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Article

Moisture and Salinity Drive the Vegetation Composition of Wadi Hargan, Riyadh, Saudi Arabia

by
Ahmed M. Abd-ElGawad
1,2,*,
Abdulaziz M. Assaeed
1,
Saud L. Al-Rowaily
1,
Basharat M. Dar
1 and
Jahangir A. Malik
1
1
Plant Production Department, College of Food & Agriculture Sciences, King Saud University, P.O. Box 2460, Riyadh 11451, Saudi Arabia
2
Department of Botany, Faculty of Science, Mansoura University, Mansoura 35516, Egypt
*
Author to whom correspondence should be addressed.
Diversity 2021, 13(11), 587; https://doi.org/10.3390/d13110587
Submission received: 6 October 2021 / Revised: 11 November 2021 / Accepted: 15 November 2021 / Published: 18 November 2021
(This article belongs to the Section Plant Diversity)
Browse Figures
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Abstract

:
Wetlands are represented in Saudi Arabia in the form of mangrove, sabkha, and wadi (valleys) systems, and these habitats are considered as a sanctuary for biodiversity. The present study aimed to identify different vegetation groups in a wetland site in Wadi Hargan near Alqurainah, Riyadh, Saudi Arabia, and to relate different plant communities and plant diversity to soil moisture, salinity, and other soil properties. Floristic analysis and vegetation structure were investigated within 15 stands along the wadi and were subjected to correlation analysis with soil factors via multivariate analysis. The floristic survey revealed the presence of 111 plant species belonging to 39 families. The most represented families were Asteraceae, Poaceae, Brassicaceae, Caryophyllaceae, and Papilionaceae, which accounted for the largest proportion (55.4%) of the total species. The therophytes were the dominant life form, where they were represented by 46.9% of the total number of species. The application of cluster analysis (TWINSPAN) to the importance value of each species based on the relative cover and density led to the recognition of four plant communities: (A) Phragmites australis—Tamarix nilotica community, (B) Zygophyllum coccineum—Acacia gerrardii community, (C) Lycium shawii—Zygophyllum coccineum community, and (D) Rhazya stricta community. The soil analysis and correlation test revealed significant variations in the content of salinity, moisture, CO3, Cl, SO4, Ca, Mg, and Na among the plant communities. It can be concluded that soil moisture and salinity factors were the fundamental driving forces for plant community structure in the studied wadi. The wadi was moderately grazed, mainly by camels; thereby, the invasive plant Rhazya stricta dominated the central region of the wadi. Also, human interference was observed at the end of the wadi, where some weeds sprouted such as Malva parviflora. The presence of those two rare wetland species, Adiantum capillus-veneris and Ficus salicifolia, in the study area, showed the unique properties of the studied wadi and necessitate an urgent biodiversity conservation action to protect its natural vegetation from overgrazing and human interference.

1. Introduction

Despite the arid climate of Saudi Arabia, there are several wetlands predominant in mangrove, sabkha, and wadi (valleys) systems [1]. Wetlands are considered as analogous to keystone species in that they play a disproportionately large role within their ecosystem relative to their small size [2,3,4]. Wetlands play an important ecological role in carbon sequestration [5] and biodiversity conservation [6,7,8]. They support unique assemblage of vegetation [9] and maintain suitable habitat for migrating birds [10]. Wetlands have a broad spectrum in Saudi Arabia, where they can be categorized into eight systems: coastal, sabkha, karst, mountain, geothermal, wadi, and man-made systems [1,11].
Plant community distribution is controlled by many processes, including biotic processes, such as plant dispersal, growth, herbivory, and mortality, as well as abiotic factors and processes, such as substrate, topography, climate, or disturbance. Therefore, the structure of a plant community is the product of these complex and interacting processes [12]. The two most important abiotic factors controlling plant communities in arid areas are soil moisture and salinity [13]. Soil moisture plays a crucial role in shaping desert plant communities [14]. Soil moisture availability controls species distribution and richness as few species can withstand extremely poor water conditions [15]. Halophyte species distribution are mostly determined by soil moisture and salinity [16,17,18]. However, Xi, et al. [17] suggested that the water gradients had a more significant and more direct effect than salinity gradients on plant species and communities, but it depends on scale and ecosystem types [19].
Wetlands are prone to the impact of human activities outside their boundaries that alter their hydrologic system [20,21]. Such activities include changes in watershed land use, road construction, and other factors or processes that affect water recharge or subsurface flow paths. Conservation of wetland systems to sustain freshwater biota poses a challenge to scientists and decision-makers to realize linkages required to control damaging factors and restore their impacts. Evaluation and monitoring of wetland vegetation help close critical gaps of information needed to make sound future conservation decisions. Few studies have been done regarding Saudi Arabia’s wetlands services their sustainable conservation and use [1]. The study and evaluation of wetlands as hotspots for biodiversity will help in supporting their conservation and uses, as well as provide substantial information for scientists, policymakers, and stakeholders for sustainable management. The vegetation analysis of 63 sabkhas in the central region of Saudi Arabia showed that soil salinity, texture and nutrients were the main factors affecting plant distribution [22]. A study by Galal, et al. [23] showed an alteration of the natural status of the desert-wetland ecosystems, southwestern Saudi Arabia has occurred. Thus, urgent conservation action is required. Despite their ecological importance, our knowledge and understanding of desert wetlands are limited. According to our preliminary field observation of Wadi Hargan, we recorded some rare species such as Adiantum capillus-veneris and Ficus salicifolia which indicate the unique properties of this wadi, that could be ascribed to the water source. We hypothesize that the environmental factors; soil moisture and salinity discriminate best between the vegetation types identified by cluster analysis and explain a high proportion in the variability of plant species richness and stand structure. The objectives of this work were: (1) to identify different vegetation groups in a wetland site in Wadi Hargan near Alqurainah, Riyadh, Saudi Arabia, and (2) to relate different plant communities to soil moisture, salinity, and other soil properties.

2. Materials and Methods

2.1. The Study Area

The location of Wadi Hargan is approximately 55 km northwest of Riyadh City, Saudi Arabia situated between 25°03.975′ N and 46°12.157′ E (Table S1). The Wadi is surrounded by flat rocky beds devoid of any vegetation. Flat rocky beds bordering this wadi from all directions are largely exposed with almost no soil cover and have insufficient groundwater to facilitate vegetation. The wadi has varying altitudes ranging from 824 to 797 m.a.s.l. in the upstream and downstream areas, respectively. The wadi was selected for study because of its different vegetation diversity in spite of having arid conditions around. Water seeps from the upstream bottom base of the wadi forming a runnel flowing all along the study area, thus giving it a form of a wetland ecosystem with highly saline groundwater in gypsum formation. The area has a mean maximum temperature of 43 °C in August and an average minimum of 9 °C. in January. The average total annual rainfall is ≈130 mm [24].

2.2. Vegetation Analysis

Fifteen stands were randomly selected along the wadi to represent the study area, during spring 2019, taking patchy vegetation into consideration (Figure 1). In each stand, a 20 × 20 m quadrat was used. In each quadrat, the plant species were listed, and the density was determined according to Bonham [25], while the cover of each species was estimated according to the Braun-Blanquet scale [26].
The importance value was calculated by the summation of the relative value of density and cover of each plant species. The nomenclature of plant species was assessed according to Collenette [27] and Chaudhary [28], while the life forms of the species were identified according to Raunkiaer [29]. The chorotypes of all species were made to assign the recorded species to World Geographical Groups according to Zohary [30].

2.3. Soil Analysis

Within each quadrat, three soil samples, at a depth of 10–40 cm, were collected at three random points. Part of the collected samples was kept immediately in moisture tins for the determination of soil moisture, and the remaining samples were pooled to form one composite sample. The samples were air-dried at room temperature for one week and then dried in an oven at 65 °C and sieved using a 2-mm sieve. The soil moisture was determined by the weight-loss method, based on three replicas per each quadrat. Soil texture was determined according to Bouyoucos [31]. Soil water paste, in the ratio of 1:5, was prepared, and immediately the soil electrical conductivity (EC) and pH were measured [32]. Carbonates were estimated by titration using 0.1 N HCl [33], and SO4 content was determined gravimetrically according to Piper [34], using barium chloride. The soluble cations (Na and K) were measured using flame photometry (PHF 80B Biologie Spectrophotometer), while Ca and Mg were estimated using the atomic absorption spectrometer (A Perkin-Elmer, Model 2380, Waltham, MA, USA) according to Allen, et al. [35].

2.4. Data Analysis

To recognize the plant communities in the study area, the data of the importance values, derived from density and cover, of the plant species within 15 stands were subjected to two-way indicator species analysis (TWINSPAN) for classification, and detrended correspondence analysis (DCA), for ordination [36,37,38]. The soil variables for the identified communities were subjected to one-way ANOVA and the mean values were separated based on Duncan’s test at 0.05 probability level to examine the significant difference among plant communities. In order to detect the relationship between the dominant and important plant species of the four identified communities on one hand and soil variable data, on the other hand, canonical correspondence analysis (CCA) according to Ter Braak and Smilauer [39] was conducted.

3. Results

3.1. Vegetation Composition

The floristic survey of the study area revealed the presence of 111 plant species; 51 perennials and 60 annuals (Table S2). These plant species belong to 39 families, where the most represented families were Asteraceae, Poaceae, Brassicaceae, Caryophyllaceae, and Papilionaceae, which represent 55.4% of the total species (Figure 2). The therophytes were the dominant life form, representing 46.9% of the total number of species (Figure 2).
The application of cluster analysis (TWINSPAN) to the data of importance values of each species, based on the relative cover and density, led to the recognition of four plant communities (Figure 3 and Table 1). These communities were (A) Phragmites australis—Tamarix nilotica community, (B) Zygophyllum coccineum—Acacia gerrardii community, (C) Lycium shawii—Zygophyllum coccineum community, and (D) Rhazya stricta community.
The community of Phragmites australis—Tamarix nilotica colonizes the wadi’s head, where the soil moisture and salinity were high, and it was the most diverse community (40 species). It attained the highest richness (Simpson diversity index = 0.95). Moreover, other important hydrophytic and halophytic species were recorded such as Aeluropus lagopoides and Juncus rigidus (Table 1). The Zygophyllum coccineum—Acacia gerrardii community inhabits the first section of the wadi, where the moisture content decreased. This community attained the Simpson diversity index of 0.91 and Shannon-evenness of 0.76. The other important species in this community were Acacia ehrenbergiana, Rhazya stricta, and Cynodon dactylon.
The Lycium shawii—Zygophyllum coccineum community is represented the central region of the wadi, where the water content is very low. This community attained the highest evenness (Shannon-evenness of 0.76) and richness (Simpson index of 0.95). Rhazya stricta, Acacia tortilis, Cynodon dactylon, and Ochradenus baccatus attained the highest importance values in this community. Finally, Rhazya stricta community colonized the last portion of the wadi, where it is characterized by sandy habitat, and it contained 20 species. The Simpson index of this community was 0.92, while the Shannon-evenness was 0.76. The other important species of this community were Lycium shawii, Artemisia sieberi, Zygophyllum cocineum, Acacia tortilis, and Acacia ehrenbergiana (Table 1).

3.2. Vegetation-Soil Relationship

The soil analysis of the studied stands revealed significant variation among the identified communities (Table 2). Soil salinity, moisture, CO3, Cl, SO4, Ca, Mg, and Na contents showed a highly significant (p < 0.05) difference among the plant communities. However, sand, silt, and K contents did not show a significant difference. The community of Phragmites australis-Tamarix nilotica attained the highest soil moisture, salinity, Cl, SO4, Na, Ca, and Mg. However, the community of Lycium shawii—Zygophyllum coccineum exhibited the lowest content of moisture, sand, SO4, K, Ca, and Mg. The lowest salinity content was recorded for Rhazya stricta community, which inhabits the wadi tail.
The correlation between the environmental (edaphic) factors and CCA axes showed that plant species along the first axis were positively correlated with moisture, salinity, Cl, SO4, Na, Ca, and Mg (Table 3). The CCA revealed that Phragmites australis—Tamarix nilotica community was segregated on the right side of the CCA biplot, and it was correlated to the soil moisture, salinity, Cl, SO4, Na, Ca, and Mg. Correlation analysis between the soil variables and dominant and important plant species is shown in Figure 4. Aeluropus lagopoides, Juncus rigidus, Phragmites australis, and Tamarix nilotica showed a positive correlation with salinity, Cl, SO4, Na, K, Ca, and Mg. On the other hand, the invasive plant Rhazya stricta showed a negative correlation with all these soil parameters.

4. Discussion

Although, the climate in Saudi Arabia is arid, there are various wetlands habitats such as sabkha, mangrove, and wadi systems [1]. These habitats play a vital role in the conservation of biodiversity as they support a unique assemblage of plant communities. Wadi systems are considered the most distinguishable landforms in deserts. Wadis are usually located on gentle slopes and have braided stream patterns due to water deficiency and abundance of sediments [40].
The floristic analysis revealed the predominance of therophytes reflecting the prevailing desert environment, where annuals flourished during the rainy season. These annual plants have high reproductive capacity phenotypic plasticity enabling them to thrive in the desert environment [41]. The preponderance of Asteraceae, Poaceae, and Brassicaceae in the present study was in harmony with other previous studies in different wadis [42,43,44,45,46,47]. Asteraceae and Poaceae families are the largest families worldwide, particularly in arid and semi-arid regions [48,49].
Four plant communities were identified via the classification of stands. Among these communities, Phragmites australis—Tamarix nilotica community was the most diverse and has the highest Simpson diversity index. This community colonizes the head of the wadi, where it receives the highest amount of water. It is worth mentioning here that the road construction that cut the wadi head led to trapping of water that percolates toward the wadi stream. This makes the head of the wadi mostly moist (17.76%) year-round, and we consider that this is the reason for high plant diversity in that location. In this community, hydrophytes were observed such as Phragmites australis, Juncus rigidus, Tamarix nilotica, and Aeluropus lagopoides. This community colonizes the head of the wadi, where it receives a high amount of water. Also, the higher soil water content of this community enabled maidenhair fern; Adiantum capillus-veneris to inhabit the shaded places of this habitat. Very few studies in the Riyadh region or other regions having similar climatic conditions indicated the presence of A. capillus-veneris [50,51,52] and Ficus salicifolia [53]. The presence of those two rare wetland species in the study area necessitates an urgent biodiversity conservation action.
The soil analysis and the CCA revealed that the Phragmites australis—Tamarix nilotica community was affected by the content of soil moisture, salinity, Cl, SO4, Na, Ca, and Mg. Salinity is one of the most important factors affecting plant communities’ assemblage [54,55]. Water is one of the crucial factors that affect the plant community structure, dynamics, and composition in arid regions [17,56]. The water of the desert ecosystem includes precipitation, sand adsorbed water, surface runoff, air-water, and groundwater [57]. Due to the higher rate of evapotranspiration in the desert ecosystem, salinity often increases, hindering plant water uptake [58]. In this context, salinity is one of the most important factors affecting plant communities’ assemblage [54,55]. A study by Gong, et al. [55] reported that aridity and salinity control plant community structure rather than soil fertility. In the present study, the community of Phragmites australis—Tamarix nilotica contained important salt-tolerant species, which reflect saline environmental conditions, for example, Juncus rigidus, Tamarix nilotica, and Aeluropus lagopoides. These species are considered bioindicators for salinity [59].
Along the wadi, the gradient of soil moisture content and salinity decreased. Therefore, the plant communities changed dramatically, where the Zygophyllum coccineum-Acacia gerardii and Lycium shawii—Zygophyllum cocineum communities colonized the central region of the wadi. In these communities, the Acacia trees (Acacia gerardii, Acacia ehrenbergiana, and Acacia tortilis) colonize this region forming a woodland community with association of other xerophytes such as Lycium shawii, Ochradenus baccatus, Zygophyllum cocineum, Rhazya stricta, and Cynodon dactylon. These plants are the common plants in various wadis in desert habitats of Saudi Arabia [27,28,60,61,62].
The invasive plant Rhazya stricta forms the last community in the wadi, where the diversity of species becomes low. This community showed a negative correlation with most of the soil parameters (salinity, Cl, SO4, Na, K, Ca, and Mg), which reflects that this weed can grow in poor soil. The invasive plants have higher colonization in nutrient-poor environments compared to native ones [63,64]. It is worth mentioning here that we observed anthropogenic interference, particularly the grazing, at the end of the wadi, and we think that the presence of some annual species like Malva parviflora is a result of this factor. This species was possibly introduced as a result of supplementary feeds provided to livestock in impermanent paddocks.

5. Conclusions

The floristic and vegetation analysis of the Wadi Hargan, Riyadh, Saudi Arabia, showed distinct four plant communities along the wadi. These communities showed substantial variation in their structure and assemblage. The content of salinity, moisture, CO3, Cl, SO4, Ca, Mg, and Na were the soil factors that affect the distribution and structure of these communities. Moreover, it can be concluded that soil moisture and salinity factors were the key driving forces for plant community structure in the studied wadi. The wadi is subjected to moderate grazing, mainly by camels; thereby, the invasive plant Rhazya stricta was dominant in the central region of the wadi. Also, human interference was observed at the end of the wadi, where some weeds sprouted such as Malva parviflora. The wetlands are considered hotspots for plant biodiversity; therefore, we recommend including the studied wadi under the conservation strategy to protect its natural vegetation from overgrazing and human interference.

Supplementary Materials

The following are available online at https://www.mdpi.com/article/10.3390/d13110587/s1, Table S1: The coordinates and elevation of the studied stands along Wadi Hargan, Saudi Arabia, Table S2: The floristic analysis of the recorded plant species in the study area.

Author Contributions

Conceptualization, A.M.A.-E., A.M.A. and B.M.D.; Formal analysis, A.M.A.-E., A.M.A., J.A.M. and B.M.D.; Investigation, A.M.A.-E., A.M.A., S.L.A.-R. and B.M.D.; Methodology, A.M.A.-E., A.M.A. and B.M.D.; Resources, A.M.A.-E., S.L.A.-R. and A.M.A.; Writing—original draft, A.M.A.-E., A.M.A. and B.M.D.; Writing—review & editing, A.M.A.-E., A.M.A., S.L.A.-R., J.A.M. and B.M.D. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by the Deanship of Scientific Research at King Saud University through research group No (RG-1441-302).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not available.

Acknowledgments

The authors extend their appreciation to the Deanship of Scientific Research at King Saud University for supporting this work through research group No (RG-1441-302).

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. (A) Map of Riyadh region showing the study area indicated by star (★), (B) Google Earth map showing the sampled stands (●).
Figure 1. (A) Map of Riyadh region showing the study area indicated by star (★), (B) Google Earth map showing the sampled stands (●).
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Figure 2. Plant families of the recorded plant species (a) and the life forms according to Raunkiaer’s classification (b).
Figure 2. Plant families of the recorded plant species (a) and the life forms according to Raunkiaer’s classification (b).
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Figure 3. TWINSPAN dendrogram of different sampled stands based on the importance values of the recorded perennial species (n = 49). Indicator species names are abbreviated to the first three letters of both genus and species. Mal par: Malva parviflora, Ero lac: Erodium laciniatum, and Tam nil: Tamarix nilotica.
Figure 3. TWINSPAN dendrogram of different sampled stands based on the importance values of the recorded perennial species (n = 49). Indicator species names are abbreviated to the first three letters of both genus and species. Mal par: Malva parviflora, Ero lac: Erodium laciniatum, and Tam nil: Tamarix nilotica.
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Figure 4. CCA ordination bi-plot between the soil variables and the dominant and important plant species of the four identified communities. Plant species names are abbreviated to the first three letters of both genus and species. Acacia ehrenbergiana, Acacia gerardii, Acacia tortilis, Aeluropus lagopoides, Artemisia sieberi, Cynodon dactylon, Cymbopogon commutatus, Phragmites australis, Juncus rigidus, Lycium shawii, Rhazya stricta, Tamarix nilotica, and Zygophyllum coccineum, and EC: electrical conductivity.
Figure 4. CCA ordination bi-plot between the soil variables and the dominant and important plant species of the four identified communities. Plant species names are abbreviated to the first three letters of both genus and species. Acacia ehrenbergiana, Acacia gerardii, Acacia tortilis, Aeluropus lagopoides, Artemisia sieberi, Cynodon dactylon, Cymbopogon commutatus, Phragmites australis, Juncus rigidus, Lycium shawii, Rhazya stricta, Tamarix nilotica, and Zygophyllum coccineum, and EC: electrical conductivity.
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Table
Table 1. Plant communities of the perennial species recorded in the study area.
Table 1. Plant communities of the perennial species recorded in the study area.
ParameterPlant Community
ABCD
Stand no.5334
Species no.40212120
Simpson index0.950.910.940.92
Shannon-evenness0.810.760.860.76
No.Plant speciesAverage of importance value
1Acacia ehrenbergiana Hayne7.20 ± 1.38 *21.25 ± 5.888.16 ± 3.8217.27 ± 3.05
2Acacia gerrardii Benth.4.99 ± 1.9030.67 ± 10.2516.49 ± 3.135.09 ± 2.24
3Acacia tortilis (Forssk.) Hayne5.88 ± 2.55---12.88 ± 6.0218.65 ± 3.45
4Adiantum capillus-veneris L.4.42 ± 2.72---------
5Aeluropus lagopoides (L.) Thwaites22.60 ± 7.78---------
6Alhagi graecorum Boiss.1.34 ± 0.821.29 ± 0.67---1.55 ± 0.68
7Artemisia monosperma Delile---5.90 ± 1.54---
8Artemisia sieberi Besser1.17 ± 0.72---6.98 ± 1.7322.50 ± 5.54
9Artemisia pycnocephala (Less.) DC.0.69 ± 0.43---------
10Astragalus spinosus (Forssk.) Muschl.------6.07 ± 1.6910.05 ± 2.77
11Atriplex leucoclada Boiss.1.90 ± 0.81---------
12Blepharis ciliaris (L.) B.L.Burtt0.69 ± 0.43------3.26 ± 0.84
13Cenchrus ciliaris L.3.97 ± 1.02---5.00 ± 2.34---
14Cucumis prophetarum L.0.56 ± 0.35---------
15Citrullus colocynthis (L.) Schrad.------1.90 ± 0.89---
16Cynodon dactylon (L.) Pers.3.14 ± 1.3412.98 ± 3.36811.00 ± 2.59---
17Cymbopogon commutatus (Steud.) Stapf2.27 ± 1.409.80 ± 2.93---3.97 ± 1.74
18Ephedra foliata Boiss. ex C.A.Mey.0.56 ± 0.35---------
19Ephedra ciliata Fisch. & C.A.Mey.---3.44 ± 0.967.22 ± 3.37---
20Fagonia bruguieri DC.1.92 ± 0.491.70 ± 0.89---2.19 ± 0.97
21Farsetia aegyptia Turra1.26 ± 0.48---1.90 ± 0.891.55 ± 0.68
22Ficus salicifolia Vahl2.05 ± 1.26---------
23Gymnocarpos decandrus Forssk.1.84 ± 0.47------1.55 ± 0.68
24Haloxylon salicornicum (Moq.) Bunge ex Boiss.2.67 ± 1.64---------
25Helianthemum lippii (L.) Dum. Cours.1.28 ± 0.482.91 ± 0.767.27 ± 0.301.81 ±
26Hyparrhenia hirta (L.) Stapf3.16 ± 1.373.61 ± 0.975.61 ± 1.31---
27Juncus rigidus Desf.22.31 ± 3.60---------
28Lycium shawii Roem. & Schult.5.77 ± 0.973.91 ± 2.0331.22 ± 8.1922.46 ± 9.88
29Moricandia sinaica (Boiss.) Boiss.---11.37 ± 3.761.84 ± 0.861.45 ± 0.64
30Ochradenus baccatus Delile4.82 ± 0.811.35 ± 0.7011.62 ± 1.496.00 ± 1.52
31Panicum turgidum Forssk.1.32 ± 0.813.12 ± 1.63------
32Pennisetum divisum (Forssk. ex J.F.Gmel.) Henrard---------9.38 ± 4.12
33Pergularia tomentosa L.0.56 ± 0.35---1.90 ± 0.89---
34Phoenix dactylifera L.3.25 ± 1.23---------
35Phragmites australis (Cav.) Trin. ex Steud.29.97 ± 9.78---------
36Polygonum aviculare L.0.56 ± 0.35---------
37Prosopis farcta (Banks & Sol.) J.F.Macbr.1.32 ± 0.81---------
38Pulicaria undulata (L.) Kostel.0.91 ± 0.563.26 ± 0.852.83 ± 1.321.36 ± 0.60
39Reseda muricata C.Presl------4.23 ± 1.01---
40Rhanterium epapposum Oliv.2.69 ± 1.102.09 ± 1.09------
41Rhazya stricta Decne.---14.81 ± 3.8921.84 ± 7.1947.34 ± 5.06
42Scirpoides holoschoenus (L.) Soják1.18 ± 0.72---------
43Scrophularia deserti Delile---2.09 ± 1.09------
44Stipagrostis plumosa Munro ex T.Anderson---3.30 ± 1.72------
45Tamarix nilotica (Ehrenb.) Bunge27.71 ± 4.93---------
46Teucrium polium L.0.59 ± 0.36---------
47Typha domingensis Pers.5.49 ± 3.37---------
48Zilla spinosa (L.) Prantl0.56 ± 0.351.70 ± 0.894.62 ± 1.154.22 ± 1.09
49Zygophyllum coccineum L.15.40 ± 3.4659.41 ± 13.2729.41 ± 0.7118.36 ± 5.63
* values are average of the importance values of species based on the relative cover and density ± standard error. A: Phragmites australis—Tamarix nilotica community, B: Zygophyllum coccineum—Acacia gerrardii community, C: Lycium shawii—Zygophyllum coccineum community, and D: Rhazya stricta community.
Table
Table 2. Soil characteristics of the four determined plant communities in the study area.
Table 2. Soil characteristics of the four determined plant communities in the study area.
ParametersPlant CommunityF Valuep Value
ABCD
Clay (%)7.01 ± 1.46 *AB5.34 ± 0.44 B11.39 ± 1.93 A6.54 ± 1.14 AB3.7880.0213 *
Silt (%)6.86 ± 1.25 A5.66 ± 0.66 A9.51 ± 2.17 A7.31 ± 1.19 A1.2730.3028
Sand (%)86.13 ± 2.60 AB89.00 ± 0.57 A79.10 ± 3.95 B86.15 ± 1.86 AB2.7210.0633
pH8.30 ± 0.10 A8.16 ± 0.15 A8.45 ± 0.08 A8.22 ± 0.12 A1.0930.3683
EC (dS m−1)2.50 ± 0.15 A0.85 ± 0.23 B0.42 ± 0.02 BC0.30 ± 0.05 C52.000<0.0001 ***
CO3 (%)0.69 ± 0.08 B1.35 ± 0.18 A1.20 ± 0.08 A1.43 ± 0.15 A6.3660.0020 **
Cl (meq/L)4.54 ± 0.74 A2.15 ± 0.38 B1.38 ± 0.44 B0.60 ± 0.07 B13.034<0.0001 ***
SO4 (meq/L)23.91 ± 2.65 A2.49 ± 0.51 B0.69 ± 0.09 B1.06 ± 0.21 B69.373<0.0001 ***
Ca (meq/L)16.90 ± 2.43 A2.79 ± 0.53 B1.44 ± 0.20 B2.61 ± 0.34 B33.846<0.0001 ***
Mg (meq/L)8.15 ± 1.39 A2.28 ± 0.73 B0.69 ± 0.09 B1.51 ± 0.43 B17.343<0.0001 ***
Na (meq/L)4.59 ± 0.99 A1.13 ± 0.54 B0.42 ± 0.16 B0.31 ± 0.07 B12.500<0.0001 ***
K (meq/L)0.38 ± 0.08 A0.40 ± 0.13 A0.20 ± 0.03 A0.35 ± 0.03 A1.2880.2978
Moisture (%)18.76 ± 2.70 A0.97 ± 0.12 B0.65 ± 0.09 B0.94 ± 0.14 B43.734<0.0001 ***
* values are average ± standard error. EC: electrical conductivity. Within each row, means followed by the same superscript letter are not significantly different at the 0.05 level using Tukey’s HSD test. *** p < 0.001, ** p < 0.01, * p < 0.05. A: Phragmites australis-Tamarix nilotica community, B: Zygophyllum coccineum—Acacia gerrardii community, C: Lycium shawii—Zygophyllum coccineum community, and D: Rhazya stricta community.
Table
Table 3. Inter-set correlations between environmental variables and site scores with CCA axes.
Table 3. Inter-set correlations between environmental variables and site scores with CCA axes.
VariableAxis 1Axis 2Axis 3
Eigenvalues0.6310.3690.288
Percentage28.51316.68413.016
Cum. Percentage28.51345.19758.213
Species-environmental correlations0.9990.9870.994
Clay−0.1900.2000.111
Silt−0.2030.257−0.153
Sand0.207−0.2410.028
pH0.2710.6100.083
EC0.867−0.2520.301
CO3−0.8130.0700.185
Cl0.865−0.2200.121
SO40.917−0.277−0.002
Ca0.814−0.384−0.099
Mg0.815−0.5050.019
Na0.826−0.1200.053
K0.154−0.1370.354
Moisture0.9400.183−0.036
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Abd-ElGawad, A.M.; Assaeed, A.M.; Al-Rowaily, S.L.; Dar, B.M.; Malik, J.A. Moisture and Salinity Drive the Vegetation Composition of Wadi Hargan, Riyadh, Saudi Arabia. Diversity 2021, 13, 587. https://doi.org/10.3390/d13110587

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Abd-ElGawad AM, Assaeed AM, Al-Rowaily SL, Dar BM, Malik JA. Moisture and Salinity Drive the Vegetation Composition of Wadi Hargan, Riyadh, Saudi Arabia. Diversity. 2021; 13(11):587. https://doi.org/10.3390/d13110587

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Abd-ElGawad, Ahmed M., Abdulaziz M. Assaeed, Saud L. Al-Rowaily, Basharat M. Dar, and Jahangir A. Malik. 2021. "Moisture and Salinity Drive the Vegetation Composition of Wadi Hargan, Riyadh, Saudi Arabia" Diversity 13, no. 11: 587. https://doi.org/10.3390/d13110587

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