Botanical Diversity of Arid Steppe in South East of Algeria (Biskra)

In the light of climate change, it is important to acquire the information on the diversity of flora in order to ensure rational use of steppe rangelands. The present study aimed at diagnosing the botanical and the taxonomic diver - sity of the arid steppe plant communities in South East of Algeria. A total of 216 phytoecological sampling, were collected in three sites and one sample for each month during 2017 and 2018. The vegetation was analyzed using various species diversity parameters (abundance, species richness, life forms, alpha and beta diversity indices and disturbance index). Results show that 985 plant individuals were classified into 27 species, 27 genera and 14 families, with predominance of Chenopodiaceae and Asteraceae in the arid steppe of El-Haouch, and remarkable dominance of Chamaephytic and Therophytic plants in different phytoecological groups. The state of vegetation degradation in a susceptible environment on Algeria’s rangeland in the South East which is confirmed by the low values of Shannon, Jaccard indices and the values of disturbance index ranged between 50 and 85.71%. The alpha diversity parameters of the different phytoecological groups have low values, which reflect a more fragile homo - geneous ecosystem, unfavorable life conditions and the absence of certain species of high pastoral value.


INTRODUCTION
In arid and semi-arid regions, rangelands are important areas for the conservation of biodiversity in terms of species and habitats [Kideghesho et al., 2013], and are sources of livelihood for the communities; provide food for livestock and fauna, medicinal plants and other diverse ecosystem services [Abule et al., 2007;Selemani, 2020]. Algeria rangelands cover more than 8.4 % of the country's surface area [Neffar et al., 2018]. This transition area is located between the isohyets 400 mm in the North and 100 mm in the South [Aidoud et al., 2006].
In arid steppic rangelands, severe climatic conditions promoted the existence of a specialized plant community [Quezel and Santa, 1963 Hubert [1994], the specific diversity of steppic vegetation is an opportunity for livestock grazing.
Over the last three decades, steppic rangelands have suffered from rapid degradation [Slimani et al., 2010] by climatic factors [Bensmira et al., 2015] and human activities such as overgrazing. The impact of overgrazing is reflected by the rarefaction and even disappearance of some useful plant species with high forage value, the abundance and even dominance of some less palatable species, and the development of unpalatable species [Ghiloufi et al., 2015]. However, the area of grazing rangeland has decreased at the expense of marginal crops [Demnati et al., 2017].
The steppic rangelands of the region of Biskra have very diverse natural resources and benefits. Indeed, despite its importance, few studies such as Haoumel [2018] and Chaouch Khaoune [2018], have been conducted in this region. In addition, agropastoralism in the region of El-Haouch remains the principal activity at local and regional level, it was noted that the number of sheep has increased from 20 475 heads in 1996 to 52 143 in 2019 [DPAT, 2021].
This study aimed to diagnose the botanic diversity in the region of El-Haouch (Biskra), with establishing phytoecological groups and analyzing plant species composition, in addition to the assessment of botanical diversity by estimating richness (annual and perennial plants), life forms, diversity (alpha and beta-diversity) and disturbance index.

Study area
The region of El-Haouch (34°33'43'' N, 06°03'05'' E) is located in the South of Biskra (southeastern Algeria) (Fig. 1). Climate is arid. During the period 1987-2019, precipitation was marked by low amounts (152 mm) and high irregularity (49 mm in 2017 to 343 mm in 1994), maximum temperatures are higher than 26 °C throughout the year, reaching 40 °C in July and August, minimum temperatures can reach 7 °C in winter and 28 °C in summer, annual relative humidity ranges around 41%, with long dryness period (Fig. 2).
Phytoecological sampling sites were selected according to altitude, geomorphology of the landscape and homogeneity of ecological conditions (Fig. 1).
The soils of the samples sites have poor physicochemical characteristics, in which pedological analyses reveal that sites have highly saline soils (electrical conductivity included = 10.2 dS/m at site 3), which are typically sandy and slightly alkaline (pH = 7.42-8.49), highly deficient in organic matter (0.25-1.76%) and moderately calcareous (CaCO 3 content varies from 22.01 to 32.75%).
For each sample and specie, its abundancedominance index was noted from + to 5 according to the scale of Braun-Blanquet et al. [1952]. The identification of existing species was determined referring to several authors Santa [1962-1963] and Ozenda [1977], in addition to online resources (www.telabotanica.org).

Individualization of phytoecological groups
On the basis of agglomerative hierarchical clustering (AHC), abundance-dominance data for each plant species surveyed in the 216 samples were used to establish homogeneous phytoecological groups [Bouallala et al., 2020]. The AHC considers similarities between surveys within the same group to discriminate subgroups of very similar surveys [Mecheroum et al., 2021].

Taxonomic structure
The taxonomic structure of each phytoecological group was calculated using the ratios of family richness to species richness (F/S) for each sample. The taxonomic structure of the different phytoecological groups depends on environmental conditions. However, the relationship between taxonomic relationships and ecological variables in this environment were examined using Pearson correlation tests.

Life cycle
The determination of morphological types, annual and perennial species, was based on the work of Quézel and Santa [1962;1963] and Ozenda [2004].

Life form
According to Raunkiaer's classification [revised by Ellenberg and Mueller-Dombois, 1967], plants can be classified according to their biological form "life form" determined by the phenological state of the species that reflects the expression of its adaptation to its environment, which is related to the protection of the meristem from the soil surface during the unfavorable season. The following main life forms were considered: Chamaephytes, Hemicryptophytes, Phanerophytes and Therophytes.

Alpha diversity
Species richness (S): total number of species present in a given sample site [Magurran, 2004]. Shannon diversity index (H'). S: the specific richness in the sampled site, ni: number of individuals of species i in the sampled site, N = total number of individuals of species S.
The evenness index "E", was calculated as the ratio between the Shannon diversity index, where S is the specific richness in the sampled site and the theoretical maximum diversity.

Beta diversity
Spatial similarity between different phytoecological groups was assessed by Vann's diagram and qualitatively by Jaccard (J) and Sørensen indices (S).   (5) where: a -the number of species unique in site 2, c -the number of species unique in site 1, b -the number of species common to site 1 and 2 [Sorensen, 1948;Wolda, 1981;Rahman et al., 2019].

Disturbance index
The disturbance index was calculated to measure the rate of therophytization in the different phytoecological groups [Loisel and Gamila, 1993].
where: Th -the number of therophytes; Ch -the number of chamaephytes; S -the species richness.

Life forms
Except for the rangelands established on wadi beds, chamaephytes species have the highest values in the biological spectra of life forms in the rangelands of aeolian formations (G2) and saline accumulation rangelands (G3) with (50 ± 0; 74.60 ± 4.49), respectively (Table 4). Therophytes (34.71±7.49) are dominant in wadi beds rangelands (G1), geophytes are observed only in these rangelands with 13.33% and 17.65% in year    Table 3. Descriptive statistics of ration of family richness to species richness (F/S) and Pearson correlation tests (r: correlation coefficient, P: P-value) between the taxonomic ration (F/S) and phytoecological groups in arid steppe of southeast Algeria (Biskra)

Similarity analysis between phytoecological groups
The Venn diagram showed that (1; 4) plant species were common to all phytoecological groups in year 2017; 2018, respectively, including four species common between groups G1 and G2 in 2018, and five species common to groups G2 and G3 in 2018. Of the 27 plant species recorded in the conducted study, 4 species were exclusively present in group 2 in 2017, 10 species in group 1 in 2017, and 4 species in G3 in 2018 (Fig. 6).

Beta diversity
The similarity analysis showed the presence of only one common species between the three phytoecological groups in 2017 (Anabasis articulata), and four species Anabasis articulata, Atriplex halimus, Astragalus armatus and Tamarix gallica, in 2018 in the three phytoecological groups.
The similarity analysis (beta biodiversity) between the three phytoecological groups taken two by two showed Jaccard index values ranging from 0.08 to 0.42. The low similarity observed between the different phytoecological groups is explained by a low specific richness in the different phytoecological groups. Therefore, the species are totally different indicating that the different local environmental conditions determine a turn-over of important species. The Sørensen index values ranged from 0.40 to 0.81 between G2 and G3 in 2018, G1 and G2 in 2017, respectively (Table 5).

Disturbance index
The disturbance index becomes important when the area is increasingly degraded. Indeed, during both years, i.e. 2017 and 2018, this index   (Table 6). In arid regions, most plant families are represented by only one or two genera and most genera by only one or two species [Boughani, 2014;Kouba et al., 2021;Mechroum et al., 2021;Azizi et al., 2021]. Correlation tests show that the differences in taxonomic structure can significantly remit from one plant community to another depending on its environmental conditions [Fan et al., 2017]. For example, the obtained results demonstrate that F/S taxonomic ratios increase in steppes of good ecological conditions (wadi beds rangelands and aeolian formations rangelands).

DISCUSSION
Perennial plants are characterized by morphological and anatomical adaptive strategies that consist mainly in an increase of the absorbing system and a reduction of the evaporating surface, allowing them to survive more or less long periods, depending on the degree of disturbance [Ozenda, 1991]. In the arid rangelands of southern Tunisia, perennial species are the essential component of these rangelands . A strong and chronic anthropogenic disturbance can decrease the floristic richness and induce the replacement of woody species by perennial species whose floristic composition remains strongly linked to the effect of this disturbance on the soil properties [Mcintyre et al., 1995 Hemicryptophytes are represented by one species of the family Poaceae, one species of Euphorbiaceae, one species of Asteraceae and one species of Boraginaceae. Bouallala [2013] confirmed that the presence of hemicryptophytes in sandy soils and dunes is represented by psammophytes. The absence of geophytes in eolian formation and salt accumulation courses, confirming their regression in grasslands and steppe areas [Barbero et al., 1989;Henni et al.,2012]. The absence of this biological type in aeolian formation and saline accumulation rangelands is related to the climatic gradient favoring the development of short-lived species [Aidoud, 1983;Hachemi et al., 2015]. Phanerophytes are located in mesic habitats receiving irrigation water, such as wadi beds and irrigation channels [Bouallala, 2013;Bradai et al., 2015;Bouallala et al., 2020].
These very low values of alpha diversity alter the capacity of ecosystems to react to disturbances, thus reflecting a rarefaction or even disappearance of certain species, especially those of good pastoral value . Similarly, Aïdoud [1989] measured an index of Shannon diversity of 2.69 and equitability of 0.5 in the Southern Oran steppes. This reduction is explained by a homogeneous system that is more fragile in its ecological contributions [N'zala, 1997]. According to [Dajoz, 1982

CONCLUSIONS
The diagnostic of the botanic diversity can further explain the relationships between the species distribution and the environmental factors. This study showed that the plant composition is principally marked by the dominance of Chenopodiaceae and Asteraceae families, and the codominance of Chamaephytes and Therophytes, in different phytoecological groups; this particular situation favors the installation of Chamaephytization and the phenomena of Therophytization.
The alpha diversity parameters of the different phytoecological groups have low values, which reflect a more fragile homogeneous ecosystem, unfavorable life conditions and the absence of certain species of high pastoral value. The high dissimilarity observed between phytoecological groups reflects a state of degradation in this arid steppic rangeland. Biodiversity studies provide a more complete understanding of vegetation in arid steppe and its functioning in the ecosystem, by analyzing plant components and patterns at multiple spatial and temporal scales. The region of El Haouch remains a strong link in the agropastoral economy of Algeria, to preserve this fragile ecosystem, it is necessary to consider rational management programs to restore and improve the steppe vegetation cover.