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Patterns of vegetation diversity and soil carbon storage along a transect from Al-Madinah Al-Munawwarah to Al-Rayis in the Hijaz Mountains, Saudi Arabia
*Corresponding author: E-mail address: 444204175@student.ksu.edu.sa (N Al-Shugairan)
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Received: ,
Accepted: ,
Abstract
Vegetation surveys along ecological transects are widely used to capture changes in species composition and environmental gradients across landscapes. This method is particularly valuable in arid regions, where vegetation patterns respond sensitively to soil and climatic variation. This study aims to assess the floristic composition, vegetation diversity, their environmental relationships, and soil carbon stocks along the Madinah-Rayis transect. The study covered 33 sites along the transect during the period from December 2023 to March 2023. Plant species and floral diversity were documented, and soil samples were collected and analyzed. Multivariate analysis using TWINSPAN, DECORANA, and CANACO programs was performed to determine plant communities and their relationship with environmental factors. For each community, Pearson correlation, diversity index (α,Υ), Simpson index, and Shannon index were calculated. This study also assessed the vertical distribution of soil organic carbon (SOC) content, soil bulk density (SBD), and SOC density in soil of all habitats along the transect, and carbon storage was estimated. The study region recorded 180 plant species across 112 genera from 33 different families. Five plant communities were characterized after application of TWINSPAN - VGI: Zygophyllum qatarense - Halocnemum strobilaceum, VGII: Cenchrus ciliaris - Dipterygium glaucum, VGIII: Vachellia flava - Zygophyllum simplex, VGIV: Lycium shawii - Aizoon canariense, and VGV: Aerva javanica -Aizoon canariense. Soil organic carbon storage varied significantly across habitats and vegetation groups. Abandoned farms exhibited the highest SOC content, likely due to organic inputs from litter and roots, while sand dunes had the lowest. Soil organic carbon (SOC) had shown a significant correlation with Simpson index (R2 = 0.728, p ≤ 0.05). The findings of this study are crucial for preserving the plant community diversity within the transect ecosystem in Madinah.
Keywords
Carbon storage
Diversity indices
Plant communities
Soil organic carbon
Transect ecosystem
1. Introduction
The Hijaz Mountains in Western Saudi Arabia constitute a distinct biogeographical area where notable variations in vegetation types, unique habitats, home of many endemics, endangered and rare species, and ecosystem functioning can be seen due to topographic variability, inconsistent precipitation, and a variety of soil types (Hofland et al., 2024). The western region of Saudi Arabia, with its diverse habitats such as mountains, coastal plains (Tihamah), desert plains, and wadis, is considered among the richest regions of plant diversity in the kingdom of Saudi Arabia (Kutby et al., 2025; Al-Namazi et al., 2021). Vegetation in arid and semi-arid environments not only provides habitat and forage but also significantly influences soil properties, including organic carbon storage, through litter input, root turnover, and soil stabilization (Chenchouni and Neffar, 2022). Despite their harsh climatic conditions, Saudi Arabia has an extensive flora with 835 genera represented by about 2,250 plant species (Al-Aklabi et al., 2016; Alharthi et al., 2023). The vegetation in Saudi Arabia has been affected by several factors, including the topography, climate, soil, and human activities in the formation and distribution of plant communities (Almalki et al., 2022). The transect analysis of vegetation has valuable applications in various socio-economic activities, including nature management and specifically in the sustainable use of natural resources, biodiversity preservation and conservation, as well as identifying global changes in plant cover (De Cáceres et al., 2018).
Soil organic carbon (SOC) is the primary component influencing soil fertility and other environmental issues. Soils represent the largest carbon stores within the terrestrial carbon cycle (Shari et al., 2024; Prabha et al, 2019). SOC substantially influences soil fertility by modifying the physical and chemical characteristics of the soil and liberating nutrients in a form available to plants. The SOC content is usually favored by the balance between supply and decomposition processes over time (Eid and Arshad, 2025). Some research studies at large spatial scales have confirmed that the patterns of SOC retention on soil are mainly controlled by climate, vegetation, and soil conditions (Chen et al., 2018; Yang et al., 2007). It is reported that soils with vegetation have greater carbon sinks when compared with unvegetated, dry soils (El-Sheikh et al, 2018). SOC stocks are disproportionately affected by vegetation patterns in arid regions, where carbon inputs are limited and moisture availability closely controls decomposition rates. There are many reports that increasing vegetation diversity enhances the soil organic carbon storage in different ecosystems, such as wetlands (Liu et al., 2024), forests (Chen et al., 2023), and agricultural ecosystems (Chen et al., 2020). Various plant species, ranging from xerophytic shrubs to halophytic communities on coastal plains, interact with edaphic factors and microclimatic gradients to influence soil carbon turnover and accumulation (Eid et al., 2023). Thus, studying the diversity of plants along environmental gradients offers important information about the biological mechanisms controlling the storage of carbon in dryland ecosystems.
This study focuses on vegetation analysis and carbon storage along the transect from Madinah to Al-Rayis crossing the Hijaz mountains. This transect is important because it consists of several different habitats in the western region, especially from Madinah to Al-Rayis, such as littoral marshes, coastal desert plains, mountains, wadis, and ruderal habitats. Most of these habitats are threatened by human activities. Although many studies were done on Saudi Arabia’s vegetation diversity and floristic structure, there have been few environmental transect studies of vegetation and carbon storage along the Madinah-Al-Rayis transect. Therefore, this study aims to assess the floral diversity, dominant plant communities along the different habitats, environmental factors that affect the vegetation structure, and carbon storage in different soil types along the different habitats of the Madinah-Al-Rayis transect. These study findings might lead to a better knowledge of biodiversity-ecosystem functional linkages in various arid landscapes and provide baseline information relevant to conservation and carbon management strategies in Saudi Arabia.
2. Materials and Methods
2.1 Study area
The study area is located at 23°35′ and 24°22′N and 38°32′ and 39°26′E and rises from 0 m to about 2400 m above sea level (Fig. 1). It is traversed by the Madinah to Al-Rayis Road for a distance of about 200 km. Madinah has various geomorphological units with different habitats, is located in the northern part of the Arabian Shield (Al-Hilal, 2006). The transect from Madinah to Al-Rayis has many phytoecological regions, including the salt marshes in Al-Rayis, the Tihamah coastal plain, the Hejaz mountains mountain range, and the upland plateau that extends eastward from the Hejaz mountains to the interior, where Madinah is located. Each of these sectors comprises various eco-geomorphological units with different habitats (Batanouny & Baeshin, 1983). The vast differences in terrain, rock types, and soil properties clearly impact the water revenue of the various habitats. Consequently, the plant cover exhibits considerable differences from one locality to the other. Because of these variations in the habitats found in the transect, this area has a higher level of plant diversity than other areas (Batanouny & Baeshin, 1983).
- Transect from Al-Madinah Al-Munawwarah to Al-Rayis (Google Earth, 2023).
2.2 Sampling sites and plant collection
Thirty-three stands were selected along the Transect from Al-Madinah to Al-Rayis. The sample procedure was conducted in the spring of 2023, when most species were in high abundance. (Supplementary File 1). Stand area was 50 m2 and chosen to represent the seven habitats of the transect (Four stands on salt marshes, of which one was a mangrove habitat; six stands on sand dunes; six stands on the top of ridge; four stands on the base of ridge; three stands on the slope of ridge; seven stands on the wadi bed and three stands on an abandoned farm) which were selected to represent a wide range of physiographic and environmental variation along the transect (Fig. 2). In each stand, all plants sampling was recorded and soil samples were collected. The collected plant specimens were identified according to (Chaudhary, 1999, 2000, 2001; Collenette, 1999; Migahid, 1996) and deposited in KSU Herbarium. The plant cover of each species in each stand was estimated as abundance percentage values (El-Sheikh et al., 2010; Kent, 2012). In addition, species life forms and chorotypes were determined (Raunkiaer, 1934; Zohary, 1973).
- Distribution of the selected sites in Transect from Al-Madinah Al-Munawwarah to Al-Rayis (Google Earth, 2024).
2.3 Vegetation analysis
For obtaining species cover data, a matrix comprising 33 sample stands × 180 common species cover values, and another matrix including 33 sample stands × 180 species cover values and soil variables were generated. Multivariate analyses were employed on both data sets for classification and ordination of the transect vegetation. The first matrix underwent numerical classification via Two-way indicator species analysis (TWINSPAN) (Hill, 1979b). Detrended correspondence analysis (DECORANA) (Hill, 1979a) was applied to the same first matrix data set in order to obtain an efficient graphical representation of the ecological structure of vegetation groups identified using TWINSPAN and to verify the identified vegetation units. Canonical Correspondence Analysis (CCA) was used to determine any relationship between vegetation associations and environmental variables (El-Sheikh et al., 2010) by using the CANOCO software according to (Ter Braak & Smilaeur, 2002).
2.4 Plant diversity analysis
Ecologically relevant diversity indices were measured for the identified vegetation groups in the transect. The transect plant diversity and its populations were studied by measuring alpha (α) and gamma (ϒ) diversity. For each vegetation group and habitat, Species richness (α diversity) was determined by calculating the average number of species per stand, i.e., α diversity = No of sp./log A area. Gamma species diversity (ϒ-diversity) was calculated as the total number in each vegetation group. The Shannon-Wiener index “Ĥ “ and the Simpson index “ were calculated (Magurran, 1988; Pielou, 1975).
2.5 Soil analysis and carbon storage in soil
Soil samples were obtained from three random locations inside each stand at a depth of 0-20 cm and subsequently combined into a single sample per stand. The hydrometer method (Bouyoucos, 1962) was employed to determine soil texture. Soil moisture was assessed by drying in a convection oven at 105°C. Organic matter was quantified using soil combustion at 600°C for 4 h. A soil water extract was made (1:5) by adding 20 g of dry soil to 100 mL of deionized water for estimating pH and electrical conductivity (EC) in mmohs/cm by means of a pH/EC meter.
Soil nutrient elements such as calcium, potassium, sodium, magnesium and iron were determined using ICP-MS (Inductively coupled plasma – mass spectrometry, model nexion 300D). Nitrogen and phosphorous were determined using UV- visible spectrophotometer and their concentration were expressed in mg/l (Allen et al., 1986).
To evaluate soil carbon storage, soil samples were collected as a monolayer at a depth of 20 cm using a soil auger, as this is the most biologically active and accessible soil layer in this habitat. The study area was distinguished by extremely hard, compacted soils that prohibit deeper sampling and confine most plant roots, particularly herbs and shrubs, to the upper soil profile. Soil samples were then desiccated in an oven at 105°C for 72 h and subsequently weighed to ascertain the SBD (g cm−3) (Wilke, 2005), employing the equation: ρi = mi/vi, where ρi, mi, and vi represent the SBD, soil mass, and soil volume of the ith layer, respectively. Dried soil samples were tested for SOC content by measuring the SOM using the loss-on-ignition method at 5500C for 2 hours (Jones, 2001). SOM was converted to SOC using the equation, specifically designed for this calculation: SOC = 0.21 × SOM1.12. Further, SOC stock, which is quantified as mass per unit surface area to a specified depth, was calculated (Meersmans et al., 2008), using the equation: where SOCs is the SOC stock in soils (t C ha−1), ρi, SOCi, and Ti are SBD, SOC content, and thickness of the ith layer, respectively, k is the number of layers, and Dr is the reference depth.
2.6 Statistical analysis
Multivariate analysis using TWINSPAN, DCA, and CCA was used to evaluate the cover estimations. The SBD and SOC values were subjected to a two-way ANOVA using SPSS® Statistics 28, with site and depth serving as the two independent variables. To analyze the variations in the examined parameters across different locations, one-way ANOVA was utilized. The differences between means were assessed using Duncan’s multiple range test (p < 0.05). Pearson’s correlation analysis was employed to evaluate the relationship between SBD and SOC.
3. Results
3.1 Floristic diversity
A total of 180 species belonging to 112 genera and 33 families were recorded from different stands (Supplementary File 2). The species-to-genus ratio in the study area was found to be 1.61. The most abundant family was Poaceae with 25 different species (14%), followed by Fabaceae with 24 different species (13.3%) and Brassicaceae with 16 species (9%) (Fig. 3). There were several families, which were represented by only a single species (0.56%) such as, Aizoaceae, Asphodelaceae, Urticaceae, Rubiaceae, Neuradaceae and Apiaceae.
- Plant families of the recorded species in the transect vegetation.
3.2 Plant life forms
The predominant life forms identified were annual herbs (39%), followed by perennial herbs (17%), shrubs (15%), subshrubs (11%), annual grasses (7%), and perennial grasses (7%). Trees were by far the least, representing only 4% of the entire species (Fig. 4). Regarding the chorotypes, mono-regional elements comprised the largest proportion of species at 55.56%, followed by bi-regional elements at 34.44%, while pleuri-regional elements accounted for the least share at 10% (Fig. 5). Among the monoregionals, the Saharo-Arabian region (18.89%) has the highest share of species, followed by the tropical region (11.67%). The high value of bi-regional elements belongs to the Saharo Arabian-Irano Turanian (8.89%) and Mediterranean-Irano Turanian (6.67%). Among the pleuri-regional elements, Mediterranean-Saharo Arabian-Irano Turanian (4.44%) and Mediterranean-Euro Siberian- Irano Turanian (2.22%) elements dominated.
- Life forms of the recorded species in the transect vegetation.
- Chorotypes of the recorded species in the Transect vegetation Am= America; COSM: Cosmopolitan; ES: Europe-Siberian; IT: Irano Turanian; Med: Mediterranean; SA: Saharo Arabian; SH: Sahelian; SM: Somalia Masai; TR: Tropical; AF: African; SZ: Sudano-Zambezian; SU: Sudano.
3.3. Vegetation composition
3.3.1 Plant communities
The application of TWINSPAN dendrogram divided the data set into five vegetation groups separated at level 4 (Fig. 6a). These five groups were characterized and named after the dominant and subdominant species as VGI: Zygophyllum qatarense - Halocnemum strobilaceum, VGII: Cenchrus ciliaris - Dipterygium glaucum, VGIII: Vachellia flava- Zygophyllum simplex, VGIV: Lycium shawii - Aizoon canariense, VGV: Aerva javanica -Aizoon canariense. The application of DCA confirmed the separation among these communities (Table 1; Fig. 6b). The VGI: Zygophyllum qatarense - Halocnemum strobilaceum community consists of 3 stands (9.37%) of the total number of sample stands, which inhabit sand dunes (33%) and salt marshes (67%). The plants associated with this community were Astragalus vogelii (P=33, C=5%), Dipterygium glaucum (P=33, C=3.3%), Erodium laciniatum (P=33, C=2%), Stipagrostis plumosa (P=33, C=1.6%), Halopeplis perfoliata (P=33, C=1%) and Suaeda divaricata (P=33, C=0.3%). The VG II: Cenchrus ciliaris - Dipterygium glaucum community consists of 6 stands (18.8%) of the total number of sample stands, which inhabit the sand dunes (66%), the slope of the ridge (17%), and the foothill (17%). The plants associated with this community were Zygophyllum simplex (p=100; C=10%), Panicum turgidum (P=67; C=4.6%), Tribulus terrestris (P=50; C=1.8%), Lepidium sativum (P=50; C=1%), Gisekia pharnaceoides (P=50; C=0.5%), Spergularia diandra (P=50; C=0.4%) and Stipa capensis (P=33; C=5.5%). The VG III: Vachellia flava - Zygophyllum simplex community consists of 6 stands (18.8%) of the total number of sample stands, which inhabit the sand dunes (17%), salt marshes (17%), the top of the ridge (17%), the wadi bed (17%), and the abandoned farm (32%). The plants associated with this community were Amaranthus graecizans (p=83, C= 0.7%), Leptadenia pyrotechnica (p=50, C=7.8%), Senna italica (p=50, C=1.8%), Aerva javanica (p=50, C=1.5%), Tribulus terrestris (p=50, C=1.3%), Calotropis procera (p=50, C=0.8%) and Cenchrus ciliaris (p=50, C= 0.7%). The VG IV: Lycium shawii - Aizoon canariense community consists of 13 stands (40.6%) of the total number of sample stands, which inhabits the top of ridge (38%), foothill (24%), and the wadi bed (38%). The plants associated with this community were Forsskaolea tenacissima (p=92, C=3.4%), Rumex vesicarius (p=85, C=2.3%), Aristida adscensionis (p=69, C=1.5%), Picris babylonica (p=69, C=0.8%), Blepharis ciliaris (p=54, C=4.1%), Aerva javanica (p=54, C=0.9%) and Asphodelus tenuifolius (p=46, C=0.8%). The VG V: Aerva javanica -Aizoon canariense community consists of 4 stands (12.5%) of the total number of sample stands, which inhabit the slope of the ridge (50%), the wadi bed (25%), and the abandoned farms (25%). The plants associated with this community were Zygophyllum simplex (P=100, C=23%), Forsskaolea tenacissima (P=100, C=4%), Asphodelus tenuifolius (P=75, C=2.7%), Vachellia tortilis (P=75, C=6.2%), Maerua crassifolia (P=50, C=5%), Tribulus terrestris (P=50, C=1.3%), and Citrullus colocynthis (P=50, C=1.25%).
- Relationship between the five plant communities after the application of the (a) TWINSPAN and (b) DCA.
| VG | Sites % | Stands No. | Habitat % | 1st dominant sp | C% | P% | 2nd dominant sp | C% | P% |
|---|---|---|---|---|---|---|---|---|---|
| VG I | 9 | 1, 2, 23 | Sand dunes = 33, Salt marshes = 67 | Zygophyllum qatarense | 5 | 67 | Halocnemum strobilaceum | 3 | 33 |
| VG II | 19 | 5, 6, 9, 20. 21, 22 | Sand dunes =66, Slope of ridges = 17, Foothills = 17 | Cenchrus ciliaris | 4 | 50 | Dipterygium glaucum | 1.3 | 50 |
| VG III | 19 | 3, 4,7, 8, 16, 18 | Sand dunes = 17, Salt marshes = 17, Top of ridges =17, Wadi beds = 17, Abandoned farms =32 | Vachellia flava | 10 | 83 | Zygophyllum simplex | 3 | 83 |
| VG IV | 40 | 10, 12, 13, 14, 17, 25, 26, 27, 28, 29, 30, 31, 32 | Top of ridges = 38, Foothills = 24, Wadi beds = 38 | Lycium shawii | 3 | 62 | Aizoon canariense | 3 | 85 |
| VG V | 13 | 11, 15, 19, 24 | Slope of ridges = 50, Wadi beds = 25, Abandoned farms = 25 | Aerva javanica | 0.4 | 50 | Aizoon canariense | 6 | 75 |
To validate the correlation analysis between the environmental variables and DCA axes, Canonical Correspondence Analysis (CCA) was performed using the CANOCO software. (Table 2; Figs. 7a and b). Correlation studies have demonstrated that the separation of stands along the second axis is significantly influenced in a positive manner by the Simpson index, Na, P, Ca, Mn and N (r=-0.3973*, 0.4553**, 0.4163*, 0.3569*, 0.3285* and 0.4742**) respectively, while the species evenness and shannon index correlated negatively with that axis (r=-0.3950* and -0.3904* respectively). In addition, the species numbers were correlated negatively with the first axis (r=-0.3299*). The distribution of grass species was seen on the lower negative side of the axis 1 and correlated with species numbers, species cover, silt, and clay (Fig. 7b). On the other hand, the woody species were seen on the lower positive side of the axis 1 with Evenness. Halophytes such as, Halocnemum strobilaceum, Zygophyllum qatarense, Aeluropus lagopoides, Fagonia mollis, Asphodelus tenuifolius and Pergularia tomentosa were seen on the upper positive side of the axis 2 and correlated with Simpson index, pH, sand, salinity, and Na content.
| No: | NAME | AX1 | AX2 | AX3 | AX4 |
|---|---|---|---|---|---|
| 1 | Sp. number | -0.3299* | -0.2364 | 0.0796 | 0.2878 |
| 2 | Total cover (m/100m) | -0.2938 | 0.0685 | -0.1584 | -0.3691 |
| 3 | Sp. Richness | -0.2930 | -0.2445 | 0.0970 | 0.3799 |
| 4 | Sp. Evenness | 0.0305 | -0.3950* | 0.2605 | 0.5147 |
| 5 | Shannon index (H) | -0.2733 | -0.3904* | 0.1954 | 0.5233 |
| 6 | Simpson index (C) | 0.2142 | 0.3973* | -0.2394 | -0.5387 |
| 7 | Organic matter (OM) % | 0.0965 | 0.0812 | 0.3952 | -0.2899 |
| 8 | E.C. (m.mhos/cm) | 0.2017 | 0.0226 | -0.0526 | 0.1110 |
| 9 | pH | 0.0291 | -0.0853 | 0.1450 | 0.1723 |
| 10 | TDS (ppm) | 0.1989 | 0.0216 | -0.0528 | 0.1103 |
| 11 | Sand (%) | 0.1185 | -0.0033 | -0.1259 | -0.0844 |
| 12 | Silt (%) | -0.1038 | -0.0323 | 0.0193 | 0.1180 |
| 13 | Clay (%) | -0.0916 | 0.0682 | 0.2671 | -0.0172 |
| 14 | Na (mg/L) | 0.0633 | 0.4553** | 0.0608 | 0.0302 |
| 15 | Mg (mg/L) | 0.3092 | 0.2717 | 0.0232 | 0.0480 |
| 16 | P (mg/L) | -0.1070 | 0.4163* | -0.2489 | 0.2246 |
| 17 | K (mg/L) | -0.1164 | -0.3419 | 0.0900 | 0.4598 |
| 18 | Ca (mg/L) | 0.1924 | 0.3569* | 0.0691 | 0.0285 |
| 19 | Mn (mg/L) | 0.1388 | 0.3285* | -0.4413 | -0.1886 |
| 20 | Fe (mg/L) | -0.1096 | 0.2854 | 0.2757 | 0.1675 |
| 21 | N (mg/L) | 0.0823 | 0.4742** | 0.0524 | 0.0255 |
- CCA biplot with environmental variables (arrows), the stands (a) and the abundant species represented by the first 4 letters of genus and species name (b). (For complete names of species, see Supplementary File 2).
3.4 Plant diversity – soil factors relationship
The correlation study between plant diversity and soil factors indicated a significant positive correlation of species numbers with silt (r=0.404*) and a negative correlation with Mg and Mn content (r=-0.351*, -0.346*). Additionally, species cover exhibited a positive correlation with silt (r=0.379*) and a negative correlation with pH (r=-0.403*). Shannon index was correlated positively with K content (r=0.396*) and negatively with Mn content (r=-0.469**). Simpson index was correlated with organic matter OM, Ca, and Mg content (r= 0.359*, 0.361*, and 0.435* respectively) and negatively with K content (r=-0.398*), while, species richness was negatively correlated with Mg and Mn (r=-0.371*, -0.367*) (Fig. 8).
- Heat map showing the pearson correlation between plant diversity and soil factors.
3.5 Soil characteristics of vegetation groups
The VG I: Zygophyllum qatarense - Halocnemum strobilaceum community that inhabits the sand dunes and salt marshes had the highest value for Simpson index, organic matter, TDS, salinity, N, Ca, Mg, Na and Mn content (0.51, 3.19, 3165, 6418, 3.38, 12.5, 10.8, 13.3 and 6.7 respectively) and lowest values for number of species, species cover, richness, Evenness, Shannon index and P content (6, 36.3, 1.34. 0.54.0.47 and 10.9 respectively) (Table 3). The VG II: Cenchrus ciliaris - Dipterygium glaucum community that inhabits the sand dunes, slope of ridge, and foothills has shown higher values for species cover, clay, and K (77.5, 18, and 16.5 respectively) and lowest values for sand (64.2). The VG III: Vachellia flava - Zygophyllum simplex community that inhabits the sand dunes, salt marshes, top of ridge, wadi bed, and abandoned farms has the higher value of P and Fe content (11.2 and 6.97) and lower values of pH and K content (7.77 and 11.4). The VG IV: Lycium shawii - Aizoon canariense community that inhabits the top of the ridge, foothill, and wadi bed had the higher values of sand (75.4) and lower values of Simpson index, silt, clay, and Mn (0.16, 10.8, 13.8, and 5.92 respectively). The VG V: Aerva javanica -Aizoon canariense community which inhabits the slope of ridge, wadi bed and abandoned farm had the highest values for number of species, shannon index, evenness, richness, pH and silt (21.5, 1.05, 0.8, 4.78, 8.2 and 19.8 respectively) and lowest values for organic matter, TDS, salinity, N, Ca, Mg, Na and Fe content (1.62, 42.2, 84.2, 0.3, 3.13, 3.03, 3.7 and 6.3 respectively).
| Soil features | VG I | VG II | VG III | VG IV | VG V | Mean | F- value | P- value |
|---|---|---|---|---|---|---|---|---|
| Sand % | 73.3±12.47 | 64.25±14.42 | 73.83±12.35 | 75.4±12.38 | 64.93±21.53 | 71.63 | 0.947 | 0.452 |
| Silt % | 12.33±9.58 | 17.75±10.46 | 10.82±6.38 | 10.8±8.87 | 19.88±19.1 | 13.31 | 0.961 | 0.444 |
| Clay % | 14.37±2.89 | 18±7.64 | 15.35±11.11 | 13.8±4.41 | 15.2±5 | 15.07 | 0.425 | 0.789 |
| Organic matter % | 3.19±0.78 | 2.3±1.33 | 1.76±0.91 | 1.69±1.24 | 1.62±1.32 | 1.94 | 1.231 | 0.320 |
| TDS ppm | 3165.33±2606.16 | 1955.83±4626.74 | 141±215.22 | 113.86±187.04 | 42.25±15.22 | 722.42 | 2.083 | 0.110 |
| E.C mmohs/cm | 6418.33±5285.64 | 3911.83±9253.39 | 281.33±430.46 | 226.57±375.54 | 84.25±32.67 | 1452.21 | 2.114 | 0.106 |
| pH | 8.02±0.08 | 7.94±0.53 | 7.77±0.68 | 8.1±0.37 | 8.2±0.21 | 8.01 | 0.779 | 0.548 |
| N (mg/L) | 3.38±2.45 | 1.93±4.05 | 0.3±0.08 | 0.76±1.74 | 0.3±0.06 | 1.07 | 1.458 | 0.241 |
| P (mg/L) | 10.96±1.49 | 11.22±1.72 | 11.27±2.31 | 11.1±2.55 | 11.01±2.12 | 11.13 | 0.016 | 0.999 |
| K (mg/L) | 13.77±15.5 | 16.57±7.29 | 11.47±5.17 | 13.44±5.21 | 14.73±2.41 | 13.84 | 0.469 | 0.758 |
| Ca (mg/L) | 12.51±7.98 | 7.67±10.37 | 4.35±2.12 | 4.19±3.08 | 3.13±1.03 | 5.48 | 1.978 | 0.125 |
| Mg (mg/L) | 10.87±6.52 | 6.06±6.84 | 3.95±2.24 | 3.46±1.42 | 3.03±0.6 | 4.64 | 3.035 | 0.034* |
| Na (mg/L) | 13.28±7.26 | 10.83±15.13 | 5.2±1.65 | 5.95±6.07 | 3.71±0.99 | 7.09 | 1.140 | 0.358 |
| Fe (mg/L) | 6.56±0.58 | 6.81±0.87 | 6.97±1.17 | 6.7±1.24 | 6.3±1.36 | 6.71 | 0.232 | 0.918 |
| Mn (mg/L) | 6.7±2.11 | 6.56±0.84 | 6.07±1.26 | 5.92±1.4 | 6.43±1.53 | 6.20 | 0.384 | 0.818 |
| Sp no. | 6±6.24 | 17.83±4.26 | 13±6.32 | 18.43±4.16 | 21.5±9.4 | 16.58 | 4.617 | 0.005** |
| Total cover | 36.33±27.06 | 77.5±19.95 | 61.17±28.26 | 75.21±27.09 | 76.25±32.55 | 69.67 | 1.645 | 0.191 |
| Sp. richness | 1.34±1.44 | 3.9±0.95 | 2.88±1.36 | 4.13±1.16 | 4.78±2.01 | 3.68 | 4.149 | 0.009** |
| Evenness | 0.54±0.47 | 0.74±0.11 | 0.72±0.11 | 0.79±0.11 | 0.8±0.17 | 0.75 | 1.455 | 0.242 |
| Shannon H (log10) | 0.47±0.48 | 0.93±0.21 | 0.74±0.19 | 0.99±0.19 | 1.05±0.31 | 0.89 | 3.983 | 0.011* |
| Simpson C | 0.51±0.44 | 0.19±0.1 | 0.28±0.11 | 0.16±0.09 | 0.17±0.16 | 0.22 | 3.582 | 0.018* |
3.6 Carbon storage in soil
3.6.1 SBD, SOC, SOC density, and SOC stock in various habitats
The soil bulk density (SBD) varied from 0.71 – 0.92 g/cm3 in the various study habitats. Sand dune habitat had the highest SBD (0.92 ± 0.06 g/cm3), followed by salt marsh habitat (0.91 ± 0.02 g/cm3), while abandoned farm habitat had the lowest SBD (0.71 ± 0.15 g/cm3). The SOC density varied significantly, ranging from (6.22±3.02 kg C/m3) in the sand dune to 13.85±4.27 kg C/m3 in the abandoned farms. The soil organic carbon (SOC), which is the measure of carbon concentration, was highest in abandoned farm (18.36±7.76) and lowest in sand dune (6.73±3.14). The results indicated that the top of ridge stored the largest (1.22 t C/ha) amount of carbon per hectare of any individual habitat type while the slope of ridge had the lowest carbon stock (0.38 t C/ha) (Table 4).
| Habitats | SBD (g cm3) | SOC (g C/kg) | SOC density (kg C/m3) | SOC stock (t C/ha) |
|---|---|---|---|---|
| Salt marsh | 0.91±0.02 | 11.23±1.75 | 10.15±1.45 | 0.73 |
| Sand dune | 0.92±0.06 | 6.73±3.14 | 6.22±3.02 | 0.67 |
| Top of ridge | 0.86±0.07 | 13.6±7.62 | 11.3±5.61 | 1.22 |
| Slope of ridge | 0.84±0.12 | 8.73±3.83 | 7.06±2.13 | 0.38 |
| Foothill | 0.87±0.11 | 12.95±10.55 | 10.38±6.69 | 0.75 |
| Wadi bed | 0.82±0.1 | 8.4±4.19 | 7.14±4.29 | 0.90 |
| Abandoned farm | 0.71±0.15 | 18.36±7.76 | 13.85±4.27 | 0.75 |
| F-value | 1.161 | 1.706 | 1.802 | 1.747 |
| P-value | 0.357 | 0.159 | 0.138 | 0.15 |
3.6.2 SBD, SOC, SOC density, and SOC stock in five vegetation groups
The bulk density of soil (SBD) varied from 0.84 – 0.90 g/cm3 among the five vegetation groups (Table 5). The VGII: Cenchrus ciliaris - Dipterygium glaucum community had the highest SBD (0.90 ± 0.10 g/cm3), followed by VGI: Zygophyllum qatarense - Halocnemum strobilaceum community (0. 89 ± 0.04 g/cm3), while VG IV: Lycium shawii - Aizoon canariense community had the lowest SBD (0. 84 ± 0.09 g/cm3). The SOC was highest (14.19±5.88) in the VGIII: Vachellia flava - Zygophyllum simplex community and lowest (7.85±4.01) in VG II: Cenchrus ciliaris - Dipterygium glaucum community. The soil organic carbon density (SOC density) varied from 6.92±3.28 kg C/m3 in the VG II: Cenchrus ciliaris - Dipterygium glaucum community to 11.9±4 kg C/m3 in the VG III: Vachellia flava - Zygophyllum simplex community. Significant variations in SOC stock were found among the five vegetation groups. The results indicated that the VG IV: Lycium shawii - Aizoon canariense community stored the largest (2.04 t C/ha) amount of carbon per hectare while the VG V: Aerva javanica -Aizoon canariense community stored the least carbon of all vegetation groups sampled (0.38 t C/ha).
| VG | SBD (g cm3) | SOC (g C/kg) | SOC density (kg C/m3) | SOC stock (t C/ha) |
|---|---|---|---|---|
| VGI | 0.89±0.04 | 10.36±2.26 | 9.26±2.2 | 0.67 |
| VGII | 0.90±0.10 | 7.85±4.01 | 6.92±3.28 | 0.75 |
| VGIII | 0.87±0.10 | 14.19±5.88 | 11.9±4 | 1.29 |
| VGIV | 0.84±0.09 | 10.7±7.63 | 8.74±5.54 | 2.04 |
| VGV | 0.85±0.10 | 11.48±8.9 | 9.11±5.85 | 0.66 |
| F-value | 0.575 | 0.873 | 0.721 | 0.843 |
| P-value | 0.683 | 0.492 | 0.585 | 0.51 |
3.6.3 Relationships between vegetation diversity indices with SBD, SOC, and OM
Soil bulk density (SBD) exhibited no significant correlations with plant diversity indicators, such as Simpson index, Shannon index, evenness, species richness, species number, and total cover (all p≥ 0.05). Soil organic carbon (SOC) had shown a significant positive correlation with simpson index (R2 = 0.728, p ≤ 0.05), but other diversity indices showed weak or non-significant relationships. Conversely, soil organic matter (OM) exhibited no significant relationships with any of the diversity indices (p > 0.05) (Fig. 9).
- Correlation between vegetation diversity indices and (a) soil bulk density; (b) soil organic carbon and (c) soil organic matter.
4. Discussion
In the present study, floristic diversity and vegetation of different habitats along the transect of Madinah to Rayis ecosystem in Madinah, Saudi Arabia, and the relationship between environmental factors that affects the vegetation composition and distribution of plant communities were analyzed. This study has some identical perceptions on the vegetation patterns of the Hijaz Mountains near Al-Madinah, when compared to the study conducted by (Batanouny 1983), which identified 23 plant communities predominantly consisting of trees, shrubs, perennial herbs, and annuals. Our study also provided a broader floristic inventory, documenting 180 species from 112 genera and 33 families, and used multivariate analyses to categorize vegetation and compute diversity indicators. Both results emphasize the impact of soil on vegetation structure and stress the relevance of Vachellia communities, as well as perennial and annual species, in structuring the environment. This study also documented the distribution of soil organic carbon, soil bulk density, and SOC density in soil of all habitats along the transect.
Thirty-six per cent of the total families recorded in this study, were represented by only one genus per species, which is a common feature of desert flora of Saudi Arabia (AlNafie, 2008). This result is similar to other studies, in western part of Saudi Arabia ((Hofland et al., 2024; Alharthi et al., 2023). The floristic composition showed that Fabaceae and Poaceae were the dominant families, which is in line with other studies (Alofi, 2019; Abdel Khalik et al., 2017; Chaudhary & Al-Jowaid, 2013; Migahid, 1996). In this study, annual herbs outnumber other life forms because of their short life span, which helps to withstand ecosystem instability. The study location lies within a dry arid zone, with very hot summers and mild winters. The perennial shrubs and subshrubs are able to withstand aridity, high temperature, and low rainfall (Zahran, 1982). Our results are consistent with earlier research on the arid vegetation in other regions of Saudi Arabia. (Abdel Khalik et al., 2013; Al-Nafie, 2006; Al Mahdi, 2016; Alatar et al., 2012; Alfarhan, 2001; Alharthi et al., 2023; Alofi, 2019; El-Sheikh et al., 2013; Osman et al., 2014). Among the chorotypes, the Saharo -Arabian elements constitute the major floristic structure in the transect since, the location of transect of Madinah to Rayis, is in the Saharo-Arabian region (Zohary, 1973). Wickens (1977) and Boulos (1997) reported that the Saharo-Arabian region is characterized in general by the dominance of shrubs and sub-shrubs, a low number of species, and few endemic species. Saharo -Arabian plant species are good indicators of arid desert environment, while Mediterranean species indicate mesic environment (Alfarhan, 2001; Mandaville, 1990; Zohary, 1973). Similar results were attained by many authors (Alatar et al., 2012; Alatar et al., 2015; Alharthi et al., 2023; El-Sheikh et al., 2013; Hofland et al., 2024). Also, the presence of many bi-regional and multiregional elements in the transect, is because of the location of the study area within the transition zone between Africa, Mediterranean, and Irano-Turanian zones. A sizable portion of the plant species identified in this study have established economic significance. Conserving these indigenous plant communities is essential for ecological balance as well as upholding cultural values.
Five vegetation groups had been recorded in the study area after using the classification and ordination programs (TWINSPAN and DECORANA). Some of these plant communities were comparable with other studies on vegetation diversity in western Saudi Arabia. For example, the Acacia ehrenbergiana (= Vachellia flava) community was reported by Batanouny and Baeshin (1983) while studying the vegetation on Madinah – Badr Road across the Hijaz Mountain. Zygophyllum qatarense was reported by Alharthi et al. (2020), who studied the vegetation on the coastal land of the Red Sea. Halocnemum strobilacem was reported by Elkordy et al. (2022), who studied the vegetation of Jabal Al-Ward in Tabuk. There is also a partial similarity in some plant communities, such as Vachellia spp, Lycium shawii, and Cenchrus ciliaris with other studies in the Najd region (Alatar et al., 2012; El-Sheikh et al., 2013; Alatar et al., 2015). The wadi habitats have been subjected to urbanization, that resulted in the growth of exotic species such as Euphorbia serpens, Euphorbia prostrata, Heliotropium curassavicum, Cenchrus ciliaris, Calotropis procera, and Asphodelus tenuifolius. This is in line with some other studies, which reported that the vegetation in areas affected by humans would have more exotics and annual plants leading to increased species richness and plant cover (Alatar et al., 2012; Alharthi et al., 2023; Shaltout & El-Sheikh, 2002).
Correlation analysis of plant diversity and soil factors in this study specifies that the species numbers showed positively correlation with silt and negative with Mg and Mn content, while, species cover was positively correlated with silt and negatively with pH. The silt soil is appropriate for the growth of woody plants where their long roots can extend deep into the soil to absorb water (Al-Nafie, 2006). Regarding soil pH in the study area, we found that the soil is alkaline. The pH was correlated negatively with species cover, leading to the species diversity increase. These plant species are adaptive to alkaline soils in the dry desert environment. Conversely, if the soil pH is low, it means there is a high relative dominance of plants on the site, and the species diversity decreases. Similar correlations were reported by Alatar et al. (2012), Abdel Khalik et al. (2013), and Alofi (2019).
SBD measurements are often required as an input parameter for models that predict soil processes (El-Sheikh et al., 2018; Heuscher et al., 2005). Furthermore, SBD is used to measure soil strength, porosity, site productivity, and/or mechanical resistance to plant growth (Drewry et al., 2008; Tamminen & Starr, 1994). SBD is influenced by some physical and chemical properties of soil, such as the amount of organic matter, soil texture, constituent minerals, and porosity (Chaudhari et al., 2013). According to data, vegetation cover improves soil quality in abandoned farm habitats, which lowers the SBD. The current study demonstrates that the SBD of the abandoned farm was the lowest of all habitats examined, which could be due to the extensive growth of plant roots that can clearly lower the SBD (Han et al., 2010). Berendse et al (2015) have reported the significance of plant diversity for the reduction of SBD by providing organic matter and protection from erosion processes. Our findings revealed that the soils of abandoned farm habitats had the highest SOC content as compared to other habitats. The increased SOC content in the soil of the abandoned farm is probably because of the local plant growth, primarily from underground roots and litter fall.
Our study shows that vegetation diversity, particularly Simpson’s index, significantly enhances soil organic carbon (SOC) storage. Diversity in vegetation strongly influences the chemical profile of SOC by supplying lignin and carbohydrates. Possible reasons for the variation in SOC density (kg Cm3) are the effects of chemical and physical properties of the soil, such as pH, soil type, and mineral elements, or interference from the external environment, such as species composition, micro-climate, biological activity, and primary productivity (Zhan et al., 2013; Mcleod et al., 2011). Our study findings offer valuable insights for conservation planning, carbon management strategies, and sustainable land-use practices in the fragile ecosystems of western Saudi Arabia.
5. Conclusions
This study examined the floristic composition, plant community structure, and soil carbon dynamics in various habitats along the transect from Al-Madinah Al-Munawwarah to Al-Rayis. A total of 180 plant species from 33 families were documented, with Poaceae and Fabaceae as the predominant families. The life-form spectrum was marked by the dominance of annual herbs indicative of adaptations to the arid environment. Five different plant communities were recorded using multivariate analysis, each linked with particular environmental gradients and soil properties. The storage of soil organic carbon (SOC) shows considerable variation among different environments and vegetation groupings. Abandoned farms demonstrated the highest soil organic carbon (SOC) concentration, presumably due to organic contributions from litter and roots, whereas sand dunes revealed the lowest levels. The research highlights the significant interaction among vegetation diversity, soil characteristics, and soil carbon storage in arid habitats.
Acknowledgement
The authors acknowledge the support from Ongoing Research Funding Program, (ORF-2026-182), King Saud University, Riyadh, Saudi Arabia.
CRediT authorship contribution statement
Nada Al-Shugairan: Conceptualization, sample collection, data collection, experiments, writing – original draft, review and editing; Abdurahman A. Alatar: Conceptualization, data analysis, review and editing; Waleed A. Alsakkaf: Sample collection, data collection, review and editing; Ahmed Qahtan: Software, data analysis, review and editing. Mohamed A. ElSheikh: Conceptualization, design, sample collection, software, data analysis, review and editing.
Declaration of competing interest
The authors declare that they have no competing financial interests or personal relationships that could have influenced the work presented in this paper.
Declaration of generative AI and AI-assisted technologies in the writing process
The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.
Funding
Ongoing Research Funding Program, (ORF-2026-182), King Saud University, Riyadh, Saudi Arabia.
References
- Floristic diversity and vegetation analysis of Wadi Al-Noman, Mecca, Saudi Arabia. Turk J Bot. 2013;37:894-907. https://doi.org/10.3906/bot-1209-56
- [Google Scholar]
- Floristic composition and vegetation: Environmental relationships of Wadi Fatimah, Mecca, Saudi Arabia. Arid Land Res Manag. 2017;31:316-334. https://doi.org/10.1080/15324982.2017.1318188
- [Google Scholar]
- Ruderal Habitats and Plant communities of the Uohod Mountain region of Madinah, Saudi Arabia. Riyadh: MSc Thesis, College of Science, King Saud University; 2016.
- Main vegetation types and plant species diversity along an altitudinal gradient of Al Baha region, Saudi Arabia. Saudi J Biol Sci. 2016;23:687-697. https://doi.org/10.1016/j.sjbs.2016.02.007
- [Google Scholar]
- Vegetation, floristic diversity, and size-classes of Acacia gerrardii in an arid wadi ecosystem. Arid Land Res Manag. 2015;29:335-359. https://doi.org/10.1080/15324982.2014.968692
- [Google Scholar]
- Vegetation analysis of Wadi Al-Jufair, a hyper-arid region in Najd, Saudi Arabia. Saudi J Biol Sci. 2012;19:357-368. https://doi.org/10.1016/j.sjbs.2012.04.003
- [Google Scholar]
- A floristic account on Raudhat Khuraim central province Saudi Arabia. Saudi J Biol Sci. 2001;8:80-103.
- [Google Scholar]
- Remote sensing of 10 years changes in the vegetation cover of the northwestern coastal land of Red Sea, Saudi Arabia. Saudi J Biol Sci. 2020;27:3169-3179. https://doi.org/10.1016/j.sjbs.2020.07.021
- [Google Scholar]
- Biological change of western Saudi Arabia: Alien plants diversity and their relationship with edaphic variables. J King Saud Univ Sci. 2023;35:102496. https://doi.org/10.1016/j.jksus.2022.102496
- [Google Scholar]
- Chemical analysis. In: Moore P. D., Chapman S.B., eds. Methods of Plant Ecology. Oxford: Blackwell scientific publications; 1986.
- [Google Scholar]
- Landforms characterization of Saudi Arabia: Towards a geomorphological map. Int J Appl Earth Observation Geoinformation. 2022;112:102945. https://doi.org/10.1016/j.jag.2022.102945
- [Google Scholar]
- Rawdhat As-Sabalah (A study in biogeography and environmental protection) Saudi Geogr Soc 2006:1-152. (in Arabic)
- [Google Scholar]
- Natural plant species inventory of hotspot areas in Arabian Peninsula: Southwest Al-Baha region, Saudi Arabia. Saudi J Biol Sci. 2021;28:3309-3324. https://doi.org/10.1016/j.sjbs.2021.02.076
- [Google Scholar]
- Wadi Al-Aqiq Ecosystem in Saudi Arabia: Plant Communities Diversity in Relation to Environmental factors. Riyadh: MSc Thesis, College of Science, King Saud University; 2019.
- Plant communities along the medina-badr road across the hejaz mountains, Saudi Arabia. Vegetatio. 1983;53:33-43. https://doi.org/10.1007/bf00039769
- [Google Scholar]
- Loss of plant species diversity reduces soil erosion resistance. Ecosystems. 2015;18:881-888. https://doi.org/10.1007/s10021-015-9869-6
- [Google Scholar]
- Endemic Flora of the middle east and north Africa. In: Barakat H.N., Hegazy A.K., eds. Reviews in ecology: desert conservation and development. Cairo: Metropole; 1997. p. :229-260.
- [Google Scholar]
- Hydrometer method improved for making particle size analyses of soils 1. Agron J. 1962;54:464-465. https://doi.org/10.2134/agronj1962.00021962005400050028x
- [Google Scholar]
- Soil bulk density as related to soil texture, organic matter content and available total nutrients of Coimbatore soil. Int J Sci Res Publications. 2013;3:1-8.
- [Google Scholar]
- Flora of the Kingdom of Saudi Arabia. Vol Vol. 1. Riyadh, KSA: Ministry of Agriculture Water; 1999.
- Flora of the Kingdom of Saudi Arabia. Vol Vol. II, parts 1–3. Riyadh, KSA: Ministry of Agriculture and Water; 2000.
- Flora of the Kingdom of Saudi Arabia. Vol Vol. 2, Parts (1,2,3). Riyadh, KSA: Ministry of Agriculture and Water; 2001.
- Vegetation of Saudi Arabia. Vol Vol. 2nd. National Center for Agricultural Research and Livestock, Ministry of Agriculture; 2013. (in Arabic)
- Plant diversity enhances productivity and soil carbon storage. Proc Natl Acad Sci USA. 2018;115:4027-4032. https://doi.org/10.1073/pnas.1700298114
- [Google Scholar]
- Effects of plant diversity on soil carbon in diverse ecosystems: A global meta-analysis. Biol Rev Camb Philos Soc. 2020;95:167-183. https://doi.org/10.1111/brv.12554
- [Google Scholar]
- Tree diversity increases decadal forest soil carbon and nitrogen accrual. Nature. 2023;618:94-101. https://doi.org/10.1038/s41586-023-05941-9
- [Google Scholar]
- Soil organic carbon stock in arid and semi-arid steppe rangelands of North Africa. CATENA. 2022;211:106004. https://doi.org/10.1016/j.catena.2021.106004
- [Google Scholar]
- Wildflowers of Saudi Arabia. National Commission for Wildlife Conservation and Development (NCWCD); 1999.
- Global overview of plot-based vegetation classification approaches. phyto. 2018;48:101-112. https://doi.org/10.1127/phyto/2018/0256
- [Google Scholar]
- Pasture yield and soil physical property responses to soil compaction from treading and grazing — a review. Soil Res. 2008;46:237-256. https://doi.org/10.1071/sr07125
- [Google Scholar]
- Modelling the distribution of soil organic carbon in polluted and non-polluted areas of mangrove forests (Avicennia marina) Regional Studies in Marine Science. 2025;85:104165. https://doi.org/10.1016/j.rsma.2025.104165
- [Google Scholar]
- Modeling soil organic carbon at coastal sabkhas with different vegetation covers at the red sea coast of Saudi Arabia. JMSE. 2023;11:295. https://doi.org/10.3390/jmse11020295
- [Google Scholar]
- Floristic diversity of jabal Al-Ward, Southwest Tabuk Region, Kingdom of Saudi Arabia. Agronomy. 2022;12:2626. https://doi.org/10.3390/agronomy12112626
- [Google Scholar]
- Vegetation ecology of phytogenic hillocks (nabkhas) in coastal habitats of Jal Az-Zor National Park, Kuwait: Role of patches and edaphic factors. Flora - Morphology, Distribution, Functional Ecol Plants. 2010;205:832-840. https://doi.org/10.1016/j.flora.2010.01.002
- [Google Scholar]
- Distribution of soil organic carbon in Wadi Al-Thulaima, Saudi Arabia: A hyper-arid habitat altered by wastewater reuse. CATENA. 2018;170:266-271. https://doi.org/10.1016/j.catena.2018.06.017
- [Google Scholar]
- Vegetation of thumamah nature park: A managed arid land site in Saudi Arabia. Rend Fis Acc Lincei. 2013;24:349-367. https://doi.org/10.1007/s12210-013-0246-0
- [Google Scholar]
- Estimating soil organic carbon storage and distribution in a catchment of Loess Plateau, China. Geoderma. 2010;154:261-266. https://doi.org/10.1016/j.geoderma.2009.10.011
- [Google Scholar]
- Using soil physical and chemical properties to estimate bulk density. Soil Science Soc of Amer J. 2005;69:51-56. https://doi.org/10.2136/sssaj2005.0051a
- [Google Scholar]
- Decorana-A Fortran program for detrended correspondence analysis and reciprocal averaging. Ithaca: Cornell University; 1979a.
- TWINSPAN-A Fortran program for arranging multivariate data in an ordered two-way table by classification of the individuals and attributes. Ecol Systematics. 1979b;90
- [Google Scholar]
- The vegetation around the foothills of the Hijaz Mountains, Saudi Arabia. Rend Fis Acc Lincei. 2024;35:437-449. https://doi.org/10.1007/s12210-024-01239-8
- [Google Scholar]
- Laboratory guide for conducting soil tests and plant analysis. CRC press; 2001.
- Vegetation description and data analysis: a practical approach. John Wiley Sons; 2012.
- Floristic composition of Shamansir mountain, West Saudi Arabia, as sustainable economic resources. Sci Rep. 2025;15:16800. https://doi.org/10.1038/s41598-025-00441-4
- [Google Scholar]
- Increasing plant diversity enhances soil organic carbon storage in typical wetlands of northern China. Front Plant Sci. 2024;15:1467621. https://doi.org/10.3389/fpls.2024.1467621
- [Google Scholar]
- Ecological Diversity and Its Measurement. Berlin: Springer; 1988. https://doi.org/10.1007/978-94-015-7358-0
- Flora of Eastern Saudi Arabia. Riyadh: Kegan Paul International, London & N.Y. jointly with the National Commission for Wildlife Conservation and Development; 1990. p. :130-155.
- A blueprint for blue carbon: Toward an improved understanding of the role of vegetated coastal habitats in sequestering CO2. Frontiers in Ecol & Environ. 2011;9:552-560. https://doi.org/10.1890/110004
- [Google Scholar]
- A multiple regression approach to assess the spatial distribution of soil organic carbon (SOC) at the regional scale (Flanders, Belgium) Geoderma. 2008;143:1-13. https://doi.org/10.1016/j.geoderma.2007.08.025
- [Google Scholar]
- Flora of Saudi Arabia. Vol Vol. (1-3). Saudi Arabia: Riyadh University Publication; 1996.
- Floristic diversity and vegetation analysis of Wadi Arar: A typical desert Wadi of the Northern Border region of Saudi Arabia. Saudi J Biol Sci. 2014;21:554-565. https://doi.org/10.1016/j.sjbs.2014.02.001
- [Google Scholar]
- Ecological diversity. Wiley New York; 1975.
- Carbon sequestration potential in different land uses: A review. Int J Environ Res Dev. 2019;15:727-736.
- [Google Scholar]
- Raunkiaer, C., 1934. The life forms of plants and statistical plant geography being the collected papers of C. Raunkiaer. Oxford at the Clarendon Press. https://books.google.com.sa/books?id=LJj9swEACAAJ
- Vegetation of the urban habitats in the Nile Delta region, Egypt. Urban Ecosystems. 2002;6:205-221. https://doi.org/10.1023/a:1026105612771
- [Google Scholar]
- Assessing the distribution of soil organic carbon under three plant species across coastal sabkhas: A comparative analysis. Sustainable Environment. 2024;10 https://doi.org/10.1080/27658511.2024.2418160
- [Google Scholar]
- Bulk density of forested mineral soils. Silva Fenn. 1994;28 https://doi.org/10.14214/sf.a9162
- [Google Scholar]
- Ter Braak, C.J., Smilaeur, P., 2002. CANOCO reference manual and CanoDraw for Windows user’s guide. Software for canonical community ordination (version 4.5). M. Power. www.canoco.com
- Wickens, G., 1977. Some of the phytogeographical problems associated with Egypt. 7-8.
- Determination of chemical and physical soil properties. In: Soil biology, monitoring and assessing Soil Bioremediation Soil Biology, monitoring and assessing soil bioremediation. Berlin, Heidelberg: Springer Berlin Heidelberg; p. :47-95. https://doi.org/10.1007/3-540-28904-6_2
- [Google Scholar]
- Storage, patterns and environmental controls of soil organic carbon in China. Biogeochemistry. 2007;84:131-141. https://doi.org/10.1007/s10533-007-9109-z
- [Google Scholar]
- Vegetation Types of Saudi Arabia. Jeddah, Saudi Arabia: King Abdel Aziz University Press; 1982.
- Spatial distributions and sequestrations of organic carbon and black carbon in soils from the Chinese Loess Plateau. Sci Total Environ. 2013;465:255-266. https://doi.org/10.1016/j.scitotenv.2012.10.113
- [Google Scholar]
- Geobotanical foundations of the Middle East. CRC Press; 1973.