Towards an integrated understanding of terrestrial ecosystem feedbacks to climate change

Since 1870, fairly consistent growth in the amount of carbon stored by the terrestrial biosphere has offset the equivalent of c. 29% of anthropogenic greenhouse gas emissions (Le Qu er e et al., 2015). However, coupled carbon–climate models do not agree as to how this sink will be affected by projected changes in climate over the next century (Friedlingstein et al., 2014). To help constrain this uncertainty, ecologists have used increasingly creative and innovative approaches to better understand the terrestrial carbon sink across multiple scales and levels of organization. For example, researchers are now considering coordinated responses of multiple ecosystem processes, utilizing an array of research methodologies and frameworks. These integrated approaches were on display during two organized oral sessions at the recent 100 Annual Meeting of the Ecological Society of America: one titled ‘Effects of climate warming on aboveground–belowground feedbacks in terrestrial ecosystems’ and another titled ‘Creative approaches for addressing ecological uncertainty in Earth System Models’. The speakers in these two organized sessions demonstrated the use of integrated approaches to answering ecological questions to improve our understanding of how terrestrial ecosystems will respond and feed back to future climate change. Although achieving a mechanistic, quantifiable understanding of every process and feedback within and among ecosystems is not possible, considering the system as a whole, including processes not yet fully understood, is critical. QuinnThomas (Virginia Tech, Blacksburg, VA, USA) concluded his talk on how nitrogen limitation is represented in Earth SystemModels (ESMs) (Thomas et al., 2015) by showing a photograph of a single tower of the Palace of Westminster overlaid on top of Monet’s classic impressionist painting of the entire Palace, titled ‘London Fog.’ Thomas juxtaposed the clarity of the smaller tower photograph against the blurred background of the Palace in its entirety to caution the scientific community against focusing too narrowly on a particular ecosystem response to climate change simply because we understand only a subset of the ecosystem. This presentation illustrated the importance of taking a more integrated approach when trying to understand the complexities of ecosystem responses to global change, even if the entirety of the picture is not perfectly clear. This report provides examples of three integrative approaches to understanding terrestrial ecosystem responses and feedbacks to climate change on display at the meeting. These include: (1) focusing on the connection between aboveground and belowground processes; (2) usingmodels to generate testable hypotheses; and (3) integrating observations, experiments, andmodeling across a range of spatial and temporal scales.