Composition, distribution patterns and habitat divergence of street trees in the Greater Cairo City, Egypt

M. M. Abd El-Ghani*, M. M. Abou-El-Enain**, A. I. Aboel-Atta** , Ethar A. Hussein**

*The Herbarium, Faculty of Science, Cairo University, Giza 12613, Egypt; *Author for correspondence

                                                         (e-mail: elghani@yahoo.com)

**Department of Biological and Geological Sciences, Faculty of Education, Ain Shams University, Roxy, Heliopolis 11341, Cairo, Egypt

ABSTRACT:

Species diversity of the tree flora of 38 districts in the Greater Cairo city was studied with reference to landscape differentiation of species make-up. Three main habitats including 14 sites with 263 sample plots were considered (35 urban parks, 76 road islands and 152 street verges). In total, 378 of vascular plant species belonging to 264 genera and 79 families were recorded in urban areas of the Greater Cairo city. The most species-rich (44.7%) families were Fabaceae (36 spp.), Asparagaceae, Poaceae (21 spp.), Moraceae (19 spp.), Asteraceae (17 spp.), Euphorbiaceae and Malvaceae (15 spp.), Arecaceae (14 spp.), Lamiaceae (11 spp.), whereas the remaining families (70) constituted together 193 species. Ficus (18 spp.) was the highest among the species-rich genera, followed by Euphorbia (11 spp.), Asparagus, Brachychiton, Callistemon, Citrus and Pinus (4 spp. each). 257 genera contained only 1-3 species e.g. Cereus, Koelreuteria, Strelitzia, Terminalia, Carica and Toona. Growth form spectra revealed that, the recorded trees (139 spp.) belonged to 32 families; shrubs (79 spp.) to 30 families, herbs and others (160 spp.) to 48 families.

Keywords: Urban biodiversity, street trees, urban trees, metropolitan flora, Egypt, growth forms, green spaces.

Introduction

The proportion of the world’s population living in urban areas is increasing rapidly such that by 2030 almost two-thirds of the world’s population will reside in cities (United Nations, 2007). Urban landscapes are generally dominated by human infrastructure: building (residential and industrial); transport links (roads, pavements, railways, canals); and open land required for parking vehicles and disposal of waste. There also, sometimes substantial, areas of green space: gardens, parks, playing fields, golf courses, road verges and grounds of public institutions comprise nearly half of the land area (Baines, 1995). Urban- industrial ecosystems differ from non-urban ones in a number of ways. Most of the factors which affect ecosystems in cities (climate, soil, water conditions, human impact, etc.) are comparable to the site conditions in non-urban areas; the combination of these factors creates unique urban-industrial ecosystems. Consequently, the city has to be regarded as a new type of environment with species compositions and habitats peculiar to urban-industrial areas (Maurer, 2002).

Biodiversity conservation in greater cities faces an uphill battle due to rapid development and urbanization (Tsai, 1999). The considerable magnitude, extent and pace of urban expansion have brought drastic habitat degradation and biodiversity losses at different scales (Czech & Krausman, 1997; Cilliers, et al., 2004; Prasad & Badarinth, 2004; McKinney, 2006). Consequently, the sustainability of towns and cities is becoming an environmental issue of increasing concern. In this regard, urban greening is of primary interest because it provides numerous ecosystem goods and services which benefit humankind (Colding et al., 2006), a key one of which is biodiversity (Jim & Chen, 2009). Biodiversity in cities provides social and biological functions to residents, including ecological balance, ecosystem services, environmental protection, outdoor recreation, aesthetic enjoyment, nature education, and refuges and dispersal centres for wildlife species (Box & Harrison, 1994; Reduron, 1996; Tsai, 2001; Cilliers et al., 2004). The sustainable development of human society could be achieved with the help of ecological sustainability, in which urban biodiversity conservation could play a useful role.

Egypt's population still grows each year by approximately 1.5 million people. United Nations projections indicate that the population will grow from 62.3 million in 1995 to 95.6 million by 2020. Increased habitat fragmentation is of particular concern in Greater Cairo city because it is located on the Nile River. Habitat loss and fragmentation are important factors contributing to a reduction in the planet's biodiversity. Besides resource extraction in mining, fishing, and forestry, most habitat loss and fragmentation is due to urban and agricultural development (Wasylikowa et al., 1991). Urban green spaces provide sustenance for many floral and faunal species. They contribute notably to urban diversity conservation (Box & Harrison, 1994; Sukopp, 2002; Thompson et al., 2003; Smith et al., 2006). Many studies focused on plant diversity (e.g. Pyšek, 1989;  Zerbe et al., 2003; Turner et al., 2005; Smith et al., 2006), others on animals (e.g. Melles et al., 2003; Shochat et al., 2004), or in both plants and animals (Angold et al., 2006).

Despite the growing acknowledgement of the importance of green spaces and trees in the urban environment, most of the research into, and understanding of, urban greening is centered on examples from the developed world, predominantly from European and North American countries, and has been investigated by many authors e.g. Wittig (2004), Loram et al. (2007), Ken (2009), and Stewart et al. (2009). In Egypt, there is a limited literature on urban greening, and even less on urban forestry, including street trees (El Hadidi and Boulos, 1988; Soliman & Amer, 2002). However, most of the vegetation studies were stressed on the Egyptian wild flora (Täckholm, 1974; Boulos & El Hadidi, 1994; El Hadidi & Fayed, 1995; Boulos, 1995; 1999; 2000; 2002; 2005 and 2009), which indirectly increased the knowledge about identification, description, and recording the wild plants. Hence there is a paucity of documentary studies on the cultivated plants in parks, avenues and urban areas generally in Egypt and specifically in the Greater Cairo.

The present study aimed at: (1) evaluating the current status of species diversity of the tree flora of selected areas in the Greater Cairo city with reference to the landscape differentiation of species make-up; (2) application the methods of quantitative analysis of vegetation to study the arborescent components; (3) evaluating the similarity and divergence of floristic composition in three major urban green landscape types (urban parks, road islands and street verges) by using quantitative methods of community ecology; and (4) exploring the underlying nteractions between human disturbance, habitat conditions and tree composition.

The study area

Egypt is divided into four major geomorphologic areas: Nile River (Valley and Delta), Western Desert, Eastern Desert, and Sinai Peninsula. The Nile Valley known as Upper Egypt extends along the Nile River from Aswan to the outskirts of Cairo, while the Nile Delta is known as Lower Egypt. The Nile Delta is a classic delta with a triangular shape situated in North Egypt where the Nile River spreads out and drains into the Mediterranean Sea. The area chosen for the present study i.e. Greater Cairo region is located at southern of the Nile Delta, 165 km south of the Mediterranean Sea and 120 km west of the Gulf of Suez and Suez Canal; between 29˚ 45΄, 30˚ 10΄ of the northern latitudes and between 31˚ 05΄ and 31˚ 30΄ of the eastern longitudes (Fig. 1). Its center (Cairo city) is found along the Nile River, immediately south of the point where the river leaves its desert-bound valley and branches into the low-lying Nile Delta region. It extends on a total area of about 717 Km2 as an administrative semi-official entity including Giza city and some of its suburbs; Shubra-Al-Khaymah of the Qalyubia province. It comprises 38 districts (Fig. 1) along both banks of the Nile from Shubra-Al-Khaymah in the north to Helwan in the south (Robaa, 1999; Bondok, 2004). Shubra-Al-Khaymah and El-Qanater regions of Qalyubia province have previously been covered (Hussein, 2011 and El-Sheikh et al., 2004, respectively) so that they are excluded from the present study.

Study area is considered as one of the world's 15أکبر المدن في النمو الحضري والسکاني. largest cities in urban and population growth, where almost 20% of all Egyptians lived in the urban agglomeration known as Greater Cairo (Robaa, 1999).

Climatically the study area is in the subtropical climatic region; the climate is a mixture between the Mediterranean and the desert, but often with high humidity due to the river valley's effect. من بين الظواهر الجوية المعلقة هي الغبار والعواصف الرملية التيAmong the outstanding weather events are the dust and sandstorms that ضربة کثيرا في المواسم الانتقالية من الربيع (مارس إلى مايو) والخريف (من سبتمبر إلىfrequently blow in transitional seasons of spring (March to May) and autumn (September to تشرين الثاني).November). في فصل الربيع، ومن المعروف منخفضات الصحراء الساخنة مثل المنخفضات ريح حارة. In spring, hot desert depressions are known as the Khamsin depression. فهيThey areيترافق دوما مع الرياح القوية الحارة والجافة في کثير من الأحيان محملة بالغبار والرمال وزيادة في الغلاف الجوي always associated with strong hot dry wind often laden with dust and sand increasing the atmosphericالتلوث.Pollution.في فصل الشتاء (ديسمبر إلى فبراير) أن المناخ العام للمنطقة القاهرة الکبرى هي In winter (December to February), the general climate of the Greater Cairo region isبارد، في حين رطبة والأمطار خلال فصل الصيف (يونيو إلى أغسطس)، والمناخ في القاهرة حار وجاف وشح الأمطار. cold, moist and rainy while during summer (Jun to August), Cairo's climate is hot, dry and rainless (Robaa, 1999). High temperatures in winter range from 19°C to 29°C, while night-time lows drop to below 11°C, often to 5°C. In summer, the highs rarely surpass 40°C, and lows drop to about 20°C. Rainfall is sparse, but sudden showers do cause harsh flooding. The average long-term of climatic data over 10 years (from 2003-2013) for this region is obtained from Egyptian Meteorological Department, Cairo. The urbanization and industrialization have increased very rapidly in Greater Cairo, ولا سيما في النصف الثاني من القرن الماضي مما تسبب زيادة في تلوث لهاparticularly in the second half of the last century causing an increase in the pollution of its الغلاف الجوي.atmosphere. وهذا بدوره له دور فعال في تکثيف لمشکلة تلوث في القاهرة This in turn has an effective role in intensifying the problem of contaminating Cairo’sبيئة مع العديد من الشوائب والمخاطر البيئية (Robaa وحافظ، 2002). environment with various impurities and environmental hazards (Robaa & Hafez, 2002).

Fig. 1: Satellite image of the Greater Cairo city showing sites of the study area.

Methods

Field work and data collection

This study focused on landscape tree flora in urban area of the Greater Cairo City. Field trips were conducted to sites of the study area; each site was divided into a number of randomly selected sample plots which were surveyed periodically during the period of study from winter 2012 to summer 2014 to enumerate the growing species and record their distribution patterns. Distributed randomly, the sites were selected in different areas of both old and new suburbs to record; as much as possible; the similarity and divergence of tree communities in urban green landscape types. Three main habitats were considered: (1) street verges (SV), represented by the area of land that lies between the road edge and the property boundary; (2) road islands (RI), viz. medians and central islands are the portion of the roadway separating opposing directions of the roadway

and represented by a planter space that located in the middle of the street; and (3) urban parks

 (UP), delineated open green areas are at least 2500 m², with a minimum width of 10 m, mostly

dominated by vegetation and water, and generally reserved for public use, such as gardens, zoos, parks. For this purpose, 14 sites included 263 sample plots (35 urban parks, 76 road islands and 152 street verges) in the three recognized habitats were evaluated as representative samples that accommodate most landscape trees and main site variations.

The present floristic status has been described in terms of species presence/absence. Taxonomic diversity and growth forms in each urban habitat have been also estimated and graphically compared. Specimens of the recorded taxa have been identified and checked at both the herbaria of Cairo University (CAI)

and the Orman garden. Photographs were taken and vouchers are kept (excluding palms and succulents) at the Herbarium of the Biological and geological Sciences Department, Faculty of Education, Ain Shams University. Wild species nomenclature follows Täckholm (1974), Boulos & El Hadidi (1994), El Hadidi & Fayed (1995) and Boulos (1995; 1999; 2000; 2002; 2005 and 2009). Systematic and nomenclatural revisions of the recorded taxa have been aided by each of Hooker & Jackson (1893), Bailey & Bailey (1976), Huxley et al. (1992), GRIN (2012), W3Tropicos (2014).

Data analysis

A data matrix was constructed based on a binary code (presence/ absence) for the scored species in the study area. Data was processed by multivariate analysis using Multivariate Statistical Package MVSP for Windows, version 3.1 (Kovack, 1999). All other statistical analyses are carried out using SPSS for windows version 10.0 (SPSS, 1999).  For the classification of vegetation, cluster analysis using minimum variance as agglomeration criterion (Orloci, 1978) was applied to squared Euclidean distance dissimilarity matrix and the obtained groups are represented in a dendrogram. In order to reveal possible intrinsic patterns, vegetation ordination with Principal Coordinates Analysis (PCoA) is preformed using the product-moment correlation as a coefficient. It is preferred over PCA (Principal Components Analysis) because the former performs better on data sets with missing data (Rohlf, 1972). Sites that are more similar in vegetation structure (species composition and abundance) were depicted as being closer together in the diagram.

Results

General floristic features

The study revealed a total of 378 taxa in 79 families and 264 genera of the seed plants were recorded in urban areas of the Greater Cairo city. Generally, the most species-rich families were Fabaceae (36 species), Asparagaceae and Poaceae (21 species for each), followed by Moraceae (19), Asteraceae (17), Euphorbiaceae and Malvaceae (15 species each), Arecaceae (14), Lamiaceae (11 species) and comprise about 44.7% of the recorded species. The other remaining families (70) were represented by less than ten species, and constituted together 193 species, as Bignoniaceae and Myrtaceae (9 species each), Apocynaceae and Solanaceae (8 species each), Acanthaceae and Araceae (7 species each), Brassicaceae, Cactaceae, Rutaceae and Verbenaceae (6 species each), Amaranthaceae, Anacardiaceae, Araliaceae and Rosaceae (5 species each), and Convolvulaceae, Cupressaceae, Pinaceae and Sapindaceae (4 species each). Fifty two families are represented by 1-3 species; amongst others, these families include Araucariaceae, Oleaceae, Cycadaceae, Geraniaceae, Sterculiaceae, Cannaceae and Zygophyllaceae. The present results also indicated that, Ficus (18 species) is the highest among the species-rich genera, followed by Euphorbia (11), Asparagus, Brachychiton, Callistemon, Citrus and Pinus (4 species each). It is noted that 257 genera contain 1-3 species only, examples of these species are: Cereus, Koelreuteria, Strelitzia, Terminalia, Carica and Toona were recorded.

Growth forms spectra (Fig. 2) revealed that, flora of the study area is classified into: trees (139 species; among them 14 were palms, 11 were conifers and two were cycads), shrubs (79), annuals (54), perennial herbs (53), succulents (22), climbers (18), tree-like (7) and cacti (6). Woody perennials (trees and shrubs) constituted the main bulk of the flora of urban area in the Greater Cairo City (218 species) represented 57.7% of the total flora. The recorded trees belonged to 32 families; the most common are Fabaceae (24 species), Moraceae (21 species), Palmae (14), Malvaceae and Myrtaceae (9 species each). Shrubs are represented by 30 families; mostly Euphorbiaceae (9 species), Apocynaceae and Fabaceae (6 species each). On the other hand, herbs with the other remaining growth forms were represented by 160 species belonged to 48 families; of which Poaceae contributed the heighest number of species (21), Asparagaceae (17) then Asteraceae (15 species).

Floristic composition of habitats

Street verges

The species compositions of street verges are collected from 14 sites to represent the plant life in this habitat. Altogther, 246 species belonging to 181 genera and 69 families are recorded (Table 1). More than 50% of these species belonged to 8 species-rich families arranged in the following sequence: Fabaceae (23 species), Moraceae, Poaceae (17 for each), Malvaceae (12), Arecaceae, Asparagaceae (11 for each), Euphorbiaceae and Lamiaceae (9 species for each). However, 44 families are represented by only 1-2 species (e.g. Nyctaginaceae, Salicaceae, Casuarinaceae, Meliaceae, Musaceae and Rhamnaceae). The genera that contained the highest number of species are Ficus (16), Euphorbia (6), Citrus (4), Ceiba and Pinus (3 for each). It was noted that 176 genera contained 1-2 species only (e.g., Bauhinia, Bougainvillea, Cassia, Ipomoea, Albizia, Enterolobium and Jacaranda).

Growth forms spectra are varied greately in the street verges habitat where trees (103 species) showed the highest representation of the total number of recorded species (Fig. 3) followed by shrubs (47), Perennial herbs (32), Annual herbs (31), Succulents (14), Climbers (12), Tree-like (5) and Cacti (two species). Woody perennials (trees and shrubs) constituted the main bulk (150 species) of the flora of street verges representing 61% of the total flora. The most important recorded woody perennials are Ficus microcarpa (P=94.1%), Delonix regia (P=83.6%), Ficus benjamina (P=75%), Ficus elastica var. Decora (P=67.8%), Phoenix dactylifera (P=52%) and Morus sp. (P=49.3%). Canna indica (P= 12.5%), Phragmites australis (P=5.3%), Lolium perenne and Ruscus aculeatus (P=3.3% each) are the most important perennial herbs. Annual herbs such as Chenopodium murale (P= 28.9%), Amaranthus hybridus (P=25%), Sonchus oleraceus (P=17.8%), Euphorbia peplus (P=16.4%), Solanum nigrum (P=13.2%), Portulaca oleracea (P=11.2%) and Trianthema portulacastrum (P=7.2%) were noted. Succulents, climbers and cactus plants are modestly represented such as Yucca guatemalensis (P=55.3%), Euphorbia umbellata (P=28.3%), Sansevieria trifasciata (P=14.5%), Ipomoea cairica (P=9.2%) and Opuntia ficus-indica (P= 0.7%).

Road islands

To recognize the species composition in road islands habitat, species are collected from 76 selected sample plots representing most of the plant life. Such plots are regularly distributed in the 14 studied sites in Greater Cairo city. Altogether 224 species of vascular plants belonging to 161 genera in 58 families are recorded; from which nine constituting most of the studied species with a percentage of 50.9%. Species-rich families are Fabaceae (22 species), Poaceae (18 species), Moraceae (15 species), Asparagaceae (13 species), Asteraceae, Euphorbiaceae (11 species each), Malvaceae (10 species), Arecaceae (8 species) and Lamiaceae (6 species). Thirty-four families are represented by 1-2 species; amongst others, Araucariaceae, Cannaceae, Geraniaceae, Lytharaceae, Meliaceae, Strelitziaceae and Tropaeolaceae were recorded. The most species-rich genera are Ficus (14 species), Euphorbia (8), Citrus (4), Brachychiton, Cyperus and Yucca (3 species each), whereas the other remaining genera are either represented by 2 or one species.

The growth forms analysis (Fig. 3) indicated that the Trees (79 spp.) are highly represented followed by Annual herbs (45 spp.), Shrubs (42 spp.), Perennial herbs (38 spp.), Succulents (13 spp.), Climbers (5 spp.), Cacti and Tree-like (1 spp. each). Woody perennials constituted the main bulk of the flora, where 121 species (54% of the total flora of the city) were recorded. The most important recorded woody perennials are Ficus microcarpa (P=77.6%), Ishingtonia robusta (P=72.4%), Acalypha wilkesiana (P=67.1%), Nerium oleander (P=64.5%), Dodonaea viscosa (P=56.6%), Phoenix dactylifera (P=52.6%), and Delonix regia (P=50%). Among the important perennial herbs are Cynodon dactylon (P=84.2%) and Alternanthera brasiliana (P=35.5%). The annuals included; Amaranthus hybridus (P=50%), Poa annua (P=47.4%) and Euphorbia peplus (P=46.1%).

Cleary, this habitat characterized by a mixture of wild and cultivated species, for example of wild species; Amaranthus hybridus, Poa annua, Euphorbia peplus, Sonchus oleraceus, Paspalidium geminatum, Plantago major and Urtica urens, while the cultivated species included Ficus microcarpa, Washingtonia robusta, Nerium oleander, Dodonaea viscose, Delonix regia, Hibiscus rosa-sinensis and Lantana camara.

Urban parks

Thirty-five sample plots are selected to represent most of the plant life in urban park habitat. They are conducted to sites of the present study area except those of El-Matariya, El-Maadi, El-Mohandessin and El-Dokki districts. The vascular flora contained a total of 346 species from 246 genera and 77 families. The largest families in terms of the number of species are each of Fabaceae (34 species), Asparagaceae (18), Asteraceae, Poaceae (17 spp. each), Moraceae (15), Arecaceae (14), Euphorbiaceae, Malvaceae (12 spp. each) and Lamiaceae (10 species). Furthermore, 41 families comprised 1-2 species; amongst others, they include Crassulaceae, Strelitziaceae, Zamiaceae, Cucurbitaceae, Rubiaceae and Sapotaceae.

The results indicated also that the highest species-rich genera are Ficus (14 species), Euphorbia (10 species), Callistemon, Pinus and Citrus (4 species for each), whereas 241 genera contain 1-3 species only, examples of these species are: Asparagus, Opuntia, Araucaria, Cordia, Terminalia, Vitex, Anisacanthus, Ruellia and Mimusops. Analysis of the growth form spectra revealed that, the majority of the recorded species are woody perennials (57.8% of the total flora), whereas Trees comprised 127 species of the total number of recorded species followed by shrubs (73 species), Perennial herbs (51 species), Annual herbs (48 species), Succulents (20 species), Climbers (15 species), Tree-like (7 species) and Cacti (five species).

The most important recorded woody perennials are Ficus microcarpa (P= 94.3%), Acalypha wilkesiana ‘Mooeri’, Delonix regia, Hibiscus rosa-sinensis (P= 85.7% for each), Platycladus orientalis, Lantana camara (P= 82.9% for each) and Dodonaea viscose (P= 80%). Cynodon dactylon (P= 94.3%), Plantago major (P= 71.4%), Alternanthera brasiliana (P= 68.6%), Centaurea cineraria (P= 57.1%), Gazania rigens (P= 48.6%) and Asparagus densiflorus (P= 42.9%) are the most important perennial herbs. Annual herbs such as Amaranthus hybridus (P= 85.7%), Euphorbia peplus (P= 82.9%), Chenopodium murale (P= 71.4%), Sonchus oleraceus, Poa annua (P= 68.6% each), Oxalis corniculata (P= 60%) and Melilotus indicus (P= 57.1%) were noted. Several growth forms of succulent, climber and cactus plants were modestly represented such as Yucca aloifolia (P= 45.7%), Agave americana (P= 40%), Sansevieria trifasciata (P= 34.3%), Ipomoea cairica (P= 20%) and Opuntia ficus-indica (P= 5.7%).

Actually, urban park habitat is marked by the presence of greatest biological diversity between all the studied habitats, it included some ornamental plants; such as Cassia javanica subsp. nodosa, Plumeria rubra, Thevetia peruviana, Gazania rigens, Kalanchoe marmorata and Platycladus orientalis. Also, it contained shade plants; e.g. Ficus benghalensis, Ficus benjamina, Ficus elastica, Ficus religiosa, Melaleuca ericifolia and Brachychiton discolor, hedge plants; e.g. Dodonaea viscosa, Duranta erecta, Hibiscus rosa-sinensis and Malvaviscus arboreus, fruit plants; such as Casimiroa edulis, Mangifera indica, Psidium guajava, Hyphaena thebaica, Phoenix dactylifera, Citrus aurantium, C. limon, C. reticulata, C. sinensis, Carica papaya, Musa sp. and Cordia sebestena. It comprised some medicinal plants; amongst others, Aloe vera, Mentha sativa, Rosmarinus officinalis and Ocimum basilicum, poisonous plants; e.g. Melia azedarach and Cynanchum acutum, vegetables plants; for example Solanum lycopersicum var. lycopersicum, Malva parviflora and Eruca sativa. Also, it included some timber plants (e.g. Eucalyptus camaldulensis, Dalbergia sissoo and Cassia fistula), oil plants (e.g. Olea europaea var. europaea), and fiber plants (e.g. Bombax ceiba and Ceiba pentandra).

Fig. 2: General distribution pattern of the growth forms

 for the recorded species in the study area.

Fig. 3:Distribution patterns of the growth forms for the recorded species in the three studied

urban habitats. Abbreviations: SV = Street Verges, RI = Road Island and UP = Urban Parks

General distribution patterns of species in the habitats

The total number of recorded species and species richness of the recognized habitats showed remarkable differences (Table 1). While the public gardens had the highest species number and richness (346 species), followed by street verges (246 species), the road islands had the lowest ones (224 species).  Species of fifty-three families were widely distributed and represented in all the studied urban habitats. In the same time, eight families were confined to either the urban parks habitat (6) or the road islands habitat (2).

The results revealed also that some of the recorded species had wide ecological range of distribution, besides F. microcarpa, Cynodon dactylon, Delonix regia and Washingtonia robusta which are widely planted in all three habitats, 164 species were shared between them. Fifty-seven species were shared between street verges and urban parks, 38 between road islands and urban parks, and 7 species only between street verges and road islands. On the other hand, 108 species (28.6% of the total) demonstrated a certain degree of consistency, where they are exclusively recorded or confined to a certain habitat and do not penetrate elsewhere. These species are distributed as follows: 83 in the urban parks, 14 in the street verges and 11 in the road islands.

Eight different growth forms were observed in all the studied urban habitats. In general, trees are the dominant growth forms followed by shrubs and herbs.

 Arborescent species constituted 37% of the total number of recorded species, mostly native to tropical, sub tropical and temperate species. The urban parks and road islands shared in high percentage of herbs (99 and 83 species respictively) comparable to street verges.

Classification of species composition in the three studied habitats by using cluster analysis based on the species percentage yielded two major vegetation groups A & B (Fig. 4). Group A can be divided into two sub groups; Group A1 comprised thirteen sites from street verges habitats and Group A2 included 14 sites of road islands and one site of street verges habitats. Group B included 14 sites from urban parks habitats. This classification of the examined habitats is confirmed by the Principal Coordinate Analysis (PCoA; Fig. 5), which demonstrated the segeration of the three groups along the first two axes. The first (eigenvalue = 2.115) and second (eigenvalue= 0.923) axes accounted of the overall floristic variance. Along PCoA axis 2, the urban parks (Group B) occupied the extreme negative end; while all of street verges except one site (group A1) are located in the extreme positive end of the same axis. The road islands and the rest site of street verges (group A2) occupied an intermediate position between groups A1 and B.

Table 1: Distribution of the recorded species in relation to the three habitats recognized

in the study area, with their presence values (P%). For abbreviations, see Fig. 3.

Fig. 4. Cluster analysis dendrogram of the studied habitats.

Fig. 5. Prinicipal Coordinates Analysis (PCoA) of the three habitats,

with three groups clearly separated   along axes 1 and 2.

Discussion

Studies on urban ecology and biogeography have provided ample evidence of high biodiversity in urban areas. In a study on the species enrichment in urbanized areas in comparison with the surrounding countryside; Kühn, Brandl & Klotz (2004) reported that, plant diversity in urban area is higher in cities than surrounding areas. The present data are compatible with such findings as the total recorded number of vascular plants in urban area was 378 species belonging to 264 genera and 79 families. The majority of species were belonging to families: Fabaceae, Asparagaceae, Poaceae, Moraceae, Asteraceae  Euphorbiaceae, Malvaceae, Arecaceae, and Lamiaceae. The most

species rich genera was Ficus (18 species) followed by Euphorbia (11 species). The surrounding areas especially the agro-ecosystem of the Greater Cairo has less diversity of such genera (Hussein, 2011). Furthermore, comparison of the genera in terms of the largest number of species recorded in the present investigation and in similar studies e.g. El-Hady (2007) on the public gardens in Greater Cairo in Egypt, and El-Hady (2011) on East Cairo city; revealed the same conclusion.

Gatrell & Jensen (2002) attributed the increasing spread of trees in the urban ecosystem to their sizeable stature, wide crown, dense foliage and excellent shading effect.

A large number of species with large final dimensions, indicating their potential ability to offer a high leaf area index to bestow environmental and ecological benefits. On the other hand, El-Hady (2007; 2011) and Hamdy (2010); in their studies on the species diversity in different localities of Egypt; pointed out that, woody perennials constituted the main bulk of the flora of urban area.  In the present study,

trees are the dominant growth form for the plants in the examined habitats, followed by shrubs and annuals. These data could support the conclusion of Gatrell & Jensen (2002). Furthermore, the recorded woody perennials herein represented 57.7% of total flora of the studied urban area in the Greater Cairo city (218 species). Thus, the present data is congruent with those of El-Hady (2007; 2011) and Hamdy (2010).

Previous studies on the urban ecosystem in each of the East Africa (Agnew, 1994); Taipei city, China (Jim & Chen, 2009); Sheffield, UK (Ken, 2009); Road sides between Al-Kobba and Al-Obour area, Egypt (Amin, 2011); East Cairo city (El-Hady, 2011) and Nordic cities (Sjöman et al., 2012) raveled that, the urban ecosystem is dominated by three main habitats namely street verges, road islands and urban parks, each of which has its own species diversity. In the present study, the three vegetation groups identified within the urban ecosystem of Greater Cairo City are separated along the PCoA first two axes with their indicator species: (1) group A1 inhabits the street verges. (2) Group A2 is situated in road island habitats, which represent, in most cases; either small forms (phases) or transitional areas between street verges and public gardens habitats. (3) Group B included species of common occurrence in urban park habitats. Also, the results of this study showed that the most species rich habitats are the public gardens, while street verges and road islands are the least diversified habitats. This variation in plant diversity between the studied habitats could be attributed to three main reasons, namely natural/ human factors, air pollution by heavy metals and trampling. 

The natural and human factors have always been reported to have differential effects on tree diversity in different habitats (Serra et al., 2008). Generally, urban parks with site heterogeneity and multiple functions accommodate the highest richness, and streets (road island and street verges) with acute site limitations the poorest represented by plant species. Street trees serve similar environmental benefits such as air pollutant removal (McPherson et al., 1997), wildlife habitats (Clark et al., 1997) and ornamental functions (McPherson et al., 1999). Street trees are beset by a stressful growth regime; they share similar management concerns and challenges. The common physical and physiological constraints also restrict species selection. Usually, the relatively narrow roadside corridor and underground utilities severely confined tree growth in compact city environment (Jim, 1992). The heavy shading, air pollution, poor soil quality, restricted soil volume and soil compaction would exclude many species from roadside use (Bassuk & Whitlow, 1987; Jim, 1999).

Street trees habitats are subjected to continuous trampling, which may directly affect its species composition and the species richness (the number of species present). This finding agrees with the previous studies on the effects of trampling loss of vegetation cover (Agnew, 1994).

The divergence in species composition between parks and streets is conspicuous. Differences in site conditions and landscape intentions have generated marked species differentiation. Urban parks are mainly semi-natural sites with less human modifications than street habitats. The findings imply that human-oriented functions could accumulate species diversity in urban parks to a high level. These results corroborate results obtained by Nair (1993), Eichemberg et al. (2009), and Jacob (2002). Comparing with streets, urban parks in general are blessed with a genial (a better) environment condition with subdued negative growth factors. Both site limitations and deleterious human impacts are less arresting, and more management inputs and cares are regularly introduced to foster tree performance. This tree growth regime is conducive to longevity, stability in the tree population and a general resistance to changes. Unlike the more changeable street trees, in urban parks the initial tree flora will tend to linger for decades.

Davis & Glick (1978) pointed out that, the goals of garden ecology are to create or retain a wide range of habitat, include all plant layers, preserve ecologically rich edges, and protect links between habitats such as hedges and road verges. In the present study, road islands take an intermediate position between street verges and urban parks, the species diversity of which is mainly determined by their special environmental condition. This may be due to high similarity between these two habitats, where road islands represent, in most cases; transitional areas of public gardens. They shared in high percentage of herbs (99 and 83 species respectively) comparable to street verges. The weed assemblages in the shaded, cool and humid habitats are rich in the weed species especially shade-tolerant plants such as Euphorbia peplus and Oxalis corniculata that thrive in the dense shade of these habitats. The results revealed also that some of the recorded species had wide ecological range of distribution, besides F. microcarpa, Cynodon dactylon, Delonix regia and Washingtonia robusta which are widely planted in all three habitats, 164 species were shared between them.

The presence of ecological races suited to specific habitat conditions and the very effective vegetative spread by runners, in addition to seed production of these species may explain their wide ecological amplitude. Ramakrishnan & Singh (1966) had reached a similar conclusion. Shaltout & Sharaf El-Din (1988) reported that the flourishing of Cynodon dactylon in many of habitats may be related to their great plasticity under different situations; which is further supporting the present conclusion.

Conclusions and implications

One of the main constraints to conserving plant diversity is a lack of the necessary skills and knowledge in many organization and local communities. The increasing cultural disturbance could reduce natural potential and the conservation and ecological values of flora. Therefore, understanding the status and dynamics of species diversity marks the first step in nature and biodiversity conservation in urban areas. Based on our findings, we have deduced some implications to promote and preserve urban biodiversity in urban areas. On the one hand, introducing more indigenous species could create biologically rich urban forests to benefit not only humans but also the sustainability of urban ecosystems, especially for street habitats with a small species cohort. It can be concluded that, biodiversity in urban ecosystems could be enhanced by creating or enhancing a wide range of habitats, and varied habitats could be inserted in tandem with the city’s development and redevelopment. Additionally, our data clarified the importance of preserveing large patches of native vegetation when possible, because they are adapted to the local soil, climate, and wildlife. New ideas and practices in urban green space design should be adopted. On a city-wide scale, plan for a maximum of no more than 52% urban land cover and more than 64% total forest cover.

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