was greater where three-square was most prevalent. Nutria feeding 
reduced the density of Olney's three-square and caused some openings; 
and stands were improved with protection from nutria (exclosures 1 
and 2) and with a reduced nutria population in 1956 combined with 
more nearly optimum water conditions. With optimum growing con- 
ditions the loss of Olney's three-square in large stands to nutria 
might have been less than that experienced in 1955. 
Olney's three-square is the most important food of geese and 
muskrats in the Gulf Coast marshes (Lynch, 1941). In feeding on 
three-square, nutria compete to some extent with muskrats and 
wintering geese. 
Stands of big cordgrass were so high and dense on Transects A 
and C as to impair vision when the transects were laid out, but lost 
their identity as stands by 1955. The stands on Transects A and C 
and a colony near the saltmeadow cordgrass type of Transect C were 
almost completely destroyed by nutria, as were already debilitated 
stands on Transect B. Nutria activity was more intense in big 
cordgrass stands than in other vegetative types and big cordgrass 
rhizomes provided a preferred food. Big cordgrass protected from 
nutria (exclosure 3) continued to thrive. 
All big cordgrass stands on the transects showed less than 
optimum growth when the transects were established. We cannot say 
with certainty whether this condition was due to nutria activity 
previous to our study, or to changes in the habitat. The growth 
