Abdulaziz M. Assaeed

Soil Seed Bank of a Desert Range Site Infested with Rhazya stricta in Raudhat al-Khafs, Saudi Arabia

Knowledge of the dynamics of soil seed bank in rangelands is important in planning for range management and improvement. A three-year study of soil seed bank was conducted in an area infested with Rhazya stricta Decne. The object of the study was to evaluate annual and seasonal variations in the soil seed bank over three degrees of infestation by R. stricta (low, moderate, and heavy). Soil samples were placed in germination trays in a growth chamber and irrigated. Emerging seedlings were identified and counted by species. Species were grouped into shrubs, legumes, grasses, and forbs. Results revealed the presence of seeds of 44 species, mostly annuals. Low similarity was observed between above-ground vegetation and soil seed components. Significant annual and seasonal variations were observed among groups of species. Generally, seed bank size and species richness were higher under the lower level of R. stricta infestation. It is concluded that most of the desirable species that have the potential of growing in the area are disappearing.

Effects of open grazing and livestock exclusion on floristic composition and diversity in natural ecosystem of Western Saudi Arabia

Livestock grazing is one of the main causes of rangeland degradation in Saudi Arabia. Fencing to exclude grazers is one of the main management practices used to restore vegetation and conserve biodiversity. The main objectives of this study were to investigate the changes in plant diversity and abundance, floristic composition and plant groups of the major life forms in response to thirty-five years of grazing exclosure in western Saudi Arabia. These vegetation attributes and palatability were compared in 30 sampling stands located in the excluded and grazed sites. Our results showed that livestock exclusion significantly increased covers, density and species richness of annuals, grasses, perennial forbs, shrubs and trees. Exclosure enhanced the abundance and richness of palatable species and depressed the development of weedy species. About 66.7% of the recorded species at the excluded site were highly palatable compared to 34.5% at the grazed site. In contrary, about 55.2% unpalatable species were found in the grazed site compared to 25.8% in the protected site. Jaccard’s similarity index between the excluded and grazed sites showed lower values of 0.39%, 0.40% and 0.31% at levels of families, genus and species, respectively. The results suggest that establishing livestock exclusion may be a useful sustainable management tool for vegetation restoration and conservation of plant diversity in degraded rangelands of arid regions.

Use of spatial analysis to test hypotheses on plant recruitment in a hyper-arid ecosystem

Mounds originating from wind-blown sediment accumulation beneath vegetation (nebkhas) often indicate land degradation in dry areas. Thus far, most nebkha research has focused on individual plants. Here, we aimed to explore population-scale processes (up to scales of about 100 m) that might explain an observed nebkha landscape pattern. We mapped the Rhazya stricta Decne. population in a 3 ha study site in a hyper-arid region of Saudi Arabia. We compared the spatial patterns of five different cohorts (age classes) of observed nebkha host plants to those expected under several hypothesized drivers of recruitment and intraspecific interaction. We found that all R. stricta cohorts had a limited fractional vegetation cover and established in large-scale clusters. This clustering weakened with cohort age, possibly indicating merging of neighboring vegetation patches. Different cohort clusters did not spatially overlap in most cases, indicating that recruitment patterns changed position over time. Strong indications were found that the main drivers underlying R. stricta spatial configurations were allogenic (i.e. not driven by vegetation) and dynamic. Most likely these drivers were aeolian-driven sand movement or human disturbance which forced offspring recruitment in spatially dynamic clusters. Competition and facilitation were likely active on the field site too, but apparently had a limited effect on the overall landscape structure.

Forage yield and survival of native range species under supplementary irrigation in Central Saudi Arabia

The increase of livestock production in Saudi Arabia has resulted in a parallel increase in demand for forage production and hence greater exploitation of ground water for irrigation. The current trend of water conservation policies necessitates finding alternate sources of forages that consume less water than the traditional forage crops. The objective of this study was to evaluate the forage yield and survival of some range species under certain levels of supplementary irrigation. The evaluated species were Atriplex halimus , Atriplex leucoclada, Farsetia aegyptia, Salsola villosa and Artemisia sieberi. The supplementary irrigation treatments were: yearlong irrigation with an amount of 480 mm water, summer and fall irrigation (240 mm), summer irrigation (120 mm) and no supplementary irrigation. Results showed that supplementary irrigation of native range species during summer season increased yield by more than 3-fold over the rain-fed stand. This increase was associated by improvement in the plant survival. Of the five species evaluated, the two saltbushes A. halimus and A. leucoclada produced exceptionally high yield. This study suggested that there is a great potential for the use of native range species as efficient alternatives for the high water demanding traditional forages in arid regions. Key words: Forage yield, range plants, supplementary irrigation. INTRODUCTION It is estimated that about 216,000 ha of agricultural lands in Saudi Arabia are currently cultivated with forage crops, producing nearly 326,000 tons per year (Ministry of Agriculture and Water, 2002). The main forage crops are alfalfa and rhodesgrass. The most important limitation to forage crop production is their high demand for the already scarce water resources. With incessant increase in demand for red meat, the demand for forage production will continue to increase. It is estimated that average national demand from alfalfa and rhodesgrass is over 2 million tons/ year (Alabdulkader et al., 2012). It is estimated that alfalfa requires 30,000 to 37,000 m

Evaluation of genetic diversity of Panicum turgidum Forssk from Saudi Arabia

The genetic diversity of 177 accessions of Panicum turgidum Forssk, representing ten populations collected from four geographical regions in Saudi Arabia, was analyzed using amplified fragment length polymorphism (AFLP) markers. A set of four primer-pairs with two/three selective nucleotides scored 836 AFLP amplified fragments (putative loci/genome landmarks), all of which were polymorphic. Populations collected from the southern region of the country showed the highest genetic diversity parameters, whereas those collected from the central regions showed the lowest values. Analysis of molecular variance (AMOVA) revealed that 78% of the genetic variability was attributable to differences within populations. Pairwise values for population differentiation and genetic structure were statistically significant for all variances. The UPGMA dendrogram, validated by principal coordinate analysis-grouped accessions, corresponded to the geographical origin of the accessions. Mantel’s test showed that there was a significant correlation between the genetic and geographical distances (r = 0.35, P < 0.04). In summary, the AFLP assay demonstrated the existence of substantial genetic variation in P. turgidum. The relationship between the genetic diversity and geographical source of P. turgidum populations of Saudi Arabia, as revealed through this comprehensive study, will enable effective resource management and restoration of new areas without compromising adaptation and genetic diversity.

Impact of off-road vehicles on soil and vegetation in a desert rangeland in Saudi Arabia

Off-road vehicle driving is considered as main contributor to land degradation in arid regions. This study examined the impact of off-road vehicles (ORV) on soil and vegetation in a natural recreational desert meadow of Raudhat Khuraim, Saudi Arabia. Vegetation canopy cover and plant height away from road tracks were assessed. Also, species density and canopy cover, bare ground cover and soil attributes were assessed in four microhabitats; tracks, inter-tracks, verges, and away from vehicle tracks (undisturbed natural areas). Results show that the cover of forbs and grasses was negatively associated with distance from road verges. It was observed that the height of woody species responded negatively to distance away from tracks. Cover of native species decreased under verge, inter-track and track microhabitats giving more opportunity for weeds to flourish. Bare ground was highest (60.7%) in tracks. ORV impact on soil bulk density was clear with an increase of 38% under tracks compared to soils of undisturbed natural vegetation and a similar decrease in porosity was observed. On the other hand, soil electrical conductivity was significantly higher (5.45 mS cm−1) under disturbance compared to 1.32 mS cm−1 in undisturbed natural vegetation. Organic matter and nitrogen were not affected significantly by ORV disturbance. The results emphasize that managing off-road vehicle driving is essential for conserving native vegetation.

Molecular and phytochemical analysis of wild type and olive cultivars grown under Saudi Arabian environment

This study aimed to assess genetic variability at molecular and phytochemical levels among the four most commonly grown olive cultivars and the wild-type olive of Saudi Arabia. Sixty-six and 80 amplicons were generated from 9 random amplified polymorphic DNA (RAPD) and inter simple sequence repeats (ISSR) primers, each, producing an average of 95.9 and 86.44% polymorphism for the two markers, respectively. The PIC values were 82.2% for the RAPD and 85.4% for the ISSR markers and the discrimination power for both the markers was 11.1%. The UPGMA cluster analysis based on the RAPD and ISSR data resulted in the aggregation of cultivars and wild accession with a good bootstrapping value according to their origin. Furthermore, a total of 199 compounds were identified in the cultivars based on peak area, retention time, and molecular formula using GC–MS analyses of methanolic and ethanolic extracts. These compounds were classified according to their chemical class; most of them were fatty acids, alcoholic compounds, carboxylic acids, aldehydes, heterocyclic compounds, ketones, alkanes, and phenols. Genetic and phytochemical distances were significantly correlated, based on the Mantel test. The Saudi wild accession also had high numbers of fatty acids and their esters, and can be used in breeding programs for generating new genotypes with interesting characters.

Vegetation and condition of arid rangeland ecosystem in Central Saudi Arabia

Saudi Arabia rangeland ecosystems have undergone intense processes of degradation for many decades because of extreme climate and human activities such as overgrazing and socioeconomic changes. In this study, Hail and Qassim Regions of Saudi Arabia covering an area about 79610.73 km2 were selected to study the rangeland vegetation and condition. Haloxylon salicornicum was the most dominant species, covering more than 56% of the total area. The second prominent community was Acacia-Lycium shawii, which covers about 21% of total area. It was found that about 65% of vegetation in the surveyed area is in good or very good condition compared with about 31% in poor or deteriorated condition. Effective measures such as determination of carrying capacities and development of grazing systems have to be implemented to ensure resources sustainably.