magnitude of such factors are difficult to accurately analyze 

 with current technology, but they are recognized as important 

 considerations that extend project effects beyond the bounda- 

 ries of the immediate site. 



4. Key attribute alterations 



The key attribute alteration involves the direct removal of plant 

 assemblages and alteration of habitats that occur within the shot 

 lane and associated staging areas. Existing plant assemblages are 

 replaced by earlier successional stages following completion of 

 testing. In general, detrimental effects on consumer populations 

 and plant assemblages are small in magnitude at the ecosystem level. 

 Effects are mitigated by (1) the rather restricted area modified by 

 the activity as compared to nearby similar habitats that remain 

 unaltered, and (2) the relatively rapid (within one yr) plant 

 reestablishment which follows cessation of seismic exploration. 

 Vegetation losses are compensated for by the increased ecological 

 diversity resulting along the seismic corridor. Woodland communi- 

 ties require considerable recovery time to reestablish original site 

 conditions. Grassland recovery occurs within two yr. 



Access to site. 



1. Activity sequence 



The survey crew enters and stakes the route. Clearing crews may 

 follow to remove larger trees or other dense vegetation. Heavy 

 construction machinery begins shaping the road base by stacking and 

 packing earth. Base material is most frequently borrowed from both 

 sides of the road, or occasionally it may be trucked in. The fill 

 is shaped and compacted. Drainage is provided along the roadbed via 

 the borrow ditches and under the road by culverts. Surfacing, if 

 necessary, is accomplished using layers of shell or crushed rock. 

 Construction ceases with the completion of surfacing and removal of 

 heavy earth-moving equipment. Periodic maintenance requires filling 

 holes, ruts, and small washouts with shell or gravel or by grading. 

 Periodic replacement of broken conduit or boards may be necessary. 



2. Primary ecological alterations 



2.1 Creation of an unvegetated roadway 6 to 7 m (20 ft) wide and up 

 to several km long 



152 



