. Ordinarily, the plants are removed just below 

 the top of the ground by a spade, leaving the underground parts undisturbed. 

 This method has yielded very interesting results. 



Quadrats have loeen denuded in the fall after the majority of the plants 

 have completed their growth. This is largely owing to the fact that other 

 field work is less pressing at this time. Denudation can be done as well in 

 the spring, though the invasion will be slower in this case, since the seeds 

 which have accumulated will be partly or entirely removed. During the first 

 season the denuded quadrat should be mapped every month, and, if the in- 

 vasion be rapid, photographed also. In open formations, especially those of 

 a xerophytic nature, a single chart and photograph made at the end of the 

 season are sufficient. In a few cases of this sort, indeed, no invaders have 

 appeared until the second year. Beginning with the second season, a single 

 record taken near the close of the growing period will suffice. Denuded 

 quadrats are labeled, dated, and filed exactly as other permanent quadrats, 

 but it should be noted that the first member of the chart and photograph 

 series is that which records the original vegetation of the area denuded. 



215. Physical factors. When denuded quadrats are single, their physical 

 factors must be observed in the usual way. If they are associated with per- 

 manent ones, the ordinary readings are made for the latter, and those factors 

 which are affected by exposing the soil are alone taken for the denuded area. 

 These are the water-content, soil and surface temperatures, and in some sta- 

 tions at least the humidity near the surface. As everywhere, water-content 

 is the most important, but the temperature at or near the surface has a 

 marked effect upon germination. Because of its bearing upon the latter, the 

 surface water-content is usually determined also. This has been done by 

 taking a surface sample 2 inches square and i inch deep. Denuded quadrats 

 naturally show considerable differences from year to year as the action of the 

 invaders becomes more pronounced. To this fact is due much of their value 

 as aids in interpreting succession. 



Aquatic Quadrats 



216. fcope. The preceding discussion of quadrat methods is based wholly 

 upon their use in terrestrial formations. Wet meadow and dry bog are the 

 wettest places in which quadrats have been used. It is clear, however, that 

 with certain necessary modifications, quadrats can be used as successfully^ 

 though not as conveniently, in many water formations as in land ones. The 

 tapes need to be raised above the surface of the water by longer stakes, and 



