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Cushion shrubs encroach subhumid rangelands and form fertility islands along a grazing gradient in Patagonia

Abstract

Purpose

We assessed changes in soils and vegetation associated with different plant life forms and increasing grazing intensity (GI) in a subhumid grassland of Patagonia (Argentina), with vast portions of these grass steppes in degraded states.

Methods

We reconstructed the historic GI gradient of the study sites and characterised the vegetation cover. We sampled the soil beneath patches of grass and shrub and their bare interspaces, as well as the height of the hummocks and the thickness of superficial horizons. We used multivariate analysis, inferential tests, simple regressions and the relative interaction index to measure the effect of historical grazing in these rangelands.

Results

The soil in interspaces between shrubs was the most degraded, with particle and fertility losses. While the soil of vegetation patches did not differ in any fraction, the soil beneath shrub patches was far more fertile. The soil of the sites with cushion shrubs developed the typical spatial heterogeneity of the fertility island effect, and their fertility decreased with increasing GI. With increasing GI, the relative cover of cushion shrubs grew and the total grass cover decreased, while the percentage of bare soil increased.

Conclusions

The increasing grazing intensity favoured the transition of this subhumid grassland to shrubland. Grazing as an exogenous factor triggers processes of vegetation change and soil degradation, which lead to the encroachment by the cushion shrub Mulinum spinosum and fertility island development. This self-reinforced degradation process, well documented in arid and semiarid environments, also occurs in subhumid rangelands of the forest-steppe ecotone.

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Data availability

Data is available by request from the corresponding author.

Code availability

Not applicable.

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Acknowledgements

We especially acknowledge Jorge and Juan Cignetti, members of the family owning Estancia Rio Percy, and Ernesto Phillips, the ranch manager, who shared with us their time and willingly answered our questions. We acknowledge Federico Gomez and Manuela Tarabini, who helped with the NDVI and PPNA calculations and fieldwork. We thank Carolina Amaturi, Agustina Arzaguet, Alexander Cottescu, Florencia Cuerda, Selva Cuppari, Micaela Facelli, María Figueroa, Emilio Moya, Jonás Nahuelmir, Pedro Noli and Paul Winter for their help during field and/or laboratory work. We are grateful to our internal reviewer, Dr Pablo Bouza. We greatly appreciate the comments of the Section Editor Dr Matthew A. Bowker and the anonymous reviewers, which were of utmost importance in improving the quality of our work. This research was supported by Consejo Nacional de Investigaciones Científicas y Técnicas, Agencia Nacional de Promoción Científica y Técnica (PICT-ANPCyT 1876-13), and Secretaría de Ciencia y Técnica de la Universidad Nacional de la Patagonia San Juan Bosco (PI 1505).

Funding

CONICET grant Anexo IF-2018–67419068-APN-GRH#CONICET – Consejo Nacional de Investigaciones Científicas y Técnicas – Argentina.

Project PICT-ANPCyT 1876–13 – Agencia Nacional de Promoción Científica y Técnica – Argentina.

Project PI 1505 Res.R/9 nº 330–2019 – Secretaría de Ciencia y Técnica – Universidad Nacional de la Patagonia San Juan Bosco – Argentina.

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Correspondence to Braian Vogel.

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The authors declare that they have no conflict of interest or competing interest.

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Responsible Editor: Matthew A. Bowker.

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Vogel, B., Rostagno, C.M., Molina, L. et al. Cushion shrubs encroach subhumid rangelands and form fertility islands along a grazing gradient in Patagonia. Plant Soil (2022). https://doi.org/10.1007/s11104-022-05398-1

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  • DOI: https://doi.org/10.1007/s11104-022-05398-1

Keywords

  • Relative Interaction Index
  • Volcanic soil
  • Ecotone
  • Land degradation
  • Erosion
  • Resource island