Understanding carbon and vegetation dynamics in the boreal hotspot

Boreal forests represent one of the largest forested area on earth, accounting for more than 25 percent of the world’s forests. The boreal region also hosts large belowground carbon pools, partially in a frozen state and in form of peat, which, altogether, amount to about 1000 GtC. The boreal region is a hotspot in global change research because it witnessed the largest warming trend on the globe over the last decades, which may induce substantial changes in the functioning of land ecosystems. Current GCM simulations indicate that this warming trend will continue in the future decades resulting in substantial permafrost melting. In addition, changes in the regional and temporal patterns and intensity of precipitation are predicted, leading to an increase of extreme climate events, e. g. droughts which in turn will increase fire occurrence and insect calamities. How will the boreal forest respond and how will it feed back to climate change via changes in trace gas, water and energy exchange? What is the net balance of positive (e. g. accelerated soil respiration, intensification of fire regimes, etc.) and negative feedbacks (higher C sequestration, expansion of deciduous forest)? How will snow and forest cover impact the overall albedo? How fast will these changes occur? – are we expecting a gradual transition or are there thresholds phenomena and sudden regime shifts?
The goal of the ‘boreal hotspot’ session will be (1) to formulate a project that addresses the above questions and builds upon the existing modelling tools and expertise within GINGKO, (2) to identify key areas where model changes or improvements are necessary both in terms of parameterization and process representation (more/other PFTs, age-class cohort managment, permafrost-fire interaction, methane etc.) and (3) to develop a realistic workplan of how such a project can be realised (workforce, funding, timeframe etc.).

Representation of soil processes

The pedosphere is undoubtedly a complex and heterogeneous part of the Earth System and – being a large carbon reservoir and water storage system – plays an important role for the feedback between the climate and the carbon/water cycles. Models operating at continental to global scales certainly have to abstract from this complexity and thus represent the soil in a simplified manner, mostly neglecting vertical structure and the role of soil biota for biogeochemical processes. Indeed, a number of phenomena can be explained or described with these modeling approaches that may be called ‘dead-soil paradigm’ models because they treat soil carbon dynamics as purely physical processes.

However, observational and experimental evidence is accumulating that the current “dead-soil-paradigm” representation of the soil system and the assumption of homogeneous soil properties with depth are oversimplifications that lack processes and biological-physical interactions which may play an important role for the dynamics of the ecosystem at time scales from years to millennia. In addition, high horizontal heterogeneity of the vertical soil structure has been poorly represented on global scale so far, partly due to a lack of data for parameterization and validation.

The first aims of this initiative are

• to review current soil modeling approaches existent in the GINKGO partners         
• to identify the key interactions between the biological and the physicochemical soil systems that are neglected in current modeling approaches and are likely to influence the biogeochemical cycles for a large part of the terrestrial biosphere and thus have the potential to significantly impact the Earth System as a whole
• and to establish concrete collaboration on selected sub-topics with the goals of implementing existing knowledge in current models, modelling experiments, conceptual model development or establishing benchmark and validation strategies

The connecting objective is to transfer such new understandings into a global ecosystem (or Earth System) model by formulating valid abstractions of soil function and structure across scales, and by the derivation of global soil properties that are required to run or validate such improved global model.

Insights into Biospheric Modelling via Macrotheories

Several theoretical approaches have been suggested to describe biospheric functioning at the macroscopic level.  These include for instance the concept of multiple steady states in the atmosphere-biosphere system, optimization approaches, the thermodynamic principle of Maximum Entropy Production, and the Gaia hypothesis.  This session will discuss these approaches by addressing the following questions:    

• How can these theories be tested?
• What predictive insights can these theories provide?
• Do we have the appropriate modeling tools to test these theories?
• How can these theories improve and/or aid model and scenario development?

The goal of the discussion is (a) to identify a key research topic that highlights the research expertise on macrotheories within GINGKO and (b) to come up with a work plan to address this topic.