Valeriana occidentalism Mertensia arizonica, Agastache 

 urticifolia. Delphinium occidentale, and Polemonium 

 foliosissimum. Combinations of these occur in varying 

 but usually noticeable amounts. Other common forbs 

 include Thalictrum fendleri, Stellaria jaynesiana, 

 Osmorhiza chilensis, Vicia americana, and Lathyrus spp. 

 Substantial amounts of grasses are usually interspersed 

 among the forbs; most common and abundant of these 

 are Bromus carinatus, Agropyron trachycaulum, and 

 Elymus glaucus. Pocket gophers frequently churn the 

 relatively deep, loose soil of this type, providing condi- 

 tions amply suited for the growth of such annuals as 

 Nemophila breviflora, Polygonum douglasii, Collomia 

 linearis, and Galium bifolium. 



POTR/SESE is a major climax aspen community type 

 that is especially prevalent in northern Utah. Occasional 

 stands classified into this type could be considered serai 

 communities within the A. lasiocarpa/0. chilensis habitat 

 type (Mauk and Henderson 1984) if A. lasiocarpa were 

 able to actively invade and replace the aspen overstory. 

 Prolonged heavy grazing in this type will probably cause 

 a substantial reduction in species diversity. If abusively 

 grazed by sheep, a decrease in the more palatable forbs 

 can be expected with a corresponding increase in E. 

 glaucus, B. carinatus, and R. occidentalis. Such use by 

 cattle will tend to shift community composition strongly 

 toward R. occidentalis and possibly Lathyrus spp. In 

 some cases, S. serra may also increase substantially 

 under heavy cattle use. Prolonged abusive grazing by 

 either class of livestock would likely eliminate many of 

 the more palatable perennials and favor an increase in 

 annuals (fig. 8). 



The potential of the type for wood production appears 

 to be slightly better than the average for all of the 

 aspen community types. We sampled 64 stands within 

 this type for production. Tree basal area ranged from 

 46 to 302 ft^/acre (10.7 to 69.4 m^/ha) and averaged 

 152 ft^/acre (35.0 m^/ha). An average 99 percent of this 

 was aspen. Site index at 80 years for aspen ranged 

 widely from 32 to 85 ft (9.8 to 25.9 m), and averaged a 

 moderate 54 ft (16.5 m). Aspen reproduction also varied 



greatly. Sucker numbers ranged between none to well 

 over 8,100/acre (20 000/ha), and averaged slightly over a 

 moderate 2,500/acre (6 100/ha). Approximately half of 

 these suckers were in the 1- to 4.6-ft (0.3- to 1.4-m) 

 height class. 



Undergrowth production in this extensive type varies 

 greatly but overall appears to be about average for all 

 aspen types. Based on a sample of 59 stands, it ranged 

 from 234 to 2,853 lb/acre (263 to 3 202 kg/ha) and aver- 

 aged 1,149 lb/acre (1 289 kg/ha). The bulk of this under- 

 growth, 72 percent, consisted of forbs; graminoids com- 

 prised 25 percent, and shrubs 3 percent. Of the 

 vegetation, 79 percent was classified as either desirable 

 or of intermediate forage suitability. The type, therefore, 

 is at least moderately productive livestock range, partic- 

 ularly for sheep. Shrub cover usually is incidental; struc- 

 tural diversity is therefore low even though species 

 diversity may be high. Thus, the type is only of rela- 

 tively moderate value as wildlife habitat because of the 

 absence of an effective shrub component in the 

 undergrowth. 



Not only is the POTR/SESE c.t. common in Utah, 

 aspen communities with similar vegetation structure and 

 characterizing species are widespread elsewhere. The 

 P. tremuloides/R. occidentalis community type 

 described for the Caribou and Targhee National Forests 

 in Idaho (Mueggler and Campbell 1982) apparently is a 

 generalized combination of stands that fall within our 

 POTR/SESE c.t. and POTR/HELA c.t. Those stands 

 similar to our POTR/SESE type have many of the same 

 characteristics but lack the Lathyrus spp. and Vicia 

 americana that are common in the Utah stands. Both 

 the P. tremuloides/R. occidentalis and P. tremuloides/ 

 Ligusticum filicinum types described by Youngblood and 

 Mueggler (1981) for western Wyoming contain stands 

 similar to our POTR/SESE c.t. except for the lack of 

 Lathyrus spp. and V. americana in the Wyoming stands 

 and the greatly reduced occurrence of L. filicinum in the 

 Utah stands. About half the aspen stands Hoffman and 

 Alexander (1980, 1983) used to characterize the 

 P. tremuloides/T. fendleri habitat type in northwestern 



Figure 8.— Prolonged 

 abusive grazing can reduce 

 the productive undergrowth 

 of the Populus tremuloides/ 

 Senecio serra c.t. (fig. 7) to 

 an impoverished condition 

 dominated by such annuals 

 as Nemophila breviflora, 

 Collomia linearis. Polygonum 

 douglasii, and Galium 

 biflorum, with only trace 

 amounts of the former 

 perennial cover. An example 

 is this stand on the Nebo 

 Loop Road, Uinta National 

 Forest. 



25 



