Paspalum decreased from 1954 to 1955 and increased in 1956 to 
cover a larger area than in 1954. The probability of the latter 
change is approximately 0.20 (n = 9). 
The increase in nonvegetated ground on Transect D reflected a 
change in the density of sawgrass, since that was the most abundant 
vegetation present. During March 1956 the sawgrass at one place 
on the transect appeared to be less dense than elsewhere, and by 
June this tendency was marked along a quarter of the transect. 
Apparently the sawgrass was dying, for dead, broken-off clumps were 
present. During early summer the following year the marsh was swept 
clean by a hurricane, and the ultimate fate of the die-off could not 
be determined. 
Exclosures 
Exclosures were established to ascertain the effect of nutria 
on vegetation by protecting it from the nutria. Data for exclosure 1 
aiken in table III. During the 5 months between construction 
and the first vegetation measurements, vegetation improved visibly 
inside the exclosure, and the difference between mean weights per 
Sample inside and outside the exclosure at tne end of this period 
in 1953 was significant at the 6 percent level with the higher mean 
inside. In 1956 there was a significant difference (3 percent level) 
between means, with the higher mean inside. Number of stems of all 
species, however, was not significantly different inside and out- 
side during the 4 years. In 1956 the vegetation inside the exclosure 
13 
