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<p><i>Araucaria araucana</i> forests in the southern Andes are heavily used for livestock grazing, yet the joint responses of stand structure, regeneration, and genetic diversity to grazing exclusion are not well understood. We used a 15-year natural experiment in the Ralco National Reserve (Chile) comparing a fenced, ungrazed site with an adjacent grazed site. We integrated data from 16 forest plots, four regeneration transects (128 subplots), and amplified fragment length polymorphism (AFLP) markers to assess changes in the two tree species present (<i>A. araucana</i> and <i>Nothofagus obliqua</i>), which jointly constitute 100% of the canopy basal area. Livestock exclusion increased <i>A. araucana</i> basal area by 4.2-fold and shifted the composition towards <i>Araucaria</i> dominance (PERMANOVA). Both sites retained inverse-J diameter distributions, but the ungrazed site had more small trees. Regeneration responses were strong: seedling density increased 5.2-fold and vegetative resprouts 3.5-fold in the ungrazed site, though vegetative regeneration dominated overall. A zero-inflated model showed that grazing primarily increased the probability of no regeneration occurring rather than affecting densities within occupied microsites. In contrast, adult genetic diversity and spatial genetic structure were similar between sites. Expected heterozygosity, spatial autocorrelation, and UPGMA clustering indicated high genetic connectivity with no detectable differentiation. Our results demonstrate that 15 years of exclusion drive strong structural and demographic recovery while genetic signals remain unchanged, supporting management strategies that combine livestock-free refuges with reduced stocking in surrounding forests.</p>

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Livestock exclusion and structural recovery of Araucaria Araucana forests in the Southern Andes of chile: evidence from a 15-year natural experiment

  • 期刊论文

  • 发表日期：

    2026年2月18日

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  • Rolando Rodríguez,
  • Eduardo Acuña,
  • Rodrigo Hasbún,
  • Simón Sandoval,
  • Francisco Montecino,
  • Burkhard Müller-Using,
  • Fernando Olave,
  • Rafael Carrasco

摘要

Araucaria araucana forests in the southern Andes are heavily used for livestock grazing, yet the joint responses of stand structure, regeneration, and genetic diversity to grazing exclusion are not well understood. We used a 15-year natural experiment in the Ralco National Reserve (Chile) comparing a fenced, ungrazed site with an adjacent grazed site. We integrated data from 16 forest plots, four regeneration transects (128 subplots), and amplified fragment length polymorphism (AFLP) markers to assess changes in the two tree species present (A. araucana and Nothofagus obliqua), which jointly constitute 100% of the canopy basal area. Livestock exclusion increased A. araucana basal area by 4.2-fold and shifted the composition towards Araucaria dominance (PERMANOVA). Both sites retained inverse-J diameter distributions, but the ungrazed site had more small trees. Regeneration responses were strong: seedling density increased 5.2-fold and vegetative resprouts 3.5-fold in the ungrazed site, though vegetative regeneration dominated overall. A zero-inflated model showed that grazing primarily increased the probability of no regeneration occurring rather than affecting densities within occupied microsites. In contrast, adult genetic diversity and spatial genetic structure were similar between sites. Expected heterozygosity, spatial autocorrelation, and UPGMA clustering indicated high genetic connectivity with no detectable differentiation. Our results demonstrate that 15 years of exclusion drive strong structural and demographic recovery while genetic signals remain unchanged, supporting management strategies that combine livestock-free refuges with reduced stocking in surrounding forests.