Joshua Tree National Monument Research Articles

Stratospheric influence on surface ozone in the Los Angeles area during late spring and early summer of 2010

The influence of stratosphere‐to‐troposphere transport (STT) on surface ozone (O3) concentrations in the greater Los Angeles area during the CalNex and IONS‐2010 measurement campaigns has been investigated. Principal component analysis (PCA) of surface O3measurements from 41 sampling stations indicates that ∼13% of the variance in the maximum daily 8‐h average (MDA8) O3between May 10 and June 19, 2010 was associated with changes of 2–3 day duration linked to the passage of upper‐level troughs. Ozonesondes launched from Joshua Tree National Park and airborne lidar measurements show that these changes coincided with the appearance of stratospheric intrusions in the lower troposphere above southern California. The Lagrangian particle dispersion model FLEXPART reproduces most of these intrusions, and supports the conclusion from the PCA that significant transport of stratospheric air to the surface occurred on May 28–30. This intrusion led to a peak 1‐h O3 concentration of 88 ppbv at Joshua Tree National Monument near the ozonesonde launch site on May 28, and widespread entrainment of stratospheric air into the boundary layer increased the local background O3 over the entire area to ∼55 ppbv on May 29–30. This background was 10–15 ppbv higher than the baseline O3 in air transported ashore from the Pacific Ocean, and when combined with locally produced O3 led to several exceedances of the current National Ambient Air Quality Standard (NAAQS) on the following day.

Oxidant air pollution effects on plants of Joshua Tree National Monument

Joshua Tree National Monument (JOTR) is located about 100 km east of the Los Angeles Basin, site of the heaviest concentration of photochemical oxidant (O 3) air pollution in the US. This investigation was conducted to measure O 3 concentrations in JOTR and to determine the effects of O 3 on vegetation in the park. Potentially phytotoxic concentrations of O 3 were recorded in JOTR in 1984 and 1985, but peak concentration occurred at night, when most plant species would be less sensitive to O 3. No O 3 effects were observed on permanent vegetation observation plots in JOTR in 1984 or 1985. Controlled exposures of native summer annual and woody perennial species to O 3 showed that most did not develop visible O 3 injury symptoms except at concentrations higher than those expected in the park. However, Rhus trilobata Nutt. was injured at 0·10 ppm O 3, 4 h per day for 4 days. This species would be a useful bioindicator to assess the effects of O 3 on native desert plants.

Pattern and mortality in Colorado Desert plants.

We tested for intraspecific interference among Colorado Desert shrubs using an integrated analysis of spatial pattern and juvenile mortality. The data set included 7,000 woody perennials of 24 species in a mapped hectare of Joshua Tree National Monument, California. The site is dominated by Ambrosia dumosa (62.0% of the stems), with Larre tridentata a conspicuous secondary species (2.3% of the stems). Analyses of static pattern for common species showed: (1) aggregated adults and juveniles for Ambrosia dumosa, Erigonum fasciculatum, Mirabilis bigelovii, and Sphaeralcea ambigua, with more aggregation among juveniles than adults; (2) randomly distributed adults and juveniles for Krameria grayi, Opuntia rasmosissima, Simondsia chinensis, and Yucca schidigera. The summed volumes and distances between nearest conspecific neighbors were positively correlated for Ambrosia dumosa and Larrea tridentata, but not significantly correlated for eight remaining species with ≥100 individuals. Static pattern suggests only weak evidence for negative interactions in Ambrosia and Larrea, and little evidence for other species. Alternative mechanisms other than negative interaction that could give rise to these static patterns are discussed. Juvenile mortality was documented for four common species (Ambrosia dumosa, Eriogonum fasciculatum, Mirabilis bigelovii, and Sphaeralcea ambigua) that experienced substantial mortality. Analyses show: (1) the proportion of individuals that died was independent of the initial density of conspecifics; (2) distance to conspecific adults did not differ for juveniles that died versus those that survived; and (3) death was no more likely for juveniles that contacted other plants than for those that were isolated. The exception was a vine, Mirabilis bigelovii, whose juveniles survived better in contact with other plants. In sum, neither spatial pattern nor patterns of mortality showed clear evidence of negative intraspecific interference.

Current Status of the Chisel-Toothed Kangaroo Rat in Joshua Tree National Monument

Current Status of the Chisel-Toothed Kangaroo Rat in Joshua Tree National Monument

Mites and other microarthropods from the Joshua Tree National Monument, California

An account is given of the microarthropods collected from juniper litter and from the soils of oases in the southern California desert. Particular attention is paid to the mite component of this fauna and descriptions are given of five new species of Cryptostigmata, namely Joshuella striata, Haplochthonius variabilis, Eremaeus magniporus, Passalozetes californicus and Zygoribatula heteroporosa. A detailed sampling programme was undertaken only at the juniper site, but the results obtained from the entire survey, and comparisons with the fauna of neighbouring semi‐desert areas, indicate that each of the microhabitats sampled has its own characteristic assemblage of species populations.

Habitat Utilization by Neotoma lepida in the Mohave Desert

Habitat utilization by the desert woodrat, Neotoma lepida , was investigated in the Mohave Desert. Neotoma lepida occurs in three types of habitat in Joshua Tree National Monument—semidesert rock outcrop, desert wash, and cactus. Construction of houses and dietary composition of food caches and stomachs were analyzed for each habitat and were found to be different. The desert woodrat has successfully increased its exploitation of these habitats by constructing houses from whatever materials are available in a particular habitat and also by utilizing a wide taxonomic and morphologic spectrum of food plants. Such methods of habitat utilization have, in those cases investigated, provided a degree of plasticity enabling successful coexistence with competing species.

Woodrats and Cholla: Dependence of a Small Mammal Population on the Density of Cacti

In the deserts of Southern California, stands of jumping cholla cactus (Opuntia bigelovii) are usually inhabited by desert woodrats (Neotoma lepida). The density of woodrats is obviously correlated with the density of cacti. On our study area, an alluvia fan in Joshua Tree National Monument, 80% of the variability in the density of woodrats could be attributed to variation in the density of cacti. The turnover of the woodrat population (mortality and replacement) apparently was greatest in areas of low density of cacti. The dependence of woodrat populations on the density of cholla may be attributed to the fact that the cacti provide most resources required by the woodrats; food, water, materials, for den construction, and a means of avoiding predation. Woodrats also are abundant in some habits where there is little or no cactus of any king, so that their dependence on cholla is not obligate.

Activities of Certain Species of Eleodes in Relation to Season, Temperature, and Time of Day at Joshua Tree National Monument (Coleoptera: Tenebrionidae)

Members of the genus Eleodes at Joshua Tree National Monument live under daily and seasonal environmental extremes. Overt activity is consonant with these conditions. The data from five different laboratory and fiield procedures indicate that surface activities generally occur when the ambient temperatures are between 12-280C. As ambient temperature increases, Eleodes spp. select relatively cooler microhabitats; as ambient temperature decreases, Eleodes spp. select relatively warmer microhabitats. In the spring the insects are mostly diurnal; in the summer they are usually crepuscular or nocturnal; most beetles hibernate during the winter. Much of the activity period is spent foraging on small green herbs; however, individuals will eat almost any plant and sometimes animal material that they encounter. Inactive periods are spent in sheltered microhabitats such as rodent holes and crevices between rocks. Beetles of the genus Eleodes Eschsholtz are members of one of the most conspicuous groups of desert animals. They are large black ter- restrial insects, usually having moderately long legs. Eleodes spp. are of considerable interest because they principally live in North Amer- ican deserts (McColloch, 1918) and seemingly are exposed to intense solar radiation, high temperatures and low humidity (Buxton, 1924; Jaeger, 1950). Investigators are beginning to look at the adaptations for desert existence found within this genus. Tanner and Packham (1965) reported on population dynamics at the Nevada atomic test site. Ahearn and Hadley (1969) investigated the effects of tempera- ture and humidity on water loss in the laboratory. Hadley (1970)

A Tenebrionid Beetle, Eleodes grandicollis valida,11 with Supernumerary Legs

A female Eleodes grandicollis valida Boheman with 2 complete right mesothoracic legs and a right mesothoracic leg bud was collected from a pitfall trap 24 Sept., 1968, at Lower Covington Flat in Joshua Tree National Monument, Riverside County, Calif.

Water Economy of the White-Crowned Sparrow and Its Use of Saline Water

range are the arid portions of southern California and adjacent regions (Grinnell and Miller, 1944). It is one of the most conspicuous winter-visitant sparrows in Joshua Tree National Monument, located in the transition between the Mojave Desert and the Colorado Desert in California (Miller and Stebbins, 1964). In addition Banks (1963) reports the occurrence of large flocks of White-crowned Sparrows (not subspecifically designated) on several of the desert islands in the Gulf of California during March and April 1962. The physiology of photoperiodically influenced phenomena in the White-crowned Sparrow has been intensively investigated by Farner and his colleagues (for example, Farner, 1964); King (1964) has recently reported on its metabolism and body temperature, and Morton (1965) has analyzed its food intake and feeding periodicity. In spite of these many investigations and in spite of its frequent habitation of xeric situations in the winter, information on the water relations of the Whitecrowned Sparrow is fragmentary. This investigation undertakes to examine the water economy of the Whitecrowned Sparrow in order to expand our knowledge of its general biology. Specifically, the study attempts to assess the ability of the White-crowned Sparrow to maintain water balance on the desert and to utilize saline water that may be present in desert springs and as sea water in portions of its winter range.

Geochronologic Studies in the Eastern Mojave Desert, California

Age determinations using the and methods were made on samples of muscovite, biotite, and potassium feldspar from four areas of igneous and metamorphic rocks of Precambrian or presumed Precambrian age in the eastern Mojave Desert. In the Marble Mountains the results indicate that the granite was emplaced approximately 1,400 million years ago. No positive evidence of a significant subsequent thermal metamorphism was obtained. The Rb-Sr age of potassium feldspar from a granite inclusion in a mafic dike suggests that short-term thermal metamorphism may not be an important mechanism in the consideration of strontium loss from potassium feldspar. The age of recrystallized biotite from the inclusion suggests that the dike was emplaced during the Jurassic period. In the Mountain Pass district the data suggest two earlier Precambrian events. The country rock was formed by regional metamorphism and pegmatite injection approximately 1,650 million years ago, whereas the younger potassium-rich igneous rocks and intrusive carbonate rocks apparently were emplaced approximately 1,400 million years ago. In Joshua Tree National Monument and the Kilbeck Hills no positive evidence for the Precambrian age of the metamorphic rocks was obtained.

The Discovery of Chiggers (Acarina, Trombiculidae) in the Nasal Passages of Cricetid Rodents from California, with Descriptions of Two New Species

Two new chiggers from the intranasal passages of cricetid rodents from Joshua Tree National Monument, California are Microtrombicula nasalis sp. n. off Peromyscus eremicus, Peromyscus crinitus, Peromyscus truei, and Neotoma lepida; and Microtrombicula wrenni sp. n. off Peromyscus eremicus and Peromyscus crinitus. These species are closely related to Microtrombicula ornata (Loomis and Lipovsky) and Microtrombicula merrihewi (Loomis and Lipovsky) from the central United States. The presence of chiggers in the nasal passages of vertebrates was reported initially by Fain and Vercammen-Grandjean in 1953 from mammals of Africa. More recently Audy and Nadchatram (1957) described intranasal chiggers from rats in Malaysia; Southcott (1957) announced the discovery of a new chigger from the respiratory passages of a Pacific sea snake, and Yunker and Jones (1961) described two new genera of intranasal chiggers from bats of Panama. The latter were the first to be reported from the order Chiroptera and from the New World. The above reports prompted examination of the nasal passages of small mammals, which resulted in the discovery of two species of intranasal chiggers in mice and rats (family Cricetidae) of California. These chiggers were found in the anterior portion of the nasal passages of four species of cricetid rodents: Neotoma lepida Thomas, Desert Wood Rat; Peromyscus crinitus (Merriam), Canyon Mouse; Peromyscus eremicus (Baird), Cactus Mouse; and Peromyscus truei (Shufeldt), Pifion Mouse-trapped in late December 1961 and early February 1962 in Joshua Tree National Monument, California. The total number of larvae of both species per host varied from 1 to 8 (avg. 3.5 larvae), except for a single Cactus Mouse infested with 93 larvae. This mouse contained both species of chiggers, including more than 60 fully engorged larvae in the nasal passages. The presence of unengorged larvae in this mouse seems to indicate that February is a period of activity of the free-living larvae. S udies of these chiggers revealed that they represent two new species which seem to belong in the genus Microtrombicula Ewing, as redefined by Vercammen-Grandjean (1960). They are closely related to Microtrombicula ornata (Loomis and Lipovsky) and Microtrombicula errihewi (Loomis and Lipovsky) originally placed in the genus Trombicula and later in the ornata group (Loomis, 1956: 1324). T e species M. merrihewi was obtained from bats in Oklahoma and M. ornata from cricetid rodents taken in Kansas and Colorado. They were reported as being found in the ears of their hosts. From available information on the r recovery, these chiggers seem to have been obtained from detergent water placed under the living host and from washing the dead mammals. They were not taken directly f om the ears. In light of the discovery of these new, closely related species in the nasal passages, it seems probable that Microtrombicula ornata and M. merrihewi are also intra-

An Archaeological Survey of the Deep Tank-Squaw Tank District, ]oshua Tree National Monument, California. William J. Wallace and Edith S. Taylor. An Excavation at the Squaw Tank Site, Joshua Tree National Monument, California. Willam J. Wallace and Roger J. Desautels. Archaeological Research Associates, Contributions to California Archaeology, No. 4, Pts. I and II, Los Angeles, 1960. 44 pp., 3 figs.,

An Archaeological Survey of the Deep Tank-Squaw Tank District, ]oshua Tree National Monument, California. William J. Wallace and Edith S. Taylor. An Excavation at the Squaw Tank Site, Joshua Tree National Monument, California. Willam J. Wallace and Roger J. Desautels. Archaeological Research Associates, Contributions to California Archaeology, No. 4, Pts. I and II, Los Angeles, 1960. 44 pp., 3 figs., 13 pis. $2.00. - Volume 28 Issue 2

Ecology of Desert Plants. IV. Combined Field and Laboratory Work on Germination of Annuals in the Joshua Tree National Monument, California

In the studies of the annuals of the Joshua Tree National Monument, Death Valley, and the Coachella Valley, made prior to 1948, it appeared that the temperatures which prevailed at the time of the infrequent rainfalls were a critical factor in determining which species would germinate. The difference in summer and winter flora was shown to be due to this factor (Went 1948, 1949, Went and Westergaard 1949). The extension of these observations in the present paper consists of the attempt to define in more detail the correlation between rainfall and temperature, and germination. The study has extended from the fall of 1948 to the fall of 1953. It was thought that temperature, in combination with rainfall, might explain other differences than those of summer and winter, for it is a conspicuous feature of the flowering of the desert annuals that a rather small portion of the number of native species will blossom in any one year. At one time, two or three species may dominate, appearing most profusely; the following year these may scarcely appear at all, quite different species predominating. Yet three, five, or even seven years later the first ones may appear again, and in the same locations. The present study is directed toward the question whether their appearance might be due to recurrence of favorable rain-temperature

Ecology of Desert Plants. I. Observations on Germination in the Joshua Tree National Monument, California

Plant communities exist due to interaction between the individual members and between these and the environment. This introduces such a complexity, that a physiological analysis of the community as a whole seems impossible at present. But as the starting point of such an analysis the desert communities offer an unusually favorable opportunity. In the first place the vegetation cover is not closed, so that 'interactions between plants are greatly reduced, and their influence on each others' immediate surroundings is relatively small. Under such conditions direct correlations between plants (the influence of one plant on the other) are more easily found, as shown by Went ('42). This wide spacing of the plants is of special importance in germination, because that process tends to occur much more frequently in open areas than in a closed cover of existing vegetation. In still another respect, desert plants are particularly favorable experimental material. They are subjected to more extreme conditions than other plants, so that their responses can be expected to be geared to greater climatic differences. Therefore laboratory experiments are likely to show larger differences in response than when plants of more equitable climates are used. Finally, everything which happens in the desert vegetation can be rather easily attributed to distinct climatic occurrences such as a particular rain. With these considerations in mind a series of trips were made, during the years 1945-1947, to study the vegetation of the Joshua Tree National Monument, located 200 km. (130 miles) due east of Los Angeles. The altitude of the areas most commonly visited varies between 800 and 1500 m. (2500-5000 ft.). The San Bernardino and San Jacinto mountains shield the area from the climatic influence of the ocean. Along its west boundary the Little San Bernardino Mountains, reaching a height of 1700 m., separate the area from the Coachella Valley. From the west the altitude of the broad valleys of the National Monument falls gradually to 800 m. in the north and east, with intervening mountain ranges. The climate can best be described with the help of figures 1, 2 and 3. Climatic records are kept by the Cooperative Weather Station at Twentynine Palms, just north of the Monument at 650 m., and daily temperatures are recorded at Hidden Valley at 1400 m. by Mr. Randolph.' Annual rainfall at Twentynine Palms amounts to 136 mm. but at Hidden Valley and higher altitudes in general the rainfall is considerably greater, especially during July, August and September, when thunderstorms break over the mountains. Figure 1 shows the monthly distribution of rainfall, the number of cloudy days and the relative humidity in the afternoon at Twentynine Palms, with an indication of the seasonal differences in rainfall. The winter rains are fairly evenly distributed over the whole National Monument, but the summer rains are highly localized, as figure 2 shows. This figure gives the approximate location of rainbursts ac-

Endemic Birds of the Little San Bernardino Mountains, California

The Little San Bernardino Mountains which bound the Coachella Valley of California to the northeastward attain heights of somewhat over 5000 feet. Barren in aspect on their southern face, they nonetheless support along their crests and on their northern slopes large tracts of pifion-juniper woodland and open chaparral growth of scrub oak, mountain mahogany, and manzanita. These plant associations mark an Upper Sonoran belt which extends 40 miles southeastward from Morongo Pass. A small area of woodland and chaparral occurs still farther eastward on Eagle Mountain, separated by a gap of at least 20 miles from the area in the Little San Bernardino Mountains. Northwardly the woodland occurs scatteringly over a plateau, which is the heart of the Joshua Tree National Monument, to the mountains immediately south and west of Twentynine Palms, San Bernardino County. The Upper Sonoran area lies between the Colorado and Mohave deserts and adjoins similar areas of coastal southern California only to the westward where, at the eastern flank of the great San Bernardino Mountain mass, there is a narrow connection across Morongo Pass with the chaparral and woodlands of western Riverside and San Bernardino counties. This peninsula of the Upper Sonoran Zone, seemingly because of its constricted base, its length, and the arid, open aspect of its plant growth influenced by desert climate and surrounding desert lowlands, has developed and conserved in partial isolation distinctive races of some permanently resident types of birds. Their degree of distinctness is surprisingly great in view of the imperfect westward barrier to the transfer of individuals between coastal populations and those of the Little San Bernardino Mountains. Three endemic forms, a Mountain Quail, a Plain Titmouse, and a Bush-tit, are herewith described. Further details of their ranges will doubtless be forthcoming as additional biological exploration in the area is conducted. I am indebted to the National Park Service, and particularly to Mr. James Cole, Custodian of Joshua Tree National Monument, for the opportunity to investigate the vertebrate fauna of the Monument area which embraces the ranges of these new subspecies.