Floristic diversity of Wadi Ar'ar, Saudi Arabia

ABSTRACT One of the most countries containing which have biologically diverse, is Saudi Arabia. Among the plant species recorded in Saudi Arabia, about 30% are rare and around 18 plant species are thought to have been disappeared locally. The study aims to provide the researchers in various scientific fields with a list of wild plants available in the examined region. The current work focused on an analysis of life forms, life span and chorotypes in four fenced areas (Aoasa, Mayla, Goraba and Aqra) of wadi Ar'ar. A bout of 273 taxa belonging to 35 families and 169 genera of vascular plants were recorded. Phytogeographically, the listed species were classified into three groups; monoregional, biregional and pluriregional. Twenty four species were listed as cosmopolitan, paleotropical or pantropical. One important step in preserving our wild plants is to expand knowledge of vegetation and find solutions to preserve the environment and species from extinction.


Introduction
Saudi Arabia is a wide dry desert with a size of approximately 2,250,000 km 2 occupying the greatest section of the Arabian Peninsula. So, xerophytic flora is a significant visibility of plant life in this area [1]. Saudi Arabia located between longitudes 34°40 E-55°45 E and latitude 15°45 N-34°35 N [2,3].
The geological history of this region indicates that this region shares with the flora of the west Africa, the southeast & northeast Asia and the north & northwest Mediterranean. The vegetation of Saudi Arabia belongs to Saharo-Sindian phytogeographical region [4].
There are many previous studies that have been described the Flora of Saudi Arabia [5][6][7][8]. Furthermore, Collenette [9] illustrated the Flora of Saudi Arabia. Osman et al. [10] were described the flora in wadi Ar'ar as well as, vegetation analysis in this area. Flora of Saudi Arabia includes about 2243 plant species. Approximately 656 species subsist in small populations while, 500 species are coexisting in limited areas. Moreover, around 100 species have been recorded as endangered [11].
There are no permanent streams and lakes in Saudi Arabia; however, it contains a number of Wadis in different parts of the country [12]. The vegetation in the Wadis is variable from year to year. It depends on several environmental factors as physiographic factors, geographical location, moisture content and human activities [13][14][15][16].
Food shortage and Lack of available resources are among the most important problems facing Saudi Arabia. Therefore, Saudi Arabia is working to adopt new styles in various fields, especially the agricultural field [17]. Vegetation structure is the greatest significant agents influencing pasture production [18], in addition to, the anthropogenic effects (wood cutting, overgrazing and over cultivation) [19].
Wherefore, Saudi Arabia in 1985 had established the Saudi Wild life Commission to preserve wild life and restore ecological balance. In this time, the Saudi Wild life Commission operates 15 fenced areas [20].
The Northern Border Region is one of the greatest essential regions of Saudi Arabia because it contains many fenced areas as (Aoasa, Mayla, Goraba and Aqra). This work aims to assess the floristic diversity in fenced areas of Wadi Ar'arregion. Furthermore, the life forms, vegetation types and chorotypes of the gathering species taken into seeing.  during January to 23°C during August and July, meanwhile average upper air temperature differs from 16°C during January to 42°C during August ( Figure 2). The maximum values of rainfall (Precipitation) were recorded during March (6 mm), on the other hand, there is no rainfall (Precipitation) were recorded during June, July, August and September ( Figure 2). The direction of the prevailing winds throughout the year is west winds (Figure 3). Using ESRI Arc GIS ver. 10.5. to create a map showing the study area.
Survey of four fenced Areas of Wadi Ar'ar-Northern Border region was conducted between March 2014 and March 2018 to represent the flora during different seasons. About 240 positions distributed across all of the major zones of the study area were selected. Plant species registered after complete identification according to Collenette [9], Cope [21], Migahid [6], Chaudhary [22], Täckholm [23] and Boulos [24][25][26][27][28]. Herbarium specimens were saved in the herbarium of the Biology Department, Science College, Northen Border University. Vegetation types named according to http://www.theplantlist.org/. Categories of Life forms were identified after Raunkiaer [29], as modified by Govaerts et al. [30]. Phytogeographical affinities made to determine the listed species in world geographical groups according to Eig [31].
In respect to vegetation type, the majority of the registered species in this survey were Annuals with 170 of the total recorded species (62.3%), followed by the perennials with 89 species (32.6%). Annual / Biennial was represented by 5 species (1.8%), Annual / Short perennial was represented by 4 species (1.5%) and Biennial was represented by 2 species (0.7%). Both Annual / Perennial, Short perennial and Biennial / Short perennial were showed by one species each (0.4%) (Table 2, Figure 5).

Discussion
The current study focused on the description of flora in four fenced Areas (Aoasa, Mayla, Goraba and Aqra) of Wadi Ar'ar. A total of 273 taxa belonging to 35 families and 169 genera were recorded. The major families in terms of number of species were Asteraceae, Poaceae and Fabaceae. Those outcomes were in conformity with Osman et al. [10], who mentioned Asteraceae, Poaceae and Fabaceae were the widely common families in Wadi Ar'ar. Also, those outcomes were largely consistent with many investigations achieved in many habitats in Saudi Arabia [32][33][34]. Farrag [32] mentionedAsteraceaewas the most common family in their studies. In addition to, Al-Turki and Al-Qlayan [35]; El-Ghanem et al. [36]; Alatar et al. [12] and Abdel Khalik et al. [37] mentioned Poaceae and Fabaceae were the most common families in their studies. It is worth mentioning that Poaceae, Fabaceae and Asteraceae comprise the major bulk of Flora in Saudi Arabia [9,38]. Poaceae is also the largest family scattered in the world Flora [39]. In the present study six families represented by 2 species, while 11 families represented by a single species. One of the salient features of the plant composition of Saudi Arabia's Flora is that a few families were of plant importance as in most subtropical and tropical deserts and many plant families were represented by a single or two species [40]. This may be due to the fact that a few number of plants were endure harsh environments in these areas. Meanwhile, other plants could not survive in these difficult conditions.
In regard to life span, the plurality of the registered species in this research were Annuals with 170 species (62.3% of the total recorded species). Those outcomes were in conformity with Shaltout et al. [41] & Al-Rowaily et al. [42], who mentioned that, the main components of vegetation type in Saudi Arabia were annual plants.
Plants life form distribution that grow in dry areas is widely linked to landform and topography [43,44]. In this study the most dominant life form was Therophytes (65.2%). This may be due to many factors such as hot, dry climate, animal interference and human influences. These results agree with many previous studies conducted in different desert habitats in Saudi Arabia [9,10,12,15,22,[35][36][37]40,[45][46][47][48]. Therophytes was the dominant life form in an arid desert region because of dry climate, overgrazing [49,50]. Moreover, the Therophytes high percentage was too credited to human activities [51].
Phytogeographically, the registered species were classified into three groups; monoregional, biregional or pluriregional. A total of 93 species representing 34.1% of the entire number of listed species were monoregional of several affinities. The highest monoregional Phytochorion was Saharo-Sindian (37 species). Biregional geoelements were represented by 112 species forming 41% of recorded species and the highest biregional phytochorion was Irano-Turanian-Saharo-Sindian region represented by 31 species. Pluriregional geoelements were represented by 44 (16.1%) of registered species. The highest Pluriregional phytochorion was Mediterranean-Irano-Turanian-Saharo-Sindian region represented by 18 species. The remaining 24 species were divided as follows: 4 Palaeotropical, 6 Pantropical and 14 Cosmopolitan. These outcomes were in conformity with Osman et al. [10]. Danin & Plitman [52] and Abd El-Ghani & Amer [53] referred to Sudano-Zambezian and Saharo-Arabian phytochoria decline moving north also were replaced by Irano-Turanian and Mediterranean phytochoria. This may be due to several reasons, as Sudano-Zambezian and Saharo-Arabian plants were good indicators of desert habitats, on the other hand Mediterranean species point to extra mesic habitats.

Conclusion
The studied, fenced areas appeared relatively high floristic diversity as a result of their protection from overgrazing. The decline in the species number in such area in comparison to other areas in Saudi Arabia is attributed to the intense human effect (overgrazing, wood cutting and development). Thus, it is recommended that additional ecological studies must be accomplished to investigate the impact of environmental and geographical variables on the plant diversity and community in this significant area. As well advised that preservation plans should be begun at once to keep the plant diversity in this hotspot.

Significance statement
This study highlights the importance of preserving the natural resources, which Saudi Arabia is rich in, particularly wild plants that regarded as a vital component of Saudi Arabia's natural wealth, through the enactment of laws and regulations to keep them from extinction. This study helps researchers to know the vegetation of the study area and reveal rare and threatened plants that many researchers were not able to explore.

Disclosure statement
No potential conflict of interest was reported by the authors.