Assessing the impact of permafrost-vegetation interaction on treeline dynamics in Siberia with the individual-based, spatially explicit treeline model LAVESI coupled to the permafrost land-surface model CryoGrid

Tundra-taiga ecotone dynamics play a relevant role in the global carbon cycle. However, it is rather uncertain whether these ecosystems could develop into a carbon source rather than continuing atmospheric carbon sequestration under global warming. This knowledge gap stems from the complex permafrost-vegetation interactions, not yet fully understood. Consequently, shedding light on the role of current and future active layer dynamics is crucial for an accurate prediction of treeline dynamics, and thus for aboveground forest biomass and carbon stock developments.

We make use of a coupled model version combining CryoGrid, a one-dimensional permafrost land-surface model, with LAVESI, an individual-based and spatially explicit forest model for larch species (Larix Mill.) in Siberia. Following a parametrization against an extensive field data set of 100+ forest inventories conducted along the Siberian treeline (97-169° E), we run simulations for the upcoming centuries forced by climatic change scenarios.

The coupled model setup benefits from the detailed process implementation gained while developing the individual models. Therefore, we can reproduce the energy transfer and thermal regime in permafrost ground as well as the radiation budget, nitrogen and photosynthetic profiles, canopy turbulence, and leaf fluxes, while at the same time, predicting the expected establishment, die-off, and treeline movements of larch forests. In our analyses, we focus on vegetation and permafrost dynamics and reveal the magnitudes of different feedback processes between permafrost, vegetation, and current and future climate in Northern Siberia.