*3.7.1 Biological adaptation*

Biological types are considered as an expression of a flora adaptation strategy to environmental conditions [62], which represent a privileged tool for the description of the physiognomy of vegetation. Emberger [63] affirms that the rate of therophytes increases with the aridity of the environment. Therophysation is a characteristic of arid areas; it expresses a strategy of adaptation under unfavorable conditions and a form of resistance to climatic rigors [64–66]. Therophytes are more resistant to summer drought than hemicryptophytes and geophytes, since they pass summer as seeds while the others remain as vegetative organs.

According to Raunkiaer [65]; Floret *et al.* [67], chamaephytes are the best adapted for low temperatures and aridity and the absence of these spacies testifie the anthropization of the environment [68–70].

They partially reduce their organs of perspiration and assimilation in the summer, and can develop some forms of adaptation to drought (reduction of the leaf area) as well as by the development of the root system with the proliferation of thorny species such as *Astragalus armatus, Atractylis serratuloides* characteristic of steppe areas [35].

In hemicryptophytes, the perennial organs located at soil level are protected by leaf sheaths (sometimes reduced to fibrils) or old withered leaves as in *Plantago ovata, Echium trygorrhizum*. The roots, sometimes considerably developed, are often sheathed with a thick tomentum which fixes the grains of sand and thus protects them from desiccation (*Malva aegyptiaca, Paronychia arabica*) [35].

The majority of species of this type are nanophanerophytes or shrub-like pseudosteppes 1 to 4 m long, including *Nerium oleander*, *Genista saharae, Retama raetam, Retama sphaerocarpa, Rhus tripartita,Tamarix articulata, Ziziphus lotus*. These types of steppes generally occupy sites with a relatively favorable water balance: terraces of the hydrographic network, dayas, cliffs, deep sandy substrates in topographic position. They often constitute relatively favorable environments [35].

#### *3.7.2 Morphological adaptation*

For steppe plant formation, evapotranspiration depends on the leaf area and the stage of development of the plants. The perennial steppe vegetation is therefore adapted to morphological modification during the plant's development stage: Among these forms of adaptation we can cite the decrease in leaf area (plants can have small very thick leaves or reduced to thorns, which allows them to limit their water losses (*Fagonia glutinosa, Fagonia latifolia, Zilla spinosa, Launaea arborescens*). One of the strategies is leaf modification (leaf drop, or leaf area reduction), by microphyllia, most steppe species have very small leaves *Salsola vermiculata* or small *Rhanterium suaveolens* [71].

The flattening of vegetative system is fixed on the ground (*Neurada procumbens*).

Cushion formation (pincushion habit) is also a form of adaptation to the xeric environment with a morphological modification, for example the species (*Anabasis aretioides,Teucrium polium, Astragalus armatus, Atractylus humilis*), can take a ball appearance or pincushion and prickly padded xerophyte includes the species Oxyhedron (*Juniperus oxycedrus*). Some plants may have considerably developed underground organs (Rhizomatous) (*Scorzonera undulata*). The leaves can also take *Biophysical Effects of Evapotranspiration on Steppe Areas: A Case Study in Naâma… DOI: http://dx.doi.org/10.5772/intechopen.97614*

shape in needles or scales; it is the case of the following species *Hammada scoparia, Hammada schmittiana,Thymelaea microphylla, Ephedra alata, Genista saharae, Retama retam* [35].

According to Ozenda [72], for the case of amaranthaceae (*Zygophyllum album, Gymnocarpos decander*), are thus carriers of tiny leaves or even are completely leafless, sometimes the leaves are transformed into thorns to constitute reserves in accumulating water in the tissues (crassulescent leaves or at least semi-succulence and aquiferous tissues). The constitution of water reserves in the tissues and color change where the whitish appearance is the most representative: *Thymelia microphylla, Phoenix dactylifera,* ...

A form of sclerophyllia (extravaginate innovations at upper nodes) remarkable in some of the species of Poaceae (*Panicum turgidum*); these innovations protect against wilting [73]. Some trees adapt to the cold by loss of leaves (*Pistacia atlantica*, *Ziziphus lotus*), others will opt for leaves in needles (*Juniperus oxycedrus, Juniperus phoenicea, Rosmarinus officinalis*) [35].

Thus, the reduction of the vegetative apparatus constitutes a remarkable adaptation to very difficult environmental conditions. This results in the tolerance of certain ligneous plants which opt for a morphological plasticity which reflects the capacity for resilience in response to disturbances of biotic or abiotic origin. These species bury their woody structures below ground level or spread their root system on supports with greater water availability (*Pistacia atlantica, Ceratonia siliqua, Hammada scoparia*, etc.) [35].

#### *3.7.3 Physiological adaptation*

According to Scheromm [74], long water deficits result in progressive changes in the structure of the plant, which aim to reduce its transpiring surface (leaf surface, thickening of the cuticles), but which also induce a decrease in its production. Long water deficits induce more irreversible changes, especially in morphology (reduction of evaporation surfaces).

Thickening of leaf cuticles was reduce the rate of evaporation. The leaf surface is covered with a cuticle formed from cutin embedded in a cuticular wax matrix. It therefore reduces the evaporation of water from the surface of the epidermis. Sometimes the plant spends the dry season as a fleshy bulb or rhizome or as a seed (Therophytes) [75].

The increase in the root system increases biomass and consequently transpiration and reduces evaporation from the soil [76]. The significant growth of the root system compared to the aerial system is drawn from the moisture from the depths [77].

The significant development of the root system, was both on the surface and deeper through taproots (*Hammada scoparia*). This modification is manifested by a horizontal extension of the root system (psammophytes) with a horizontal network of roots and especially of rootlets almost in contact with the soil surface to benefit from the slightest rain or dew. For example, the species *Stipagrostis pungens*, however, has strong vertical roots for anchoring and draws from certain moisture from the depths. Or by a vertical extension of the root system is constituted by a taproot in a fairly large number of perennial species (*Moricandia arvensis, Scorzonera undulata, Astragalus armatus ...)*. Some perennial species may have roots capable of exploring horizons with several meters deep and most often up to the water table. As it progresses in depth to reach the moisture, the root system will present a particularly dense network of rootlets that colonize the inter-leaf spaces of the soil, this is the case of: *Helianthemum hirtum, Hammada scoparia, Hammada schmittiana, Anabasis articulate* and *Astragalus armatus* (**Figure 7**) [78, 79].

**Figure 7.** *Some steppe species from the Naâma region (western Algeria).*
