Soil erosion facilitates shrub encroachment in Patagonian herbaceous steppes

PAULA ESTELÍ ROMERO OVALLE; ALEJANDRO JORGE BISIGATO; MARÍA VICTORIA CAMPANELLA

LAND DEGRADATION & DEVELOPMENT

JOHN WILEY & SONS LTD

Lugar: LOndres; Año: 2021

1085-3278

Previous studies in northeastern Patagoniasuggested that, mainly as a consequence of overgrazing by sheep, the herbaceoussteppes are being replaced by shrub steppes dominated by Chuquiraga avellanedae as a consequence of shrub encroachment. Theherbaceous steppe presents a thick sandy loam to loamy sand A horizon lying ona clay horizon while the shrub steppe presents the clay horizon at or near thesoil surface. The thickness reduction of the remaining A horizon and theformation of desert pavements are evidence of soil erosion. As previous studiessuggested that shrub encroachment co-occurs with the erosion of the sandy Ahorizon, we hypothesized that shrub encroachment is favored by the presence ofan argillic horizon near soil surface. We expected that C. avellanedae emergence and establishment would be higher as theclay horizon is closer to the soil surface and A horizon are reduced. Weperformed field and greenhouse experiments to evaluate seedling emergence andestablishment along a gradient of A horizon thickness. We found that thepresence of a relatively thin sandy layer on the surface had a negativeinfluence on both shrub emergence and establishment.  The summer drought was not a critical periodfor the seedlings. Conversely, the highest seedling mortality took place duringlate winter in sandy soils, suggesting that these soils are more susceptible to frost heaving than clay soils. Inconclusion, soil erosion in the north-eastern Patagonian steppes wouldindirectly facilitate shrub encroachment due to differences in frost heavingsusceptibility between sandy and clay soils.