Wave-dampening structures will improve plant survival rates if they reduce wave energies 

 sufficiently. An additional benefit of wave-dampening fences is that suspended solids settle out if 

 the wave velocity is decreased enough, as has been illustrated by a project conducted by Mike 

 Windham of the Louisiana Department of Wildlife and Fisheries. This concept is also being 

 explored by John Day and Raoul Baumans (Louisiana State University Center for Wetland 

 Resources) in a study of marsh accretion resulting from brush fences. 



Exclosures 



The severe herbivore pressure to which transplant material is subjected greatly affects survival. 

 To date, nutria (Myocaster coypus) have been observed to decimate unprotected bitter panicum 

 (Panicum amarum) (Mendelssohn and Hester 1985b), smooth cordgrass, cutgrass (unpublished data 

 of the author), and baldcypress (Taxodium distichum) (Louisiana Sea Grant 1987) plantings. Nutria 

 are not the only pests, but because of their numbers they may be the worst. Exclosures have been 

 used successfully (Figure 2) but this increases the cost per planting unit enormously. In certain 

 areas, herbivore exclosures can double as wave-dampening fences and water hyacinth barriers 

 (Figure 3). However, this must be approached with caution because nutria have been known to 

 gnaw through plastic in order to feed on transplants (Louisiana Sea Grant 1987). Chemical 

 herbivore repellents are another alternative, but their effectiveness in protecting transplants from 

 nutria has not been documented to date. 



The author has conducted a herbivore exclosure transplant experiment using S. altemiflora in 

 a highly organic marsh southeast of Cut Off, LA All unprotected plants were removed within 3 

 weeks, presumably by nutria. After 12 weeks, 85% of the protected plants had survived. These 

 had vigorous growth and basal sprouts (unpubl. data). 



Water hyacinth (Eichhomia crassipes) can be an especially insidious problem for vegetative 

 restoration efforts in freshwater areas. Large rafts of this species can enter an area where it was 

 previously absent and wreak havoc on transplants. Typically, an extreme change in water levels 

 causes mass movement of this plant over considerable distances; the plants can then be blown 

 against a bank by prevailing winds. This process can cause mechanical damage and the removal 

 of transplanted material. This can be avoided by placing a physical barrier such as a wave- 

 dampening fence or poultry wire fence around the plantings. If fences are oriented parallel to the 

 bank, it is important to attach a perpendicular skirt that prevents waterborne material from getting 

 behind the fence (Figure 1). Alternatively, water hyacinth may prove to be a valuable species for 

 erosion control when used to fill the space within fences to reduce wave energy. Field trials of 

 this concept are planned by the author. 



PROJECT DESIGN AND PRIORITIZATION 



Desigft 



To determine the best design for a proposed project, the following procedure is recommended. 

 1) Use a planting decision tree similar to that shown in Figure 4, but tailored to Louisiana 

 conditions, to determine appropriate techniques. 2) For each alternative, consult a site evaluation 

 . form similar to that shown in Figure 5. Each technique would be assigned a likelihood of success. 

 3) Estimate the cost of implementing each alternative at the site in question. 4) Evaluate the 

 site's value as a sustainable resource base. 5) Employ Bayesian statistical methods to find the 

 approach that would maximize overall expected benefits. 



226 



