A woody plant community and tree-cacti associations change with distance to a water source in a dry Chaco forest of Argentina

Abstract

In semiarid regions, livestock is concentrated around water sources generating a piosphere pattern (gradients of woody vegetation degradation with increasing proximity to water). Close to the water source, livestock may affect the composition, structure and regeneration strategies of woody vegetation. We used the proximity from a water source as a proxy of grazing pressure. Our objectives were (1) to compare woody vegetation attributes (richness, diversity, species composition, density and basal area) and ground cover between sites at two distances to a water source: near (higher grazing pressure) and far from the water source (lower grazing pressure), and (2) to quantify and compare cases of spatial association among the columnar cacti Stetsonia coryne (Salm-Dyck) Britton and Rose (Cactaceae), and the dominant tree Bulnesia sarmientoi Lorentz ex Griseb. (Zygophyllaceae). We used a paired design with eight pairs of rectangular plots distributed along a large and representative natural water source. We found lower total species richness, plant density and soil cover near than far from water source, and more cases of spatial associations between the two species studied. Our results show evidence of increased livestock impacts around water sources. However, we found no difference in terms of species composition or basal area at near versus far sites. We conclude that grazing pressure might be changing some attributes of the woody plant community, and that the association of young trees with thorny plants (grazing refuge) could be a regeneration mechanism in this semiarid forest with high grazing pressure.

Changes in Richness and Species Composition after Five Years of Grazing Exclusion in an Endemic Pasture of Northern Mexico

“…The same response was observed in dry forest ungrazed during 7-8 years [46]. However, other studies have shown that heavy grazing modifies richness, density, and species diversity of woody plants [47,48], as well as spatial distribution [49], reduction in tree emergence, and survival [50].…”

Direct and indirect relationships between logging intensity and regeneration of two timber species in the Dry Chaco of Argentina

“…Shrubs can provide an important source of fruits for wildlife (Caziani and Protomastro, 1994;Ponce et al, 2012), or offer forage biomass for native and domestic herbivores (Bucher, 1987;Catan and Degano, 2007;Cora et al, 2005;Quiroga and Esnarriaga, 2014). Also, shrubs can promote regeneration niches that other plants can use for their establishment, growth and survival (Barchuk et al, 2005;Caccia et al, 2009;Tálamo et al, 2015aTálamo et al, , 2015bTrigo et al, 2017). Understanding how forestry affects understory vegetation structure and the regeneration of timber species is key to assess the sustainability of logging and measure potential consequences to ecosystem function.…”

Reduced geographic variation in roars in different habitats rejects the acoustic adaptation hypothesis in the black‐and‐gold howler monkey (Alouatta caraya)

“…Canopy closure was measured at four different points along each transect (0, 16, 33, and 50 m) using a spherical densiometer (Paletto & Tosi, ). We sampled vertical structure at the same four points (0, 16, 33, and 50 m) on each transect, by holding up a 2‐m telescopic rod (marked at 1‐m intervals and extensible up to 15 m) and recording the number and height of contacts of woody vegetation on the rod (Lopez de Casenave, Pelotto, Caziani, Mermozand, & Protomastro, ; Trigo et al, ). Although tree height varied between sites from around up to 20 m in Yacutinga (pers.…”