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' Table 3. 1. Cover classes in a Landsat TM-derived classification Area Area ' Class acres (% of total Water 1,875 12 Deep marsh 323 2 Shallow marsh 724 5 Mature Cottonwood 640 4 Mixed Cottonwood 488 3 Young Cottonwood 210 1 Cottonwood/saltcedar 162 1 Saltcedar/willow 125 < 1 Saltcedar 836 5 Saltcedar/whitetop/grass 626 4 Whitetop/grass 1,453 9 Native grass 1,050 7 ' Sagebrush 5 < 1 Rabbitbrush Greasewood 8 4,073 < 1 26 ' Barren 2,922 19 Irrigated agriculture 188 1 Vegetation Monitoring in Recently Restored Floodplains Our second objective was to determine whether giant whitetop has invaded sites where levees were excavated, and whether any individuals were flowering and thus contributing to ' further spread of the species. We collected observational data along three transects at each of the eight levee removal sites (nine total levee removal sites). The transects ran across each excavated site, in a direction parallel to the river channel, at the following locations: on the river , side of each cut, through the center of the cut, and on the floodplain side of the cut (see Figure 3.1). Observations of the species present, age in years, and reproductive status were collected every 0.5 meters along each transect. The percent cover of each species or functional group was estimated by dividing the number of observations of that species by the total number of observations at the site. Transect data were recorded once per month in June, July and August of 1998. Site Characteristics Influencing the Distribution of Giant Whitetop Since many riparian species depend on specific hydrologic and geomorphologic conditions for regeneration, their distributions are often associated with geomorphic factors. Several researchers (e.g. Phipps 1979, Franz and Bazzaz 1977) have performed multivarie .w analyses of variables thought to be responsible for vegetation distributions and four?4A?ai a fc,7,, ?® 1 23