From field observations to improved land surface models: The case of dwarf-shrubs in Norway

Dwarf-shrubs are a fundamental component of boreal, Arctic, and alpine ecosystems, where they contribute substantially to ecosystem carbon sequestration and long-term storage, potentially influencing feedback mechanisms between terrestrial ecosystems and the global climate system. To date, dwarf-shrubs remain inadequately represented in most land surface models, while their interactions with climate are highly uncertain. As part of the DURIN project, we aim to develop and implement a new dwarf-shrub plant functional type in the Community Land Model (CLM) coupled with the Ecosystem Demography model FATES (Functionally Assembled Terrestrial Ecosystem Simulator). Combining information from field observations and vegetation modelling, we will provide new insights on the roles and contributions of dwarf-shrubs in climate-biosphere feedbacks, and ultimately contribute to an enhanced Earth system model performance in predicting future changes in the boreal and Arctic region.

This objective involves calibrating CLM-FATES using the extensive field observation data collected across four sites in Norway as part of the DURIN project, ranging from physiology to ecosystem fluxes, carbon allocation, below-ground interactions, and soil properties. These measurements capture habitat change (open and forested) as well as latitudinal and inland-coastal gradients, providing crucial information on environmental controls of dwarf-shrubs and ensuring robust model parameterization and calibration. The DURIN data will be used to calibrate key physiological and ecosystem parameters in the model, including those related to photosynthesis, carbon allocation, and plant-soil hydraulics. They will also support further model developments of a dwarf-shrub plant functional type, such as revised allometric relationships, improved biomass allocation schemes, or enhanced parameterization of cold and drought stresses. Here, we present the first results from integrating these field observations into CLM-FATES, outlining the emerging representation of dwarf-shrubs in the model and the next steps in its development.