Vegetation–environment relationship and floristic diversity of Wadi Al-Sharaea, Makkah Province, Saudi Arabia

Alien Plant Invasions of the Natural Habitat in the Western Region of Saudi Arabia: Floristic Diversity and Vegetation Structure

The western region of Saudi Arabia is a major vegetation diversity hotspot with wide range of habitats and variant climatic and topographical characteristics. The vegetation diversity in this region has not been fully studied to monitor the changes that happen over time in these habitats. This study aims to identify the floristic diversity and vegetation structure of the plant species in invaded habitats of the western region of Saudi Arabia. A total of 58 stands in the different invaded habitats (i.e., mountains, protected areas “ridge mountain habitat”, wadis, farmlands, ruderal areas, and coastal areas) were examined. A total of 146 plant species (94 native and 52 alien species) distributed among 132 genera and 49 families were recorded. Asteraceae, Poaceae, and Fabaceae were the most represented families and accounted for approximately 35% of the identified species. Multivariate analysis of the identified species clustered them into four main vegetation groups: VG I dominated by Opuntia ficus-indica-Juniperus phoenicea, VG II dominated by Reichardia tingitana-Heliotropium aegyptiacum, VG III dominated by Prosopis juliflora-Acacia seyal-Abutilon pannosum, and VG IV dominated by Suaeda monoica. The ecological information represented in this study may help in monitoring the changes in vegetation diversity across the western region of Saudi Arabia and designing the required conservation plans.

Soils with more clay and dense vegetation were rich in soil carbon along Wadi Al-Sharaea, Makkah, Saudi Arabia

In arid ecosystems, lack of vegetation and nutrients can negatively impact soil carbon (C) content. In the current study, our goals were to assess soil C stocks to a depth of 50 cm in an arid ecosystem (Wadi Al-Sharaea, Saudi Arabia) and determine their relation to different vegetation cover. To address our research objective, a total of 102 quadrate (randomly selected) were established along the desert wadi. Soil samples were collected to a depth of 50 cm with 5 cm interval, then Soil Bulk Density (SBD, g/cm³), Soil Organic C Content (SOC, g C/kg), and stocks (kg C/m²) were estimated. Both soil mechanical and chemical analyses were conducted for a composite soil sample. Study sites were categorized based on their visual vegetation cover (VC) percentage (%) into three major groups: 1) scarce vegetation cover (VC less than 25%); 2) medium vegetation cover (VC is higher than 25% and less than 75%); and lastly 3) dense vegetation cover (VC is higher than 75%). Soils were characterized by higher sand content (48.2%, both fine and coarse compiled) than silt (36.7 ± 1.64%) or clay (10.1 ± 1.28%). There were significant differences among soil Calcium (Ca) and Potassium (K) content (p < 0.05), while those plant communities with medium vegetation cover showed the highest soil content of Ca and K (1.7 ± 0.24 and 0.2 ± 0.03 meq/l, respectively). Plant communities with dense vegetation cover had the lowest SBD (1.96 ± 0.03 g/cm³) and the highest SOC stocks (14.9 ± 2.1 kg C/m²). Moreover, our data analyses indicated that SBD and SOC content had strong and negative correlation, where soils with dense vegetation cover had the most significant correlation (R² = 0.95). Our results recommend that soil carbon stocks to a depth of 50 cm based on different vegetation cover of arid ecosystems should be implemented on global soil carbon budget to better elucidate factors controlling SOC content at the regional and global scales.

Do Spatially Structured Soil Variables Influence the Plant Diversity in Tabuk Arid Region, Saudi Arabia?

Plant diversity is affected by spatial variables as well as soil physical and chemical variables. In this study, plant species and soil variables were investigated in five sites of Tabuk Province (Saudi Arabia), namely Aldesah, Alzetah, Alawz, Harra and Sharma, to understand if the spatially structured soil variables (pH, electric conductivity (EC), soil texture, calcium, potassium, phosphorus, phosphate, total organic matter (OM), bicarbonate and sodium) influence the plant diversity. A total of 163 plant species belong to 41 families and 124 genera were reported from the 5 sites. Diversity indices including the species richness (alpha), evenness, Brillouin, Menhinick, Margalef, equitability and estimated Chao-1 were significantly different among the studied sites with pronounced high values in Sharma and Aldesah. The highest value of beta diversity was reported in Aldesah (0.253) followed by Sharma (0.171). According to the principal coordinates of neighbourhood matrix (PCNM) analysis, 11 positive spatial vectors (variables) were found. However, after running the forward selection procedures (using 2 stopping criteria), only 3 spatial vectors were retained (PCNM 1 (adj–R2 = 0.043, F = 5.201, p = 0.004), PCNM 2 (adj–R2 = 0.027, F = 3.97, p = 0.006) and PCNM 3 (adj–R2 = 0.019, F = 3.36, p = 0.007)). The linear models between the selected spatial variables (PCNM vectors) and soil variables were produced to investigate their spatial structure. In the first model, the first PCNM 1 axis showed significant relationship with pH and potassium (adj–R2 = 0.175, p = 0.046). In the second model, the second PCNM 2 axis had a significant relationship with OM and sodium (adj–R2 = 0.561, p < 0.001). Lastly, sodium was the only factor significantly correlated with the third PCNM 3 axis (adj–R2 = 0.365, p = 0.002). In conclusion, the spatially structured variables of soil did not show strong influence on plant diversity except pH and potassium, which were correlated with PCNM 1, OM and sodium, which were correlated with PCNM 2, and sodium, which was correlated with PCNM 3.