More than 10 years ago, a group of researchers launched an international collaboration that is now known as the Nutrient Network (NutNet). Their intent was to explore the relationship between productivity and diversity in grasslands—how much plant matter there is in an area, and how many species it contains. NutNet researchers would each carry out the same simple measurements and then pool their data. By combining information from many more sites than one researcher could realistically study, the collaborative could rigorously examine the effects of climate, soils and human land use on the productivity-diversity relationship. Researchers also agreed on an experimental design—manipulating soil nutrients and herbivory—to impose on sites. Sharing data from these experiments would provide a strong ability to distinguish the impacts of these factors on productivity and diversity.
From its earliest conversations, NutNet has since grown into a global collaborative comprised of almost 100 sites. It’s open to any researcher willing to support his or her own site, share data freely, and follow the same basic protocols. These protocols govern details like the size of plots, how to measure plant abundance, and how fertilizer and herbivory treatments are applied. Yet while these steps are consistent across the world—and the sites themselves are all grasslands—the study areas differ strongly in terms of the environments in which they occur, and in their response to treatments.
Professor Jon Bakker joined NutNet soon after it began and has collected data annually since 2007. Together with Professor Janneke Hille Ris Lambers from the UW Department of Biology, he measured the productivity and diversity of three grassland sites in western Washington (Janneke was a key participant for the first few years but is no longer actively involved). They decided to conduct the NutNet experiment at one site, Smith Prairie, located near Coupeville on Whidbey Island, Wash., on land owned by the Pacific Rim Institute for Environmental Stewardship. “This site is a low-elevation grassland, and it’s dominated by European invasive species,” he says. “There are other sites that are alpine, high-elevation grasslands; my site is cool, others are hot and humid.”
The experimental area at Smith Prairie is divided into plots, some of which are fenced to keep herbivores like rabbits and deer out, and all of which receive varying fertilizer treatments. “What we’re doing at Smith Prairie is a small experiment,” he says, “but the power comes when you have that same experiment repeated at multiple sites around the world—and you can start to look for global patterns.”
With these ever-growing data sets, and with its open collaborative mission, NutNet has spurred a large number of publications. To date, 30 NutNet-related papers have been published in the peer-reviewed literature, and Jon has co-authored about half of these, including four in 2016.
Those 2016 papers appeared in several high-impact journals. In February, James Grace led a paper in Nature, “Integrative modelling reveals mechanisms linking productivity and plant species richness.” In May, Andrew Tredennick led a “Technical Comment” in Science, “Comment on “Worldwide evidence of a unimodal relationship between productivity and plant species richness.”” That same month, Habacuc Flores-Moreno led a paper in Philosophical Transactions of The Royal Society B Biological Sciences, “Climate modifies response of non-native and native species richness to nutrient enrichment.” Finally, in September, Stanley Harpole led another paper in Nature, “Addition of multiple limiting resources reduces grassland diversity.” (Each of these papers has involved a large group of authors, whose roles in the paper are identified in a table that accompanies the publication.)
Other papers are in preparation, including one that Jon is leading. In addition, new sites are being added to NutNet continually, and the sheer volume of plots worldwide enables researchers to explore countless angles and collaborations. Jon recently joined ecologists and computer scientists from Australia, for example, on a project testing the effectiveness of automated estimates of ground cover.
Jon sees great potential to revisit earlier analyses, and to continue drawing new collaborators from other areas of the world. After all, each new site, along with each new data set, adds nuance and breadth to the global experiment—and helps all of the researchers bring greater clarity to the questions driving NutNet.
Photos © Jon Bakker.