Impacts of Anthropogenic Disturbance on Vegetation Dynamics: A Case Study of Wadi Hagul, Eastern Desert, Egypt

Irresponsible human interventions, encroachment of natural habitats, and climate change negatively affect wildlife. In this study, the effects of human influence on Wadi Hagul, an unprotected area in the north of the Egyptian Eastern Desert that has recently been subjected to blatant encroachments of vegetation, were studied. The most important of these threats is the construction of the new road Al-Galala–Wadi Hagul–Zafarana. In Wadi Hagul, 80 species are reported in this study; the most represented plant families are Asteraceae (15 species) and Brassicaceae (6 species). Perennial, chamaephyte and Saharo-Arabian species were recorded in the highest percentage. Detrended canonical correspondence analysis showed that latitude, longitude, altitude, silt, sand contents, pH, and CO32− content are the factors that have the highest effect on vegetation distribution in the studied stands. Several invasive and alien species such as Euphorbia prostrata have been listed; these species typically have a negative effect on native species. The Soil Adjusted Vegetation Index (SAVI) indicated a decrease in plant cover during the study period, as compared to previous years. In 2013 and 2020, SAVI ranged from −0.02 to 0.42 and from −0.18 to 0.28, respectively. Recently, the violation and destruction of wildlife have increased, therefore, preserving it along with general biodiversity has become an urgent necessity.


Introduction
Land degradation and vegetation reduction caused by external stresses, affect biodiversity and natural ecosystems and the numerous services they provide [1]. Environmental deterioration, habitat changes, inappropriate vegetation management, translocation, fragmentation, and deforestation modify biotic and abiotic ecosystem components, resulting in changes in ecological processes such as vegetation dynamics [2][3][4]. Overgrazing, road building, overharvesting, solid wastes, salinization, industrialization, urbanization, and military activities are considered to be the main anthropogenic activities that lead to changes and transformation of vegetation and natural habitat loss in arid and semi-arid environments [5][6][7].
In terrestrial ecosystems, climate and land cover changes such as cover, height, biomass, relative humidity, soil temperature, moisture, fertility, and erosion affect the structural properties of vegetation [8]. Biodiversity decline is influenced by various types of human activities, including land cover changes, the introduction of invasive species, the vegetation and geological aspects of Wadi Hagul: upstream, middle, and downstream. Two distinct plant communities can be found in the upstream section of Wadi Hagul's main channel: one is dominated by Zilla spinosa on elevated terraces of mixed deposits. The other is dominated by Launaea spinosa and represents a further stage in the building up of the wadi bed. In the middle section, Leptadenia pyrotechnica community occurs. In the downstream section, the vegetation is dominated by Hammada elegans with individuals of Launaea spinosa and Lygos raetam [44].
This paper focuses on Wadi Hagul, which has neither attained sufficient interest from intended responsible parts nor ecological studies, although it is considered an environment rich in various plants including a number of endangered plants, whereas other Eastern desert wadis of Egypt have received both interest and studies convenient for them. Therefore, the objective of this study is the estimation of vegetation cover in Wadi Hagul through the illustration of the relationship between environmental factors in the studied localities and the distribution of plant communities. The study also aimed at comparing vegetation changes and at testing new methods to record the reasons for changes in vegetation dynamics by calculating the temporal patterns of SAVI during 2013, 2015, and 2020 in Wadi Hagul, Eastern Egyptian Desert.

Study Area
Wadi Hagul lies between 32 • 09 32 E and 32 • 17 27 E and between 29 • 48 28 N and 29 • 57 43 N, with an area of 350 km 2 (0.16% of the Eastern Desert total area). The main canal of Wadi Hagul extends until it reaches the Gulf of Suez, with a width ranging from 6 to 10 km and a length of approximately 36 km. Wadi Hagul is considered to be one of 15 wadies located on the Red Sea coast. It is situated 112 km west of Cairo, between Gebel Ataqa and the Kahaliya ridge [44]. Wadi Hagul is characterized by a dry desert climate with little rain, high temperatures, and a high evaporation rate. The three sections represent dry natural habitats inhabited mainly by xerophytic plants. The dominant species are Fagonia mollis, Echinops spinosus, and other xerophytic plants [45].

Floristic Study
To estimate the vegetation cover in Wadi Hagul, 20 stands were chosen to represent different plant habitats in Wadi Hagul. A total of 20 stands were selected for the study of the vegetation of Wadi Hagul during the spring and summer seasons of 2019 and 2020. In each stand, four quadrates were chosen (quadrate area = 10 m × 10 m = 100 m 2 ) ( Table 1 and Figures 1 and 2). Vegetation cover was measured using visual estimation. Recorded plant species in all localities were identified, and life span was documented according to Boulos [46][47][48][49][50]. Life form and floristic category were recognized after Raunchier [51], Tutin et al. [52], and Davis [53].

Soil Analyses
Many soil factors were examined in order to determine the characteristics of the soil in the study area. From each stand, four soil samples were collected and merged to form a homogeneous and representative sample of a single locality. Fifteen soil factors were analyzed: soil texture (sand, silt, and clay), pH, total dissolved salts, electrical conductivity, magnesium, calcium, sodium, potassium, chloride, bicarbonate, carbonate, sulfate, and organic carbon content. Soil texture was determined according to Estefan et al. [54] using a pipette method. Digital portable pH, TDS, and EC meters (Adwa ® , Adwa Instruments, Plants 2021, 10, 1906 4 of 19 Szeged, Hungry) were used to calculate pH, total dissolved salts (T.D.S.), and electrical conductivity (E.C.). Magnesium and calcium were determined using a titration method according to Page et al. [55]. A flame photometer at wavelengths of 589 and 767 nm was used to determine sodium and potassium, respectively [54]. Chlorides, bicarbonates, and carbonates were determined using a titration method [56]. Sulfates were determined after Estefan et al. [54] using the turbid metric method. Organic carbon was determined using a titration method [57].

Statistical Analyses
Descriptive statistical measures (mean, median, standard deviation, range, minimum, maximum, and interquartile range) for different soil factors were determined using Sigmaplot ver. 12.5.
Several biodiversity indicators were measured such as Shannon s and Simpson s diversity indices, species richness, and evenness were extracted using PC-ORD ver. 5 software [58]. Hills numbers were calculated using the R program.
To clarify the relationship between environmental factors, especially soil factors, the study area was divided into three areas: the beginning of the Wadi (stands 1 to 7), the middle (stands 8 to 14), and the end of the Wadi (stands 15 to 20). A detrended canonical correspondence analysis (DCCA) was performed using CANOCO ver. 4.5 and CanoDraw ver. 4.1 [59].

Vegetation Change
To confirm the negative impact of human interventions on the vegetation cover in Wadi Hagul, SAVI was calculated in the study area during different years. Satellite images for 2013, 2015, and 2020 were obtained from the Landsat 8 satellite (Band 4 and Band 5) during the spring season using the website https://earthexplorer.usgs.gov/; accessed on 15 April 2021. Due to the position of the satellite in its orbit, haze, dust, and sun angle, satellite images have some defects which should be processed. Satellite images should be geometrically, atmospherically, and radiometrically corrected to become ready for extracting the required data. For that, satellite image processing software ENVI 5.3 and Arc GIS 10.5 were used to correct the collected satellite imageries. Soil Adjusted Vegetation Index (SAVI) was calculated according to the following equation: SAVI = ((Band 5 − Band 4)/(Band 5 + Band 4 + L)) × (1 + L)).
where, L = The amount of green vegetation cover (For example, 0.5).
Then the study area (Hagul) was extracted from the satellite images.

Soil Characteristics
Soil samples were taken at a depth of 0 to 30 cm in the studied localities, and 15 soil factors were analyzed. Soil pH, TDS, and EC values ranged 7.4 to 8.5, 82 to 9840 ppm, and 0.128 to 15.375 dS/m, respectively. Calcium, magnesium, sodium, and potassium contents ranged 0.7 to 49 meq/L, 0.22 to 28 meq/L, 0.21 to 63 meq/L, and 0.104 to 11.2 meq/L,  In the current study, 80 taxa were recorded, whereas Abdelaal [60] listed 98 taxa. The number of species recorded in this study was 19 (not recorded in the previous study), whereas 38 species were recorded by Abdelaal [60]. A total of 61 plant species were shared between the two studies ( Table 2).
The averages of species richness, evenness, and Shannon's and Simpson's indices were 3, 0.556, 0.722, and 0.3755, respectively. Hill s number when Q = zero, gamma, alpha and beta diversity were 63, 9.7 and 6.5, respectively. Hill s number when Q = one, gamma, alpha and beta diversity were 8.2, 4.3 and 1.9, respectively. Hill s number when Q = two, gamma, alpha and beta diversity were 5, 3.3 and 1.5, respectively.

Soil Characteristics
Soil samples were taken at a depth of 0 to 30 cm in the studied localities, and 15 soil factors were analyzed. Soil pH, TDS, and EC values ranged 7.4 to 8.5, 82 to 9840 ppm, and 0.128 to 15.375 dS/m, respectively. Calcium, magnesium, sodium, and potassium contents ranged 0.7 to 49 meq/L, 0.22 to 28 meq/L, 0.21 to 63 meq/L, and 0.104 to 11.2 meq/L, respectively. Carbonate, bicarbonate, chloride, and sulfate contents ranged between 0.15 and 0.45%, 0.305 and 0.61%, 0.5 and 43 meq/L, and 1.2 to 76 meq/L, respectively. Organic carbon, clay, and silt contents in all soil samples were less than 1.4%, 5%, and 15%, respectively. In addition, sand contribution in all soil samples was more than 81% (Table 3).

Discussion
In Wadi Hagul, 80 plant species belonging to 30 families were recorded. Among them, Asteraceae, Brassicaceae, and Zygophyllaceae were the most frequent families. These results are very similar to those reported in 2009 by Zahran and Willis [44] (31 species recorded) and in 2000 by Marie [61] (37 species recorded), who found that Asteraceae and Zygophyllaceae were the most common plant families in Wadi Hagul. By contrast, in 2016, Abdelaal [60] recorded 98 species, where Asteraceae and Poaceae were the most frequent families. Eight families (Aizoaceae, Cistaceae, Cleomaceae, Liliaceae, Neuradaceae, Polygonaceae, Urticaceae and Verbenaceae), each represented by only one plant species, were recorded in Abdelaal [60], and none of them were recorded in this study. Asteraceae were reported as the most common family in other Eastern desert wadies (Wadi Asyouti and Wadi Habib) [62]. Asteraceae was known for having a proportion of salt-tolerant and xerophytic species [63]. Asteraceae makes up the bulk of floristic composition in Egypt. It is represented by 98 genera, and 234 species [48,64]. Mashaly [65] reported a list of 62 species, with no alien species found.
The perennial plant group was most represented (67.5%) in the current study; this is consistent with the results of Zahran and Willis [44], Marie [61], and Abdelaal [60], who studied vegetation in the same study area during previous years. Regarding the number of annual species in Wadi Hagul, it has changed over the years of the study. This may be due to variation in the total rainfall during the studied years.
Life forms of species depend mainly on adaptation to the environment, particularly climate [66][67][68][69]. Life forms of desert plants are closely related to precipitation [70,71] and are correlated with both landform and topography [72][73][74]. In the present study, the chamaephyte life form was most represented (40%). Therophyte was the second most common life form (31.3%). These results are in accordance with the results of Abd El-Galil [75], who studied the floristic composition of Wadi Al-Assiuty, Eastern Desert, Egypt.
In arid and semi-arid regions, chamaephyte and therophyte were found to be the most common life-forms [76][77][78].
Species richness, which refers to the number of various plant species in the stands, is one of the most important indices of species diversity. In the studied stands, the average of species richness recorded three species, which is a low number. This could be due to a variety of factors, including the severe environment and climate that characterize the study area, which may be an obstacle to the growth of some plant species. Species evenness is a description of the distribution of species abundance in a community. The average of species evenness was 0.7. Species evenness is measured on a scale of 0 to 1, with 0 representing the lowest evenness (one species has 100% coverage) and 1 representing the highest evenness (coverage is evenly spread among a number of species). This may be due to the presence of a very dominant species in a community causes the less competitive species to be suppressed [82]. Shannon index depends strongly on species richness [83]. Simpson index is not a very intuitive measure of diversity since higher values indicate lower diversity [84].
The results of DCCA analysis indicated that latitude, longitude, altitude, silt and sand contents, pH, and CO 3 2− content are the most important factors affecting the distribution of vegetation in Wadi Hagul. These results are somewhat consistent with those of Mashaly [62], who stated that the most influential soil factors for the distribution of vegetation in Wadi Hagul are soil texture, Na + , pH, and organic matter. Abdelaal [60] mentioned that K + , Na + , organic matter, moisture content, pH, E.C., and Cl − were the most affecting soil parameters for the distribution of vegetation in Wadi Hagul. Plant species associated with the increase in the proportion of sand in the soil and soil pH were Tamarix nilotica, Ochradenus baccatus, Launea nudicalus, Launea nudicalus and Rumex vesicarius. The longitude and the amount of Mg 2+ in the soil were the most important factors associated with many plant species such as; Zilla spinosa, Zygophyllum simplex and Zygophyllum coccineum. Most of the salinity factors (E.C., T.D.S., Ca 2+ , Cl − , Na + and K + ), CO 3 2− , HCO 3 − and the percentage of silt in soil were associated with some species such as; Lycium shawii, Leptadenia pyrotechnica, Panicum turgidum and Haloxylon salicornicum. Latitude, altitude and the amount of organic carbon in soil were important factors in the distribution of some plant species such as Echinops spinosus, Erodium laciniatum, Erodium glaucophyllum and Reaumuria hirtella.
Many of the threatened plant species recorded in previous studies were not recorded in this study, including Aizoon canariensis, Artemisia judaica, Ifloga spicata, Silene viviani, Sphaerocoma hookeri, Helianthemum lippi, Astraglus spinosus, Senna alexandrina, Salvia aegyptiaca, Schismus barbatus, Hyoscyamus muticus, and Verbena officinalis. As a result, action must be taken to safeguard threatened species by a variety of measures, including the establishment of protected areas, criminalizing exposure to endangered plants, creating a gene bank for these plants, and attempting to increase their numbers in practice.
In this study, many alien and invasive species, such as Euphorbia prostrate, were recorded [85]. The introduction of invasive and alien species into natural habitats represents a threat to existing species. Assaeed et al. [86] indicated that invasive and exotic plants may pose a threat to natural resources and biodiversity, especially in arid habitats. Successful invaders often exhibit great degrees of adaptability, allowing them to thrive in a variety of environments [87,88]. Plant shoot and root system features are thought to be good morphological criteria for predicting successful invasion in many habitat types [89]. Many invasive species contain allelopathic chemicals that enable them to invade and control plant communities [90].
Climate changes, in addition to human encroachments such as the construction of roads and the establishment of new cities, pose the main pressure on vegetation. Climate changes and human impact negatively affect biodiversity in several Wadies in the Egyptian Eastern Desert [91].
In this study, SAVI decreased during 2013 (from −0.02 to 0.42), 2015 (from −0.011 to 0.32), and 2020 (from −0.18 to 0.28). This result could be due to various human impacts in Wadi Hagul such as the construction of the new road Al-Galala-Hagul-Zafarana, which is 84 km long and 24 m wide and crosses Wadi Hagul, in addition to many other threats such as overgrazing, plant collection, and increasing demand for energy, which have led to exploration for oil and natural gas near Wadi Hagul. Large population growth in recent times has also led to increasing demand for building materials and opening quarries inside Wadi Hagul, which resulted in a local increase in transport and pollution. Finally, it was discovered that if environmental conditions (such as human interventions and climate changes) alter and become unsuitable for plant growth, they have a negative impact on vegetation cover, thus lowering the SAVI values.
In recent times, the preservation and protection of wildlife have become an urgent necessity, especially in the light of misuse of natural resources and encroachment of wildlife. Economic development and wildlife conservation can be simultaneously achieved by following the principles, rules, and requirements of sustainable development for balanced usage of available resources.

Conclusions
This study was conducted in an unprotected area, Wadi Hagul, Eastern desert, Egypt, to evaluate the relationship between environmental factors and the distribution of plant species, as well as evaluate the negative effects of uncontrolled human activities on both floristic composition and vegetation structure. Climate change, reflected in high temperatures and a lack of rain, also has a negative impact on vegetation cover in the study area, which is classified as a semi-arid desert. Ecosystems in general, especially deserts, are greatly affected by irresponsible human interventions. Hence, plans and strategies should be developed to conserve biodiversity. Within this context, the outcomes of this study, as well as those of other similar studies, will aid in the implementation of necessary environmental protection measures. Our study clearly showed a decreasing trend of SAVI across Wadi Hagul during 2013, 2015, and 2020. Physical factors, rather than anthropogenic, were the primary driving force for vegetation dynamics, whereas the effects of anthropogenic factors may be magnified when physical environmental factors provide unsuitable ambiance for vegetation growth. Other indexes must be measured to estimate vegetation cover, especially in unprotected areas subject to major human interventions, as can be carried out in future studies.