A note on growing season food habits of mountain gazelles and Nubian ibex in Saudi Arabia

Perennial plants eaten by mountain gazelle (Gazella gazella) and Nubian ibex (Capra ibex nubiana) were examined during the 1994 growing season (May and June) in the Ibex Reserve, Saudi Arabia. Individual plants were assigned a browse rating based on extent of vegetative tissue removal. Gazelles and ibex were found to have a diverse diet, but were primarily browsers of woody plants.     

Water use patterns of mule deer (Odocoileus hemionus) and the effects of human disturbance

To aid the effectiveness of water developments, patterns of deer visiting water sources and the responses of deer to disturbance were examined. Deer visited water sources day and night, but not all deer at water sources drank. Thus, the assumption that radio-telemetry locations within arbitrary distances of water indicate drinking events may lead to overestimates of watering frequency. Human disturbance did not preclude or seriously impede use of water by deer. Deer reacted by adjusting the amount of time spent at water sources, moving away from water to return later and/or increasing the frequency with which they drank.     

Use of large Acacia trees by the cavity dwelling Black-tailed Tree Rat in the Southern Kalahari

Recent extensive harvesting of large, often dead Acacia trees in arid savanna of southern Africa is cause for concern about the conservation status of the arid savanna and its animal community. We mapped vegetation and nests of the Black-tailed Tree Rat Thallomys nigricauda to assess the extent to which the rats depend on particular tree species and on the existence of dead, standing trees. The study was conducted in continuous Acacia woodland on the southern and eastern edge of the Kalahari, South Africa. Trees in which there were tree rat nests were compared with trees of similar size and vigour to identify the characteristics of nest sites. Spatial analysis of tree rat distribution was conducted using Ripley's-L function. We found that T. nigricauda was able to utilize all available tree species, as long as trees were large and old enough so that cavities were existing inside the stem. The spatial distribution of nest trees did not show clumping at the investigated scale, and we therefore reject the notion of the rats forming colonies when inhabiting continuous woodlands. The selection of a particular tree as a nest site was furthermore depending on the close proximity of the major food plant, Acacia mellifera. This may limit the choice of suitable nest sites, since A. mellifera was less likely to grow within a vegetation patch containing a large trees than in patches without large trees.     

The impact of shade on establishment of shrubs adapted to the high light irradiation of semi-arid environments

Light may be an important limiting resource that influences community structure of chenopod shrublands. As part of a larger study that aimed to determine the factors that influence chenopod community structure, the focus of this study was the influence of plant canopy on the growth and establishment of smaller plants. We therefore measured the height and cover of three chenopods (Enchylaena tomentosa, Maireana brevifolia and Maireana georgei) when growing within and outside of the canopy of Atriplex bunburyana under field conditions. All three chenopods had lower cover and E. tomentosa was taller when growing within the canopy of A. bunburyana in comparison to those growing outside of the canopy. The chenopods were then grown under three artificial shade regimes. Plant height, cover, biomass, relative leaf area and photosynthetic surface area measurements showed that each species responded differently to shade. E. tomentosa biomass was facilitated by shade. This was inferred by an increase in total plant biomass. M. brevifolia, in contrast, tolerated shade by increasing above-ground biomass allocation. M. georgei was adversely affected by the shade regimes: root biomass decreased in response to shade. Competition for light is, therefore, likely to influence chenopod community structure of semi-arid and arid environments.     

The influence of elevation, shrub species, and biological soil crust on fertile islands in the Mojave Desert, USA

We quantified soil nutrients and biological crust cover (bryophytes and lichens) under the canopies of three species of Mojave Desert shrubs and in interspaces between shrubs at three elevations to determine the effects of shrub species, soil crust, and elevation on islands of soil fertility. Means of pH, organic matter, total Kjeldahl nitrogen, nitrogen mineralization, and gravimetric soil moisture are significantly greater in soils under Ambrosia dumosa (Gray) Payne, Larrea tridentata Cov., and Coleogyne ramosissima Torr. than soils from adjacent interspace microhabitats. Although soil moisture and soil organic matter increase by a factor of 1.5 from the low elevation to the high elevation site, the ratio of shrub to interspace concentrations, or the difference in mean soil variables between shrubs and interspaces, is effectively constant and independent of elevation. Total bryophyte and lichen cover is relatively low (24.5%), however, there are 11 species of bryophytes and two species of lichens distributed across three elevations with the highest species richness and cover at the low-elevation site. Bryophyte and lichen cover is correlated with silt but is not related, consistently, to soil nutrients. Overall, the balance of processes controlling spatial aggregation of soil nutrients under shrubs is remarkably insensitive to potential differences in organic inputs among elevations, shrub species, and soil crust surfaces.     

Islands in a sea of sand: use of Acacia trees by tree skinks in the Kalahari Desert

In the Kalahari desert the tree skink Mabuya striata sparsa occupies Acacia trees separated by areas of open sand. On a single day in austral spring, the effects of tree size and structural complexity, presence of colonial nests of weavers, and fallen limbs on lizard abundance, and of time of day and air temperature on numbers of lizards active, location on trees, ground, or ground cover, and occupation of sunny, shaded, or partially shaded sites were examined. Multiple regression showed that the numbers of adult and total lizards increased with tree size, amount of ground cover, and air temperature. Neither number and size of sociable weaver nests nor complexity of tree shape affected lizard abundance. Proportions of lizards on trees and ground did not vary with time of day; neither did height above ground among individuals on trees. The proportions of lizards fully exposed to the sun was higher early and late in the day than at midday, when more lizards occupied shaded sites.     

The diet of the Long-eared Owls, Asio otus, in the desert of northwest China

The contents of regurgitated Long-eared Owls (Asio otus) pellets collected in Minqin Desert Experimental Research Station of northwestern China were analysed. A total of 303 individuals representing five species of rodents and one of bird were identified in the pellets. By frequency, the most common species taken by Long-eared Owls was Meriones meridianus, followed by Cricetulus barabensis and Phodopus roborovskii. By biomass, Meriones meridianus was the most important species taken, followed by C. barabensis and Rhombomys opimus. Our results suggest that the Long-eared Owls were nocturnal hunters and fed on a wide range of animals with respect to their habitats.     

The replacement of arborescent cactus species along a climatic gradient in the southern Chihuahuan Desert: competitive hierarchies and response to freezing temperatures

In the southern region of the southern Chihuahuan Desert three common species of arborescent cacti are distributed over a north-west to south-east climatic gradient; Opuntia leucotricha, O. streptacantha, and Myrtillocactus geometrizans. In general, O. leucotricha is more abundant in the colder north-west section; M. geometrizans in the warmer south-east zone, not occurring in the north-west; and O. streptacantha reaches its greatest abundance in the centre of the region. We studied the potential replacement process between the three species due to canopy interference as well as the effect of a disturbance, freezing temperature, on their survivorship. Canopy interference between adjacent individuals of M. geometrizans/O. streptacantha and O. streptacantha/O. leucotricha indicated a potential replacement sequence of O. leucotricha replaced by O. streptacantha which, in turn, is replaced by M. geometrizans. In contrast, the damage caused by an extreme low-temperature event hardly affected O. leucotricha. It did however cause severe damage to individuals of O. streptacantha in the north-west of its distribution with little or no damage to individuals in the more south-eastern populations studied. M. geometrizans had a similar pattern of damage to O. streptacantha over its range in the region but at each site where the two species occurred together, that damage was more severe. Our observations suggest that disturbance in the form of extreme freezing temperatures is the mechanism that limits the distribution of these three arborescent cacti in the southern Chihuahuan Desert and allows their co-existence regionally.     

Status of an endangered subspecies: the peninsular pronghorn at Baja California

During November 1993, we traversed by ground and by air the Vizcaíno Desert, the last redoubt of the peninsular pronghorn (Antilocapra americana peninsularis). A total of 29 h of aerial census was performed and a total of 1900 km²were covered by ground, totalling 400 man hours of survey. At present the peninsular pronghorn population consists of 175 individuals, and inhabits an area of approximately 5000 km². Because of the impossibility of controlling its activities over such an area and because of the present small population size, we propose to manage part of the population in semi-captivity at Mesa de la Choya island, with the objective of assuring the survival of this subspecies, the most endangered mammal in Mexico.     

Gas exchange responses of a desert herbaceous perennial to variable sunlight in contrasting microhabitats

Over the course of a day, aridland plants experience a range of incident photosynthetic photon flux (PPF) spanning three orders of magnitude. Rapid photosynthetic responses to changes in PPF have large effects on individual plant carbon gain and water use patterns, hence are important to plant distribution and success. We investigated the response over time of photosynthesis (A), stomatal conductance (g), and inter-cellular CO₂ concentration (C_i) to step changes in PPF in a long-lived aridland perennial that typically occurs in two contrasting microhabitats, shade under shrubs of other species and unshaded inter-shrub spaces. An initial rapid response in A and C_i for plants in both microhabitats occurred after abrupt changes in PPF. This was followed by slower changes in these parameters during the rest of the light or dark period. Stomatal conductance responded more gradually to step changes in PPF. The initial increase in A after a dark cycle was significantly greater for plants under shrubs than for plants in inter-shrub spaces, but other changes in A, g and C_i did not differ. We attribute the similar responses in plants from different microhabitats to natural variations in solar radiation and limited selection for differentiation due to population gene pools dominated by plants in the open. Our results support the hypothesis that variable light regimes select for photosynthetic gas exchange processes that closely track changes in incident PPF. Our data also support the hypothesis that gas exchange responses to variable light regimes in aridland plants minimize trade-offs between carbon gain and water loss.     

Carbon accumulation, nitrogen and phosphorus use efficiency of Sophora davidii seedlings in response to nitrogen supply and water stress

A greenhouse experiment was conducted to explore whether additional nitrogen (N) supply could enhance carbon (C) accumulation, and phosphorus (P) use efficiency (NUE_P) of Sophora davidii seedlings under dry conditions. Two-month-old seedlings were subjected to a completely randomized design with three water (80, 40 and 20% water field capacity (FC)) and three N supply (N0: 0, Nl: 92 and Nh: 184 mg N kg⁻¹ soil) regimes. Water stress decreased C, N and P accumulation, NUE_P, N and P uptake efficiency (NUtE_N and NUtE_P) regardless of N supply. The S. davidii seedlings exhibited strong responses to N supply, but the responses were not consistent with the various N supply levels. Nl increased C, N and P accumulation, and improved NUE_P, NUtE_N and NUtE_P in the same water treatment. In contrast, Nh did few or even depress effects on C, N and P accumulation, and NUE_P, although NUtE_N and NUtE_P increased with Nh in the same water treatment. Even so, NUE_N decreased with increase of N supply in the same water treatment. The results suggested that appropriate or low N supply should be recommended for S. davidii seedling establishment in dry environment by improving C accumulation and NUE_P.     

Hydrogeomorphic control on tree growth responses in the Elton area of the Cheshire Saltfield, UK

Increment cores were sampled from oak (Quercus robur) and ash (Fraxinus excelsior) growing at Elton, an area of the Cheshire Saltfield that has experienced significant subsidence and damage to the natural and built environments in the latter part of the twentieth century. Ring-width measurements for Elton trees permitted the construction of one main site chronology (Elton) and four sub chronologies (Elton A, Elton B, Elton C, Elton ASH). Ring-width difference between these and a control chronology identified periods of sustained growth reduction in oak trees commencing in AD 1859/1861, 1886 and 1934. Growth reductions after 1934 are related to watertable draw down caused by brine pumping from a concentration of nine boreholes at Elton, up to 2 km from tree sampling locations. Growth reductions in 1859/1861 and 1886 are likely to be the result of earlier phases of brine pumping in the Wheelock Valley, up to 5 km to the east of Elton, and these reductions correlate well with historic records of subsidence and pumping activity. Cessation of pumping in 1977 led to a lagged growth recovery in oak trees between 1981 and 1986, indicating that an artificial drought had been imposed on the Elton area for a period in excess off 100-y. This research demonstrates a hydrological separation of surface water and groundwater in an area where salt beds are overlain by till and that ring-width records of Q. robur can be used to reconstruct watertable variability and also the spatial impact of solution mining.     

Amelioration of soil fertility by woody perennials in cropping fields: evaluation of three tree species in the semi-arid zone of Nigeria

Soil was sampled from cropping fields in radial patterns from beneathAcacia albida, Parkia bigloboza(Jacq.) Benth. andEucalyptus camaldulensisDehnh. near Zaria, Nigeria. Results of analysis show a significant coarsening of soil texture and a decrease in organic matter and cation exchange capacity with increasing distance from all three tree species at a depth of 0–15 cm. Concentrations of nitrogen and some exchangeable cations decreased significantly with increasing distance from beneath acacia and parkia, and soil pH decreased with increasing distance from eucalyptus. The implication of the results for land management are discussed in relation to increasing productivity and soil use sustainability.     

Effects of early season defoliation ofAnthyllis cytisoides(a Mediterranean browse species) on further herbivore attack

To determine if defoliation of a woody plant affects foraging by folivorous insects, we examined the infection rate (number of leaves damaged per total number of leaves sampled on marked stems) ofAnthyllis cytisoidesunder three experimental treatments: 10, 50 and 90% plant defoliation. Observations were made for three age classes, established by trunk base perimeter (equal to or lower than 11 cm, between 11 and 20 cm, larger than 20 cm). Plants respond positively to artificial defoliation by increasing total vegetative length of the stem and total inflorescence length. This response is most evident in young individuals.Response to herbivory was measured as overall infection rate and also as infection rate by different feeding guilds—chewing, mining, or sucking insects. We found that increased defoliation elicited increased resistance of leaves to insect attack. This was particularly evident in young plants. Different insect guilds respond in different ways. Attack by chewing insects declines with defoliation for all plant age classes; only sucking insects which feed on the oldest plants reduce feeding rate with plant defoliation. Finally, mining insects present the opposite trend in young and senescent plants.     

Ecophysiological studies inHesperaloe funifera(Agavaceae): a potential new CAM crop. The effect of light availability on photosynthesis and growth

Hesperaloe funifera(Agavaceae) is being investigated as a new specialty-fiber crop for arid lands. The objective of this study was to examine the effects of reduced solar radiation on photosynthesis and growth in this CAM species.Peak CO₂uptake integrated through 24 h was found to be highest during the fall. Although shading greatly reduced CO₂uptake in fall and winter, the decrease was not statistically significant for the spring and summer. Total biomass was significantly different for the three light treatments, with average fresh weights of 5243 g, 4488 g, and 3671 g for the full-sun, 53%-sun, and 20%-sun treatments, respectively. The greatest differences were found in the crown growth, which would affect future production of both leaves and flower stalks.Photosynthesis and growth results suggest that the cultivation ofHesperaloe funiferawill be favored in well-lit environments characteristic of arid or semi-arid climates.     

Effect of plant species on shrub fertile island at an oasis–desert ecotone in the South Junggar Basin, China

Shrub fertile islands are a common feature in arid ecosystems. To examine the effect of plant species on the spatial patterns of soil chemical and physical properties surrounding individual shrubs, two deciduous shrub species with different morphologies (Tamarix spp. and Haloxylon ammodendron Bge.) were studied at an oasis–desert ecotone in South Junggar Basin. Soil samples were collected under the shrub crown (canopy), at the vertically projected limit of shrub crown margin (periphery), and in the space between shrub crowns (interspace) at two depths, 0–10 and 10–20 cm, to analyze their physical and chemical properties. The results show that the fertile islands of Tamarix spp. are enriched with more soil nutrients (significantly higher, P<0.05; soil organic matter (SOM); total nitrogen (TN) and available nitrogen (AN); to a deeper depth (>20 cm) and in a larger area (beyond the canopied area) compared to that of H. ammodendron (significantly higher, P<0.05, soil nutrients detected only for AN; <20 cm in depth; smaller than the canopied area). Soil texture patterns surrounding the shrubs of the two species are even more different, with more coarse particles under the Tamarix spp. canopies compared to the interspace between shrubs but fewer under the H. ammodendron canopies compared to the interspaces. These variations are attributed to the difference in morphology of the two studied species: the Y-shaped crowns of H. ammodendron are less capable of capturing and maintaining litter under them than the hemispheroidal crowns of Tamarix spp., which leads to the less well developed fertile islands surrounding H. ammodendron shrubs.     

Effect of supplemental feeding on spatial distribution and browse utilization by white-tailed deer in semi-arid rangeland

We investigate the risk that supplemental feeding of white-tailed deer (Odocoileus virginianus) to improve trophy quality may degrade rangeland through overutilization of forage plants near the feeders. We divided a South Texas ranch into 6 areas (each 1100 ha). Supplemental feed was provided year-round in a centrally placed feeder in 3 areas, no supplement was provided in the 3 control areas. Radio-telemetry collars were fitted on 2 bucks and 2 does in each area. Spatial distribution of these deer was assessed using the CALHOME program. Feed supplementation did not alter home range size of does but did reduce their 50% core area. Bucks without supplemental feed showed 2 spatial strategies; sedentary bucks had home range distributions similar to supplemented bucks, while commuter bucks moved to supplemented areas during the breeding season. Browsing pressure near feeders and control sites was assessed by measuring consumption of seedlings set in arrays radiating from feeders and control points. Deer browsing was heavier near feeders than at the control sites, and the probability of a seedling being browsed increased with proximity to the feeder. We caution against long-term supplemental feeding in fixed locations because of the potential for localized range degradation around the feeders.     

Precipitation impacts on mule deer habitat use in the chihuahuan desert of Mexico

In arid lands, food resources and predation risk become major decision factors in mule deer habitat use. We examined variables related to these two factors that might determine mule deer (Odocoileus hemionus) habitat use in a warm desert at two spatial scales: the macro-habitat scale, which relates to home range decisions, and the micro-habitat scale, which relates to decisions made during foraging. Our prediction was that habitat use should primarily be explained by food variables and, to a lesser degree, by variables related to predation risk by pumas (Puma concolor). We mapped all deer pellet groups in 72, 1 ha quadrats in the Mapimí Biosphere Reserve and measured food and habitat variables over two years with different precipitation amounts. The area was used more intensively during the dry year. Under drier conditions, deer habitat use was explained primarily by food resource variables and secondarily by variables related with predation risk. During the wetter year, food resources became unimportant while cover and visibility explained deer habitat use. The data suggest that the tradeoffs deer are willing to make between food resources and predation risk in an arid environment are strongly affected by food resource levels, as influenced by precipitation.     

The effect of radiation on seedling growth and physiology in four species of Prosopis L. (Mimosaceae)

Domestication of wild plants needs efforts focused particularly on the development of the theoretical basis of plant responses to environmental conditions. The objective of this study was to assess the effect of radiation on seedling growth and physiology of Prosopis alba, P. chilensis, P. flexuosa and P. glandulosa. Seedlings were grown in a greenhouse and randomly assigned to three light environments: full-sun, 52% sun, and 38% sun. No significant differences were found in the rate of leaf appearance and plant height 60 days after the light treatments began. Instantaneous CO₂uptake was not affected by the light environment during leaf development and did not differ among species. Variations in radiation availability resulted in significant differences in biomass accumulation, shoot/root ratio, protein and total non-structural carbohydrates contents. The practice of shading seedlings reduces the chances of survival ofProsopis due to an increase of the shoot/root ratio and a reduction of total biomass, stored carbohydrates, and the C:N balance.     

Effect of rain enrichment on soil respiration of Nitraria sphaerocarpa community in a hyperarid area

In order to analyze the effect of rain enrichment on soil respiration rate of a Nitraria sphaerocarpa community, we measured soil respiration rate in bare and vegetated areas in a hyperarid area （Dunhuang） during the growing season. Results show that rain enrichment can increase bare and vegetated soil respiration rates. The more rainfall enrichment, the greater the increment and the longer duration time effect for soil respiration rate. 200% （16 mm） and 300% （24 mm） of rain enrichment can significantly increase bare soil respiration rates by 90% and 106% （P〈0.01）, respectively. By contrast, areas with 100% （8 mm）, 200% （16 mm） and 300% （24 mm） of rain enrichment can significantly increase shrub area respiration rates by 68%, 157% and 205% （P〈0.01）, respectively. The response time of bare and vegetated soil respiration to rainfall enrichment is asynchronous. Response variable of soil respiration in vegetated soil is higher （118%） than in bare soil. There was significant positive correlation between soil respiration rate and soil water content during the growing season （P〈0.01）. For every 1 mm increment of precipitation, soil respiration rate increased by 0.01 and 0.04 pmol/（m2.s）, respectively in vegetated and bare soils.