Changes between Version 65 and Version 66 of Documentation/TrunkFunctionality4


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Timestamp:
11/01/20 13:21:33 (22 months ago)
Author:
luyssaert
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  • Documentation/TrunkFunctionality4

    v65 v66  
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    326326=== Phenology === 
    327 Describes r6614. The pft-specific parameter '''always_init''' controls whether the phenology depends on the reserves (set to .FALSE.) or is forced (set to .TRUE.). Note that a forced phenology (thus always_init = .TRUE.) has no ecophysiological basis, it is a numerical approach to stabilize the vegetation cover. A stable vegetation cover is particularly welcome in coupled simulations but likely hides real vegetation dynamics (especially under future climate conditions) or problems in other routines or parameter settings. If a PFT keeps dying in an area where it is currently present, this would hint at a problem with the current model/parameters. If a PFT keeps dying under future conditions, it may be a real response (depending on the PFT). If forced phenology is used, plants will develop an initial canopy in phenology irrespective of whether the plant had sufficient carbon and nitrogen reserves and for evergreen species irrespective of whether the canopy was viable at all. This setting basically overcomes a mortality event at the expense of taking up carbon and nitrogen from the atmosphere. When used in combination with impose_cn = n, an inconsistency is introduced: impose_cn = n reflect the desire to close the nitrogen cycle, always_init = y opens a backdoor in the nitrogen cycle.  
    328  
    329 From a conceptual point of view, ORCHIDEE trunk is all about vegetation dynamics and thus instabilities in the vegetation cover. In ORCHIDEE trunk there are two processes that can deal with dying PFts including evergreens PFTs. First, ok_recruitment could used. If ok_recruitment = .TRUE. a decrease in the canopy cover will result in more light reaching the forest floor which in turn should trigger recruitment of -for the moment- the same PFT. Generation can take over from each other without loosing the canopy cover entirely. Second, if there are insufficient reserves to grow no leaves, there will be no or insufficient gpp, the carbon reserves will be consumed by respiration processes, the plants will be killed, the biomass transferred to the litter pools and the same or another PFT (see section on species change) will be replanted. ORCHIDEE trunk was developed to work with always_init = .FALSE. so this has become the default value, contrary to previous versions of the trunk where always_init = .TRUE. is the default. 
     327Describes r6918. The pft-specific parameter '''always_init''' controls whether the phenology depends on the reserves (set to .FALSE.) or is forced (set to .TRUE.). Note that a forced phenology (thus always_init = .TRUE.) has no ecophysiological basis, it is a numerical approach to stabilize the vegetation cover. A stable vegetation cover is particularly welcome in coupled simulations but likely hides real vegetation dynamics (especially under future climate conditions) or problems in other routines or parameter settings. If a PFT keeps dying in an area where it is currently present, this would hint at a problem with the current model/parameters. If a PFT keeps dying under future conditions, it may be a real response (depending on the PFT). If phenology is always initialized, plants will develop an initial canopy in phenology irrespective of whether the plant had sufficient carbon and nitrogen reserves and for evergreen species irrespective of whether the canopy was viable at all. This setting basically overcomes a mortality event at the expense of taking up carbon and nitrogen from the atmosphere. When used in combination with impose_cn = n, an inconsistency is introduced: impose_cn = n reflect the desire to close the nitrogen cycle, always_init = y opens a backdoor in the nitrogen cycle.  
     328 
     329From a conceptual point of view, ORCHIDEE trunk is all about vegetation dynamics and thus instabilities in the vegetation cover. In ORCHIDEE trunk there are two processes that can deal with dying PFTs including evergreens PFTs. First, ok_recruitment could used. If ok_recruitment = .TRUE. a decrease in the canopy cover will result in more light reaching the forest floor which in turn should trigger recruitment of -for the moment- the same PFT. Generations (cohorts) can take over from each other without loosing the canopy cover entirely. Second, if there are insufficient reserves to grow leaves, there will be no or insufficient gpp, the carbon reserves will be consumed by respiration processes, the plants will be killed, the biomass transferred to the litter pools and the same or another PFT (see section on species change) will be replanted. ORCHIDEE trunk was developed to work with always_init = .FALSE. so this has become the default value, contrary to previous versions of the trunk where always_init = .TRUE. is the default. 
     330 
     331Temperature is a very consistent climatological variable in the sense that each year the summer is warmer than the winter (even in so-called cold years). This implies that temperature driven phenology is very robust in the sense that the PFT will develop a canopy each year. Soil moisture, however, is much less predictable and in very dry or very yet years the seasonal patterns may differ a lot. Especially when soil moisture criteria are combined with other criteria (pheno model: moigdd) there are years that the criteria are never met and that the PFT never develops leaves. This is not at all observed. Even farmers would plant crops when the conditions are far from optimal (typically because they have to plant the crops before they know that the conditions will be far from optimal). If set the yes, the flag'''ok_force_pheno''' will start the growth of a canopy a predefined number of days () after the average budbreak data for that PFT at that location. Test simulations over the Americas showed that over a 30 year period forced phenology was used 5 to 10% of the years between 1901 and 1930 for PFT10, 12 and 13. This flag did little or nothing to the phenology of the other PFTs with the pheno model moigdd.      
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