niger ) , and green ash ( Fraxinus penn - 

 sylvanica ) . Monte (1978) found fresh 

 marsh and swamp spoil banks to be domi- 

 nated by 47% and 69% upland trees and 

 shrubs, respectively, after 30 years. 



During its ecological succession, a 

 spoil bank consolidates and slumps, and 

 some of its organic sediments oxidize 

 and disappear. Bank elevation gradually 

 diminishes, increasing the flooding 

 frequency that ultimately determines the 

 makeup of the plant community. The 

 composition of the climax community is 

 extremely sensitive to elevation. The 

 highest and oldest spoil banks resemble 

 natural levee ridge (upland forest) 

 habitat, in terms of species composi- 

 tion; however they would have to survive 

 for hundreds of years in order for the 

 plant community to reach maturity. With 

 a subsidence rate of about 1 m per cen- 

 tury, this is unlikely to occur. 



Because spoil banks become colo- 

 nized by a variety of plant and animal 

 species not normally associated with 

 wetlands, some workers have described 

 this feature as being ecologically 

 beneficial (e.g., Monte 1978). Local 

 increase in habitat and species diver- 

 sity is far outweighed in most cases, 

 however, by the widespread disruption of 

 natural hydrology that spoil banks 

 create . 



The ecological impacts of spoil 

 banks on the habitats on which they are 

 superimposed are variable. Neverthe- 

 less, these impacts can be divided into 

 local (direct) impacts and general 

 (cumulative) impacts. Local impacts 

 include the direct loss of wetlands be- 

 cause of sediment deposition, and the 

 imposition of a barrier to water flow 

 between marsh and open water. This 

 interruption of flow can stress wetland 

 vegetation by reducing its flushing 

 action and nutrient acquisition, and 

 changing its salinity regime. These 

 changes may reduce primary productivity, 

 as demonstrated by Mendelssohn et al. 

 (1981). Even a few centimeters of 

 artificial increase in elevation may 

 interrupt water movement. Spoil banks 

 also prevent the local export of plant- 

 derived carbon into natural water bodies 

 or canals. 



Spoil banks in wetlands may also 

 increase local species diversity by al- 

 lowing the colonization of upland vege- 

 tation and the migration of large 

 animals (including cattle) into the 

 marsh. Mammals that often inhabit spoil 

 banks include raccoons, deer, rabbits, 

 and armadillos. Many birds use spoil 

 banks as nesting areas, and migratory 

 birds use them as resting areas. In- 

 creased habitat for terrestrial fauna 

 resulting from spoil banks must be 

 weighed against losses in wetland pro- 

 ductivity caused by hydrological 

 modifications. Areas of higher elevation 

 in marsh areas may in some cases be 

 marginally beneficial. The major 

 problem with spoil banks in the MDPR is 

 their effect on wetland hydrology and 

 the negative impact this has on primary 

 productivity. 



Spoil banks are usually long, un- 

 broken, linear elements built without 

 regard to local patterns of water move- 

 ment. Spoil banks could be constructed 

 to have minimum impact on local hydrol- 

 ogy, thus providing "islands" of species 

 diversity without incurring additional 

 ecological costs, but this is seldom if 

 ever the case. In almost all instances 

 the spoil is the result of a canal whose 

 purpose is to link two points with the 

 shortest possible transport distance, 

 i.e., a straight line. 



There are numerous dramatic exam- 

 ples of the inadvertent impact of spoil 

 banks on wetland hydrology and via- 

 bility. One of the best documented 

 examples is a portion of the des Alle- 

 mands swamp forest study area described 

 by Conner et al. (1981). This acci- 

 dentally impounded swamp is dying and 

 turning into a stagnant bog. 



Can this situation be changed? 

 Studies are underway to determine the 

 effectiveness of spoil bank modifica- 

 tions as follow: backfilling canals and 

 eliminating the adjacent spoil banks, 

 creating numerous breaks in the spoil 

 bank to allow water movement, placing 

 the original spoil in less harmful ways, 

 and alternatives to canals and spoil 

 banks in general. The results of these 

 studies will have significant management 

 implications . 



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