The new plant functional diversity model JeDi-BACH (version 1.0) in the ICON Earth System Model (version 1.0)

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Abstract
While it is clear that vegetation takes part in shaping terrestrial climate through various interactions with the atmosphere, it is not so obvious what role plant functional diversity plays here. So far a tool for investigating this question in land-atmosphere simulations was missing. The new tool JeDi-BACH (version 1.0), described here, closes this gap by combining the Jena Diversity Model (JeDi) with the land component JSBACHv4 of the ICON Earth System Model (version 1.0). In practice, the low-diversity plant parametrization of JSBACH employing plant functional types (PFTs) was replaced by the trait based high-diversity vegetation description of JeDi. The key novelty introduced by the implementation of JeDi into JSBACH is that the composition of terrestrial ecosystems emerges dynamically from environmental filtering based on functional trade-offs. Thereby, in contrast to the PFT approach, a richer set of plant strategies adapted to the ruling environmental conditions is obtained without a priori knowledge of the vegetation distribution. Besides documentation of this new implementation of JeDi, the paper also presents results from first exploratory simulations with interactive land-atmosphere coupling. We find a systematic dependence of simulated terrestrial climate on potential diversity in our experiments. Moreover, when investigating the reaction to changes in trait parameters, we find that at low diversity, simulated local climate varies with the particular composition of vegetation, while at high diversity simulated terrestrial climate proves to be rather insensitive due to a dynamic re-organization of the plant community structure. Apparently, the many more dynamic degrees of freedom of the highly diverse vegetation in JeDi-BACH make this model behave very differently (less tunable) than conventional land components based on only a few PFTs. Besides fundamental research on the relation between diversity and climate, JeDi-BACH may be useful for the investigation of non-analogue climates (e.g., paleoclimate) where we lack knowledge on the structure and distribution of vegetation.
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