Plant communities along the international coastal highway of Nile delta , Egypt

The construction of highways promotes several changes in the roadside habitat, vegetation, and plant invasion. The present study aimed to describe the plant communities-environment interactions of the international coastal highway from Port-Said to Abu-Qir, northern Nile delta coast of Egypt. A total of 146 species (83 annuals, 4 biennials, and 59 perennials), belonging to 116 genera and 33 families were recorded in 80 stands. The Mediterranean chorotype is the most represented. The cluster analysis of stands yielded four communities. The community I was dominated by Silybum mariannum, community II was dominated by Mesembryanthemum crystalinum, Community III is the largest one and was co-dominated by Hordeum murinum and Senecio glaucus and community IV was codominated by Cakile maritima and S. glaucus. Diversity indices showed more richness of communities II and more evenness of community IV. Electric conductivity, porosity, soil texture, Na+, Cland bicarbonate showed significant variation among communities. The soil of C. maritima and S. glaucus community was more saline (1.78 ms cm-1). The application of CCA showed that communities II and III were mainly correlated with salinity and organic matter. The present study revealed that roadside habitat of the international coastal highway dominated by different plant communities which correlated with the habitat structure, salinity, and anthropogenic activities. Furthermore, nine invasive species were recorded in this study which could be attributed to the increment of human activities after the construction of the highway.


Introduction
The coastal areas of Egypt face several serious problems including high erosion rates, water logging and soil salinization, as well as several anthropogenic activities especially unplanned construction of villages and ecosystem degradation.The Nile Delta coast has a number of big cities with high population such as Alexandria, Rosetta, Damietta, and Port-Said.The international coastal highway, connecting the most eastern and western towns in Egypt, was constructed a parallel to the northern coast (El Raey, 1997;Eid and El-Marsafawy, 2002).
The Egyptian coastlines extend for about 3500 km along both Mediterranean Sea and Red Sea.The Mediterranean coastal land of Egypt extends between Sallum (on the Libyan borders) eastward to Rafah (on the Palestinian borders) for about 970 km with an average width ranging between 20-25 km in northsouth direction (Zahran and Willis 2009).
The number of roads is progressively increased today all over the world as human development grows and people rely on cars for transportation on a daily basis (Forman, and Alexander, 1998).The highways and agricultural (small) roads in Egypt make a network connected together with about 41000 km.Most of these roads are found in Nile Delta (18.7%) followed by Nile Valley (15.7%).In addition, the rate of car traffic ranged between 1000-2000 vehicle/day on the regional roads to more than 6000 vehicle/day on international coastal highways (Iraqi et al., 2002).
In natural vegetation of the deserts, the main factor affecting the abundance is the anthropogenic activities (Abd El-Ghani et al., 2013).Road and rail construction are some of these activities creating direct like degradation and/or fragmentation of the existing habitats and indirect impact on vegetation (Spellerberg, 1998;Jackson, 2000).
In roadside areas, the vegetation is mainly influenced by anthropogenic factors, geographical differentiation, and topography (Ullmann et al., 1990).The roadsides are characterized by a high proportion of therophytes and provide the main habitat for invasive species (Stottele, 1995).The impacts of invasive species on roadside vegetation have hardly been quantified as most studies focused on the impact on vegetation in the adjacent landscape (Sargent, 1984).Moreover, soil disturbance and modification of roadside substrates due to road construction result in increased non-native species cover and richness at roadsides (Greenberg et al., 1997).
The flora and the vegetation of the roadside habitat in Egypt attract the attention of many researchers (Morsy et al., 2008;Abdel Rahman and El Hadidy, 1958;Abd El-Ghani et al., 2013;El-Amier and Abdulkader, 2015).Moreover, the vegetation of the international coast highway from ElArish to Rafah on Sinai coast of Egypt was studied by Abd El-Ghani and El-Sawaf (2005).However, the vegetation composition of roadside habitat of the major part of the international coastal highway, northern Egypt, still not studied well.Therefore, the present study aimed to describe the plant communities of the international coastal highway from Port-Said to Abu-Qir, northern Nile delta coast of Egypt, as well as determine the vegetation-environment interactions.

Study area
The international coastal highway along the middle section of the Egyptian Mediterranean coastal zone is located in north Nile delta, between Abu-Qir (31°19′27.5″N30°04′00.6″E)and Port Said (31°16′09″N 32°18′19.1″E),and extends for about 230 km (Fig. 1).The area was chosen for its high environmental diversity.It represents the middle part of the international coastal highway that links Egypt with the countries of North Africa in the west, and those of the eastern Mediterranean in the east.
In coastal belt of Nile Delta, desert reclamation and agricultural processes were practiced and salient features in the study area.Irrigated gardens are another conspicuous feature along part of the seashore.In many instances, cultivation of barley, maize, tomato, sesame and watermelons was achieved.
Although, the climate of Nile delta coast is not so different from climates of the western and eastern Mediterranean sections, its vegetation is so different.Moreover, it is not only affected by sea water but also affected the leakage water from the River Nile branches (Damietta and Rosetta branches) as well as the northern lakes (Zahran and Willis, 2009).

Vegetation analysis
A quantitative survey of the roadside vegetation was made during the period from March to May of the year 2015 and 2016.Eighty stands were randomly chosen in the roadside of the international coastal highway where considerable variation in vegetation was encountered.In each of the studied stands, three plots (5 m × 5 m) were distributed in the left and right sides as well as in the central part of the road, if any.Plant density and cover were measured according to Shukla and Chandel (1989) in each plot.Relative values of density and cover were calculated for each plant species and summed up as the importance value (IV).The lists of species recorded are identified according to Tackholm (1974) and Boulos (1999Boulos ( -2005)).The chorology of the plant species within the study area was cited according to Zohary (1966 and1972).The plant life forms were identified according to the scheme of Raunkiaer (1934).

Plant species diversity
Species richness and evenness were calculated for each community by determination of Shannon-Wiener diversity index (H), Simpson Diversity Index (D) and Shannon-evenness index (E) using the following equations: Where, Pi = ni/ N and ni is the total number of a particular species (s) and N is the total number of all species.

Analysis of soil samples
One composite soil sample was collected from each stand (0-20 cm depth) and transferred to the laboratory in a polyethylene bags.The soil samples were dried, sieved and stored until further analysis.For the dry samples, soil texture, water holding capacity (W.H.C.), porosity, amount of organic carbon and sulfate content were determined according to Piper (1947), while calcium carbonate content was determined according to Jackson (1962).Soil solution (1:5) was prepared and electrical conductivity and pH values were recoded immediately using portable meter (Model Corning, NY 14831 USA) (Jackson, 1962).Moreover, chloride content was determined by the method adopted by Jackson (1962).Carbonate and bicarbonate were determined by titration using 0.1N HCl (Pierce et al., 1958).However, Na + and K + concentration was estimated by Flame Photometer (Model PHF 80 Biologie Spectrophotometer), while Ca 2+ and Mg 2+ were determined using atomic absorption spectrometer (A Perkin-Elmer, Model 2380.USA) (Allen et al., 1974).

Data analysis
The cluster analysis of the stands was performed using the Community Analysis Package program, version 1.2 according to Hill and Smilauer (2005).However, the ordination of stands (Principal Component Analysis, PCA) and Canonical Correspondence Analysis (CCA) were performed using MVSP Program version 3.2 (ter Braak, 1988).The soil variables for each community were subjected to one-way ANOVA and the mean values were separated based on Duncan's test at 0.05 probability level, using COSTAT 6.3 program.

Chorological affinities
Chorological analysis of the surveyed flora in the study area (Table 1) revealed that 68 species (46.58% of the total flora) were bi-and pluriregional Mediterranean elements.Monoregional chorotypes extending their distribution all over the Saharo-Sindian (10 species) and Mediterranean regions (23 species) amounted to 22.6% of the recorded flora.On the other hand, Cosmopolitan, Palaeotropical, Pantropical and Neotropical chorotypes constituted 28 species of the total recorded flora (Fig. 3).

Vegetation analysis
The TWINSPAN classification based on the importance value of 146 plant species, recorded in 80 stands, separating 4 plant communities (eigenvalue = 0.37) was shown in Fig. (4).Each plant community comprises a set of stands which are similar in their vegetation and named after the first and second dominant species with the highest important values (Table 2).Community I was dominated by Silybum mariannum; as well as this community was the smallest one and consequently less diverse and resembled by 5 stands.Moreover, this community also contained other important associated species with high importance value such as Hordeum murinum, Malva parviflora, Chenopodium murale, Carduus pycnocephalus and Urtica urens (Table 2).However, community II was dominated by the ice plant (Mesembryanthemum crystalinum), with 97 associated plant species distributed in 19 stands, amoung these associated species, Melilotus indicus and Malva parviflora were the most important.

Plant diversity of the plant communities
The identified plant communities demonstrated differences in species richness and evenness (Table 2 and Fig. 6).The communities II (Mesembryanthemum crystalinum community) and IV (Cakile maritima and Senecio glaucus community) showed more richness, while the community I (Silybum mariannum community) was the lowest diverse one, where its Simpson index was 0.94.On the other hand, according to the plant evenness, the communities IV and I attained the highest Shannon-Wienner index of 0.87 and 0.86, respectively (Fig. 5), however, the community III (Hordeum murinum and Senecio glaucus community) was showed the lowest plant evenness.

Soil-vegetation relationships
The soil analysis of the represented stands of the four separated plant communities indicated considerable significant variations in soil variables, although others did not show significant variation (Table 3).Electric conductivity, porosity, soil texture, Na + , Cl -and bicarbonate showed significant variations (P < 0.05) among the identified communities.The soil texture of all communities is mainly composed of coarse sand fraction, while the community co-dominated by Hordeum murinum and Senecio glaucus showed the highest value of sand fraction.The soil of Cakile maritima and Senecio glaucus community was more saline (1.78 ms cm -1 ) compared to other communities, as expected.Moroever, this community showed the highest values of Na + , Cl -and bicarbonates.Howevere, the other measured soil variables (pH, WHC, calcium carbonate, organic carbon, sulphate, K + , C 2+ and Mg 2+ ) did not showed a significant variation betweeen the identified communities (Table 3).
The application of CCA on the important plant species with environmental (soil) variable showed diferrent correspondene of the different plant species with the soil characteristcs (Fig. 7).The plant species of community I exhibit a close relationship with sulphate and K + .However, communities II and III were mainly correlated with salinity and organic matter, where they were positively correlated with electric conductivity, organic carbon and Na + , while Cl -content was negatively correlated with the both communities (Fig. 7).Community IV showed postive correlation with both Mg 2+ and Ca 2+ , while it was negatively correlated with pH and clay content.

Discussion
The international coastal highway is one of the most important roads in Egypt, where it connect the country from east to west.This highway crosses along semi natural areas with different habitats, contained very important natural flora and fauna.The construction of this road resulted in changes in the plant composition as well as increases the human activities along the coastal part of the country.
The floristic analysis of the present study revealed that roadside habitat of the international highway comprises 146 plant species, mainly annuals, where the plants were flourished after the rainfall.This part of the country received the highest amount of the rainfall in the winter season (Zahran and Willis, 2009).Annual plants characterized by high reproductive capacity, as well as ecological, morphological and genetic plasticity (Grime, 1979;Kowarik, 1985).
In harmony with other related studies, Asteraceae, Poaceae, Chenopodiaceae, Fabaceae and Brassicaceae were the major families and also is the most common families in Mediterranean North African flora (Abd El-Gawad and Shehata, 2014;El-Amier et al., 2014).Asteraceae is the largest and most widespread family of the flowering plants in the world (Walters and Keil, 1996).
Nine invasive species were recorded in this study representing 8.33% of the invasive species in the Nile region of Egypt (Shaltout et al., 2016), which corroborated to the increasing human activities along the highway.The transportation is considered as one of the most important way for the invasive plant to spread in new localities.Moreover, soil disturbance and modification of roadside substrates due to road construction result in increased nonnative species cover and richness at roadsides (Greenberg et al., 1997).
The life form analysis of the recorded species showed that therophytes are the most represented form, where it may be attributed to their short life cycles that enable them to resist the instability of the environmental condition, the climate of the Mediterranean region, topography variation and biotic influence (Heneidy & Bidak, 2001).Moreover, the relatively high value of hemicryptophytes of the plant species in the present study may be attributed to the ability of these species to resist drought, salinity, sand accumulation and grazing (Danin & Orshan, 1990;Danin, 1996).
The widespread of the Mediterranean chorotype of the surveyed flora in the study area reflects the Mediterranean climate of studied area.This result agrees with most of related studies (Salama et al., 2013;Barakat et al., 2014;El-Amier, 2016).Saharo-Arabian and Mediterranean chorotypes represented 22.6% of the recorded flora.This may be attributed to the fact that plants of the Saharo-Arabian species are good indicators for harsh desert environmental conditions, while Mediterranean species are considered as signal to mesic environment (El-Husseini et al., 2008;Abd El-Ghani et al., 2011).The whole country lies within the Saharo-Arabian belt of the Holarctic floristic realm (Abd El-Ghani et al., 2011).
It is worth noting that, a mixture of different floristic elements such as Cosmopoliton, Palaeotropical, Pantropical, Neotropical, Saharo-Sindian, Sudano-Zambezian, Australian and Irano-Turanuian elements are represented by variable number of species in the study area.This may be attributed to human impact, history of agriculture and capability of certain floristic elements to penetrate the study area from several adjacent phytogeographical regions (Zahran & Willis, 2009).
The roadside habitat of the international coastal highway dominated with different plant communities.In the present study we determine four communities, three (communities II, III and IV) were the richest and diverse, while community I is the smallest and less diverse one.In accordance, the ordination of the plant communities showed that these three communities were slightly overlapped, reflecting more similar vegetation structure and environmental variables.
Among the identified communities, community II, dominated with Mesembryanthemum crystalinum, was mainly correlated with salinity and organic matter which could be correlated to the habitat structure, salinity and the anthropogenic activities (Abd El-Gawad and Shehata, 2014).Also, this plant is an important species of the community III and community IV.Moreover, other salt tolerant species associated with this community such as Melilotus indicus and Malva parviflora, Phragmites australis, Chenopodium murale and Hordeum murinum.
The high ecological amplitude of Mesembryanthemum crystallinum in this community may be attributed to its adaptation to harsh environmental condition.Moreover, this species is very tolerant to salinity where it survived well in saline soils, salt spray and coastal conditions (Adams et al., 1998;El Shayeb et al., 2002), as well as it can accumulate salt in the top soil, hindering nontolerant species and subsequently increases its abundance (Dassonville et al., 2007).The identified communities in the present study are in harmony with the study of Abd El-Gawad and Shehata (2014), whom determined also four communities in the deltaic Mediterranean coast, three dominated with Mesembryanthemum crystallinum, while one community dominated with Hordeum murinum.Nevertheless, the ordination of the plant communities II, III and IV showed that they were slightly overlapped, meaning more or less similar characteristics.

Conclusion
The deltaic areas are sensitive ecosystem toward both natural hazards and human interventions.During the last decades, the Nile Delta coast in Egypt subjected to several threats, mainly anthropogenic impact.The construction of the international coastal highway made the study area accessible to urbanization; therefore, change the natural habitats and the vegetation.The present study revealed that roadside habitat of the international coastal highway dominated with different plant communities which correlated with the habitat structure, salinity and the anthropogenic activities.Furthermore, nine invasive species were recorded in this study representing 8.33% of the invasive species in the Nile region of Egypt, where it could be attributed to the increment of human activities after construction of the highway, especially reclamation practices.

Fig. 1 .
Fig. 1.Map showing the Nile delta with the study are in the northern part.

Fig. 5 .
Fig. 5.The biplot ordination of different stands of the four identified plant communities along the international coastal highway, identified from TWINSPAN.

Fig. 6 .
Fig. 6.Species diversity, richness and evenness of different identified plant communities along the international coatsal highway.

Table 1 .
Atriplex and Cyperus were the largest genus represented by four species (Table1).Floristic composition and presence value (P%) of the recorded species in the studied area.

Table 2 .
Plant communities, species diversity, and invasive species in each community along the international coastal highway.

Table 3 .
Soil variables of different plant communities obtained from TWINSPAN.