Beyond the Tree-Line: The C3-C4 “Grass-Line” Can Track Global Change in the World’s Grassy Mountain Systems

von Humboldt’s tree-line concept has dominated mountain ecology for almost two hundred years, and is considered a key indicator monitoring change in biome boundaries biodiversity shifts under climate change. Even though the of life zones elevation gradients are globally observed phenomenon, they have not been thoroughly explored many contexts. One such example ecotone, widely used conceptual tool to track regions, which limited application widespread tree-sparse, grassy systems that comprise third world’s systems. Among grasses (Poaceae), temperature linked variation photosynthetic performance community dominance C 3 4 metabolic groups, due its role limiting photorespiration photosynthesis process. Here, we investigate this shift grassland-dominated mountains demonstrate driving transition discuss potential applications ecosystem conservation worldwide. For identifying grass-dominated worldwide, measured grass-cover using satellite data. We then compiled Poaceae distribution data ten spanning from 42°S 41°N determined intervals ranges at each genus was found, testing effects temperature, precipitation, latitudinal on -C grasses. Temperature main driver dominance, with richness genera tending surpass taxonomic plants along where annual mean colder than ca. 14.6°C. Similar patterns were eight out mountains, suggesting may constitute an isotherm-driven ecotone. Consequently, offers promising impacts mountains. grass response environmental will likely major implications fire frequency severity, rangeland productivity livelihoods, food security, water budgets Given severity global these social-ecological systems, propose “grass-line” protocol be developed application.