Portal de Periódicos da CAPES

Flora of Organ Pipe Cactus National Monument.

1980; Volume: 15; Issue: 1 Linguagem: Inglês

0193-8509

Janice E. Bowers,

Rangeland and Wildlife Management

INTRODUCTION. Organ Pipe Cactus National Monument is located in southwestern Pima County in Arizona, adjacent to Mexico (Figure 1). The Monument is 133,898 ha in area and ranges from 305 to 1466 m in elevation. It receives about 23 cm of rain a year with half falling during the summer. Temperatures are high during the summer, frequently over 38°C in July and August. Freezing temperatures occur occasionally during the winter, but never last as long as 24 hours (Sellers and Hill, 1974). The western half of the Monument is dominated by Larrea tridentata (creosote bush) associations. The eastern half is characterized by palo verde-mixed cacti series and, at higher elevations, by Quercus ajoensis mixed shrub association, Ribes quercetorum-Ptelea trifoliata mixed scrub association, and Juniperus monosperma-Vauquelinia calif ornica mixed shrub association. A vegetation map following the Brown, Lowe and Pase classification system (1979) has been prepared for the Monument, along with plant association descriptions which analyze the vegetation in greater detail (Warren el al., 1980). The author gratefully acknowledges plant collections and sightings contributed by Tom Van Devender, Bob Henry, Peter Warren, Karen Reichhardt, Kim Mortensen, Warren F. Steenbergh and Steven McLaughlin; without their assistance the plant list would have been far from complete. Thanks are also due to Terry Peters, Ray Turner, David Mouat and Tony Burgess for their suggestions and ideas and to Philip and Heather Urry for their encouragement and support. This research was supported by U.S. National Park Service contract no. CX-8000-7-0027 and by grant contract no. NGL 03-002-313 from NASA. METHODS. The annotated checklist for the vascular plants of Organ Pipe Cactus National Monument was compiled through extensive plant collection and examination of herbarium specimens at the Monument and the University of Arizona. Eighteen plant-collecting trips were made during a two-year period from October 1977 through August 1979. An effort was made to visit all of the major canyons in the Ajo Mountains as well as most of the larger hills and ranges during every season of the year. RESULTS. Five hundred twenty-two taxa of plants in 325 genera and 86 families are listed for the Monument. Eighty-three species were added to the Monument's previous plant list, including two species new to Arizona (Urry, 1979). Annotations for most species include common names, habitat, elevational range, distribution and relative abundance in the Monument and phenology. Nomenclature follows Lehr (1978)1 and common names are those given by Lehr (1978) and Kearney and Peebles (1960). When specific localities are mentioned they do not necessarily represent the only places in the Monument where a species occurs. A plant which is described as widely distributed or widespread can be found in many areas of the Monument or in a large section of it, such as the Ajo Mountains. Species which are described as scattered are more restricted in their distribution, typically occurring in several areas throughout the Monument. Locally occurring species are found only in one or two areas and are usually restricted to a specific habitat. The distribution of a plant is described as unknown if the plant was seen or collected only once or twice. Difficult genera such as Galium and Sphaeralcea may also lack complete distributional data even though widespread in the Monument, due to the problem of identifying sterile or immature plants. The relative abundance of each species is described as abundant, occasional or rare. An abundant species can be seen everywhere around the observer in the areas where the plant grows. The same observer would see at least several individuals of an occasional species but would have to search carefully to find more than one individual of a rare species in an area. Relative abundance is not given for annual plants because the abundance of ephemerals varies from year to year according to rainfall. Phenology is taken primarily from Kearney and Peebles (1960) and has been supplemented by field observations. DISCUSSION. The 522 taxa of vascular plants in the Monument comprise 1.5% of the flora of Arizona. Considering the large size of the Monument, it is not particularly rich in species when compared with other areas in Arizona. For example, Sycamore Canyon in the Pajarito Mountains of southeastern Arizona is 932 ha in size and supports 625 species of vascular plants (Toolin et al., 1979) and the White Tank Mountains Regional Park in central Arizona supports nearly twothirds the number of species found at the Monument on approximately one tenth of the area (Keil, 1973). The geographic affinities of the flora are strongly Southwestern with Sonoran and Latin American plants also making a large contribution (Table 1). These three categories make up nearly 75% of the flora. Endemic plants are a small component of the flora, about 4% , as are introduced plants, which comprise about 5% .