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Theme meeting, March 19, 2019

Constraining the C cycle and its effect on climate through synergy between modeling and empiric research


You may find the program of the day here

Model Summaries

An overview of the four most important models for the C cycle within BECC context were presented with help of a common template: LPJ-GUESS (Paul Miller), COUP (Wenxin Zhang), ForSAFE (Cecilia Axelsson), Biome-BGC, (Fredrik Lagergren). The models highlighted many similar components but had distinct origins and foci. For example, ForSAFE has mainly been developed as a forest management model, while COUP has a stronger soil focus.

Paul Miller started with an infographic visualizing that IPCC prognoses come with an uncertainty because we don’t fully understand the C cycle at different scales. He emphasized that the broad basics of the terrestrial C balance are actually fairly simple (NEE = product of NPP and organic matter turnover) which provides a perspective to identify commonalities among diverse researchers.

Need for refining input data were listed as amongst others

  • Whole-ecosystem C & N pools and fluxes
  • CH4-emissions divided into a) diffusive, b) plant mediated, c) ebullition fluxes
  • C input into soils of different channels
  • Info on the heterogeneity of structure and stability of soil organic carbon
  • Info on soil microbes and their dynamics

A good opportunity for synergies is the possibility to run several models on the same experimental areas, as recently done for ForSAFE and COUP. BECC is well placed to exploit this opportunity with a large number of researchers already closely connected to several experimental infrastructures (ICOS & Sites stations for example).

Empirical scientist “pitches”

Leif & Henni: highlighted importance of herbivory and long-term animal activities on major ecosystem processes. Both Leif and Henni mentioned the existence of, and linkages to, various experimental sites which could be used to assess role of herbivory on C and nutrient cycling.

Milda: described the importance of soil aggregate formation for C accumulation. Discussions arising identified the apparent lack of aggregate formation processes on models, and the difficulty of upscaling micro-scale aggregate formation processes to the much larger scales at which other major ecosystem processes are usually considered.

Dan: described a proposal idea to experimentally simulate fire in forest soils, as a method to derive useful model functions describing how key soil processes respond to fire intensity and duration.

Leif: outlined the potential importance of the riparian zone for ecosystem C and nutrient cycles, and pointed out that this zone is often overlooked by terrestrial scientists. Discussions focused on the limited availability of data from riparian areas which make it unclear how important their contribution to landscape scale really is.

Case studies of ongoing model-empirical scientist collaborations

Albert: project on the effect of hydrological intensification on soil C. Multi-scale approach. Microscale empirical measurements of microbial growth & respiration following rewetting. Development of new biologically-based equations describing microbial responses – raises possibility to decompose overall responses into the separate responses of the various different biological processes responding. These improved equations can be included into a subcomponent of the LPJ model. There are also plans for field measurements to improve representation of how water moves through the soil column following precipitation events.

Stefan: project on the effects of rewetting previously drained forest areas. LPJ, COUP and ForSAFE model included. Some of the most productive/informative exchanges were amongst researchers working with the different models, rather than modellers and empirical scientists.

Plenary discussion

Conceptual diagrams provided by all researchers prior to attendance provided useful insights into the different perspectives, ecosystem components and spatial scales relevant to the different researchers within the group. The plenary used  these diagram as a basis to divide attendants into the following three groups to discuss urgent research questions around the C cycle that could benefit from the synergy of modeling – empirical research:

(1) Global processes;

(2) Vegetation and vegetation-soil feedbacks,

(3) Micro-scale soil processes such as aggregation and physical soil C stabilization.