Data from NUTRIENTS CAUSE GRASSLAND BIOMASS TO OUTPACE HERBIVORY 2008 - 2019

Human activities are transforming grassland biomass via changing climate, elemental
nutrients, and herbivory. Theory predicts that food-limited herbivores will consume any
additional biomass stimulated by nutrient inputs (‘consumer-controlled'). Alternatively,
nutrient supply is predicted to increase biomass where herbivores alter community
composition or are limited by factors other than food (‘resource-controlled'). Using an
experiment replicated in 58 grasslands spanning six continents, we show that nutrient
addition and vertebrate herbivore exclusion each caused sustained increases in aboveground
live biomass over a decade, but consumer control was weak. However, at sites with high
vertebrate grazing intensity or domestic livestock, herbivores consumed the additional
fertilization-induced biomass, supporting the consumer-controlled prediction. Herbivores
most effectively reduced the additional live biomass at sites with low precipitation or high
ambient soil nitrogen. Overall, these experimental results suggest that grassland biomass
will outstrip wild herbivore control as human activities increase elemental nutrient supply,
with widespread consequences for grazing and fire risk.