Wetlands and salt marshes play a variety of environmental functions and are considered a priority for the preservation of biodiversity. However, most of them are influenced by human activity, including its conversion to urban land and even to farmland (De Groot et al. 2002). One of the most common anthropic activity carried out in these environments is the direct grazing by domestic species (Gedan et al. 2009). The effect of grazing on salt marsh vegetation was studied in the northern hemisphere (Doody 2008; Bertness et al. 2002) but the knowledge is less in South American marshes (Di Bella et al. 2020).
Grazing has detrimental effects on salt marsh vegetation due to intense, sometimes selective, defoliation and trampling. This reduces the proportion of rare plant species and affects the regeneration or reestablishment of vegetation cover. However, domestic herbivores may be beneficial in some wetlands by improving floristic diversity (Di Bella et al. 2020). One key issue is the intensity of grazing, which differently affects the spatial structure of wetland vegetation and species composition, depending on factors such as grazing history, climate, and productivity (Milchunas and Lauenroth 1993). Also, grazing leads to soil compaction and the occurrence of bare areas, which frequently enables the upward capillary movement of saline water and surface salts accumulation (Cisneros et al. 1999; Di Bella et al. 2020). This is why the exploitation of wetlands requires site-specific planning in order to achieve the maximum benefit within the framework of environmental conservation (Cronk and Fennessy 2001). One of the main tools for this purpose is the grazing management, and for that it is important to estimate the receptivity of the ecosystem or the carrying capacity of the grazing system. The latter is defined as the maximum number of animals sustained by an environment without being deteriorated (Vallentine 1990). In this context, there are grazing technologies that have been adequate for sustainable management of wetland ecosystems. Also, the receptivity of those systems could be improved by applying sustainable management strategies which change vegetation cover, floristic composition and forage availability. Moreover, in many cases, a decrease in soil salinity and pH and an increase in water infiltration rates could be expected (Di Bella et al., 2020).
Numerous species thrive in saline wetlands worldwide, but among the dicots Asteraceae, Fabaceae, Solanaceae, Verbenaceae and Amaranthaceae stand out. The last is one of the most conspicuous family, including the Chenopodiaceae subfamily (Kadereit et al. 2006). An example is the genus Atriplex, which comprises 245 species distributed around the world, but mainly occurring in arid and semi-arid regions (Osmond et al. 1980). In those areas, when herbaceous vegetation reduces growth during dry or cold periods, the “browseable” biomass of Atriplex sp. constitutes a food reserve to meet the nutritional needs of livestock. On the other hand, the woody parts of Atriplex sp. limit overgrazing of these halophytic shrubs, while their canopy creates a favorable microhabitat for the development of herbaceous vegetation beneath (Mckell 1975). Sarcocornia is a genus of halophyte plants, belonging too to the Amaranthaceae family, which also grow in saline areas worldwide. Five species of Sarcocornia have been identified in South America (Kadereit et al. 2006). Some species have been used as forage as well as in phytoremediation, energy, ornamentation, and human consumption, receiving good acceptance from different consumers (Ventura and Sagi 2013). Most of these halophytes are succulents, in which the water content per unit area of the leaves is high, the cells increase in size, the leaves or stems become thicker, and the number of leaves per plant decrease (Cronk and Fennessy 2001). The succulence dilutes the internal saline concentration (mainly sodium salts) and, consequently, decreases the negative effects of salts on plants (Zeng et al. 2018).
Among the monocots growing in wetlands, the Poaceae family stand out. For example, the cosmopolitan genus Sporobolus which grows in tropical, subtropical and temperate regions, and many of its halophilic species are distributed in the Americas (Peterson et al. 2007). Most of them are used as forage resources and also in ecosystems restoration (Khan and Gul 2008). Another notable genus is Pappophorum, a perennial grass native to the Americas that grows in arid and saline environments and maintain its good forage quality until seeds ripening (Pensiero et al. 2020). The genus Distichlis is also very common. It is considered of very low forage value in environments with good to very good productivity, but in saline areas it constitutes an important forage resource (Bustan et al. 2005; Yensen et al. 1985) and provides the benefit of reducing soil erosion (Pensiero et al. 2020).
Several species of the above mentioned genera are found in the saline wetlands, depressions that interrupt the flat landscape of the Chaco-Pampas sedimentary plain (Rubio et al. 2018). This is a vast arid/semiarid area that extend in South America, mainly covering for deciduous xerophytic forests and the predominant soils are Entisols and Mollisols (Rubio et al. 2018). The area is subjected to extensive grazing of cattle and, to a lesser extent, sheep and goats. Our objective was to estimate forage offer of plant species growing in one of these saline wetlands, located in the province of San Luis, Argentina, as a first step aiming towards the use and the conservation of the forage resource.