part of the undergrowth. This suggests that it may be 

 indicative of a specific site situation, and that such 

 stands represent more or less stable conditions or climax 

 community types. On the other hand, P. aquilinum is 

 both unpalatable to livestock and reproduces readily by 

 creeping rhizomes. Overgrazing that inhibits the growth 

 of palatable forage species would encourage the growth 

 and reproduction of P. aquilinum. Judging from under- 

 growth composition, this type might also represent a 

 grazing-degraded serai stage of a POTR/SESE climax 

 community type, if the presence of P. aquilinum were 

 ignored. In either event, abusive grazing will tend to 

 encourage dominance of P. aquilinum and possibly 

 R. occidentalis at the expense of such forage species as 

 A. engelmannii, A. urticifolia, B. carinatus, and 

 E. glaucus. 



Tree production within this type is moderate to high. 

 Basal area, 99 percent of which was aspen, ranged from 

 76 to 224 ft^/acre (17.3 to 51.4 m^/ha) and averaged a 

 moderate 146 ft^/acre (33.6 m^/ha). Aspen site index at 

 80 years ranged from 47 to 78 ft (14.3 to 23.8 m) and 

 averaged a moderately high 60 ft (18.3 m). Aspen 

 reproduction varied widely but was comparatively high 

 for mature stands. It averaged approximately 7,600 

 suckers/acre (18 900 ha), of which about half were in the 

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



Although undergrowth production in this type is 

 generally high, it is of low to moderate value as Uve- 

 stock forage. Production ranged from 1,035 to 2,292 

 lb/acre (1 162 to 2 572 kg/ha) and averaged 1,570 lb/acre 

 (1 762 kg/ha). Over 90 percent of this was forbs, primar- 

 ily the unpalatable P. aquilinum. Of the total under- 

 growth, 48 percent was classified within the least desira- 

 ble forage suitability class. The type also has low to 

 moderate value as wildhfe habitat because it lacks struc- 

 tural diversity as well as having a low abundance of 

 palatable species. 



Although infrequent, the POTR/PTAQ type appears 

 fairly widespread. Hoffman and Alexander (1980, 1983) 

 identified similar aspen stands with P. aquilinum 



dominating the undergrowth as a distinct habitat type 

 on the Routt and White River National Forests in north- 

 western Colorado. The main difference in the Colorado 

 communities is the occurrence of substantial amounts of 

 Carex geyeri in most stands. 



Populus tremuloides/Senecio serra 

 Community Type (POTR/SESE c.t.) 



The POTR/SESE community type is one of the most 

 frequently encountered types in northern Utah. We sam- 

 pled 125 stands to form the data base for this type. 

 Although the type occurs principally on the Bear River 

 and Wasatch Ranges and on the west slope of the 

 Uintas, it can be found at scattered locations throughout 

 the higher elevations as far south as the Abajo Mountains 

 in the southeast and the Markagunt Plateau in south- 

 western Utah. It is primarily a middle to fairly high 

 elevation type; sampled stands ranged in elevation 

 between 6,000 to 10,300 ft (1 830 and 3 140 m). These 

 stands occurred on all exposures, mostly on gentle to 

 moderately steep slopes, and on relatively deep soils der- 

 ived from sandstone, limestone, quartzite, and granitic 

 parent materials. Stands were seldom found on volcanic 

 soils. 



Vegetation in this common type is structurally simple 

 but compositionally complex. An occasional conifer, 

 usually Abies lasiocarpa. may be present with the aspen 

 but in only small amounts. A shrub stratum per se is 

 lacking even though Symphoricarpos oreophilus and 

 Sambucus racemosa are often present as incidental spe- 

 cies. Consequently, the aspen undergrowth consists 

 almost exclusively of a broad assemblage of herbaceous 

 species characterized by a diverse mixture of tail forbs, 

 no one of which is consistently dominant, accompanied 

 by low forbs, graminoids, and annuals (fig. 7). Although 

 Senecio serra is used as an epithet representing the taU 

 forb group, it need not be present for a stand to qualify 

 for this community type. Species of tall forbs commonly 

 encountered include S. serra, Rudbeckia occidentalis, 



Figure 7.— The Populus 

 tremuloides/Senecio serra 

 c.t. is one of thie most 

 common aspen types, 

 especially in northern Utah. 

 This stand occurred at 

 8,600 ft (2 620 m) elevation in 

 the upper Cottonwood Creek 

 drainage on the Manti-LaSal 

 National Forest northeast of 

 Fairview. The undergrowth 

 typically consists of a diverse 

 and productive mixture of tall 

 forbs, low forbs, and 

 graminoids. 



24 



