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RESULTS AND DISCUSSION 
To find out the vegetation type composition for each of 
the final regions, the vegetation zone map was overlaid 
with the Seasonal Land Cover Regions compiled from 
March-October 1990 AVHRR imagery. The dominant 
vegetation types for each region is list in Table 2. East 
Table 2. Major vegetation types in vegetation regions 
regions 3, 9, 10, and 6 are dominated by agricultural 
crops while west regions are 2 and 8 are used mainly for 
ranches. Natural Tallgrass Bluestem Prairie covering east 
regions 3 and 9 has been replaced by cropland. Most of 
the western grassland is in native short grasses grazed by 
livestock. 
  
  
  
  
  
  
  
  
  
  
  
  
  
Zone Major vegetation types 
1 Wheatgrass, blue grama, needleandthread, needlegrass 
2 Bluestem, grama, wheatgrass, small grains 
3 Corn, soybeans 
4 Blue stem, grama, wheatgrass, buffalograss, wheat, sorghum 
5 Irrigated agriculture, mixed row crops, corn, soybeans, woodlots 
6 Irrigated agriculture, mixed row Crops 
7 Blue stem, indiangrass, switchgrass 
8 Wheatgrass, blue grama, needleandthread, big sage 
9 Corn, Soybeans, sorghum, irrigated ag, mixed woodlots 
10 Mixed crops (wheat, sorghum, corn, alfalfa, oats) 
  
  
AVHRR data have been an information source for large 
scale vegetation study. They have the potential to be an 
important vegetation surrogate in ecoregion mapping 
especially when combined with topography, soils, climate, 
and other ancillary data. Images from more than one year 
may be necessary to minimize the effect of yearly 
phenological variation and vegetation vigor variation. 
Among the images used in this study, the June layer is 
found having the best ability to differentiate regions. 
Some layers have obvious seams between two adjacent 
AVHRR paths, which could make false region boundaries. 
Image quality has to be carefully examined before input 
to the model. 
The methodology developed in this study is reproducible. 
It can be applied to other regions or other thematic data 
sets not collected by remote sensors. When more than 
one type of thematic data are used to define ecoregions, 
the importance of parameters may be different. The 
selection of variables and the weights of variables have to 
be decided according to the nature of the particular area 
being studied and the theme of ecoregion. 
ACKNOWLEDGMENT 
This research is supported by the U.S. Department of 
Agriculture (USDA) under cooperative agreement with the 
Department of Geography, University of Nebraska-Lincon. 
| wish to thank Dr. Sunil Narumalani and Sharon Waltman 
of the USDA for their helpful suggestions and supports. 
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Gallant, A.L., T.R. Whittier, D.P. Larsen, J.M. Omernik, and 
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Goward, S.N., CJ. Tucker, and D.G. Dye, 1985. North 
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International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996