Thomas R. Van Devender

Biogeographic implications of a packrat midden sequence from the Sacramento Mountains, south-central New Mexico

Abstract Thirteen packrat ( Neotoma spp.) and two porcupine ( Erethizon dorsatum ) middens from 1555 to 1690 m elevation from the Sacramento Mountains, New Mexico, provide an 18,000-yr vegetation record in the northern Chiuahuan Desert. The vegetation sequence is a mesic, Wisconsin fullglacial (18,000–16,000 yr B.P.) pinyon-juniper-oak woodland; a xeric, early Holocene (ca. 11,000–8000 yr B.P.) juniper-oak woodland; a middle Holocene (ca. 8000-4000 yr B.P.) desert-grassland; and a late Holocene (ca. 4000 yr B.P. to present) Chihuahuan desertscrub. The frequency of spring freezes and summer droughts in the late Wisconsin probably set the northern limits of Pinus edulis and Juniperus monosperma at about 34°N, or 6° south of todays limit. Rising summer tempratures in the early Holocene eliminated pinyon and other mesic woodland plants from the desert lowlands and allowed the woodland to move upslope. At this time pinyon-juniper woodland and pine forest dominated by Pinus ponderosa probably began their spectacular Holocene expansions to the north. Continued warming in the middle Holocene led to very warm summers with strong monsoons, relatively dry, cold winters, and widespread desert-grasslands. Desertscrub communities in the northern Chihuahuan Desert did not develop until the late Holocene when the biseasonal rainfall shifted slightly back toward the winter, catastrophic winter freezes decreased, and droughts in all seasons increased. The creosote bush desertscrub corridor across the Continental Divide between the Chihuahuan and Sonoran deserts was probably connected for the first time since the last interglaciation.

Holocene vegetation and climate in the Puerto Blanco Mountains, southwestern Arizona

Abstract Plant macrofossils from 21 pack rat (Neotoma sp.) middens at 535–605 m from the Puerto Blanco Mountains, southwestern Arizona, provide and excellent history of vegetation and climate for the last 14, 120 yr B.P. in the Sonoran Desert. A late Wisconsin juniper-Joshua tree woodland gave way to a transitional early Holocene desertscrub with sparse Juniperus californica (California juniper) by 10,540 yr B.P. Important Sonoran Desert plants including Carnegiea gigantea (saguaro) and Encelia farinosa (brittle bush) were dominants. Riparian trees such as Acacia greggii (catclaw acacia), Prosopis velutina (velvet mesquite), and Cerdicium floridum (blue palo verde) grew on dry, south-facing slopes in a middle Holocene Sonoran desertscrub in a warm, wet summer climate with frequent winter freezes. Modern subtropical Sonoran desertscrub formed about 4000 yr B.P. as summer rainfall and winter freezes declined. Cercidium microphyllum (foothills palo verde), Sapium biloculare (Mexican jumping bean), Olneya tesota (ironwood) and Stenocereus thurberi (organ pipe cactus) became dominant as riparian trees retreated to wash habitats. The inferences of a latest Wisconsin/early Holocene summer monsoonal maximum by J. E. Kutzbach (1983) , Modeling of Holocene climates. In “Late-Quaternary Environments of the United States,” Vol. 2, “The Holocene” (H. E. Wright, Ed.), pp. 271–277. Univ. of Minnesota Press, Minneapolis) are not supported for the Southwest. Apparently the persistence of late Wisconsin circulation patterns offset any increases in insolation.

Gentry's Rio Mayo Plants. The Tropical Deciduous Forest and Environs of Northwest Mexico

Along with some of my students and friends, I had the pleasure twice to visit this Rio Mayo region and adjacent areas via the kind courtesy of co-author Thomas R. Van Devender, who carefully pointed out all the major constituents of the various vegetation zones of vegetation. I hadnt felt as botanically inept and frustrated with a flora since I first set foot on the Chihuahuan Deserts Cuatro Cienegas Region in Coahuila, Mexico, in the 1960fs. These Rio Mayo trips forced me to reread Dr. Howard Scott Gentrys original book (1942). The fascination with the region is contagious. Gentrys accounts of 1933-1939 in poetic style and picturesque description are now more vividly appreciated. He was the first botanist to seriously explore the Rio Mayo drainage of desertic lowland plains and thorn forests and above. In the 27 months he was there, he collected 3200 numbers representing 1276 species and varieties. His annotated listing (Part 2) describes eight new species and one new variety, including five agaves and two cacti. Also, 66 Gentry collections have been newly described by other authors, all but 15 by Paul C. Standley. The new volume carefully updates, in the same format, Gentrys original account. The authors review and enlarge upon the vegetation and gazetteer via new description, photographs and specimens. Each entry of the burgeoning plant list includes not only the scientific name and classification, but also common names (in English, Spanish, and three native tongues, Guarijio, Mayo and Pima), local and overall distribution, representative documenting specimens, habitats and brief descriptions as to morphology, ecology, ethnology and ethnobotany. The amount of information provided accredits this book as a most valuable and comprehensive reference work. With some collections still in the hands of experts to be determined or newly described, the known flora boasts some 2825 taxa, more than doubling Gentrys original account. There are the 81 new taxa (Gentry 1 942); at least 40 additional taxa based on types and paratypes before the intensive collecting for the present book in the 1970s, many based still on Gentrys own collections; 54 more during the Rio Mayo revision; and 24 still in the process of being described, yielding a total of nearly 200 new taxa for this species rich diverse region, about 7% of the total flora. Shortcomings are few, but identification keys would greatly enhance the use of book. The pull-out map is black and white (in my copy) instead of the advertised color map. This book is a must for all students of Mexican botany, no doubt to be referred to innumerable times. It begs for another update several years from now.

Comparison of plant macrofossils in woodrat (Neotoma sp.) and porcupine (Erethizon dorsatum) middens from the Western United States

Fossil porcupine ( Erethizon dorsatum ) middens up to 25,000 years old were recently discovered in southwestern Arizona, south-central New Mexico, and southwestern Colorado. These deposits contain different floras than contemporaneous, woodrat ( Neotoma sp.) middens from the same sites because of contrasting diet and behavior. As might be expected from the occurrence of both woodrat and porcupine middens in the western U.S., the fossil middens of other cave-dwelling mammals are now being reported from arid lands worldwide.

Late quaternary arthropod remains from Sonoran Desert packrat middens, southwestern Arizona and northwestern Sonora

Abstract A total of 50 arthropod taxa were identified from 41 fossil packrat ( Neotoma sp.) middens from 160 to 625 m elevation in three study areas in the Lower Colorado River Valley subdivision of the Sonoran Desert. Radiocarbon dates associated with the middens range from >43,200 to 610 yr B.P. The fauna in the Tinajas Altas Mountains, southwestern Arizona, was relatively modern by ca. 10,000 yr B.P. in the early Holocene although a California juniper woodland persisted in the area until 8970 yr B.P. In contrast the fauna of the Hornaday Mountains, northwestern Sonora, increased dramatically in species richness after 4000 yr B.P. Although we are limited by poor taxonomic resolution and by insufficient knowledge of current distributions, the arthropod fauna may have been much more conservative than the regional flora during the last glacial/interglacial climatic cycle. Decreasing differences between modern and glacial climates (both temperature and precipitation) at lower latitudes and elevations may have resulted in minimal changes in the arthropod fauna of the Sonoran Desert lowlands.

Probable Occurrence of a Brown Bear (Ursus arctos) in Sonora, Mexico, in 1976

Abstract Measurements taken on the skull of a bear shot in northern Sonora, Mexico, in 1976 revealed that the skull is from a brown bear (Ursus arctos). The skull appears to be that of a juvenile (sex unknown) and, to our knowledge, represents only the fourth confirmed record of a brown bear from Sonora, although anecdotal accounts exist from the mid-1800s to early 1900s. The present record also establishes that brown bears, considered extirpated from Mexico since the 1960s, were present in Sonora within the past 30 years.