The Ecology of Selerocactus polyancistrus (Cactaceae) in California and Nevada Item Type Article Authors May, Richard W. Publisher University of Arizona (Tucson, AZ) Journal Desert Plants Rights Copyright © Arizona Board of Regents. The University of Arizona. Download date 11/10/2021 11:26:06 Link to Item http://hdl.handle.net/10150/554194 6 Desert Plants 11(1) 1994 Abstract The Ecology of Several key aspects of the ecology of Sclerocactus polyancistrus (Cactaceae) are described based on a 15 year study by the au- Sclerocactus thor. Highlights of the study, funded in part by grants from the Cactus and Succulent Society of America and the United States Navy (China Lake Naval Weapons Center), include a record of polyancistrus growth rates and the impact of predation and infestation. The study also includes the analysis of the carcass remains, identi- (Cactaceae) in fication of predators, the benefits and offsetting effects of pre- dation, and the resulting morphological abnormalities. California and Nevada Using microhystological analyses to determine the relative den- sity of discerned fragments of scats found within the carcasses, Neotoma lepida was found to be the chief predator of this spe- Richard W. May cies at elevations below 1500 m (5000 ft). At higher elevations, 4210 Elderwood Dr. infestation primarily by the cerambycid beetle Moneilema Houston, Texas 77586 semipunctatum, is the dominant cause of mortality. Returning each spring over a 15 year period (1976 -1991) to six study sites in the Mojave Desert, the author recorded apical growth measurements of over 350 stems and correlated these growth rates to rainfall and other key climatological factors. The results show that microhabitat is a major factor in this spe- cies growth rate and that the oldest plants within a given popu- lation are in excess of 50 years in age. As expected, there is a direct correlation between seasonal rainfall and the growth rate and number of flowers produced. When surveying eastern Nevada and the Canyonlands National Park areas of Utah, the author has found similar predation and infestation in S. pare /orus and S. spinosior, which indicates that some of the data collected in this study may also be appli- cable to other small stem cacti of the southwestern deserts, par- Acknowledgments ticularly within the same genus. I thank the Cactus and Succulent Society of America and the Navy at China Lake for their financial assistance as well as the Introduction Navy environmental staff and now dear friends, Tom McGill The genus Sclerocactus includes 8 species occurring from the and Bev Novak for their help in the field. Thanks also for those Mojave Desert in California and Nevada to the Great Basin who provided their unselfish and free technical expertise that Desert, Utah, western Colorado, northern Arizona, and north- turned raw field data into meaningful results. This would in- west New Mexico. Several variants exist and, most recently, at clude John Doyen and Jerry Powell at U.C. Riverside, Bill Clark least two new species have been proposed from eastern Nevada. and Paul Blom at the University of Idaho, Tom O'Farrell at Most of the species have a prominent inflorescence and sinuous EGG (Boulder City), and W. P. Stephen at Oregon State for red -maroon (some hooked) and white spines. The plants usu- their help with insect identification. Also Dave McKay at The ally have a solitary growth habit and do not branch unless dis- National Aeronautics and Space Administration at the Johnson turbed or injured. S. polyancistrus is the largest species in the Space Center who provided me the use of the SEM for seed genus. studies. Thanks also to the California BLM staff and especially Texas A &M University and the University of Wichita soil labs Although there has been a growing interest in the genus for the analysis of soil samples. For the inspiration to continue Sclerocactus, a detailed study of Sclerocactus polyancistrus has and persevere as well as for his technical assistance, I thank not been performed to date. In 1976, the author became inter- Lyman Benson. Also thanks to Gerhard Haslinger in Austria ested in this particular species as a result of several published for his expertise and skill in germinating the seeds of the rare accounts and theories concerning its ecology. For example, there form of this species. Thanks to Doris Fredendall and Maryann have been several references in literature to the "mysterious Henry who were in the field when I wasn't able. Finally, a spe- boring grub" apparently responsible for its high mortality rate cial thanks to a special friend and field expert Matt Johnson and resulting low population densities. As a result of this study, who had the patience to help me in such tedious tasks as root some questions have been answered, and general information mapping and for recommending Desert Plants as a home for about this species has been generated. this work. Unless otherwise stated, all photos and illustrations are by the author. May Sclerocactus 7 Over 40 populations were visited between 1976 and 1991 and this genus in the east where summer rainfall is more common, six study sites were selected in California and surveyed yearly, the hilum of the S. polyancistrus seed does not have a crusty primarily during late April and early May, along with several protective "cap" which resists water imbibition. The hilum on remote sites on a more infrequent basis. The total study effort other species within this genus, have this structure which is included a record of population densities, the identification of advantageous, preventing premature summer germination and predators, pollinating agents, internal stem temperature mea- a resulting high seedling mortality rate. This explains why S. surements, morphological comparison studies, soil analyses, seed polyancistrus is not present further east. morphology and germination studies, reproduction strategies, and identification of threats, both natural and by man. Unpub- The northern extent of this species range is tied to climatologi- lished field data reports were generated yearly and submitted cal factors, particularly temperature extremes. In central Ne- at no cost to the California BLM, the Nature Conservancy and vada, below -18°C (0°F) readings are not uncommon and thermal other environmental agencies. The reports carry the name Desert tolerances of the S. polyancistrus stem, roots, and seedlings Research International, a non -profit, tax exempt organization may often be exceeded. The larger more exposed stem growth formed by the author. habit of this cactus does not fare well when temperatures are extremely cold. Smaller, globose cacti (such as Coryphantha) After a brief overview, this paper will focus on this species ecol- which have a more conservative growth habit closer to the ground ogy including growth rates and the impact and nature of preda- where they are protected by the snow, fare better in these more tion and infestation. northern regions. Perhaps unlike S. polyancistrus, Coryphantha has been shown to exhibit an ability to "cold harden" (Gibson Introduction to the Species and Nobel, 1986). S. polyancistrus (Figure 1, page 18) is thinly distributed over a large portion of the Mojave and Great Basin deserts of California Winter and spring, when the bulk of the precipitation in this and Nevada. Its range lies within the basin and range physi- region occurs, constitutes the growing season for this species as ographic province. It is found most frequently in plant communi- well as for most other flora in the Mojave Desert. Since this ties dominated by Larrea, Atriplex, Artemisia sp., Grayia, species is most conspicuous when in bloom, prior knowledge of Coleogyne, Haplopappus, Ephedra, and Hymenoclea shrub a population's peak blooming period during a field survey is complexes. It is most commonly known as the Mojave Fishhook advantageous. Anthesis varies from population to population Cactus, but has also been called the Hermit Cactus, the Pine- depending upon altitude, latitudinal (north -south) location, and apple Cactus, and the Devil's Claw. For a complete taxonomic other microclimatic factors as well as abnormal fluctuations or description, the reader is referred to Lyman Benson's Cacti of the extremes of weather. Generally first to bloom are those popula- United States and Canada (1982). tions situated in the Mojave River basin and El Paso Mountains of California which bloom in late April and early May. By mid - The plant favors porous, alluvial soils most frequently derived May, the plant is in bloom over most of its range. Larger stems from igneous (granite and rhyolite), some Jura -Trias at higher elevations have been found in bloom as late as mid - metavolcanics, and sedimentary (Pliocene/Pleistocene non -ma- June. The fruit are normally ripe by early July. rine) rocks (USGS survey data). It is rarely found on dark vol- canic soils and only occasionally in areas where basaltic rocks The red and white spines are also of interest and, like most are dominant. It is seldom found in flat areas or in areas of poor cacti, serve to benefit the thermal economy of the plant. During drainage but, instead, prefers the southern and western slopes the summer, desiccation of the stem causes the spines to form a of hills with slopes less than 45 degrees. Soils are typically al- dense mat, shielding the stem from the sun. This is particularly kaline (pH usually greater than 8.0) and in soils high in cal- the case in the southern populations and at lower elevations. cium. Elevations usually range from 730 -2300 m (2400 ft.- 7600 Spine measurements by the author reveal that the plants in these ft). southern populations have spines which average 2 cm longer than those in the northern or higher elevation populations. At Summer rainfall across the region is rare.