Vegetation of Two Relict Mesas in Zion National Park

Abstract

Twelve permnnent vegetation sampling plots were established on Greatheart and Church mesas in Zion National Park, Utah. Both relict mesas are surrounded by cliffs but contain the same variety of soil conditions as the nearby “msinland.” The mesa vegetation was segregated into the following broad community types: mixed conifer forest, ponderosa pine savanna, Gnmbel oak woodland, pinyon woodland, snowberry-sagebrush steppe, and oak-sagebrush shrubland. Cover of all species was measured in the plots, in addition to tree stem density. Relationships of each community type to topo-edaphicfaetorsnnd response to ta Schmutz et al. 1967; Mason et al. 1967; Kleiner and Harper 1972, 1977a. 1977h). Studies of relict mixed conifer (Abies-Pseudotsugo-Pinus) forest, ponderosa pine (Pinus ponderma) forests or savannas, and Gambel oak (Quercus gambelii) woodlands have apparently been limited to Mason and West’s (1970) report of a brief visit to Timber Top Mesainside the Kolob Section ofZionNational Park(Masonand West 1970). These authors reached this heretofore inaccessible mesa by helicopter and noted fire evidence in the mountain brush community (dominated by Gambel oak), ponderosa pine forest, and Douglas fir (Pseudotsugo menziesii)forest. No wildlife species larger than a chipmunk (Eutamias sp.) were seen on the mesa. Since Timber Top Mesa is bounded on allsides bysheercliffs, it is apparently unvisited by large herbivores like mule deer (Dama hemionus hemionus(Rafinesque)). Thissituationlowersthe value of the vegetation structure for comparison purposes, since it did not develop with the type of browsing pressure that characterized normal “mainland” systems in pre-European times. Mule deer signs have been observed on both mesas in our study. This paper describes the vegetation on Greatheart and Church mesas. Its purpose is to provide a clearer picture of presettlement conditions of mid-elevation plateaus of southwestern Utah. Description of Study Area Greatheart and Church mesas are located in the center of Zion National Park (Fig. 2). Greatheart Mesa is I km west of the Horse Pasture Plateau and is 85 ha (210 acres) in sire. Church Mesa (an unofficial name not yet on USGS maps) lies 2 km south of the Horse Pasture Plateau and 2 km west of the Zion Lodge. Church Mesa is I50 ha (370 acres) in she. The vegetated summits of Greatheart and Church mesas lie between the elevations of 2,160 m (7,092 ft) and 2,259 m (7,410 ft), and 2,150 m (7,058 ft) and 2,254 m (7395 ft), respectively. The higher parts of the mesa tops are capped with limestone from the Carmel Formation. The remainder of each vegetated summit is underlain by sandstone and shales of the Temple Cap Formation (Hamilton 1978). The sheer 150. to 300-m (500 to 1,000 ft) cliffs that circumscribe the 2 relicts are carved from Navajo sandstone. Soils on the ridgetops are in the Paunsaugunt gravelly silt loam series, while the slopes are covered by the deeper Kolob-Detra association. Level areas near the rim of the mesas feature Kinesava fine sandy loam (Madany 1981). Soils of Zion National Park are described in more detail by Mortensen et al. (1977). The mesas are covered by vegetation quite similar in general composition to that of the nearby Markagunt Plateau. Ponderosa JOURNAL OF RANGE MANAGEMENT 37(s), September ,984 Horse Past we Plateau