Semi-desert Environment Research Articles

A survey of the mycobiota of a natural Karoo pasture

The survey of a natural Karoo pasture from 1978 to 1982 showed that a wealth and variety of fungi were present in the semidesert environment. Hyphomycetes and Coelomycetes represented 45.8% and 34.6% respectively of the taxa identified. A total of 135 genera was identified of which Altenaria altemata, Cladosporium spp. and Fusarium spp. of the Hyphomycetes, Phoma spp., Ascochyta spp. and Camarosporium spp. of the Coelomycetes and Leptasphaerulina spp., of the Ascomycetes represented the most prevalent fungi in this order. This survey has shown conclusively that Pithomyces chartarum, which is associated with photosensitivity diseases of sheep, can always be recovered from the veld if the correct isolation techniques are employed. A number of new records for South Africa, as well as undescribed species, have been found, highlighting the necessity of correct methods and intensity of approach.

Prediction of Bed-Load Transport by Desert Flash Floods

A number of predictive bed-load sediment transport equations are rated against a unique set of field data collected by automatic slot samplers during flash floods in a desert wadi. The Meyer-Peter and Müller equation is shown to perform well, providing a median ratio of calculated to observed ( C /O) bed-load flux of 1.18. The Bagnold equation is shown to underpredict considerably, with a median C /O of 0.44. The Parker equation performs better, though it still underpredicts with a median C /O of 0.78. The apparent success of the Meyer-Peter and Müller formula is attributed to the ready supply of sediment to the channel system in desert and semidesert environments. This ensures that the channel bed remains unarmored, in contrast to supply-limited, armored, perennial rivers of humid zones. It also ensures that bed-load flux responds to changing hydraulic conditions in a comparatively simple fashion.

Impact of seasonal variation in food availability and disease stress on the health status of nomadic Turkana children: A longitudinal analysis of morbidity, immunity, and nutritional status.

The possible influence of seasonal variations in rainfall, resource availability, and morbidity on immune function and nutritional status was examined in a longitudinal study of 54 nomadic Turkana children, 6 months to 10 years of age. The highly seasonal nature of rainfall in the arid semidesert environment of the Turkana District, northwestern Kenya, was associated with varying levels of animal milk production and meat and blood consumption. Despite significant seasonal variation in rainfall and food availability, the nutritional status of Turkana children, assessed through various anthropometric indicators, showed only moderate, if any, decline in the dry season. Rather, the data indicated that Turkana Children suffer from chronic mild-to-moderate malnutrition. In addition, analyses of cellular immunocompetence of the children, recognized to be a functional index of nutritional status, revealed extremely high levels of immunosuppression Year-round. Significant monthly variation in the levels of acute respiratory and gastrointestinal infections among children were found, although averages across seasons were not significantly different and did not correspond with fluctuations in rainfall or resources availability. Instead, periodic spikes in the prevalence of morbidity occurred against an already high level of infectious endemicity. The results indicate that food availability is not likely to be the sole determinant of nutritional status and that infection may be an important contribtor to the high levels of nutritional and immunological stress among nomadic Turkana Children. © 1995 Wiley-Liss, Inc.

The evolution of bird-dispersed pines

Twenty of approximately 100 species of pines (Pinus spp.) have wingless seeds, and 19 of these are in the subgenusStrobus. Eight of the wingless-seedStrobus pines are known to be dispersed by seed-storing corvids, particularly the nutcrackers (Nucifraga spp.), and the other 11 are presumed to be. The principal consequences of these nearly obligate bird-pine mutualisms include tree clustering and a population structure that differs from that of wind-dispersed pines. The wingless-seedStrobus pines in general are typified by ranges that include xeric conditions and/or high elevations, and large seeds, which are considered to be adaptive under either xeric or competitive conditions. The proposed evolutionary scenario for bird dependency begins with the distribution of ancestralStrobus pines into high elevation or semi-desert environments, sympatric with one or more seed-storing corvid forms, and an increase in seed size. We propose that dependency on birds for seed dispersal has occurred primarily in subgenusStrobus, becauseStrobus pines tend more towards winglessness and increased seed size in stressful environments than doPinus pines. Seed winglessness and other bird-pine traits probably arose from a combination of genetic drift in small populations and selection by corvids.

Formation of foreland rifts

The Lower Permian Rotliegendes troughs in Central Europe are directly comparable to the Upper Cenozoic Basin and Range province in the western United States in most tectonostratigraphic aspects. These intracratonic rifts were formed by extensional tectonics in the foreland area of major Cordilleran-type orogenies beginning 20–25 Ma after mountain building. The main characteristics of the basins include: crustal thinning from 40–45 to 30 km, change from calc-alkaline magmatic arc suites to basaltic or bimodal (basalt-rhyolite) igneous suites, normal to listric block faulting, high heat flow and hydrothermal activity, regional uplift, and immature clastic and evaporite sediments rapidly deposited within the subsiding rifts in a semi-desert environment. The genetic model proposed for these “foreland rifts” assumes that an extensional force under the continental foreland results from mantle material being drawn back towards the subducting plate by viscous drag. This force is counteracted by a compressional force produced at the trench by subducting a young, relatively buoyant plate until subduction is ended, at which time the plate breaks off and continues to sink. Tension in the foreland, possibly produced by the sinking slab, continues for some time later, causing stretching and thinning of the continental crust, extensional tectonics and higher regional heat flow and uplift. The decrease in overburden pressure and higher heat flow induces partial melting in the lower lithosphere and bimodal volcanism. Hotter asthenosphere rising up behind the trailing edge of the sinking plate causes thermal expansion and further uplift. The heat flow anomaly rapidly decays by hydrothermal activity within 15–20 Ma after last volcanism. Block faulting and rift basin infilling follow the main period of volcanism and continue until the sinking slab is decoupled from the overriding plate and no longer influences the continental foreland.

Adaptations of <i>Luzula confusa</i> to the Polar Semi-Desert Environment

Luzula confusa is both morphologically and physiologically adapted to the polar semi-desert environment of the western Queen Elizabeth Islands. This species combines the more efficient graminoid photosynthetic system and a less drought-resistant mechanism with some of the cushion plant energy-trapping characteristics such as tufted growth form and persistence of dead leaves, with consequent thicker boundary layer. In this manner, the plant is able to assimilate carbon throughout the 24-hr arctic day. The species utilizes the most favorable part of the growing season by rapid initiation of growth via relatively high photosynthetic rates, especially at low temperatures. This species is very responsive (net assimilation rates) to small changes in leaf temperature and leaf water potential. This permits the species to take advantage of small rises in leaf temperature (leaves normally 5 to 8 degrees C) and to adjust to high VPD and low leaf water potential during the occasional drought. The slow-growing, long-living conservative strategy of this species appears ideally suited to areas that are limited in their vascular plant cover because of rigorous environments. Within the range of habitats available, Luzula confusa predominates in sites of intermediate moisture with abundant cryptogams. It does not occur in the polar deserts with their drier surface soils except in snowflush communities.Key words: Luzula confusa, High Arctic, plant/water relations, net photosynthesis, plant phenology, polar semi-deserts

Root growth in a polar semidesert environment

Within the northwestern islands of the High Arctic, the vegetation and flora of King Christian Island are very representative. Five plant communities were recognized in a moisture gradient from a moss–rush moist meadow with 22 species of vascular plants and 13% cover (total plant cover 93%) to lichen barrens on low ridges with 8 species of vascular plants and 3% cover (total plant cover 24%). Root systems of 30 of the 34 known vascular plant species were examined. Root:shoot ratios (alive) are generally 0.2 to 0.7. Roots are estimated to live 1.5 years in Phippsia algida, 3.4–3.7 years in Alopecurus alpinus and Puccinellia vaginata, and 7–13 years in Luzula nivalis, L. confuse), and Cerastium arcticum. Optimal root growth occurs at 12 to 20 °C but cold field soils (1 to 3 °C) reduce these rates by 90%. Root growth was also reduced by low soil water potentials (< − 14 bars (1 bar = 100 kPa)), conditions seldom encountered in these sites. Limited root growth due to cold soils is combined with the adaptive advantages of small roots to produce small plants and sparse cover in these polar semidesert lands.