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 been 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 1 inch deep. Denuded quadrats 
naturally show considerable differences from vear 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. Scope. 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 
ro 
