Preprints
https://doi.org/10.5194/egusphere-2022-1423
https://doi.org/10.5194/egusphere-2022-1423
31 Jan 2023
 | 31 Jan 2023

Process-oriented models of autumn leaf phenology: ways to sound calibration and implications of uncertain projections

Michael Meier and Christof Bigler

Abstract. Autumn leaf phenology marks the end of the growing season, during which trees assimilate atmospheric CO2. Since autumn leaf phenology responds to climatic conditions, climate change affects the length of the growing season. Thus, autumn leaf phenology is often modelled to assess possible climate change effects on future CO2 mitigating capacities and species compositions of forests. Projected trends have been mainly discussed with regards to model performance and climate change scenarios. However, there has been no systematic and thorough evaluation of how performance and projections are affected by the calibration approach. Here, we analyzed >2.3 million performances and 39 million projections across 21 models, 5 optimization algorithms, ≥7 sampling procedures, and 26 climate model chains from two representative concentration pathways. Calibration and validation were based on >45 000 observations for beech, oak, and larch from 500 Central European sites each.

Phenology models had the largest influence on model performance. The best performing models were (1) driven by daily temperature, day length, and partly by seasonal temperature or spring leaf phenology and (2) calibrated with the Generalized Simulated Annealing algorithm (3) based on systematically balanced or stratified samples. Assuming an advancing spring phenology, projected autumn phenology shifts between 13 and +20 days by 2080–2099, resulting in a lengthening of the growing season by 7–40 days. Climate scenarios and sites explained more than 80 % of the variance in these shifts and thus had eight to 22 times the influence of phenology models. Warmer climate scenarios and better performing models predominantly extended the growing season more than cooler scenarios and poorer models.

Our results justify inferences from comparisons of process-oriented phenology models to phenology-driving processes and we advocate species-specific models for such analyses and subsequent projections. For sound calibration, we recommend a combination of cross-validations and independent tests, using randomly selected sites from stratified bins based on mean annual temperature and average autumn phenology, respectively. Poor performance and little influence of phenology models on autumn phenology projections suggest that the models are overlooking relevant drivers. While the uncertain projections indicate an extension of the growing season, further studies are needed to develop models that adequately consider the relevant processes for autumn phenology.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.

Journal article(s) based on this preprint

11 Dec 2023
Process-oriented models of autumn leaf phenology: ways to sound calibration and implications of uncertain projections
Michael Meier and Christof Bigler
Geosci. Model Dev., 16, 7171–7201, https://doi.org/10.5194/gmd-16-7171-2023,https://doi.org/10.5194/gmd-16-7171-2023, 2023
Short summary
Michael Meier and Christof Bigler

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-1423', Anonymous Referee #1, 13 Apr 2023
    • AC1: 'Reply on RC1', Michael Meier, 12 Jul 2023
  • RC2: 'Comment on egusphere-2022-1423', Anonymous Referee #2, 07 Jun 2023
    • AC2: 'Reply on RC2', Michael Meier, 12 Jul 2023

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-1423', Anonymous Referee #1, 13 Apr 2023
    • AC1: 'Reply on RC1', Michael Meier, 12 Jul 2023
  • RC2: 'Comment on egusphere-2022-1423', Anonymous Referee #2, 07 Jun 2023
    • AC2: 'Reply on RC2', Michael Meier, 12 Jul 2023

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload
AR by Michael Meier on behalf of the Authors (12 Jul 2023)  Author's response   Author's tracked changes   Manuscript 
ED: Referee Nomination & Report Request started (01 Sep 2023) by Hans Verbeeck
RR by Nicolas Delpierre (14 Sep 2023)
ED: Publish subject to minor revisions (review by editor) (04 Oct 2023) by Hans Verbeeck
AR by Michael Meier on behalf of the Authors (13 Oct 2023)  Author's response   Author's tracked changes   Manuscript 
ED: Publish as is (21 Oct 2023) by Hans Verbeeck
AR by Michael Meier on behalf of the Authors (23 Oct 2023)  Manuscript 

Post-review adjustments

AA: Author's adjustment | EA: Editor approval
AA by Michael Meier on behalf of the Authors (04 Dec 2023)   Author's adjustment   Manuscript
EA: Adjustments approved (04 Dec 2023) by Hans Verbeeck

Journal article(s) based on this preprint

11 Dec 2023
Process-oriented models of autumn leaf phenology: ways to sound calibration and implications of uncertain projections
Michael Meier and Christof Bigler
Geosci. Model Dev., 16, 7171–7201, https://doi.org/10.5194/gmd-16-7171-2023,https://doi.org/10.5194/gmd-16-7171-2023, 2023
Short summary
Michael Meier and Christof Bigler
Michael Meier and Christof Bigler

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Short summary
We analyzed >2.3 million calibrations and 39 million projections of leaf coloration models, considering 21 models, 5 optimization algorithms, ≥7 sampling procedures, and 26 climate scenarios. Models based on temperature, day length, and leaf unfolding performed best, especially when calibrated with Generalized Simulated Annealing and systematically balanced or stratified samples. Projected leaf coloration shifts btw. -13 and +20 days, extending the growing season by 7–40 days through 2080–2099.