The Jasper Ridge Global Change Experiment (JRGCE) studies the response of California grassland to 4 environmental factors changing globally. It is the only field experiment in the US that is studying the combined effects of climate warming and elevated CO2 on a natural ecosystem, and in addition, includes two other major environmental changes, altered precipitation and nitrogen enrichment.

The experiment covers 3 ha of grassland and has operated since 1997, with treatments beginning in the fall of 1998. The four global change treatments, and all possible combinations, are applied in a split-plot, randomized block design with 8 replicates, a total of 128 experimental units. A wildfire in the summer of 2003 burned two of the replicates in each treatment, dropping the level of replication to six in the main experiment, but adding fire as a replicated treatment. The study involves a third of all JRBP researchers and hosts investigators from 5 other institutions.

One major question within the JRGCE is whether global changes have additive effects or whether they are interactive, meaning that the effect of a particular treatment is altered by the presence of another. An example of this is that in some years, elevated CO2 has suppressed the enhancement of plant growth induced by added nitrogen, whereas CO2 had a positive effect on plant growth when no nitrogen was added. And in 2004, elevated CO2 stimulated production in burned plots, but not in unburned. Both of these findings may be due to altered phosphorus availability under elevated CO2, a possibility currently being tested. The presence of interacting effects demonstrates the importance of studying global change in a realistic, multi-factor context rather than trying to predict ecosystem responses based on single-factor experiments.

Other important findings are that global changes incorporated in this study can lead to reduced species diversity; that plants can reverse the tendency of warming to dry the soil; that changes in species composition under some treatments may be due to herbivory by slugs and snails; and that CO2 and nitrogen, in addition to warming, may affect the timing of flowering by plants.

JRGCE map of whole-plot treatments. Red circles=heated; yellow=elev CO2; orange=heat+CO2; white=neither. 4 blocks have control plots for infrastructure, also indicated with white.

Plot-level view of treatments. Watering and nitrogen are applied factorially to quadrants within plots.

PIs: Chris Field (Carnegie Instit. & Stanford), Harold Mooney, Peter Vitousek, Brendan Bohannan (Stanford Univ.), James Tiedje (Michigan State Univ.)

Jasper Ridge Global Change Experiment

for information on other studies at Jasper Ridge, please visit http://jrbp.stanford.edu/db/projects/list.php