Productivity of North American grasslands is increased under future climate scenarios despite rising aridity

Abstract

Grassland productivity is regulated by both temperature and the amount and timing of precipitation 1,2. Future climate change is therefore expected to influence grassland phenology and growth, with consequences for ecosystems and economies. However, the interacting e ects of major shifts in temperature and precipitation on grasslands remain poorly understood and existing modelling approaches, although typically complex, do not extrapolate or generalize well and tend to disagree under future scenarios 3,4. Here we explore the potential responses of North American grasslands to climate change using a new, data-informed vegetation-hydrological model, a network of high-frequency ground observations across a wide range of grassland ecosystems and CMIP5 climate projections. Our results suggest widespread and consistent increases in vegetation fractional cover for the current range of grassland ecosystems throughout most of North America, despite the increase in aridity projected across most of our study area. Our analysis indicates a likely future shift of vegetation growth towards both earlier spring emergence and delayed autumn senescence, which would compensate for drought-induced reductions in summer fractional cover and productivity. However, because our model does not include the e ects of rising atmospheric CO 2 on photosynthesis and water use e ciency 5,6 , climate change impacts on grassland productivity may be even larger than our results suggest. Increases in the productivity of North American grasslands over this coming century have implications for agriculture, carbon cycling and vegetation feedbacks to the atmosphere. The grassland biome is the largest in the world, covering up to 59 million km 2 (over 30% of the global land surface) 1. Grasslands constitute a key component of the terrestrial biosphere and are fundamental to the meat and dairy industries 1 , but projections of grassland growth and productivity from model intercomparison studies diverge greatly under climate change 3,4. Grassland growth and productivity are highly dynamic on fast (days-to-weeks) timescales, leading to substantial variability between years 7-9. Grassland growth is largely controlled by soil water content and the magnitude, frequency and timing of precipitation events 10-12. The response of grasslands to changes in precipitation

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