Aspen Community Types of 

 Utah 



Walter F. Mueggler 

 Robert B. Campbell, Jr. 



INTRODUCTION 



Aspen {Populus tremuloides Michx.) forests are a clas- 

 sic example of multiple-use wildlands. Traditionally 

 recognized for their importance as summer range for 

 livestock, prime habitat for many species of wildlife, 

 productive watersheds, and their scenic contribution, 

 aspen forests in the West are rapidly gaiining importance 

 as well for their potential to produce wood fiber. In addi- 

 tion, aspen lands contribute greatly to vegetation diver- 

 sity wherever they occur in the Intermountain and 

 Rocky Mountain States. 



Utah contains over 1.6 million acres (648 000 ha) of 

 aspen-dominated forests (Green and Van Hooser 1983). 

 These aspen forests span a broad range of environments 

 and are of varied successional status. Aspen thrive under 

 a variety of elevation, moisture, and soU conditions and 

 are thus associated with widely diverse vegetation types. 

 These range from the cool, moist, high-elevation spruce- 

 fir forests, where aspen frequently plays a dominant suc- 

 cessional role, to the relatively dry, low-elevation sage- 

 brush steppes where permanent, isolated aspen groves 

 are a highly valued part of the landscape. 



Aspen lands are a prominent part of the vegetation 

 complex on all six of Utah's National Forests, which 

 encompass the high plateaus and mountain ranges of the 

 State (fig. 1). These highlands form essentially a continu- 

 ous chain through the center of Utah, from Idaho and 

 Wyoming southward to the Arizona border. 



Aspen generally occupies an intermediate elevation 

 zone in these highlands, which gets progressively higher 

 as latitude decreases. On the Wasatch-Cache National 

 Forest in northern Utah (fig. 1), for example, aspen 

 forests are commonly found between 5,900 and 9,200 ft 

 (1 800 and 2 800 m) elevation. In southern Utah on the 

 Dixie National Forest, aspen forests most frequently 

 occur between 7,500 and 10,500 ft (2 300 and 3 200 m) 

 elevation. Aspen is usually a serai tree in climax sub- 

 alpine fir {Abies lasiocarpa [Hook.] Nutt.) associations at 

 the higher elevations. In such situations it may domi- 

 nate the forest community for many decades following 

 severe disturbance, such as fire or clearcutting, but will 

 gradually decline as the conifers become reestablished. 

 At lower elevations aspen can occur either as a tem- 

 porarily dominant serai species in a veiriety of climax 

 conifer associations, or it can achieve permanent domi- 

 nance as the climax forest type. The environmental con- 

 ditions related to aspen's role as a serai and as a climax 

 species remain ill-defined. 



The variety of undergrowth on aspen lands, caused by 

 the range of abiotic environments suitable for aspen 



growth and aspen's ability to function as a seral- 

 dominant as well as a climax-dominant tree, is com- 

 pounded by the general use of these lands for grazing. 

 Aspen lands have provided prime summer range for both 

 sheep and cattle in Utah since settlement in the latter 

 half of the 19th century. Some 100 years of grazing at 

 varying intensity (frequently very intense in the early 

 1900's), and by different classes of livestock, have left 

 their mark in often severe alteration of undergrowth 

 composition and production. Some of these alterations 

 are pronounced; others are subtle and difficult to assess. 



The broad environmental and successional diversity 

 encompassed by Utah's aspen lands is reflected inevita- 

 bly by variations in the forage, wildlife habitat, wood, 

 and water to be derived from these lands. Additionally, 

 equal variability can be expected in the response of 

 these lands to management activities. Such diversity 

 needs to be partitioned into manageable units to facili- 

 tate intensive resource management. This is usually 

 done by classification. Since about 1970, considerable 

 effort has been devoted to developing habitat type clas- 

 sifications for wildlands in the Western United States. 

 Habitat types, as conceptualized and used by 

 Daubenmire and Daubenmire (1968), are aggregations of 

 land units capable of supporting similar climax plant 

 communities and are based upon species composition of 

 climax communities. These classifications are useful to 

 resource managers for partitioning lands and as a basis 

 for structuring management recommendations. Habitat 

 type classifications have recently been developed for the 

 coniferous forests of northern Utah (Mauk and 

 Henderson 1984) and for southern Utah (Youngblood 

 and Mauk 1985). In these classifications, aspen was 

 primarily considered to be either a species serai to a con- 

 ifer climax or else persistently serai with unknown cli- 

 max potential. Consequently, the aspen type was 

 described only superficially. 



The widespread dominance of aspen on extensive por- 

 tions of Utah's wildlands increased the need for a clas- 

 sification that would partition the variability of this 

 important forest type. Ideally, the classification should 

 incorporate information related to the successional as 

 well as to the climax status of aspen. The habitat-type 

 approach did not appear feasible for such a classification 

 because of its reliance on potential rather than existing 

 vegetation, and the uncertain successional status of 

 aspen in different situations. Determining precisely the 

 influence of widespread disturbance, whether natural or 

 human-caused, results at best in tenuous projection of 

 potential climax composition under the range of environ- 

 ments suited to aspen dominance. A community-type 



1 



