(2) USD A Forest Service's forest survey 

 types that are related to potential natural vege- 

 tation were used to define forest ecosystems 

 (U.S. Forest Service 1967). 



The modified list, grouping ecosystems into 

 ecosystem groups, referred to in this report as 

 ecogroups, follows: 



Western Forest 

 Douglas-fir 

 Ponderosa pine 

 Western white pine 

 Fir-spruce 



Hemlock-Sitka spruce 

 Larch 



Lodgepole Pine 

 Redwood 

 Hardwoods 



Western Range 

 Sagebrush 

 Desert shrub 

 Southwestern shrubsteppe 

 Chaparral-mountain shrub 

 Pinyon-juniper 

 Mountain grasslands 

 Mountain meadows 

 Desert grasslands 

 Annual grasslands 

 Alpine 



The forest survey types were used because 

 no other classification scheme existed for the 

 forest that had an associated land base. How- 



Great Plains 

 Shinnery 

 Texas savanna 

 Plains grasslands 

 Prairie 



Eastern Forest 



White-red-jack pine 



Spruce-fir 



Longleaf-slash pine 



Loblolly-shortleaf pine 



Oak-pine 



Oak-hickory 



Oak-gum-cypress 



Elm-ash-cottonwood 



Maple-beech -birch 



Aspen-birch 



Wet grasslands 



ever, many of the forest survey types are in 

 several different stages of forest successional 

 development, causing them not to mesh, in all 

 cases, with Kiichler's plant communities. Thus, 

 some Kiichler types appear in more than one 

 FRES ecosystem. 



Within each ecosystem delineation, the land 

 areas were further subdivided so that data 

 could be analyzed on a production and condi- 

 tion basis. For the range ecosystems, produc- 

 tivity classes were expressed in terms of tra- 

 ditional concepts of herbage production. Con- 

 dition classes were based on vegetation cover, 

 composition, and vigor, as well as soil factors 

 (table 1). For the forest ecosystems, produc- 

 tivity and condition classes were expressed in 

 terms of volume of wood produced and timber 

 stand-size class. The three ownership classes 

 specified were : (1) National Forest System, (2) 

 other Federal, and (3) non-Federal. Complete 

 expansion of the land classification system 

 yields 1,224 resource units. However, all pos- 

 sible combinations did not exist. Data were col- 

 lected and evaluated for the 956 resource units 

 for which they were available. 



All the land base data used in the inventory 

 was taken from existing inventories. The acre- 

 ages were compiled by resource unit, ownership, 

 State, and one of four geographic regions (fig. 



Figure 1. 



