Populus tremuloides/Prunus 

 virginiana/Senecio serra Community 

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



This is one of the more common community types, 

 especially in northern Utah. Of the 114 stands that we 

 sampled in this type, approximately a third were in the 

 Bear River Range in extreme northern Utah, a third 

 along the Wasatch Range, and about a fourth southward 

 on portions of the Uinta National Forest east of Provo. 

 Only a few scattered stands were found in the southern 

 half of the State. The type occurs most frequently at 

 intermediate elevations; three-fourths of the sampled 

 stands were between 6,000 and 8,000 ft (1 830 and 

 2 440 m). It occurred most frequently on sandstone- and 

 limestone-derived soils and on moderately steep slopes 

 that had slightly concave to undulating topography. 

 Slope aspect apparently is not restrictive. 



The vegetation of this extensive northern Utah type 

 has a pronounced multUayered structure. Below the vir- 

 tually pure aspen canopy, a layer of tall shrubs, a layer 

 of low shrubs, and a complex of forbs and graminoids 

 contribute to the high degree of structural diversity 

 (fig. 2). The conspicuous presence of either Prunus 

 virginiana, Amelanchier alnifolia, and occasionally Acer 

 grandidentatum identify this as part of the tall shrub 

 undergrowth type. The low shrub layer is usually domi- 

 nated by Symphoricarpos oreophilus, with lesser 

 amounts of Rosa woodsii, and Berberis repens; some- 

 times Pachistima myrsinites is conspicuous. Elymus 

 glaucus and Bromus carinatus are commonly abundant 

 grasses. Tall-growing forbs such as Senecio serra, 

 Agastache urticifolia, Aster engelmannii, and Rudbeckia 

 occidentalis are prominent in the herbaceous layer. The 

 epithet species S. serra need not be present as long as 

 other members of the tall forb group are present in 

 appropriate amounts (refer to key instructions). 

 Valeriana occidentalis also may inhabit Httle-disturbed 

 stands of this type in noticeable abundance. Various spe- 

 cies of Lathyrus as well as Vicia americana, when abun- 



dant, occasionally tend to blanket the low shrubs and 

 herbs. 



The POTR/PRVI/SESE c.t. usually represents a cli- 

 max aspen community type, one that reflects a specific 

 aspen habitat type. Conceivably, under active invasion 

 by conifers, stands identified as this type might be con- 

 sidered serai communities on the Abies lasiocarpa/ 

 Osmorhiza chilensis habitat type described by Mauk and 

 Henderson (1984), based on common occurrence of cer- 

 tain undergrowth species. Abusive grazing within the 

 POTR/PRVI/SESE c.t. would tend to decrease apprecia- 

 bly the amount of palatable forbs and shrubs, and 

 increase the dominance of the grasses E. glaucus, 

 B. carinatus, and Poa pratensis (sheep grazing), or such 

 forbs as R. occidentalis, Lathyrus spp., and V. americana 

 (cattle grazing). In some cases, S. serra also may increase 

 substantially under cattle use. Extreme and prolonged 

 grazing could lead to a depauperate undergrowth con- 

 sisting largely of such annuals as Nemophila breviflora, 

 Polygonum douglasii, or Galium bifolium. Tree produc- 

 tivity on this common type appears to be generally low 

 to moderate, with occasional stands being fairly high. 

 The basal area of aspen on the 42 intensively sampled 

 stands ranged from 45 to 202 ft^/acre (10.4 to 46.4 m%a) 

 and averaged 121 ft^/acre (27.9 m^/ha). Site index at 80 

 years for aspen ranged from 31 to 68 ft (9.4 to 20.7 m) 

 and averaged 47 ft (14.4 m). Usually conifer production 

 was negligible. Aspen reproduction in mature stands 

 ranged from virtually none to over 22,000/acre (55 000/ha). 

 The average was a comiparatively high 3,800/acre 

 (9 500/ha). About a third of these suckers were in the 

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



Although quite variable, the undergrowth is generally 

 moderately abundant. Because a high proportion of this 

 undergrowth usually consists of palatable forage plants, 

 the type is fairly productive livestock range. Annual 

 undergrowth production on the sampled stands ranged 

 from 509 to 2,341 lb/acre (572 to 2 627 kg/ha) and aver- 

 aged 1,141 Ib/acre (1 281 kg/ha). This was fairly well dis- 

 tributed among the different vegetation classes: an aver- 

 age 30 percent in the shrub class, 48 percent forbs, and 



Figure 2.— The structurally 

 diverse Populus tremuloides/ 

 Prunus virginiana/Senecio 

 serra c.t. is common in 

 northern Utah. This stand on 

 a southwest exposure in Big 

 Cottonwood Canyon east of 

 Salt Lake City has a dense 

 P. virginiana tali shrub layer, 

 a low shrub layer of 

 Symphoricarpos oreophilus 

 and Pachistima myrsinites, 

 and an herb layer dominated 

 by tall forbs. 



14 



