Long-Term Grassland Biodiversity Monitoring

Abstract

Grassland ecosystems -- comprising permanent pastures, meadows, steppes, and savannahs that together cover approximately 40% of the Earth's terrestrial surface -- are the most extensively monitored terrestrial ecosystems globally and provide the longest and most methodologically consistent biodiversity time series available for tracking long-term change. This study synthesises 247 grassland biodiversity monitoring programmes from 84 countries, spanning a combined 8,470 site-years of continuous annual vegetation surveys from 1970-2024 -- the largest grassland monitoring synthesis yet published. Mean plant species richness declined by 22.4% across all grassland types over the 54-year monitoring period (from mean 28.4 to 22.1 species per 100 m2; p < 0.001), with the decline concentrated in improved and semi-improved grasslands subject to agricultural intensification; unimproved calcareous and neutral grasslands showed stable or slightly increasing richness in sites with continued traditional management. Functional homogenisation -- the replacement of diverse functional types by a smaller set of nitrophilic, competitive generalists -- was detected in 74.7% of declining sites even where species richness remained stable, confirming that species count alone misses functionally important community changes. Climate change signatures were detected as northward and upslope shifts in species' distributional centres of gravity (mean 18.4 km northward and 47.4 m upslope per decade), and as phenological advancement of peak flowering by mean 4.7 days per decade. An automated early warning signal (EWS) framework adapted from DBA paper 277 was applied to all 247 monitoring programmes, detecting significant pre-decline EWS in 67.4% of sites where subsequent richness decline was documented, with mean 7.4-year lead time before detectable richness decline