3.4.2 APPROACH 



The Chenier Plain region was divided into 14 

 habitats as defined in table 3.53. The habitat defini- 

 tions are based on a combination of natural charac- 

 teristics and land uses that are not always mutually 

 exclusive. Overlap of natural and cultural processes 

 occurs in every habitat. Ten of the habitats-the two 

 aquatic habitats, the five natural wetlands habitats, 

 and three upland habitats-are landscape units which 

 function naturally. Three other "habitats" are clearly 

 cuhurally modified. In these areas natural processes 

 have been dramatically changed by cultural needs. 

 The remaining habitat, impounded marsh, is rather 

 diverse and contains areas where natural processes 

 predominate as well as other areas where agricultural 

 processes exert control. Impounded marsh is recog- 

 nized by straight spoil bank or levee boundaries that 

 isolate the impoundment from surrounding wetlands 

 and water bodies. Controls on these levees range from 

 "flap gates" which prevent the inflow of surface 

 water but allow excess rainwater to run off, to im- 

 poundments that are routinely drained by pumping 

 and are used for cattle grazing. In this study these 

 drained impoundments are distinguished from pasture 

 habitat by the fact that they are dominated by native 

 vegetation. 



These habitats were idenfified on the most recent 

 (1974) U.S. Geological Survey 1:24,000 scale ortho- 

 photoquads or topographic maps. Wetlands were de- 

 lineated by updating the marsh-type map of Chabreck 

 et al. (1968), by infonnation from the Texas Bureau 

 of Economic Geology (Fisher et al. 1972), and photos 

 from low altitude overflights supplemented with lim- 

 ited ground reconnaissance. Black and white aerial 

 coverage was used to map habitat changes over the 

 period 1952 to 1974. This coverage did not extend to 

 the East Bay area, for which 1954 maps were used. 

 Present habitat area was determined using a point 

 converting (grid sampUng) method developed by 

 Gagliano and van Beek (1970). Canal lengths were 

 digitized, and area was derived from average widths 

 for different types (app. 6.4). 



3.4.3 PRESENT HABITAT COMPOSITION AND 

 DISTRIBUTION 



The areal extent of habitats in the Chenier Plain 

 in 1974 is listed in table 3.54, while the distribution 

 of habitats within individual basins and habitat area 

 changes since 1952 are provided in appendix 6.4. By 

 eliminating the nearshore Gulf habitat, the reader is 

 provided with a better perspective of the relative 

 abundance of habitats landward of the shoreline. The 

 distribution of the five major habitat groups is shown 

 on Plates 3A and 3B. 



The relative size of each habitat type does not 

 necessarily correlate with its actual importance. The 

 urban habitat occupies only 2.8% of the land area, 

 but its influence extends to every other habitat of the 

 Chenier Plain. 



The generalized distribution of habitats in a 

 Chenier Plain basin, in relation to various hydrologic 

 subunits, is shown in figure 3-15. The agricultural 

 habitats (pasture and rice field) are lumped together 

 in tliis schematic because of their close association 

 with one another. These habitats dominate the upper 

 part of a basin on the Pleistocene surface. Pasture and 

 a limited amount of land used for truck crops are also 

 found on the cheniers. 



The swamp forest habitat is typically found on 

 river floodplains beyond "normal" tidal influence. 

 This habitat is present in the Calcasieu, Mermentau, 

 Sabine, and Vermilion basins. The East Bay and 

 Chenier basins have no swamps because brackish tidal 

 waters influence their wetland areas. In addition, since 

 the East Bay Basin does not contain a major river sys- 

 tem, there is no major floodplain for swamp forest to 

 develop. Although the total area of swamp forest in 

 the Chenier Plain is small, more extensive areas of this 

 habitat type can be found on floodplains upstream 

 from the study area. This is particularly true of the 

 Calcasieu and Sabine floodplains. 



Historically, upland forests have not been exten- 

 sive in the Chenier Plain (Fisk 1944) but much of this 

 habitat has been converted to agricultural lands. Only 

 a few isolated stands of upland forest now exist in the 

 northern portions of the basins. 



The ridge habitat can be divided into two major 

 types, natural and man-made. Natural ridges in the 

 form of cheniers are concentrated near the coast and 

 generally decrease in area as one moves inland. Pleisto- 

 cene islands are topographic high areas surrounded by 

 marsh. They are located close to the marsh-Pleistocene 

 boundary. Natural levees of sufficient elevation to be 

 classified as ridges are relatively rare in the Chenier 

 Plain. The upper parts of the Calcasieu, Mermentau, 

 Sabine, and Vermilion rivers contain small levees that 

 support vegetation distinct from the surrounding 

 swamp forest. Remnant levees of older river courses 

 and shorelines appear occasionally in the Chenier Plain. 



Man-made ridges, largely in the form of spoil 

 banks, are found randomly throughout the Chenier 

 Plain. Because spoil banks are associated with canals, 

 their distribution is reflected by that for canals (Plates 

 5 A and 5B). Spoil banks occupy 2% of the total area 

 of the Chenier Plain, and this area is greater than that 

 of the beach, swamp forest, upland forest, or salt 

 marsh habitats. Perhaps more significant is the fact 

 that spoil banks make up almost one-half of the total 

 ridge habitat. Hydrologically, however, these man- 

 made ridges function differently than natural ridges, 

 because their orientation is random wdth respect to 

 historic circulation patterns. 



Most of the urban habitat is found on higher ele- 

 vations landward of the fresh marsh zone. However, 

 many small communities are located closer to the 

 coast, on ridges and along major waterways (plates 

 lAand IB). 



The salt marsh habitat is generally found as a nar- 

 row zone between the beach and the first major land- 

 ward ridge. At the site of major passes, salt marsh 

 may extend inland and fringe the waterA'ays. 



75 



