**1. Introduction**

The vegetation that characterizes the southern Monte ecoregion is a shrubby steppe, and, as in other drylands, it is scarce and arranged in islands of vascular plants with large interspaces between them, covered to a greater or lesser extent by a herbaceous layer. The third functional group that accompanies the shrubs and the herbaceous layer is that of the biological crusts, which is globally known as a diverse soil surface community of cyanobacteria, algae, fungi, lichens, and bryophytes [1]. Research on these biological crusts has received considerable attention, especially since Belnap and Lange´s publication [2], so that knowledge about them has grown exponentially throughout the world, highlighting their sensitivity to global change. However, in South America, there are still gaps in the framework of that knowledge [3].

It has been widely accepted that succession in biological crusts follows a general pattern, starting with cyanobacteria and algae and concluding with bryophytes at

the later successional stages, probably due to their greater hygroscopicity, higher growth rates, relative height, and deeper rhizoids [4, 5]. However, recent studies have proposed that mosses can be present from the initial phases of succession if the conditions are favorable [2, 6].

Several studies in recent decades have shown that this component of dryland ecosystems [7] is often not taken into account but has many important functions in the sustainability of these systems, such as aggregation of soil particles (resulting in soil protection), seed retention and germination [8], water infiltration [9], reduction of wind and water erosion [10], as well as nitrogen fixation [11–13], and carbon sequestration [14]. In addition, if a disturbed site is given time to re-establish the crust, it would also improve the results in terms of the establishment of seedlings [1]. Its role is especially important to maintain the stability of the soil surface against the impact of raindrops in those soils which, due to their physical and chemical characteristics, tend to form vesicular surface crusts [15] and favor desertification processes in the face of successive wetting and drying cycles. All these attributes allow us to designate biocrusts as "ecosystem engineers."

In general, the effect of disturbances has been studied on the two most visible guilds of the Monte ecoregion (grasses and shrubs), although a rational management of natural resources should consider all its components, taking account of their function within the system. The biological crust has a fundamental role not only in the conservation of the superficial structure of the soil and the possibilities of regeneration of the herbaceous cover, but also in its contribution to biodiversity. In a States and Transitions model that we proposed [16], we were able to establish that the original system in the place where we carry out our studies was formed by two states that integrated a single domain of attraction and had a high resilience. The reduction of the herbaceous and biological crust layers, and the changes in the superficial structure of the soil, generated a distance from this domain of attraction, leading the system to other very stable states of lower productivity, and would be responsible for the advance of the desertification process.

Biological crusts in the eastern Monte ecoregion are dominated by moss, and their main species are *Syntrichia prínceps* (De Not.) Mitt. and *Ceratodon purpureus* (Hedw.) (**Figure 1**) [17].

Assuming that the presence of biological crusts would be associated with the lack of disturbances which is verified in more stable systems, some authors are using the presence of biological crusts as an indicator of the condition or "health" of grasslands [18–20]. In the same sense, Song et al. [21] concluded that biological crusts act as natural regulators for vegetation patterns and thus promote ecosystem stability and sustainability.

Concerning climate change, perhaps the most worrying and great environmental problem today, studies by Rutherford et al. [22] utilizing climate manipulation treatments suggest that the elimination of key species of mosses and lichens from the biological crust community may have dramatic effects on the biogeochemical and hydrological functions in drylands.

Also, the reduction in biocrust cover due to warming will lessen the capacity of drylands to sequester atmospheric CO2. This decrease may act synergistically with other warming-induced effects, altering C cycling in drylands, and reducing soil C stocks in the mid to long term [23], which is one of the most globally valued functions in ecosystems today. In accordance with this, Durán et al. [24] propose the use of the specialized microbiome of biocrusts to be applied in a new environment to counteract the negative effects of climate change.

*Why Are Moss Biocrusts Necessary for System Conservation in a Semiarid Region of Southern… DOI: http://dx.doi.org/10.5772/intechopen.106746*

**Figure 1.** *Moss biocrust with Syntrichia prínceps (a) and Ceratodon purpureus (b) species.*

Our concern in recent years has been trying to highlight the presence of moss in our ecosystem and to quantify some of its functions and how it is affected by the occurrence of disturbances at different scales.
