nent shrub layer. Although the undergrowth was domi- 

 nated by Thalictrum fendleri, Ligusticum porteri. and 

 V. americana. those stands contained appreciable 

 amounts of F. thurberi. 



Populus tremuIoides/SitanioD hystrix 

 Community Type (POTR/SIHY c.t.) 



The POTR SIHY c.t. is a fairly uncommon and rela- 

 tively arid tj'pe found primarily in southern Utah. It 

 was usually encountered on the Aquarius and 

 Markagunt Plateaus. One stand was observed on the 

 south slope of the Uinta Mountains north of Roosevelt. 

 The 11 stands sampled in this type were on widely 

 different exposures, shallow to moderately steep slopes, 

 and on soils derived primarily from volcanic, granitic, or 

 sandstone parent materials. These stands were at eleva- 

 tions between 8.000 and 9.500 ft (2 440 and 2 900 m). 



Vegetation structure of this type is essentially two- 

 layered: a Populus tremuloides overstory with a rather 

 sparse undergrowth composed largely of graminoids. 

 Although Juniperus communis, Berberis repens, and 

 Symphoricarpos oreophilus may occasionally be present, 

 they are never abundant enough to form a distinct shrub 

 layer. The herbaceous undergrowth is usually dominated 

 by Sitanion hystrix, Stipa comata, and Poa fendleriana. 

 The most conspicuous forbs are usually Antennaria 

 microphylla, Lupinus argenteus, and Taraxacum 

 officinale. This type differs from the POTR/JUCO/SIHY 

 c.t. primarily in the lack of a distinct shrub layer of 

 J. communis or Artemisia tridentata or both, and by the 

 greater abundance of S. hystrix and S. comata. 



This appears to be a relatively stable aspen type res- 

 tricted to comparatively dry sites. Pinus ponderosa may 

 be present occasionally as an accidental species. In 

 stands where P. ponderosa is actively invading, and 

 especially if J. communis is also present, the stands 

 probably should be placed in the POTR-PIPO/JUCO c.t. 



The abundance of S. hystrix and T. officinale suggests 

 that the undergrowth has been appreciably degraded by 

 prolonged and heavy livestock grazing. Very likely 

 P. fendleriana, Bromus ciliatus. and possibly S. oreophilus 

 were more abundant in many of these stands prior to 

 the advent of domestic livestock. Continued abusive 

 grazing would favor an even greater abundance of such 

 low-palatability species as S. hystrix and A. microphylla. 

 and a loss of those species that are more palatable to 

 sheep and cattle. 



The type is only moderately productive for trees. 

 Basal area ranged from 94 to 203 ft^/acre (21.5 to 

 46.6 m- hal but averaged only 155 ft- acre (35.7 m- ha). 

 Aspen made up 96 percent of this total. Aspen site 

 index at 80 years ranged from 30 to 63 ft (9.1 to 19.2 m) 

 and averaged a moderately low 47 ft (14.3 m). Aspen 

 reproduction was also low with suckers averaging less 

 than 770 acre (1 900 ha), two-thirds of which were in the 

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



Undergrowth production is generally low and rather 

 evenly divided between forbs and grasses. Annual 

 production ranged from 319 to 823 lb/acre (358 to 

 923 kg ha) and averaged only 472 lb acre (530 kg ha). 

 Graminoids made up 47 percent of this, 51 percent was 

 forbs, and only 2 percent was in the shrub category. 



However, 62 percent of the undergrowth was desirable 

 forage and 33 percent was of intermediate smtability. 

 Although the type does not support much undergrowth, 

 it does rate high as Uvestock forage, especially for cattle. 

 This relatively dry type is rather poor wQdHfe habitat 

 because the vegetation lacks good structural diversity 

 and produces comparatively httle undergrowth. 



Aspen communities resembling this type have not 

 been reported outside of Utah. 



Populus tremuloides/Bromus carinatus 

 Community Type (POTR/BRCA c.t.) 



This serai community type was encountered primarily 

 in northern and central Utah, but one stand was 

 observed in the Abajo Mountains in the southeast cor- 

 ner of the State. The type is somewhat infrequent. We 

 sampled only 14 stands occurring at elevations between 

 7.400 and 9,400 ft (2 260 and 2 870 m) on usually less 

 than 25-percent slopes and on all exposures. The type 

 occurs primarily on sedimentary soils derived from sand- 

 stone and Umestone parent materials. 



Conifers are seldom present and never abundant in the 

 POTR BRCA c.t. The undergrowth vegetation is typified 

 by the lack of a shrub layer and the dominance of tall 

 grasses, Bromus carinatus or Elymus glaucus or both in 

 the herbaceous layer (fig. U). Shrubs, especially 

 Symphoricarpos oreophilus. are often present but never 

 in such amounts to form a distinct stratum. Principal 

 forbs most frequently present are Thalictrum fendleri, 

 Achillea millefolium, Rudbeckia occidentalis, Vicia 

 americana, and Lathyrus spp. This type is similar to the 

 POTR SYOR BRCA c.t., except for the lack of shrubs. 



Although the aspen overstory apparently is stable in 

 the POTR BRCA c.t., the undergrowth is considerably 

 altered by grazing. The tj'pe is most likely serai to the 

 POTR SESE climax community type. Heavy and 

 prolonged sheep use appear to have reduced the abun- 

 dance of tall forbs and permitted substantial increases in 

 the amount of B. carinatus, E. glaucus, and Agropyron 

 trachycaulum. The type is similar to the 

 POTR SYOR BRCA c.t., except for a lesser amoimt of 

 S. oreophilus and Geranium viscosissimum, both of 

 which tend to decrease with heavy sheep use. Thus, it is 

 possible that the POTR BRCA c.t. may also be a 

 grazing-induced serai stage of the POTR SYOR SESE 

 climax community type. Heavy grazing of the 

 POTR BRCA c.t. by cattle would tend to result in a 

 decrease of B. carinatus, A. trachycaulum, and E. glaucus, 

 and an increase of E. occidentalis, Poa pratensis. and 

 Taraxacum officinale. 



Tree production in this type appears to be only moder- 

 ately good. Basal area ranged widely between 39 and 

 189 ft-;acre (9.0 and 43.4 m- ha) and averaged a modest 

 129 ft- acre (29.6 m^, ha). Virtually aU of this was aspen. 

 Site index at 80 years for aspen ranged between 48 and 

 79 ft (14.6 and 24.1 m) and averaged a moderate 56 ft 

 (17 m). Aspen reproduction was also moderate, averaging 

 less than 1,300 suckers, acre (3 200 ha), about half of 

 which were in the 1- to 4.6-ft (0.3- to 1.4-m) height class. 



Undergrowth production in this grazing-induced type 

 is only moderate. Annual production of dry herbage 

 ranged from 371 to 1,877 lb, acre (417 to 2 106 kg/ha) 



28 



