Effects of Prosopis flexuosa on soil properties and the spatial pattern of understorey species in arid Argentina

Abstract

Abstract. In arid zones dominant woody plants are capable of causing changes in microclimate and soil properties likely to affect species composition, as well as the establishment and spatial distribution of plant species. In North American and European deserts species richness appears to be higher under the canopy of shrubs and trees, in contrast with Chilean deserts where it seems to be lower. Since Prosopis flexuosa (Fabaceae, Mimosoideae) is the most conspicuous tree in the central Monte desert, Argentina, we analysed the effect of this species on the composition and abundance of the shrub and herbaceous layers and on soil properties. We considered two mesohabitats: ‘under P. flexuosa canopy’ and ‘intercanopy areas’. In addition, we analysed the differences between two microhabitats under canopies: ‘northern part of the canopy’ and ‘southern part of the canopy’. Results indicate that species composition and soil properties are affected by both mesohabitats and microhabitats. We found a higher number of shrubs under canopies, whereas that of grasses and perennial forbs increased in intercanopy areas. Concentrations of organic matter, nitrogen, potassium and phosphorus, factors limiting biological productivity in Monte desert soils, were significantly higher under than outside P. flexuosa canopies. Electrical conductivity and concentrations of Na+, Ca++, Mg++ were higher in the northern than in the southern microhabitats. No differences in species richness, evenness or diversity were found between mesohabitats or between microhabitats. We conclude that P. flexuosa modifies the spatial pattern of plant species in the shrub and herbaceous layers and the chemical conditions of the soil, generating spatial heterogeneity on different scales.

Do facilitative interactions increase species richness at the entire community level?

“…Raffaele & Veblen 1998;Badano et al 2005;Larrea-Alca´zar, Lo´pez & Barrientos 2005), others report that nurses contain similar or lower species richness than that found outside them (e.g. Gutie´rrez et al 1993;De Villiers, Van Rooyen & Theron 2001;Rossi & Villagra 2003;Pugnaire, Armas & Valladares 2004), indicating that the facilitative effects on some species do not necessarily generate higher species richness beneath nurses. Nonetheless, nurses and their alternative habitats (open areas among nurses) are part of the same community.…”

Positive effects of shrubs on herbaceous species richness across several spatial scales: evidence from the semiarid Andean subtropics

“…The scientific literature generally refers to results at individual patch and local levels. At those scales, shrubs may harbor less (Rossi & Villagra 2003;Larrea-Alca´zar et al 2006), similar (Schade et al 2003;Badano et al 2006), or more (Akpo et al 1997;Cavieres et al 2002) herbaceous species than open areas. Studies at the local level, however, are usually carried out in a single site, but different sites may show different patterns, and hence this variability may remain undetected.…”

Invasion promotes invasion: Facilitation of C3 perennial grass dominance in mixed C3/C4 grassland by an invasive C3 woody sprouter (Prosopis glandulosa)

“…] Pohl; Laxson, Schacht, & Owens, 1997;Simmons, Archer, Teague, & Ansley, 2008). Similar situations of woody species facilitating C 3 grass growth in C 4 grasslands have occurred elsewhere, for example, Argentina (Rauber, Steinaker, Demaria, & Arroyo, 2014;Rossi & Villagro, 2003), South Africa (Stuart-Hill & Tainton, 1989), and Australia (Prober et al, 2005).…”

“…Examples of woody species facilitating the advance of C 3 grasses in C 4 grasslands occur worldwide. Rossi and Villagro (2003) Argentina that native unpalatable C 3 grasses, S. ichu and Nassella tenuissima, expanded in C 3 /C 4 mixed grassland that had previously been mostly C 4 grasses. They did not mention that P. caldenia facilitated this process; however, their statistical analysis showed a strong association between P. caldenia and these two grass species.…”