runoff and subsequent sediment and nutrient transport into adjacent 

 areas. Resulting consequences to adjacent terrestrial communities 

 may include localized burial of plants or plant parts by transported 

 sediments, but such effects are usually ^^ery restricted. Sediment 

 transport into adjacent aquatic systems may be of greater importance. 

 See the ecological analyses of marsh ecosystems for further treat- 

 ment of this aspect. 



Earthwork can alter surface water hydrology through stream blockage 

 and filling or drainage of low depressions. The micropore-water/ 

 soil-air equilibrium is altered such that soil air is increased 

 through site drainage or decreased through impoundment. Vegeta- 

 tional changes are a function of the original plant assemblages 

 present, duration of the alteration, and areal extent of the drain- 

 age modification. In terrestrial ecosystems, small-scale altera- 

 tions cause localized plant compositional shifts from mesic to xeric 

 species (with filling or drainage) or from xeric to mesic species 

 (with impoundment). Major hydrologic alterations, such as long-term 

 stream blockage or wetland drainage, result in loss of terrestrial 

 systems and formation of aquatic systems in the former case and the 

 reverse situation in the latter case. Possible shifts in the animal 

 species composition and population levels may occur depending on the 

 magnitude and duration of the vegetational changes. 



Pipeline and overhead electrical line easements require periodic 

 maintenance to suppress development of woody growth either by cut- 

 ting, mowing, or herbicide application. Grassland communities are 

 artificially selected and replace woodlands and shrubby cover types 

 as long as maintenance continues. Grassland and ecotonal consumer 

 species may benefit from habitat increases; woodland consumers 

 experience habitat losses. Habitat diversity, in terms of plant 

 species composition and age-class distribution, is altered within 

 the pipeline corridor, which can contribute to increased heterogeneity 

 in otherwise homogeneous areas. 



Soil toxicants resulting from leakage of brine and/or petrochemical 

 derivatives may reduce site plant complexity by replacing numerous 

 intolerant plant species with a few hardy pioneers capable of toler- 

 ating extreme soil conditions (i.e., high soil salinity, toxic ion 

 concentrations, or anaerobic con.! tions). Such effects are usually 

 localized due to the restricted mobility of such substances in soil 

 subst'i' 'S. Large-scale spills or discharges are treated in the 

 sectiri -)! spills and cleanup. 



3.1 Woodlands 



In wooded environments, consumers dependent upon trees and 

 understory shrubs experience long-term habitat loss or alter- 

 ation. Magnitude is proportional to the size of the easement. 



164 



