A new version of the CABLE land surface model (Subversion revision r4601) incorporating land use and land cover change, woody vegetation demography, and a novel optimisation-based approach to plant coordination of photosynthesis

• Published in: Geoscientific Model Development Vol. 11; no. 7; pp. 2995 - 3026
• Main Authors: Haverd, Vanessa, Smith, Benjamin, Nieradzik, Lars, Briggs, Peter R, Woodgate, William, Trudinger, Cathy M, Canadell, Josep G, Cuntz, Matthias
• Format: Journal Article
• Language: English
• Published: Katlenburg-Lindau Copernicus GmbH 27.07.2018; European Geosciences Union; Copernicus Publications
• Subjects: Accumulation; Age composition; Analysis; Annual variations; Anomalies; Anthropogenic factors; Atmosphere; Biodegradation; Biogeochemical cycles; Biomass; Biosphere; Capacity; Carbon; Carbon cycle; Carbon dioxide; Carbon sinks; Carboxylation; Climate; Climate and vegetation; Computer simulation; Constraint modelling; Deforestation; Demography; Earth; Earth and Related Environmental Sciences; Electron transport; Evaluation; Fertilization; Fitness; Forecasts and trends; Forest degradation; Forests; Geovetenskap och miljövetenskap; Global precipitation; Global temperatures; Heterogeneity; Hypotheses; Interannual variations; Intercomparison; Inversions; Land cover; Land surface models; Land use; Life Sciences; Mathematical models; Natural Sciences; Naturgeografi; Naturvetenskap; Northern Hemisphere; Optimization; Photosynthesis; Physical Geography; Precipitation; Reproductive fitness; Ribulose-bisphosphate carboxylase; Simulators; Soil; Spatial distribution; Temperature anomalies; Tiles; Transport; Trends; Tropical environments; Tropical forests; Vegetation; Vegetation dynamics; Woody plants; Australia
• ISSN: 1991-9603; 1991-959X; 1991-962X; 1991-9603; 1991-962X; 1991-959X
• DOI: 10.5194/gmd-11-2995-2018

The Community Atmosphere-Biosphere Land Exchange model (CABLE) is a land surface model (LSM) that can be applied stand-alone and provides the land surface-atmosphere exchange within the Australian Community Climate and Earth System Simulator (ACCESS). We describe new developments that extend the applicability of CABLE for regional and global carbon-climate simulations, accounting for vegetation responses to biophysical and anthropogenic forcings. A land use and land cover change module driven by gross land use transitions and wood harvest area was implemented, tailored to the needs of the Coupled Model Intercomparison Project 6 (CMIP6). Novel aspects include the treatment of secondary woody vegetation, which benefits from a tight coupling between the land use module and the Population Orders Physiology (POP) module for woody demography and disturbance-mediated landscape heterogeneity. Land use transitions and harvest associated with secondary forest tiles modify the annually resolved patch age distribution within secondary vegetated tiles, in turn affecting biomass accumulation and turnover rates and hence the magnitude of the secondary forest sink. Additionally, we implemented a novel approach to constrain modelled GPP consistent with the coordination hypothesis and predicted by evolutionary theory, which suggests that electron-transport- and Rubisco-limited rates adjust seasonally and across biomes to be co-limiting. We show that the default prior assumption - common to CABLE and other LSMs - of a fixed ratio of electron transport to carboxylation capacity at standard temperature (J.sub.max, 0 /V.sub.cmax, 0) is at odds with this hypothesis; we implement an alternative algorithm for dynamic optimisation of this ratio such that coordination is achieved as an outcome of fitness maximisation. The results have significant implications for the magnitude of the simulated CO.sub.2 fertilisation effect on photosynthesis in comparison to alternative estimates and observational proxies.