racemosa or S. cerulea form a conspicuous part of the 

 undergrowth; other shrubs are generally scarce, with the 

 possible exception of Salix scoulerana. The grasses 

 Bromus carinatus and Agropyron trachycaulum are 

 usually present and sometimes abundant. Certain mem- 

 bers of the tall forb group, such as Mertensia arizonica, 

 Delphinium occidentale, Osmorhiza occidentalis, 

 Polemonium foliosissimum, and Rudbeckia occidentalis, 

 are often conspicuous and may be abundant, as are 

 Thalictrum fendleri and Valeriana occidentalis. 



Although the successional status is uncertain, the type 

 probably reflects a distinct environment or habitat type. 

 Coniferous forests adjacent to these high elevation com- 

 munities usually are dominated by A. lasiocarpa. 

 Prolonged overgrazing can lead to a change in under- 

 growth composition that favors M. arizonica (if grazed 

 midsummer or late summer), R. occidentalis, and possi- 

 bly Lathyrus spp. Overgrazing will also increase the 

 amount of exposed soil and such annuals as Nemophila 

 breviflora. Polygonum douglasii, and Galium bifolium. 



The type is relatively productive for trees, even 

 though aspen apparently does not reproduce well 

 beneath the existing canopy. Tree basal area on eight 

 sampled stands ranged from 70 to 211 ft-/acre (16.1 to 

 48.5 m2/ha) and averaged 150 ft^/acre (34.5 m-'/ha). Virtu- 

 ally all of this consisted of aspen. Aspen site index at 80 

 years was moderate, averaging 54 ft (16.5 m) and rang- 

 ing from 38 to 65 ft (11.6 to 19.8 m). Aspen suckers 

 averaged only about 900/acre (2 200/ha), with two-thirds 

 in the 1- to 4.6-ft (0.3- to 1.4-m) size class. 



The undergrowth typically consists of a moderately 

 productive mixture of shrubs, forbs, and grasses. Annual 

 production ranged from 491 to 1,924 lb/acre (552 to 

 2 159 kg/ha) and averaged 1,072 lb/acre (1 204 kg/ha). Of 

 this, 35 percent was shrubs, 52 percent forbs, and 13 

 percent graminoids. About half of the undergrowth con- 

 sisted of desirable forage species and a third was of 

 intermediate forage suitabihty. The type appears to have 

 relatively moderate value both as livestock range and as 

 wildlife habitat. 



Although S. racemosa and S. cerulea may occur occa- 

 sionally as minor shrubs in aspen stands elsewhere, they 

 have not been reported before as major species charac- 

 terizing a specific community type. 



Populus trem uloides/Sym ph oricarpos 

 oreophilus/Senecio serra Community 

 Type (POTR/SYOR/SESE c.t.) 



The POTR/SYOR/SESE c.t. was the most frequently 

 encountered aspen type in Utah— almost 12 percent of 

 stands sampled. It appears to be a predominantly north- 

 ern Utah community type; over three-fourths of the 

 stands were on the Wasatch-Cache and Uinta National 

 Forests (fig. 3). The majority were encountered on the 

 Bear River and Wasatch Ranges. Stands were also found 

 in the San Pitch Mountains, the Pavant Range, and 

 occasionally in the Abajo and LaSal Mountains. It was 

 conspicuously absent from the high plateaus of southern 

 Utah. 



This is typically an intermediate-elevation community 

 type that clearly demonstrates the effect of latitude 



upon elevational distribution of a plant community. On 

 the Wasatch-Cache National Forest in northern Utah, 

 stands within this type occurred at elevations between 

 6,200 and 8.800 ft (1 890 and 2 680 m). On the Manti- 

 LaSal National Forest in central Utah, an average 2° 

 latitude farther south, the type in general occurred at 

 elevations about 1,000 ft (300 m) higher, between 7,700 

 and 9,700 ft (2 350 and 2 960 m) elevation. The type 

 appeared most frequently on slopes of less than 25 per- 

 cent steepness and on soils derived from sedimentary 

 parent materials, primarily sandstones. 



The POTR/SYOR/SESE c.t. vegetation consists of 

 three distinct strata: an overstory of pure aspen, a low 

 shrub layer, and an herbaceous layer of a rich mixture of 

 taU and low-growing plants. Tall shrubs such as 

 Amelanchier alnifolia and Prunus virginiana occasionally 

 may be present, but they are never abundant. The low 

 shrub stratum is dominated exclusively by 

 Symphoricarpos oreophilus. The herbaceous undergrowth 

 is typified by a tall forb mixture that varies considera- 

 bly between stands. The most commonly associated tall 

 forbs are Rudbeckia occidentalis, Senecio serra, 

 Agastache urticifolia, Mertensia arizonica, Aster 

 engelmannii, and Polemonium foliosissimum. The forb 

 S. serra was selected to represent this tall forb complex 

 in the type name, even though it is not present in all 

 stands within the type. Other forbs frequently present in 

 substantial amounts include Hackelia floribunda, 

 Osmorhiza chilensis. Thalictrum fendleri, and Valeriana 

 occidentalis. Usually the prominent grasses are Bromus 

 carinatus, Agropyron trachycaulum, and Elymus 

 glaucus. Species diversity within this community type is 

 often great. 



We consider this primarily an extensive climax com- 

 munity type, thus representing a distinct aspen habitat 

 type. The presence of conifers is usually accidental. 

 However, when stands are classified to this type because 

 of current lack of conifers, yet conifers appear able to 

 actively invade, such stands likely wiU be successional 

 within the Abies lasiocarpa^O. chilensis habitat type in 

 northern Utah (Mauk and Henderson 1984) or within the 



A. 'lasiocarpa/Aconitum columbianum habitat type in 

 central Utah (Youngblood and Mauk 1985). Abusive live- 

 stock grazing usually simphfies the undergrowth 

 appreciably. Extended heavy use by sheep will likely 

 shift species composition from the more palatable tall 

 forbs and S. oreophilus to that dominated by E. glaucus, 



B. carinatus, and possibly Poa pratensis. Eventually it 

 could change to a depauperate condition where only 

 unpalatable perennials and such annuals as Nemophila 

 breviflora. Polygonum douglasii, and Collomia linearis 

 remain. Excessive cattle grazing may shift composition 

 to dominance by R. occidentalis, Vicia americana. 

 Lathyrus spp., and possibly M. arizonica, and then to a 

 depauperate annual condition if such abuse persists. The 

 dense blanket of V. americana and Lathyrus spp. some- 

 times found in these stands probably is an artifact of 

 past livestock use. 



The amount of wood produced in this common commu- 

 nity type varies greatly between stands. In general, the 

 type is relatively low in fiber production. The tree basal 

 area on 42 stands ranged between 14 and 233 ft^/acre 



16 



