Climate-driven collapse risk in Chilean Araucaria forests.

Coniferous forests are increasingly threatened by the synergistic effects of climate change and land-use transformation, yet temperate systems remain underrepresented in global ecosystem collapse-risk assessments. Here, we evaluate the collapse risk of Araucaria araucana ecosystems in Chile, an ancient and culturally significant conifer, using the IUCN Red List of Ecosystems framework. Our aim was to quantify historical, current, and future degradation across four distinct Araucaria ecosystems, integrating distributional and functional criteria. We combined national forest cadasters, ecological niche modeling (ENM), and multi-source remote sensing and geospatial datasets (Landsat, MODIS, TerraClimate, WorldClim) to assess changes in extent, climatic conditions, and ecosystem functioning. Analyses included historical reconstruction (∼1750-2024), recent trends (last 20 to 60 years), and future projections under climate change scenarios, alongside indicators of water stress and canopy dynamics. All ecosystems exhibited severe historical contraction (>74%) and large recent declines, particularly in Andean systems (>46%). Projections of climate change indicate a widespread loss of suitable habitats, with coastal Araucaria forests expected to lose their suitable environmental conditions by around 2060. Functional indicators revealed escalating drought stress, increased vegetation water demand, and persistent canopy loss, consistent with climate-driven ecosystem degradation. Consequently, all ecosystems were classified Critically Endangered, with coastal Araucaria Forest being the most threatened. Our results identify climate change, especially the prolonged drought, as the main driver of the evaluated ecosystem collapse risk. This assertion is supported by the calculated relative severity and the attained threat status, which indicates that climate change may have surpassed land-use influences in recent decades as a contributing factor. This study highlights the power of integrating remote sensing data with standardized risk frameworks to detect early warning signals of ecosystem collapse. Urgent conservation and restoration actions are required to enhance resilience and prevent potentially irreversible loss of these iconic temperate forests.