Plants of intermittently flooded shorelines--Continued 
Reed canarygrass (Phalaris arundinacea) 
Willows (Salix spp. 
These waters contain, in addition to the higher plant species, abundant 
blue-green and green algae, as well as animal life, mainly in the form of 
invertebrates such as snails, insects, and crustaceans. 
In general the tendency is for plants to become arranged in zones. The 
species most tolerant to deep water occur in the center with species less 
tolerant to water arranged in rings about the border as the water decreases 
in depth. 
When undisturbed by grazing or cultivation, potholes tend to develop a 
cover of sedge or whitetop as shown in figure 4}. These species are tolerant 
of a wide range of conditions and are able to crowd out other emergents. In 
areas Of high permanence, which do not commonly go dry, these species form a 
ring around the margin as shown in the illustration. Areas of low permanence 
may become completely overgrown with pure stands of these species. 
Both whitetop and the large sedges are highly palatable to livestock 
and are often grazed to the point where other species such as cattail or 
hardstem bulrush become dominant. Figure 5 shows a pothole, mainly in 
pasture, where cattail is predominant. 
Plowing, with nearly complete removal of the vegetation, starts a new 
succession. Upon reflooding, a complex stand of vegetation may develop and 
persist for some years. Figure 6 shows an area of medium permanence which 
originally had a cover of sedge and whitetop. During the drought of the 
1930's, the large center portion was plowed. Upon reflooding, a dense stand 
of mixed vegetation, mainly hardstem bulrush, developed. Subsequent inter- 
mittent grazing of the north end produced even more complexities of the 
vegetation there. 
Figure 7 shows a medium-permanence area which in 1949 was open water 
surrounded by a margin of mixed sedge and whitetop. In 1950, when the cover 
map was made, water levels had dropped and the area had gone dry, apparently 
stimulating the growth of a. new crop of emergents, some of them shallow- 
water species. In 1951, with rising water levels, the cover at the center 
became less dense, and in 1952, with a further rise in levels, it had all but 
disappeared. Such changes in the amount of vegetation may be widespread and 
may cause great variation in the number of open-water areas in the region. 
Further variations in vegétation may be due to differences in water 
chemistry. This is discussed by Moyle (1945) and Metcalf (1931). The 
vegetation of potholes on the study area itself did not appear to be strongly 
influenced by variations in water chemistry. However, there were several 
potholes within a few miles that were so alkaline as to be practically barren. 
The density of the vegetation is a highly variable factor, and most 
species tend to become sparse as the water in which they grow increases in 
depth. They increase in density again as the water recedes. 
