and 1974. A portion of the increase can be attributed 

 to loss of upland forest and ridge habitat, but most 

 agricultural expansion has been at the expense of wet- 

 lands. Because little upland forest and natural ridge 

 area remains, future expansion in agriculture will in- 

 volve the draining of wetlands. The recent (1952 to 

 1974) picture is clear: as agricultural land is preempted 

 for urban and industrial expansion, it is replaced by 

 the increased draining of wetlands. 



The agricultural habitat has been divided into 

 pasture, rice, and non-rice cropland in table 3.55. The 

 non-rice cropland includes some sugarcane areas in 

 the Vermilion Basin, soybeans scattered throughout 

 the uplands, and truck crops in the uplands and along 

 the ridges. All three categories have experienced a net 

 gain from 1952 to 1974. The gains, however, have 

 not been uniform. It appears that there has been a 

 shght shift of agricultural land use within the confines 

 of the study area, with rice expanding into wetland 

 areas, and otlrer crops that cannot succeed on wet- 

 land soils gaining more acreage on better drained sur- 

 faces. 



3.4.6 NATURAL HABITAT CHANGES AND 



INDIRECT CHANGES CAUSED BY MAN 



Indirect or unintentional habitat changes caused 

 by man, and changes brought about through natural 

 processes have been significant and are discussed by 

 Gagliano (1973). The separation of indirect man- 

 induced change from natural change is difficult. Some 

 of the changes are the result of natural processes. 

 Shoreline erosion that results in the loss of wetlands 

 is predominantly a natural process, although man 

 may act as a catalyst. In areas where man has con- 

 structed jetties and groins he has certainly altered 

 erosion and deposition rates. Hurricanes are short- 

 term, natural stresses that affect man-altered wetlands 

 more than natural marsh areas (Chabreck and Pal- 

 misano 1973). 



Peat bums resulting from either natural or man- 

 made fires, and local "eatouts" of marsh grasses by 

 geese and muskrats (O'NeU 1949) have been docu- 

 mented as factors involved in land loss. Whereas these 

 factors may be significant on a local level, most of the 

 land loss is goverened by other processes on a basin 

 level. 



The major change in habitat types during 1952 

 to 1974 in the Chenier Plain was the loss of natural 

 marsh (includes salt, brackish, intermediate, and fresh 

 marsh) (table 3.55). Although about one-half (40,242 

 ha, 99,440 a) of the natural marsh has become im- 

 pounded marsh habitat, otlier habitat types have also 

 replaced natural marsh (table 3.56). Impounded marsh 

 habitat continues to function as wetland habitat for 

 some species such as waterfowl and marsh mammals, 

 but it has less value than natural marsh when viewed 

 as a component of the estuarine ecosystem (part 4.2). 



There has been some loss of natural marsh to 

 agriculture and to spoU banks, but most (26,280 ha, 

 64,939 a) of the remaining loss has been to inland 

 open water. Also, some inland open water habitat has 

 been changed to impounded marsh to maintain ade- 

 quate water quality and/or to control water level. 



The 28,662 ha (70,825 a) loss is equivalent to a 

 7.2% loss rate of natural marsh to open water from 

 1952 to 1974. This rate is the overall loss for the six 

 basins in the Chenier Plain and a high degree of vari- 

 ability exists between basins. 



A portion of the 7.2% loss rate can be attributed 

 to the direct conversion of wetlands to open water by 

 canal dredging. The total area of marsh lost through 

 this activity was 2,685 ha (6,635 a), a rate of 0.7% 

 for the period 1952 to 1974. The present distribution 

 of canals is shown in Plates 5A and 5B. The total area 

 occupied by canals and accompanying spoU banks is 

 4.3% of the Chenier Plain excluding the nearshore 

 Gulf. From 1.0 to 2.2% of the land area is occupied 

 by canals in each basin (table 3.57). 



Table 3.56. Loss of natural marsh* in the Chenier Plain in 1952 to 1974. 



Habitats 



replacing 



natural marsh 



Inland open water 



Nearshore Gulf 



Impoundments 



Canals 



Spoil areas 



Agriculture 



Urban 



Total 82,080 



20.2 



^Includes salt, brackish, intermediate, and fresh marsh. 



79 



