Global Grassland Patterns and Changes Revealed by Spatial Distribution of Poaceae Pollen

Abstract

Grasslands are among the most important terrestrial ecosystems on Earth. Grasslands dominated by Poaceae are essential carbon pools and play a vital role in maintaining biodiversity, absorbing atmospheric CO₂ and delivering ecosystem services. Understanding the past, current and future distributions of grasslands is important for coping with grassland degradation, developing reasonable ecological protection strategies and predicting ecosystem functions. The abundant data on Poaceae pollen abundance (PA) from global surface sediments provide valuable insights into simulating current grassland distribution patterns and forecasting their future trajectories under climate change. We created a data set containing 16,372 records with both characteristic variables (including vascular plant richness, bioclimatic, soil and elevation variables) and Poaceae PA and used a random forest model to simulate the spatial distribution of Poaceae PA. Results show a significant difference in the distribution of Poaceae PA across continents, with regions of higher abundance (e.g., ∼10% in temperate regions and ∼40% in tropical regions) closely aligned with the distribution of grasslands. Furthermore, we project the distribution of grass PA under four future climate scenarios (SSP126, 245, 370, 585) and the changes of grasslands. We find that the grassland coverage will likely increase at the end of this century. In particular, the temperate grasslands in the Northern Hemisphere are expected to expand northwards based on all the scenarios, whereas the Amazon savannas will also expand, thus encroaching on rainforests. Our findings offer a new perspective for understanding the changes in grasslands and their future development for both the scientific community and policy-makers.