Whole-ecosystem warming and CO2 manipulation to assess ombrotrophic bog responses to hypothetical future environments

Background/Question/Methods

The Spruce-Peatland Responses Under Climatic and Environmental Change (SPRUCE) experiment is an in situ warming by CO₂ manipulation of a characteristic high-carbon ecosystem. It is being conducted to identify critical environmental response functions for terrestrial organisms, communities, and ecosystems to rapidly changing climate conditions. Such research has ‘real-world’ relevance when conclusions are drawn from controlled manipulations operating in natural field settings. The experimental platform is being constructed to address climate change response mechanisms in a Picea/Larix/Sphagnum ombrotrophic bog ecosystem located in northern Minnesota. The target ecosystem located at the southern extent of the spatially expansive boreal peatland forests is hypothesized to be especially vulnerable to climate change and to have important feedbacks on atmospheric greenhouse gas levels. 

New methods for warming at plot scales (12 -m diameter) have been developed for this study.  We combine aboveground enclosure walls having an internally recirculating warm air envelope with soil deep heating to simulate a range of future warming treatments of as much as +9 °C.  Warming treatments will be repeated at both ambient and elevated CO₂ atmospheres (+900 ppm) to allow the evaluation of key interactions between vegetation response to elevated temperatures and direct effects of CO₂. Direct and indirect effects of these experimental perturbations will be tracked and analyzed over a decade for the development and refinement of models needed for full Earth system analyses. 

Results/Conclusions

A priori simulations of the effects of warming and elevated CO₂ suggest variable response for the primary producers in this ecosystem (trees and shrubs vs. Sphagnum moss), a strong interaction with nutrient cycling driven by warming induced decomposition of stored elements (esp. N), and a substantial increase in the release of greenhouse gases (CO₂ and CH₄) attenuated to some degree by photosynthetic enhancements of trees and shrubs driven by elevated CO₂ atmospheres. The ambient bog site is undergoing secondary succession from a stand removal clear cut in 1974, and is currently estimated to be transitioning from post-harvest carbon losses to annual carbon gains as the tree species become re-established.  Through the execution of this experiment we will quantify thresholds for organism decline or mortality, limitations to regeneration, biogeochemical limitations to productivity, and changing greenhouse gas emissions to the atmosphere. The experiment will allow for the evaluation of responses across multiple spatial scales including: microbial communities, bryophyte populations, various higher plant types, and some faunal groups.