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The Importance of Native Trees in Sustaining Biodiversity in Arid Lands
Abstract
The value of science is greatly increased when it is used to benefit society. Too frequently those who do and understand basic science are not involved in its applications, and those charged with resolving societal concerns, such as the management and sustainability of natural resources, are not aware of research that can assist them in making decisions. The objective of this paper is to provide professionals, who are not ecologists but who are involved in conservation and management of natural resources, a summary of ecological research that indicates desert trees are an important resource. I have chosen trees as the focus of this paper because I believe that they alone harbor a large proportion of the biodiversity in dryland ecosystems, and the sustainability and function of these ecosystems depends on their welfare. This view is not to discredit other types of vegetation, for they are important and share several biological processes and some of the biodiversity associated with trees. However, generally less is known of their ecological and functional properties. When possible I have incorporated ecological information on Acacia tortilis (samr in Arabic) from various regions of its range, including recent studies from northern Oman. Samr is a ubiquitous tree throughout the arid and semiarid regions of North Africa and the Middle East. Its dominance in many of the varied ecosystems in the region suggests it is a keystone species, one that is vital for maintaining productive ecosystems.
... These species play a critical role in maintaining the structure of the desert plant and animal communities in the harsh desert conditions. The growth and persistence of these trees could facilitate the environment for the growth of other species (Robinson, 2003;El-Keblawy and Abdelfattah, 2014). In our study, A. tortilis and P. cineraria were associated with more dominant perennials (20 and 13, respectively), compared to other indicator dominant species. ...
... These soils are rich in nutrients and have higher water holding capacity, compared to any other soils in the UAE (EAD, 2012). Secondly, both species can improve soil conditions and consequently increase plant abundance and species diversity beneath, compared to next to their canopies (Munzbergova and Ward, 2002;Robinson, 2003;El-Keblawy and Abdelfattah, 2014). For example, the presence of P. cineraria has facilitated the environment for the growth of many perennials in the UAE deserts (El-Keblawy and Abdelfattah, 2014). ...
... In addition, this tree significantly increased the values of K, N, P and organic matters beneath, compared to the open spaces beyond the canopy (El-Keblawy and . Similarly, A. tortilis enhanced beneficial microbes and improved soil characteristics (Robinson, 2003). Finally, canopy of A. tortilis has unique architecture that maximizes soil shading and reduces soil temperature around the base of the tree. ...
... The Arab World Geographer / Le Géographe du monde arabe Vol 18, no 3 (2015) significant amounts of water (Robinson 2003). Ultimately, as David Gallacher and Jeffrey Hill (2013) point out, groundwater in the U.A.E. is increasingly being depleted by the expansion of horticulture, livestock industries, and forest plantations. ...
... While some desert or endemic trees have root systems specifically adapted to grow long taproots in order to find water, groundwater depletion lowers the water table and can thus lead to the loss of plants, including trees. This then affects the overall biodiversity of arid environments, as endemic trees are an essential element in the maintenance of endemic fauna (Robinson 2003). Trees provide a variety of ecosystem services to species assemblages, such as shelter and food. ...
... The Arab World Geographer / Le Géographe du monde arabe Vol 18, no 3 (2015) significant amounts of water (Robinson 2003). Ultimately, as David Gallacher and Jeffrey Hill (2013) point out, groundwater in the U.A.E. is increasingly being depleted by the expansion of horticulture, livestock industries, and forest plantations. ...
... While some desert or endemic trees have root systems specifically adapted to grow long taproots in order to find water, groundwater depletion lowers the water table and can thus lead to the loss of plants, including trees. This then affects the overall biodiversity of arid environments, as endemic trees are an essential element in the maintenance of endemic fauna (Robinson 2003). Trees provide a variety of ecosystem services to species assemblages, such as shelter and food. ...
Beginning in the late 1940s, the British took a keen interest in expanding water
resources and developing agriculture in the Trucial States (the modern-day United
Arab Emirates). This article explores the ideological, political, and economic
motivations driving these colonial development initiatives. Ultimately, such
projects entailed a fundamental restructuring of local power relations and the
displacement of traditional methods of resource management. Devised with little
consideration of the region’s ecology, the development schemes initiated in the
mid-20th century continued to expand in the post-oil/post-federation period,
contributing to the depletion of water resources and the transformation of the
region’s biodiversity.
... The introduction of native and adaptive trees within the urban environment can also help restore significant living forms in the urban ecosystem. The benefits of life on land can be significant from demonstration projects (Robinson, 2003). The Nursery includes local and adaptive trees that will have no negative impact on local biodiversity. ...
With sustainability at the heart of Fédération Internationale de Football Association (FIFA) World Cup 2022™, Qatar has set a track to achieve carbon neutrality, committing to deliver the first‐ever carbon neutral mega event in the world. Achieving these goals require offsetting carbon emissions through quality projects within and outside the state. Tree nurseries with stress‐tolerant variants play a significant role in cutting the excess emissions from Qatar 2022, thereby supporting long‐term sustainable development. This research presents a novel approach to offset carbon emissions utilizing the carbon sequestration potential of trees planted in a tree nursery project in Qatar. The i‐Tree assessment tool and a well‐established US database are used in this regard to undertake a correlation climatic condition analysis between Doha and five locations in the United States with similar demographics as the State of Qatar. The tree nursery data along with water consumption, fertilizer use, and power consumption, were fed as the inputs to the assessment tool. The assessments were carried out considering different irrigation methods for trees and shrubs, treated sewage water with a significant amount of organic fertilizer, and desalinated water. The analysis showed a net‐carbon‐emission reduction equal to 23.482 t CO2‐eqv/year using the treated sewage water. The tree nursery project has a carbon reduction potential of 21.902% compared to the maximum carbon sequestration potential of 30.39 kg/CO2‐eqv/tree/year, when using treated sewage water and a mix of the specific fertilizer. However, the use of desalinated water holds a negative impact on the carbon balance to such a level that the introduction of trees in Middle Eastern may not positively affect climate change mitigation. It was also found that the amount of carbon footprint reduction after the FIFA World Cup 2022 is expected to increase steadily during the average life expectancy of the trees assessed, which were evaluated to be circa 135 years. The results presented support urban planners in proposing integrated sustainability planning strategies and policies. These strategies can initiate projects such as nurseries, parks, and open space areas to reduce carbon footprints, improve the city's social and economic aspects, and preserve the post‐event legacy of mega‐sporting events like the World Cup and Olympic Sports.
... Being an invasive species it has superior competitive ability and can displace the native species by influencing their growth and seed germination (Inderjit et al., 2008). hence, it is considered a potential threat to indigenous species and requires a strict check on its distribution (robinson, 2003;Sultana et al., 2014) and special attention while framing conservation and management policies. The total eradication of the species is however difficult and ecologically risky as it has established well in these forests. ...
Sinai hawthorn, Crataegus sinaica, is a rare wild tree species of economic importance with potential for medicinal uses. The in vivo seed germination of this tree species is extremely low. The present study aimed to develop an efficient in vitro seed germination that can contribute to the successful propagation, restoration, and preservation of this critically endangered species. The study examined factors that could enhance seed germination frequency (GP) and dormancy break of mature seeds. This included stratification temperature, cytokinin type and concentration, sinapic acid (SA) concentration, gibberellic acid (GA), and substituting nutrient media with water. Cold-stratified seeds for 4 weeks at 7 °C showed highest GP of 29.3%. GP of 36% was obtained on media containing 0.5 mg/L of each 6-Benzyladenine (BA) and meta-Topolin (mTp). Low concentrations of SA increased GP (50%) in both full and ½ Murashige and Skoog basal media with Gamborg B5 vitamins (MSB5). Sterile ddH2O supplemented with selected combined GA, SA, and mTp treatment showed a higher GP (46%) compared to the control. The study investigated the physiology of seed maturation during late growing season and after stratification and their correlation with germination efficiency. Stratification at 7 °C increased total soluble sugars, decreased abscisic acid (ABA) content, and increased GA. This study presents the first report on seed germination in Sinai hawthorn, highlighting the importance of environmental and physiological treatments for improved efficiency. It also offers a simple, inexpensive, method for in vitro seed germination with high efficiency that may be applied in propagation and restoration.
The research was carried out in the Aravalli Forests of Nahargarh (NWLS) and Jamwa Ramgarh Wildlife Sanctuaries (JRWLS) of Jaipur, Rajasthan, India. The vegetation structure, composition, biodiversity and plant community types were assessed across the five forest stands viz Nahargarh biological park (S1), Nahargarh Sanctuary (S2) in NWLS and Ramgarh (S3), Raisar (S4), and Digota (S5) of JRWLS, respectively. A total of 164 qaudrats of 20*20 m2 were laid to assess the vegetation data including frequency, basal area, density, importance value index (IVI), biodiversity indices (Shannon-weiner, Simpson, Pielou and Margalef’s) and plant community types. The tree basal area ranged between 18.56 -34.36 m2/ha while stand density was 923-1433 tree/ha. Our study indicated the dominance of family Fabaceae with 20 species and 11 genera with Anogeissus pendula showing the maximum frequency, density, mean basal area and IVI. Further, the agglomerative hierarchal clustering showed five types of plant communities with Anogeissus-Adhatoda as the most widely spread community in these forests. Among the two sanctuaries, species diversity was higher for JRWLS (2.83) than NWLS (2.80). The current study provides important baseline data for forthcoming research on monitoring and preserving these forest’s biological diversity. The significance of present study will provide insight into the structure and variety of tree species in tropical dry deciduous forests.
We assessed tree diversity of tropical dry deciduous forest in Rajasthan at five sites (Jalmahal, Ramgarh, Nahargarh, Jhalana and Digota). A total of 102 circular plots was laid and all tree species ≥10 cm girth at breast height were enumerated. Tree diversity totalled 69 species and the Digota site harboured the maximum number of families (19), genera (25) and species (36). Mimosaceae (7 genera and 15 species) was the most species-rich family at all the sites. Shannon diversity (2.44) and species heterogeneity (2.23) were highest for Ramgarh site while species richness and β diversity were highest for Digota (3.62 & 5.55) site. Cassia fistula, Butea monosperma and Ehretia laevis were the only species exhibiting regular distribution while all others showed random or contagious distribution. The forest composition varied across the sites. The study provides an understanding of tree distribution at landscape level.
This research quantifies the amount of nitrogen deposited by the tree locust, Anacridium melanorhodon, during an irregular population outbreak in an Acacia tortilis woodland in Oman. The average standing crop of feces was 65.28g m -2 . The mean fecal crude protein and nitrogen were respectively, 20.14 and 3.22 g/100 g ash-free dry weight. A hectare of this woodland would contain approximately 1.1 kg of fecal nitrogen beneath the trees. This single contribution by the locusts equals about one-third of the total standing crop of detrital nitrogen under perennial vegetation in a hectare of the Mohave Desert of North America. This, and the fact that grasshoppers are diverse and seasonally abundant in deserts, suggests they may be important organisms in nitrogen cycles.
In the desert ecosystem, micro-, meso-, and macro-fauna are all attracted to the canopies of whatever plants exist, the place of highest moisture, lowest daytime temperature and most abundant food sources. This paper presents the hypothesis that under conditions of desert aridity the concentrating biological transport mechanisms dominate over the dispersive physical mechanisms. This causes the phenomenon known as "fertile islands'/ -from Authors
▪ Abstract Savannas occur where trees and grasses interact to create a biome that is neither grassland nor forest. Woody and gramineous plants interact by many mechanisms, some negative (competition) and some positive (facilitation). The strength and sign of the interaction varies in both time and space, allowing a rich array of possible outcomes but no universal predictive model. Simple models of coexistence of trees and grasses, based on separation in rooting depth, are theoretically and experimentally inadequate. Explanation of the widely observed increase in tree biomass following introduction of commercial ranching into savannas requires inclusion of interactions among browsers, grazers, and fires, and their effects on tree recruitment. Prediction of the consequences of manipulating tree biomass through clearing further requires an understanding of how trees modify light, water, and nutrient environments of grasses. Understanding the nature of coexistence between trees and grass, which under other ci...
The physiognomy of dry savannas is described as a combination of discontinuous woody perennials and a continuous grassland matrix. Interactions between these two components are of vital importance for the persistence of a savanna landscape. Earlier savanna models have emphasised competition for water between the two components. Recent studies have argued that small-scale facilitating interactions between woody perennials and the herbaceous understory are also important. This phenomenon has been given little theoretical consideration in the in the savanna literature, but it has been an important topic in agroforestry and arid grassland ecology. This paper reviews some of the evidence for micro-site effects of tree and shrubs, and attempts to integrate their interactions with the surrounding open grassland.
Woody perennials modify the microclimate by interception of solar radiation and rainfall. Their root systems extract nutrients horizontally and vertically, which are concentrated in the sub-canopy soil from litter decomnposition and root turnover. Legumes are abundant in dry savannas, and may have symbiotic relationship with Rhizobium bacteria. This symbiosis increases the availability of nitrogen in the soil.
Isolated trees and shrubs initiate feedback mechanisms in their interactions with other organisms, and contribute to an uneven distribution of water and nutrients in dry savanna. This influences the species composition, and community diversity. Small-scale facilitating interaction between woody and herbaceous components and competitive interaction on larger scales, are complementary processes which together explain dynamic coexistence.
Bateman’s principle states that male fitness is usually limited by the number of matings achieved, while female fitness is
usually limited by the resources available for reproduction. When applied to flowering plants this principle leads to the
expectation that pollen limitation of fruit and seed set will be uncommon. However, if male searching for mates (including
pollen dissemination via external agents) is not sufficiently successful, then the reproductive success of both sexes (or
both sex functions in hermaphroditic plants) will be limited by number of matings rather than by resources, and Bateman’s
principle cannot be expected to apply. Limitation of female success due to inadequate pollen receipt appears to be a common
phenomenon in plants. Using published data on 258 species in which fecundity was reported for natural pollination and hand
pollination with outcross pollen, I found significant pollen limitation at some times or in some sites in 159 of the 258 species
(62%). When experiments were performed multiple times within a growing season, or in multiple sites or years, the statistical
significance of pollen limitation commonly varied among times, sites or years, indicating that the pollination environment
is not constant. There is some indication that, across species, supplemental pollen leads to increased fruit set more often
than increased seed set within fruits, pointing to the importance of gamete packaging strategies in plant reproduction. Species
that are highly self-incompatible obtain a greater benefit relative to natural pollination from artificial application of
excess outcross pollen than do self-compatible species. This suggests that inadequate pollen receipt is a primary cause of
low fecundity rates in perennial plants, which are often self-incompatible. Because flowering plants often allocate considerable
resources to pollinator attraction, both export and receipt of pollen could be limited primarily by resource investment in
floral advertisement and rewards. But whatever investment is made is attraction, pollinator behavioral stochasticity usually
produces wide variation among flowers in reproductive success through both male and female functions. In such circumstances
the optimal deployment of resources among megaspores, microspores, and pollinator attraction may often require more flowers
or more ovules per flower than will usually be fertilized, in order to benefit from chance fluctuations that bring in large
number of pollen grains. Maximizing seed set for the entire plant in a stochastic pollination environment might thus entail
a packaging strategy for flower number or ovule number per flower that makes pollen limitation of fruit or seed set likely.
Pollen availability may limit female success in individual flowers, entire plants (in a season or over a lifetime), or populations.
The appropriate level must be distinguished depending on the nature of the question being addressed.
The relationship between biodiversity and individual ecosystem processes is often asymptotic, saturating at relatively low levels, with some species contributing more strongly than others. This has cast doubt on arguments for conservation based on maintenance of the functioning of ecosystems. However, we argue that the link between biodiversity and ecosystem functioning is an important additional argument for conservation for several reasons. (1) Although species differ in importance to ecosystem processes, we do not believe that this argues for preservation of just a few species for two reasons: first, it is nearly impossible to identify all species important to the numerous systems and processes on which humans depend; second, the important species themselves may depend on an unknown number of other species in their communities. (2) Arguments for conservation based on ecosystem functioning are complementary to other utilitarian, ethical and aesthetic justifications. No single reason will convince all people or protect all species, however the combination produces a strong case for conservation of biodiversity. (3) Even if the relationship between biodiversity and ecosystem functioning is asymptotic at local spatial scales and in the short term, effects of biodiversity loss are likely to be important at larger temporal and spatial scales. (4) Initial arguments for the importance of biodiversity for ecosystem functioning were largely based on a precautionary approach (points 1-3). However, we are now moving to a scientific position based on accumulating experimental evidence. The future challenge is the integration of this scientific research with policy.
GLASOD project ISRIC ISSS FAO ITC Staring Centre
Discusses the desertification rate of arid and semi-arid lands and the limitations of their restoration. Uses a recontoured coal mine in SW Wyoming as a study site, and reviews innoculation of VA mycorrhizal fungi and succession in a disturbed landscape. Results show the natural dispersion of the spores to be great enough to be useful in detecting infection in the roots of the Agropyron species within 1-3 yr. -S.J.Yates
Plant migrations during past geological periods, long-term geological and climatic changes, recent climate and hydrology, edaphic, geological and topographical structures and the effects of man and his livestock have all played a part in the establishment and development of the flora and vegetation of Arabia. The varied and often dramatic terrain of the 2.7 million km2 of the Peninsula (Figures 3.1–3.4) is subject to a climate that ranges from the hyperarid to the humid subtropical (see Chapter 2), and the consequent complexity of the landscape is reflected in the variety of its plant life.
1. To determine whether agroforestry and silvopastoralism might be introduced more successfully into xeric or into mesic environments, the effects of isolated, mature trees of Acacia tortilis (acacia) and Adansonia digitata (baobab) on herb-aceous-layer composition and productivity, soil properties, and microclimate in a moderately mesic savanna (c. 750 mm annual rainfall) were investigated and compared with an earlier study of the effects of the same two species in a more xeric savanna (c. 450 mm annual rainfall) in Tsavo National Park (West), Kenya. 2. Similar to the more xeric site, solar radiation was reduced by 45-65% and soil temperatures were reduced by 5-12 C⚬ under both tree species. Except for early in the growing season, soil-moisture values were similar under tree canopies and in open grasslands. 3. Compared to the more xeric site, where herbaceous-layer productivity was 95% higher under trees than in the open, productivity in the mesic site was 52% higher under acacia canopies (a mean of 808 g m-2) than in the open (533 g m-2), but only 18% higher under baobab canopies (569 g m-2) than in the open (484 g m-2). 4. Concentrations of organic matter, total N, 15N, P, K and Ca were significantly higher, and C:N ratios and soil bulk density significantly lower under tree canopies than in the open at both sites. Mg concentrations were significantly higher in the open than under tree canopies at the mesic, but not the xeric, site. 5. The contrast noted in 3 above between the herbaceous layer productivity below tree canopies and that in areas beyond them was attributed higher soil-N concentrations and to reduced evapotranspiration in these N- and water-limited systems. 6. The contrast in forage production under tree canopies between xeric and mesic sites may be due to the greater importance of shade in reducing temperatures and evapotranspiration in more arid environments.
The radiation flux at winter solstice is reported for desert microenvironments under Cercidium crowns and in open desert. In addition to the net radiation flux and that of the upper and lower hemispheres, hourly radiation temperatures (equivalent black-body temperatures) were measured for soil surfaces, sky, and tree crowns. Radiation temperature-time as a limiting factor for organisms in the sense of resistance time was investigated. Winter environmental modification provided by Cercidium of 4-5 m height is large, and greater than expected. The effective (net) incoming radiation at ground level at midday in the open is more than twice that under the paloverde, and the effective (net) outgoing radiation in the open at night is more than twice as great as that under the tree. For these data, a computer model of the energy budget of a 1-kg hypothetical homoiotherm predicts (i) on the ground surface under the paloverde at night, an effective body-surface temperature of 7 degrees C with an increse of metabolic rate by only 2.6 times its standard rate; this is in sharp contrast to (ii) in the open under the night sky and on a colder ground surface, where the metabolic rate of the same animal exhibiting Newtonian cooling would have to be increased 6.2 times to balance its heat budget. The model also predicts little or no presence in the open on the ground during winter nights in the desert for small homoiotherms greatly less than 1 kg body weight, e.g., weights on the order of 100-200 g or less, unless for rapid forays of short duration.
Over a 3-year period, soil-plant systems of velvet mesquite and palo verde from the Sonoran Desert were sampled by standing crop, litter, and soil components and analyzed to describe the amount and distribution of dry matter, nitrogen, and carbon in the systems. Honey mesquite was sampled on a limited basis in southern New Mexico. Velvet mesquite averaged about one-third larger in crown area and weight than palo verde, but the two shrubs were similar in the distribution of dry matter, N, and C. Honey mesquite was much smaller and differed in distribution of dry matter, N, and C. Regression analysis showed that dry matter, N, and C in components of shrub systems of velvet mesquite and palo verde varied in a predictable manner and can be estimated with good precision using height, average crown diameter, or crown area of shrubs as the independent variable. Functional analysis showed that soil under palo verde did not accumulate N or C with increase in shrub size, whereas that under velvet mesquite accumulated N at the rate of per meter of height and C at the rate of per meter of height.
. Contrary to observations and models in which trees and herbaceous plants are viewed as competitors, we found that trees in an African savanna have positive impacts on herbaceous biomass production and composition, and on soil nutrient status. In the Turkana District of northwestern Kenya, we investigated vegetation and soil gradients along equi-angular transects radiating from the boles of individual Acacia tortilis trees. Total herbaceous biomass averaged 260 ± 17(se) g/m2 at the bole and declined to 95 ± 8 g/m2 in the tree interspaces. Soil organic carbon and total nitrogen concentrations were greatest (0.72 % and 0.083 %, respectively) in shallow soils near the bole and declined rapidly toward the interspaces and with increasing depth. Transects were also established between tree pairs to assess effects of differential canopy proximities. Grass production averaged 220 ± 21 g / m2 below overlapping canopies, 150 ± 15 g / m2 under individual canopies, and 95 ± 8 g / m2 in interstitial areas. Detrended correspondence analysis revealed that shifts in species composition were correlated with distance from tree bole out to the edge of the canopy. Species response, in terms of relative cover, to increasing distance from the bole, seemed to fall into five general classes: 1) greatest at the bole, 2) increasing with distance from the bole, 3) greatest in the mid canopy zone, 4) least at the bole and 5) no response. Trees did not influence herbaceous compositionbeyondtree canopies. It is assumed that shade cast by the tree canopy with subsequent reductions of understory water stress and temperature and increased nutrient concentrations may be the most important factors affecting understory soil and vegetation.
This review examines the following questions: (1) do soil fauna play an important regulatory role in decomposition and mineralization processes in arid and semiarid ecosystems? (2) if important, what are the mechanisms of the rate regulation, and (3) what are the management implications of these relationships? Because termites process more than half of the surface litter in hot deserts, this review focuses on faunal effects on buried litter and roots. Elimination of soil arthropods reduced rates of mass loss and coupled mass loss to soil moisture. With arthropods present soil moisture accounted for less than 50% of the variation in mass loss. Other experiments demonstrated that regulation of mass loss results from predatory mites regulating the population density of grazers, thereby preventing overgrazing of the fungi and bacteria. The regulation of microbial grazers by soil microarthropods also affects rates of mineralization and nutrient immobilization. Populations of small fungus grazing mites (Tarsonomidae) affect mineralization directly. Microarthropods tend to uncouple mineralization from abiotic constraints. Fluctuations in microbial populations and soil fauna are more a function of substrate availability than of abiotic regulation. Pulses in organic matter inputs result in periods of nutrient immobilization, the extent of which is a function of the rate of recovery of populations of key soil microarthropods.
The economic gains due to honey bee (Apis mellifera L.) agricultural pollination are evaluated. The method of analysis focuses on the gains to consumers through lower prices for crops that are benefited by honey bees. Economic demand functions for the major agricultural crops that are pollinated by bees are estimated. The amounts by which the yields of pollinated crops are increased are estimated from a variety of sources. In the final step, the surplus realized by consumers of these crops that would be lost if honey bees were depleted is determined. The annual social gains are estimated to range between 5.7 billion.
The quarrying sites in the northern part of the Kuwaiti desert comprise about 2.29% of the country's total area, which covers 17,818 km2. The population dynamic and socioeconomic transformation increased the demand for local gravel, which is deposited in thin layers (i.e., 1 to 10 m depth). The annually expected demand for gravel is about 3.3 million m3. Housing projects, road construction, and commercial and industrials projects consume about 33, 24.5, and 3.5% of the total demand for gravel, respectively. The following environmental damages caused by irrational gravel quarrying are preliminarily investigated: rupture of lag cover, soil displacement, landscape disruption, vegetation deterioration, soil compaction, and dust fallout. Radarsat images, aerial photographs, and field measurements show that soil compaction and landscape disruption are the most significant mechanisms of land degradation. The infiltration capacity of the compacted soils has decreased to one-third in comparison with uncompacted (unaffected) soils. Overexploitation of gravel resources and intensive off-road vehicles resulted in severe immediate and long-term environmental damage.
The spreading influence of salinity stress on the farmlands of coastal strip in the Wilayat of Sur, Sharqiyah region was investigated. A 4-km study transect was chosen from 2 km from the coast to 6 km inland and three zones based on farm conditions were demarcated. Within each zone three farms were randomly chosen and a total of nine farm wells were studied. Irrigation water quality clearly indicated that Zones 1, 2 and 3 could be classified as high, intermediate and low salinity zones. The improvement of water quality from high to low salinity zones was progressive and statistically significant. Seawater intrusion appears to be the cause of degradation in water quality. Irrigation water quality of high and intermediate zones was unacceptable by international standards. Expansion of farms, increased water extraction and a recharge dam upstream are all considered as factors promoting salinization. Management strategies for combating salinization are discussed. The invertebrate assemblages of the study wells have been described and the potential of some sensitive species for use as indicators of salinity stress is revealed. However, practical difficulties warrant the continued use of chemical methods to monitor salinity changes.
Plant and bird species richness and abundance in two patches of native Acacia karroo and two patches of alien Prosopis species drainage line woodland in the southern Kalahari, South Africa, were compared using 37 plot (100 m2) samples for the plants and 12 line transects (ca. 1 km long) for the birds. Vertical distribution of canopy cover differed among the four sites in all four strata. The densest Prosopis woodland had less herbaceous understorey cover, and more cover between 1 and 5 m above-ground than Acacia woodlands or the relatively openProsopis woodland. The tallest Acacia woodland differed from other sites in having 40% canopy above 5 m. The densities of all trees >50 mm basal diameter (mainly A. karroo and Prosopis, but including a few A. hebeclada and Ziziphus mucronata) did not differ among sites, but abundance of A. karroo andProsopis species differed greatly among sites. Mean plant species density per 100 m2 plot differed among sites, being greater in the Acacia woodlands than in Prosopis -dominated vegetation. The densest Prosopis woodland was the least diverse site botanically, and was also least similar to the tallest Acacia woodland, sharing only 11 plant species. The ratio of fleshy fruited plant species to all others encountered differed between woodland types being lower in Prosopis than in Acacia woodland. Individual A. karroo trees differed from size-matchedProsopis trees in being less multi-stemmed and having fewer branches in contact with the soil when mature. The numbers of species of sub-canopy plants and fleshy fruited plant species increased with the size of the trees, but tended to be lower for large Prosopis than for large A. karroo.
Population density and species diversity of microfungal communities were investigated in the rhizosphere soil of the halophytic plant Zygophyllum qatarense inhabiting saline and nonsaline habitats of the arid desert environment of Bahrain. Unlike the nonsaline habitat which is situated in the physiographic zone of multiple escarpment and backslopes, the saline site is located in the coastal lowlands and is featured by high chloride content, electrical conductivity, total soluble salts and low organic matter. Soils of both habitats are sandy, slightly alkaline, poor in nutrient sources, low in water-holding capacity and mainly dominated by a salt-tolerant flora. Quantification of data for the recovery of fungi were based on colony identification and counts by a series of ten-fold dilutions plate method, using various natural, synthetic and selective media. A total of 2780 isolates, fluctuating between 25 and 1109 per sample, were recovered during the present study among all habitats, seasons and plant sizes. Grouping of these isolates has resulted in a maximum of 28 fungal taxa varied between 5 and 15 species, of which 24 were hyphomycetes, 3 ascomycetes and one was an unknown species. All the recorded species in this study, excluding the genus Fusarium, are newly reported from the arid terrestrial habitats of Bahrain. Of the encountered fungi,Cladosporium sphaerospermum was the most dominant and frequent genus, among all plant sizes, followed by Penicillium citrinam and Aspergillus fumigatus, a finding with consistent documented data from similar arid Sahara ecosystems. Examination of data, supported by analysis of relative density values, percentage recovery rates, polar ordination and diversity indices revealed that the nonsaline habitat during the dry period yielded the highest isolate frequency, species abundance, and diversity when compared with the saline habitat. Moreover, a progressive increase in colony occurrence and species diversity was equivalently associated with increment in plant size in the nonsaline habitat. Apparently, the vast majority (moderate to low occurrence class) of the reported species are rhizosphere indigenous saprophytic cellulose-decomposers, whilst the sparse taxa (high occurrence class), e.g. C. sphaerospermum, are regarded as thermo-osmotolerant. Comparison of species richness among samples suggests that small plants inhabiting nonsaline habitats during the wet and dry season were richest in species composition. It is proposed that inter- and intra-specific variation in fungal community between the above habitats reflect not only the influence of plant age and season but also extends to critical multi-soil edaphic and biotic factors involving essentially soil moisture, salinity and root growth dynamic and exudates.
Stemflow, throughfall and bulk precipitation were collected on six creosotebushes (Larrea tridentata) during 18 events in the summer rainy season in the northern Chihuahuan Desert. The average stemflow was 16.8 +/- 1.9%; throughfall averaged 64.7 +/- 3.2%. The concentration of all ions measured were significantly higher in stemflow than in the bulk precipitation. Total nitrogen, sulfate, and calcium concentrations were more than an order of magnitude higher in the stemflow than in the bulk precipitation. Concentration of ions in the upper 10 cm of soil were generally higher in soils under shrubs than in soils between shrubs. Measured quantities of ions in dry-fall were of sufficient magnitude to account for the increased concentration in stemflow water of most ions. Increases in nitrogen in stemflow water may be due to biological activity of stem crust micro-organisms in addition to dry-fall. Dry-fall that collects on the leaves and stems of this desert shrub may contribute to the 'fertile island' effect on the soils under the canopies of creosotebushes.
Artificial shading was provided to a Sonoran Desert ecosystem with an array of 12 regularly spaced, opaque structures. Shading resulted in a cooler, moister microhabitat below and behind each structure. Open gaps between structures also exhibited moister soils relative to a control.
Ephemeral plants increased in species diversity and showed a shift in species composition in shaded microsites, but exhibited decreased total biomass relative to controls. A deciduous shrub, Ambrosia deltoidea, had more mesophytic leaves, higher leaf area, carbon dioxide assimilation and growth in shaded microsites. An evergreen shrub, Larrea tridentata, had highest carbon dioxide assimilation and growth in sunny microsites within the array of shading structures. The plant responses observed in this study illustrate the contrasting adaptations of different desert life forms from the same habitat.
Preface Historical prologue on Rock Valley studies 1. Introduction to the Mojave Desert 2. Physical geography of Rock Valley 3. Adaptations of Mojave Desert plants 4. Desert perennials of southern Nevada 5. Mojave Desert annuals 6. Adaptations of Mojave Desert animals 7. Mammals 8. Reptiles 9. Birds 10. Arthropods 11. Soil organisms and seed reserves 12. Nitrogen cycling 13. Human impacts on Mojave Desert ecosystems Literature cited Index.
Several ecological effects of samur trees (Acacia tortilis) on the understory herbaceous plants were investigated. Abundance, distribution and species richness were quantified using quadrat analysis. Total dry weight biomass, density and number of species were significantly greater in the understory microenvironment compared to open desert. Significant differences in these variables resulting from different soil moisture regimes beneath the trees were also expected among the north, south, east and west exposures, but none were found. Apparently differences in soil moisture were slight, or did not exist, due to record rains(145mm). However, nine species had significantly greater densities on certain exposures, possibly reflecting the other types of microenvironmental variability. Three taxa, Aizoon canariense, Plantago ovata and Paronychia arabica dominated the understory flora. Combined, their potential contribution to the energetics and flow of materials in this microenvironment far exceeds that of the remaining species. The importanc eof trees for maintenance of desert biodiversity and ecosystem function is reiterated.
The tradition of food webs and food chains is a proud one, with some of the pioneering efforts traceable to the studies of Summerhayes and Elton (1923) in Spitsbergen. This early effort explicitly linked detrital biotic interactions with other parts of the terrestrial and aquatic food web (Figure 3.1). Very little work on detrital food webs was conducted for several decades, with some further insights gained from the studies of Lindeman (1942), who developed the concept of trophic levels.
Dwarf shrubs play a predominant role in the natural vegetation cover of Kuwait, with the chenopod Haloxylon salicornicum widespread in northern parts of the country. A number of influences, largely anthropogenic in nature, have led to serious land degradation in many areas. The present study deals with species diversity and other floristic attributes of the ephemeral vegetation in a sand-depleted Haloxylon salicornicum community, contrasting the situation of miniature dunes formed at the base of shrubs with that of the interdune space. The importance of such dunes and their associated shrub cover as a protection against further land deterioration is examined.
Traditionally, food web studies have been part of what may be called the population-community approach to ecology (O’Neill et al., 1986). Ecosystem ecologists using the process-functional approach have usually neglected population interactions in food webs, despite the fact that a mechanistic understanding of ecosystem processes such as decomposition of organic matter and nutrient cycling requires studies of the organisms performing these processes (Moore et al., 1988; Verhoef and Brussaard, 1990). Until recently, there have been few published theoretical and empirical studies relating population dynamics and food webs to ecosystem processes (and vice versa) (DeAngelis, 1992; Jones and Lawton, 1995). A combination of the two approaches can be fruitful for solving many problems in basic and applied ecology, and studies of food webs are likely to become a substantial part of this growing industry.
The effects of isolated, mature Acacia tortilis and Adansonia digitata on their environments in Tsavo National Park (West), Kenya, were investigated. Compared to open grassland, tree canopies reduced solar irradiance by 45-65%, soil temperatures by 5-11°C, and rainfall by 0-50%. Soil water content was higher in open grassland immediately after the start of the 2 rainy seasons, higher under tree canopies during the 1st rainy season, but was equal in the 2 areas during the 2nd rainy season. Patterns of herbaceous-layer composition and above-ground net primary productivity (ANPP) under and near trees were similar, with significantly greater ANPP in the canopy zones (705 ± 39 g m -2) than in the root (430 ± 23 g m -2) or grassland (361 ± 21 g m -2) zones. Herbaceous-root biomass (0-30 cm depth) was similar in all 3 zones around both tree species (range 528-659 g m -2). Mineralizable N and microbial biomass were significantly higher in soils from the canopy than from the root and grassland zones, where organic matter, P, K, and Ca (but not Mg) declined in soils from the base of the trees towards the open grassland. Increased herbaceous-layer productivity was associated with the lower soil temperatures and greater soil fertility found under tree canopies. The soil nutrients that contributed to the greater fertility of the canopy-zone soils may have been transported to the canopy zone from surrounding soils by tree roots or deposited in dung by birds and large mammals that utilize the tree environment. -from Authors
To determine why herbaceous productivity in tropical and subtropical savannas is often significantly higher under crowns of isolated trees than in adjacent grasslands, experimental plots were established in three concentric zones, crown, tree-root and grassland, surrounding isolated trees of Acacia tortilis in low rainfall and high rainfall savannas in Tsavo National Park, Kenya. Plots were fertilised (to determine the importance of nutrient enrichment by trees), shaded(to determine the importance of of crown shade), fertilised and shaded (to identify fertiliser x shade interactions), or trenched (tree roots roots entering plots were severed to determine the importance of belowground competition between overstory trees and understory herbaceous plants). In addition, vertical root distributions of trees and herbaceous species were determined and root systems of A.tortilis saplings were excavated.
At both sites fertilisation increased herbaceous productivity in tree-root and grassland zones, but not in canopy zones; artificial shade had no effect on productivity at the low rainfall site but increased productivity in the tree-root zone at the high rainfall site; and severing roots had no effect on herbaceous productivity at the low rainfall site but increased productivity in the crown and tree-root zone at the high rainfall site. Roots of herbaceous and woody species co-occurred within the same soil horizons, but tree roots extended farther into the grasslands at the low rainfall site than at the high rainfall site.
These studies suggest that savanna trees compete more intensely with understory plants at wetter sites where their roots terminated in or near crown zones, than at drier sites, where their roots extended farther into the open grassland. Nutrients added by trees to crown zones in the form of tree litter and animal droppings increased understory productivity by fertilising nutrient limited soils. Shade contributed more to regrowth after severe defoliation than to growth under more normal conditions.
The total water output of the desert vegetation was estimated in the different microhabitats of Wadi Hoff, namely the plateau, the shaded area, and the first and second terraces of the wadi bed. The total water output depends on different factors, mainly the fresh weight of plants, their density, the climatic factors, the floristic composition, and the availability of soil moisture. In the wet season, the total water output was nearly equal in the plateau and the shaded microhabitat, although the total fresh weight of plants in the plateau was only one third of that in the shade. This is mainly attributed to the effect of shade in decreasing the transpiration rates. The water output was 114.2 kg/100 m2/day in the first terrace and 54.9 kg/100 m2/day in the shade. The lowest water output was recorded in the second terrace, amounting to 8.27 kg/100 m2/day, and this is due to the sparse vegetation and also to the dominance of Zygophyllum coccineum with its low transpiration rate. In the dry season the water output showed a slight increase in most microhabitats due to the rise in the transpiration rate of plants in that part of the year.
A major scientific revolution has begun, a new paradigm that rivals
Darwin's theory in importance. At its heart is the discovery of the
order that lies deep within the most complex of systems, from the origin
of life, to the workings of giant corporations, to the rise and fall of
great civilizations. And more than anyone else, this revolution is the
work of one man, Stuart Kauffman, a MacArthur Fellow and visionary
pioneer of the new science of complexity. Now, in At Home in the
Universe , Kauffman brilliantly weaves together the excitement of
intellectual discovery and a fertile mix of insights to give the general
reader a fascinating look at this new science--and at the forces for
order that lie at the edge of chaos.We all know of instances of
spontaneous order in nature--an oil droplet in water forms a sphere,
snowflakes have a six-fold symmetry. What we are only now discovering,
Kauffman says, is that the range of spontaneous order is enormously
greater than we had supposed. Indeed, self-organization is a great
undiscovered principle of nature. But how does this spontaneous order
arise? Kauffman contends that complexity itself triggers
self-organization, or what he calls "order for free," that if enough
different molecules pass a certain threshold of complexity, they begin
to self-organize into a new entity--a living cell. Kauffman uses the
analogy of a thousand buttons on a rug--join two buttons randomly with
thread, then another two, and so on. At first, you have isolated pairs;
later, small clusters; but suddenly at around the 500th repetition, a
remarkable transformation occurs--much like the phase transition when
water abruptly turns to ice--and the buttons link up in one giant
network. Likewise, life may have originated when the mix of different
molecules in the primordial soup passed a certain level of complexity
and self-organized into living entities (if so, then life is not a
highly improbable chance event, but almost inevitable). Kauffman uses
the basic insight of "order for free" to illuminate a staggering range
of phenomena. We see how a single-celled embryo can grow to a highly
complex organism with over two hundred different cell types. We learn
how the science of complexity extends Darwin's theory of evolution by
natural selection: that self-organization, selection, and chance are the
engines of the biosphere. And we gain insights into biotechnology, the
stunning magic of the new frontier of genetic engineering--generating
trillions of novel molecules to find new drugs, vaccines, enzymes,
biosensors, and more. Indeed, Kauffman shows that ecosystems, economic
systems, and even cultural systems may all evolve according to similar
general laws, that tissues and terra cotta evolve in similar ways. And
finally, there is a profoundly spiritual element to Kauffman's thought.
If, as he argues, life were bound to arise, not as an incalculably
improbable accident, but as an expected fulfillment of the natural
order, then we truly are at home in the universe. Kauffman's earlier
volume, The Origins of Order , written for specialists, received lavish
praise. Stephen Jay Gould called it "a landmark and a classic." And
Nobel Laureate Philip Anderson wrote that "there are few people in this
world who ever ask the right questions of science, and they are the ones
who affect its future most profoundly. Stuart Kauffman is one of these."
In At Home in the Universe , this visionary thinker takes you along as
he explores new insights into the nature of life.
Bromus tectorum is an exotic annual grass that currently dominates many western U.S. semi-arid ecosystems, and the effects of this grass on ecosystems in general, and soil biota specifically, are unknown. Bromus recently invaded two ungrazed and unburned perennial bunchgrass communities in southeastern Utah. This study compared the soil food-web structure of the two native grassland associations (Stipa [S] and Hilaria [H]), with and without the presence of Bromus. Perennial grass and total vascular-plant cover were higher in S than in H plots, while quantities of ground litter were similar. Distribution of live and dead plant material was highly clumped in S and fairly homogenous in H. Soil food-web structure was different between H and S, with lower trophic levels more abundant in H and higher trophic levels more abundant in S. In Bromus-invaded plots, the quantity of ground litter was 2.2 times higher in Hilaria-Bromus (HB) than in H plots, and 2.8 times higher in Stipa-Bromus (SB) than in S plots. Soil biota in HB generally responded to the Bromus invasion in an opposite manner than in SB, e.g., if a given component of the food web increased in one community, it generally decreased in the other. Active bacteria decreased in H vs. HB, while increasing in S vs. SB. Soil and live plant-infecting fungi were the exception, as they increased in both types of invaded plots relative to uninvaded plots. Dead-plant-infecting fungi decreased in H vs. HB and increased in S vs. SB. Most higher-trophic-level organisms increased in HB relative to H, while decreasing in SB relative to S. Given the mixed response to invasion, the structure of these soil food webs appears to be controlled by both plant inputs and internal dynamics between trophic levels. When compared to non-invaded sites, soil and soil food-web characterisitics of the newly invaded sites included: (1) lower species richness and lower absolute numbers of fungi and invertebrates; (2) greater abundance of active bacteria; (3) similar species of bacteria and fungi as those found in soils invaded over 50 yr ago; (4) higher levels of silt (thus greater fertility and soil water-holding capacity); and (5) a more continuous cover of living and dead plant material (thus facilitating germination of the large-seeded Bromus). These results illustrate that (1) soil food-web structure can vary widely within what would generally be considered one vegetation type (semi-arid grassland), depending on plant species composition within that type, and (2) addition of a common resource can evoke disparate responses from individual food-web compartments, depending on their original structure.
"Put together one of the world's best science writers with one of the universe's most fascinating subjects and you are bound to produce a wonderful book. . . . The subject of complexity is vital and controversial. This book is important and beautifully done."âStephen Jay Gould "[Complexity] is that curious mix of complication and organization that we find throughout the natural and human worlds: the workings of a cell, the structure of the brain, the behavior of the stock market, the shifts of political power. . . . It is time science . . . thinks about meaning as well as counting information. . . . This is the core of the complexity manifesto. Read it, think about it . . . but don't ignore it."âIan Stewart, Nature This second edition has been brought up to date with an essay entitled "On the Edge in the Business World" and an interview with John Holland, author of Emergence: From Chaos to Order.
We report on the energy expenditure and water flux, measured in the laboratory and in the field, of the Arabian oryx Oryx leucoryx, the largest desert ruminant for which measurements of the field metabolic rate of free-living individuals have been made using doubly labeled water. Prior to extirpation of this species in the wild in 1972, conservationists sequestered a number of individuals for captive breeding; in 1989, oryx were reintroduced in Saudi Arabia into Mahazat as-Sayd (2244km2). Apart from small pools of water available after rains, oryx do not have free-standing water available for drinking and therefore rely on grasses that they eat for preformed water intake as well as their energy needs. We tested whether oryx have a reduced fasting metabolic rate and total evaporative water loss (TEWL) in the laboratory, as do some other arid-adapted mammals, and whether oryx have high field metabolic rates (FMRs) and water influx rates (WIRs), as predicted by allometric equations for large arid-zone mammals. We measured FMR and WIR during the hot summer, when plant moisture content was low and ambient temperatures were high, and after winter rains, when the water content of grasses was high.
For captive oryx that weighed 84.1kg, fasting metabolic rate averaged 8980kJday−1, 16.7% lower than predictions for Artiodactyla. Our own re-analysis of minimal metabolic rates among Artiodactyla yielded the equation: logV̇O2=−0.153+0.758logM, where V̇O2 is the rate of oxygen uptake in lh−1 and M is body mass in kg. Fasting metabolic rate of oryx was only 9.1% lower than predicted, suggesting that they do not have an unusually low metabolic rate. TEWL averaged 870.0mlday−1, 63.9% lower than predicted, a remarkably low value even compared with the camel, but the mechanisms that contribute to such low rates of water loss remain unresolved.
For free-living oryx, FMR was 11076kJday−1 for animals with a mean body mass of 81.5kg during summer, whereas it was 22081kJday−1 for oryx in spring with a mean body mass of 89.0kg, values that were 48.6% and 90.4% of allometric predictions, respectively. During summer, WIR averaged 1310mlH2Oday−1, whereas in spring it was 3438mlH2Oday−1. Compared with allometric predictions, WIR was 76.9% lower than expected in summer and 43.6% lower in spring. We found no evidence to support the view that the WIR of large desert ungulates is higher than that of their mesic counterparts. On the basis of the WIR of the oryx averaged over the year and the water contents of plants in their diet, we estimated that an oryx consumes 858kg of dry matter per year.
Effect of the canopy morphology on the microclimate beneath Acacia tortilis
- Al Harthi
Energetics of detritivory and microb ivory in soil in theory and practice. Pages 39-50 (Editors) Food Webs. Integration of Patterns and Dynamics
- D Coleman
Ecophysiology of Prosopis cineraria in the Wahiba Sands, with reference to its reafforestation potential in Oman. Pages 257-270 (Editor) The Scientific Results of the Royal Geographic Society’s Oman Wahiba Sands Project 1985-1987
- K Brown