southeastern Idaho that is virtually identical composi- 

 tionally to our POTR/CAGE c.t. A P. tremuloides/ 

 C. rubescens type was also identified for western 

 Wyoming (Youngblood and Mueggler 1981) that resem- 

 bles the Utah type but has more structural variation. 

 Calamagrostis rubescens usually replaces C. geyeri as 

 the characterizing graminoid in these more northern 

 locations. In northwestern Colorado, a structurally and 

 compositionally similar type was identified by Hoffman 

 and Alexander (1983) as the P. tremuloides/C. geyeri 

 habitat type. Although the P. tremuloides/C. geyeri habi- 

 tat type described by Wirsing and Alexander (1975) for 

 southeastern Wyoming contains the same characterizing 

 graminoids in the herbaceous stratum, it differs struc- 

 turally from our POTR/CAGE c.t. because of the abun- 

 dance of the shrub J. communis; their type corresponds 

 more closely to our POTR/JUCO/CAGE c.t. 



Populus tremuloides/Festuca thurheri 

 Community Type (POTR/FETH c.t.) 



This infrequent community type was encountered only 

 in the southern portion of Utah on the Fishlake, Sevier, 

 and Aquarius Plateaus. The 14 sampled stands were at 

 elevations ranging from 8,000 to 9,500 ft (2 440 to 

 2 900 m), on moderately steep concave or undulating 

 slopes and over a wide variety of exposures. The stands 

 were encountered only on soils derived from volcanic or 

 granitic parent materials. 



The vegetation is characterized by an abundance of 

 the tussock Festuca thurberi in the undergrowth (fig. 10). 

 The type is differentiated from the POTR/SYOR/FETH 

 c.t. by the lack of a distinct Symphoricarpos oreophilus- 

 dominated shrub layer. However, S. oreophilus is fre- 

 quently present but only in minor amounts. The over- 

 story consists of Populus tremuloides with an occasional 

 conifer, primarily Abies lasiocarpa and Picea engelmannii. 

 Usually Stipa occidentalis is present; occasionally 

 Bromus carinatus is abundant. The most common forbs 

 associated with these grasses are Taraxacum officinale, 

 Achillea millefolium, Vicia americana, and Lathyrus spp. 



In some cases, Lathyrus spp. appears to dominate the 

 undergrowth. 



The POTR/FETH is basically a climax community 

 type. However, many of the stands in this type appear 

 to have undergone considerable grazing pressure in the 

 past, judging from the amount of T. officinale, Lathyrus 

 spp., and Poa pratensis. Possibly these stands have had 

 appreciably more S. oreophilus that may have been 

 reduced to present levels by heavy sheep use. Such 

 stands would be considered serai stages of a climax 

 POTR/SYOR/FETH c.t. Heavy sheep use would support 

 the increase of A. millefolium, T. officinale, and 

 P. pratensis: F. thurberi probably would not be adversely 

 affected unless such use were extreme. Heavy cattle use 

 would tend to reduce the F. thurberi and support an 

 increase in the remaining forbs and P. pratensis. 



This type is productive for aspen. Basal area of the 

 five stands sampled for production ranged from 134 to 

 325 ft^/acre (30.8 to 74.6 m^/ha) and averaged a high 

 199 ft-/acre (45.6 m-/ha). Virtually all of this basal area 

 consisted of aspen. Site index at 80 years for aspen 

 ranged from 53 to 63 ft (16.2 to 19.2 m) and averaged a 

 moderately high 59 ft (17.9 m). Aspen reproduction was 

 generally low. averaging approximately 1,000 

 suckers/acre (2 500/ha). Two-thirds of these were in the 

 1- to 4.6-ft (0.3- to 1.4-m) height class. 



Annual production of undergrowth varies widely but is 

 generally moderate. It averaged 1,218 lb/acre 

 (1 367 kg/ha) on the sampled stands but ranged from 448 

 to 3,492 lb/acre (502 to 3 919 kg/ha). This consisted of 58 

 percent graminoids and 41 percent forbs. A total of 89 

 percent was classified as either desirable or as intermedi- 

 ate forage suitability. Considering total productivity and 

 the high proportion of grasses, the type is fairly good 

 livestock range, especially for cattle. Lack of a shrub 

 complex, which contributes to structural diversity, limits 

 the type's value as wildlife habitat. 



Aspen communities with F. thurberi prominent in the 

 undergrowth have also been reported in Colorado. 

 Langenheim (1962) described stands in the Crested 

 Butte area in west-central Colorado that lacked a promi- 



Figure 10.— The Populus 

 tremuloides/Festuca thurberi 

 c.t. is an uncommon but 

 distinct type found in south- 

 ern Utah. This stand in the 

 upper Um Creek drainage on 

 the Fishlal<e National Forest 

 produced an unusually great 

 amount of undergrowth, 

 3,492 lb/acre (3 919 kg/ha), of 

 which almost three-fourths 

 was F. thiurberi. 



27 



