Using Experimental Methodology to Determine Grassland Response to Climate Change

Post provided by Heather Hager

©Hajnal Kovacs

In the second chapter of Grasslands and Climate ChangeMethodology I: Detecting and predicting grassland changeJonathan Newman and I take an in-depth look at the experimental methodology that has been used to determine how grassland ecosystems will respond to climate change. When we set out, we were interested in knowing, for example, the magnitudes and types of treatments applied, plot sizes, replication, study durations, and types of response variables that were measured and by how many studies. For simplicity(!), we focused on three treatment types: changes in atmospheric carbon dioxide levels, changes in temperature (mean, minimum, maximum), and changes in precipitation (increases, decreases, timing).

Using the methods of a formal systematic review, we identified 841 relevant studies, for which we extracted information on study location and experimental methodology. There were some surprises, both good and bad. For instance, mean and median plot sizes were actually larger than we had expected. On the other hand, numbers of true experimental replicates were low. Although many of the study methods were well reported, some areas lacked critical detail such as descriptions of (at least) the dominant plant species in the study area.

Meta-Analysis and Data Archiving

Word cloud of the dominant vegetation species from the studies that we looked into.

Word cloud of the dominant vegetation species from the studies that we looked into.

Among other things, we examined whether studies tested one or more of the climate change variables, and whether they investigated interaction effects, as there is no reason to expect individual effects to be additive. We also examined the magnitude and range of the climate change treatment(s) applied.  A huge variety of response variables was measured, ranging from individual to ecosystem levels.  Notably, approximately one-third of the response variables were reported in fewer than 10 studies, making meta-analyses difficult for those variables.

Given that meta-analyses and modelling will be important in synthesising climate change effects for the large range of grassland systems and combinations of climate variables, the ability to extract response data from these completed studies is critical to their future use. Many major journals, including those of the British Ecological Society, are implementing mandatory public data archiving policies.

©Hajnal Kovacs

I have made a habit out of publicly archiving my curated raw data for each of my publications, regardless of whether it is mandatory. I think this is good research policy. Therefore, I was disappointed to find that only 21 of the 841 studies provided publicly archived data, even though the majority of research has been done since the late 2000s and early 2010s, during an era of increasing awareness of the importance of data accessibility.

Final Thoughts

I’m not going to divulge all the other details here, but our methodological summary has shown where strengths can be found in the grassland and climate change research to date, as well as areas that still have a lot of potential for exploration. We hope that our identification of research gaps will be considered in subsequent research and help to develop a more comprehensive picture of the likely ecological effects of future climate change on a variety of grassland ecosystems.

Grasslands and Climate Change (ISBN 9781108163941) is part of the Ecological Reviews series. BES members get 25% off all titles in the series when buying directly from Cambridge University Press

Read David Gibson’s introduction to the book on the Journal of Ecology blog.

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