OOS 23-8
Impacts of global change on grassland ecosystems: Generalized responses revealed by collaborative network science

Wednesday, August 13, 2014: 10:30 AM
304/305, Sacramento Convention Center
Eric M. Lind, Ecology, Evolution, and Behavior, University of Minnesota, St. Paul, MN
Carly J. Stevens, Lancaster Environment Center, Lancaster University, Lancaster, United Kingdom
Elizabeth T. Borer, Ecology, Evolution, and Behavior, University of Minnesota, Saint Paul, MN
Eric W. Seabloom, Ecology, Evolution, and Behavior, University of Minnesota, Saint Paul, MN
Nutrient Network, Multiple Institutions

Global changes to climate, nutrient cycling, and species distributions are of prime concern to ecologists seeking to predict the dynamics of ecosystems in the future. Manipulative experiments offer the most direct route to functional understanding of how these changes will impact ecosystems. Yet for the most part these experimental studies are often conducted in single or only a few sites, raising the question of whether predicted ecosystem responses are general, or specific to those locations and conditions. What is needed for global understanding is homogenous data across heterogeneous conditions; this allows an examination of both generality (identical responses under different conditions) and contingency (varying responses depending on conditions).

The Nutrient Network is a globally distributed collaborative research network investigating two important ongoing global changes in grasslands: alterations to nutrient cycling and changes in herbivore communities. By using standardized experimental methodology and data collection across a variety of herbaceous-dominated ecosystems, we are able to examine both generality and contingency in response to global change. Here we highlight the value of this approach by testing the hypothesis that increases in global nitrogen availability increase grassland productivity, using a Bayesian hierarchical model including site- and plot-level predictors.  


Using identically collected data from over 40 sites on 6 continents, we found evidence for generality in grassland ecosystem response to increased global nutrient availability (atmospheric nitrogen deposition). In fact nitrogen (N) deposition was found to be superior to both known climatic drivers and local soil conditions, explaining 16% of observed variation in above ground net primary production (ANPP) globally with an increase of 1 kg ha-1 increasing ANPP by 3%. Soil pH was found to be another reliable predictor of above ground plant production. While climatic drivers such as temperature and water availability are well known to influence plant productivity, on our dataset these drivers are variable even within regions thought to contain a homogenous biome. In contrast we show direct evidence for a general response of grassland ecosystems to anthropogenic fertilization through atmospheric deposition of reactive N. Comparative, collaborative research approaches may be the key to achieving truly global understanding of global ecological change.