Coupling carbon allocation with leaf and root phenology predicts tree-grass partitioning along a savanna rainfall gradient

Haverd, V; Smith, B; Raupach, M; Briggs, P; Nieradzik, L; Beringer, J; Hutley, L; Trudinger, CM; Cleverly, J

Coupling carbon allocation with leaf and root phenology predicts tree-grass partitioning along a savanna rainfall gradient

Haverd, V Smith, B

Raupach, M Briggs, P Nieradzik, L

Beringer, J

Hutley, L

Trudinger, CM

Cleverly, J

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Publisher:: Copernicus GmbH
Publication Type:: Journal Article
Citation:: Biogeosciences Discussions, 12 (19), pp. 16313 - 16357

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Field	Value	Language
dc.contributor.author	Haverd, V	en_US
dc.contributor.author	Smith, B https://orcid.org/0000-0002-6987-5337	en_US
dc.contributor.author	Raupach, M	en_US
dc.contributor.author	Briggs, P	en_US
dc.contributor.author	Nieradzik, L https://orcid.org/0000-0002-9562-5235	en_US
dc.contributor.author	Beringer, J https://orcid.org/0000-0002-4619-8361	en_US
dc.contributor.author	Hutley, L https://orcid.org/0000-0001-5533-9886	en_US
dc.contributor.author	Trudinger, CM https://orcid.org/0000-0002-4844-2153	en_US
dc.contributor.author	Cleverly, J https://orcid.org/0000-0002-2731-7150	en_US
dc.identifier.citation	Biogeosciences Discussions, 12 (19), pp. 16313 - 16357	en_US
dc.identifier.uri	http://hdl.handle.net/10453/39967
dc.description.abstract	<jats:p>Abstract. The relative complexity of the mechanisms underlying savanna ecosystem dynamics, in comparison to other biomes such as temperate and tropical forests, challenges the representation of such dynamics in ecosystem and Earth system models. A realistic representation of processes governing carbon allocation and phenology for the two defining elements of savanna vegetation (namely trees and grasses) may be a key to understanding variations in tree/grass partitioning in time and space across the savanna biome worldwide. Here we present a new approach for modelling coupled phenology and carbon allocation, applied to competing tree and grass plant functional types. The approach accounts for a temporal shift between assimilation and growth, mediated by a labile carbohydrate store. This is combined with a method to maximise long-term net primary production (NPP) by optimally partitioning plant growth between fine roots and (leaves + stem). The computational efficiency of the analytic method used here allows it to be uniquely and readily applied at regional scale, as required, for example, within the framework of a global biogeochemical model. We demonstrate the approach by encoding it in a new simple carbon/water cycle model that we call HAVANA (Hydrology and Vegetation-dynamics Algorithm for Northern Australia), coupled to the existing POP (Population Orders Physiology) model for tree demography and disturbance-mediated heterogeneity. HAVANA-POP is calibrated using monthly remotely-sensed fraction of absorbed photosynthetically active radiation (fPAR) and eddy-covariance-based estimates of carbon and water fluxes at 5 tower sites along the Northern Australian Tropical Transect (NATT), which is characterized by large gradients in rainfall and wildfire disturbance. The calibrated model replicates observed gradients of fPAR, tree leaf area index, basal area and foliage projective cover along the NATT. The model behaviour emerges from complex feed-backs between the plant physiology and vegetation dynamics, mediated by shifting above- vs. below-ground resources, and not from imposed hypotheses about the controls on tree/grass co-existence. Results support the hypothesis that resource limitation is a stronger determinant of tree cover than disturbance in Australian savannas. </jats:p>	en_US
dc.language	en	en_US
dc.publisher	Copernicus GmbH	en_US
dc.relation.ispartof	Biogeosciences Discussions	en_US
dc.relation.isbasedon	10.5194/bgd-12-16313-2015	en_US
dc.subject.classification	Meteorology & Atmospheric Sciences	en_US
dc.title	Coupling carbon allocation with leaf and root phenology predicts tree-grass partitioning along a savanna rainfall gradient	en_US
dc.type	Journal Article
utslib.citation.volume	19	en_US
utslib.citation.volume	12	en_US
utslib.for	0499 Other Earth Sciences	en_US
utslib.for	0601 Biochemistry and Cell Biology	en_US
pubs.embargo.period	Not known	en_US
pubs.organisational-group	/University of Technology Sydney
pubs.organisational-group	/University of Technology Sydney/Faculty of Science
pubs.organisational-group	/University of Technology Sydney/Faculty of Science/School of Life Sciences
utslib.copyright.status	open_access
pubs.issue	19	en_US
pubs.publication-status	Published online	en_US
pubs.volume	12	en_US

Abstract:

Abstract. The relative complexity of the mechanisms underlying savanna ecosystem dynamics, in comparison to other biomes such as temperate and tropical forests, challenges the representation of such dynamics in ecosystem and Earth system models. A realistic representation of processes governing carbon allocation and phenology for the two defining elements of savanna vegetation (namely trees and grasses) may be a key to understanding variations in tree/grass partitioning in time and space across the savanna biome worldwide. Here we present a new approach for modelling coupled phenology and carbon allocation, applied to competing tree and grass plant functional types. The approach accounts for a temporal shift between assimilation and growth, mediated by a labile carbohydrate store. This is combined with a method to maximise long-term net primary production (NPP) by optimally partitioning plant growth between fine roots and (leaves + stem). The computational efficiency of the analytic method used here allows it to be uniquely and readily applied at regional scale, as required, for example, within the framework of a global biogeochemical model. We demonstrate the approach by encoding it in a new simple carbon/water cycle model that we call HAVANA (Hydrology and Vegetation-dynamics Algorithm for Northern Australia), coupled to the existing POP (Population Orders Physiology) model for tree demography and disturbance-mediated heterogeneity. HAVANA-POP is calibrated using monthly remotely-sensed fraction of absorbed photosynthetically active radiation (fPAR) and eddy-covariance-based estimates of carbon and water fluxes at 5 tower sites along the Northern Australian Tropical Transect (NATT), which is characterized by large gradients in rainfall and wildfire disturbance. The calibrated model replicates observed gradients of fPAR, tree leaf area index, basal area and foliage projective cover along the NATT. The model behaviour emerges from complex feed-backs between the plant physiology and vegetation dynamics, mediated by shifting above- vs. below-ground resources, and not from imposed hypotheses about the controls on tree/grass co-existence. Results support the hypothesis that resource limitation is a stronger determinant of tree cover than disturbance in Australian savannas.

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http://hdl.handle.net/10453/39967