Changes between Version 24 and Version 25 of Documentation/TrunkFunctionality4

Timestamp:

2020-03-09T19:45:35+01:00 (4 years ago)

Author:

luyssaert

Comment:

--

Documentation/TrunkFunctionality4

@@ -283 +283 @@
 From a conceptual point of view, CN-CAN is all about vegetation dynamics and thus instabilities in the vegetation cover. In CN-CAN 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. CN-CAN was developed to work with always_init = .FALSE. so this has become the default value, contrary to the trunk where always_init = .TRUE. is the default.
 
+
 === Photosynthesis (r6614) ===
 Photosynthesis is calculated as in ORCHIDEE trunk 4, and ORCHIDEE trunk 3 but the way the canopy levels are defined has changed. The reason of this change is in the albedo and energy budget for which physical layers are required. For this reason the space between the bottom and the top of the canopy is divided into x layers. x is set by the parameter '''nlevels_photo'''. Applications with ORCHIDEE trunk 4 used nlevels_photo = 10. Contrary to previous trunk versions of ORCHIDEE where each canopy layer contained 0.5 units of LAI, in ORCHIDEE trunk 4, each canopy layer will have the same depth (in m) but will contain a different amount of LAI because tree canopies are assumed spherical.
+
 
 === Plant water stress (r6614) ===
@@ -295 +297 @@
 
 === Prescribe initial vegetation (r6614) ===
-At the start of the model run or after a die-back or clear-cut new vegetation needs to be planted as ORCHIDEE does not grow vegetation from seeds. The initial dimensions of the vegetation are thus prescribed. Given that the allocation follows allometric relationships, any of the tree dimensions or any mass of any component could have been used to prescribe. The variable diameter was chosen because it is easy to (mentally) visualize the prescribed vegetation. In the run.def  '''dia_init_min''' and '''dia_init_max''' need to be prescribed. Typical values are 1 to 3 cm. If more than one diameter class is used, '''dia_init_max ''' needs to larger than '''dia_init_min'''. The larger the difference between the min and max, the more vegetation layers the canopy will be composed from. Grasses are prescribed by the parameters '''height_init_min''' and '''height_init_max''' because we have no diameter-height relationship for grasses. Note that '''dia_init_min''' and '''dia_init_max''' are the same. The fact that we have two values is a left over from previous versions of stomate_prescribe.f90.
+At the start of the model run or after a die-back or clear-cut new vegetation needs to be planted as ORCHIDEE does not grow vegetation from seeds. The initial dimensions of the vegetation are thus prescribed. Given that the allocation follows allometric relationships, any of the tree dimensions or any mass of any component could have been used to prescribe. The variable diameter was chosen because it is easy to (mentally) visualize the prescribed vegetation. In the run.def  '''dia_init_min''' and '''dia_init_max''' need to be prescribed. Typical values are 1 to 3 cm. If more than one diameter class is used, '''dia_init_max ''' needs to larger than '''dia_init_min'''. The larger the difference between the min and max, the more vegetation layers the canopy will be composed from. Grasses are prescribed by the parameters '''height_init_min''' and '''height_init_max''' because we have no diameter-height relationship for grasses. Note that '''height_init_min''' and '''height_init_max''' are the same. The fact that we have two values is a left over from previous versions of stomate_prescribe.f90 (see ticket #688).
 
 In addition, the initial number of seedlings needs to be prescribed as well. For this a parameter needs to be set. This is a critical parameter to obtain acceptable model behaviour. If it is too high, lai saturates but the stand-level GPP will be distributed over too many individuals, each individual will grow very little and so it will take very long before self-thinning is reached. If it is set too low, LAI will be too low resulting in a too low GPP and thus very slow growth. A good starting values is a bit below self-thinning. That way the vegetation starts growing, individual are killed thanks to the background mortality and within 10 to 20 years self-thinning is reached. Why not starting at self-thinning? During code development it was tried to have the model start at the exact number of trees at which self-thinning will start given the diameter of the tree. One issues was that when prescribing small individuals (1 to 3 
 cm) the calculated number of trees could in the millions and so the GPP had to be distributed over too many individuals.
 
-Depending on whether a stand is managed or not, the initial number of trees is calculated in a different way (see stomate_prescribe.f90). For managed stands (FM = 2, 3 and 4) '''alpha_rdi_upper''' and  '''beta_rdi_upper''' are used to calculate a dynamically changing RDI. For unmanaged forest (FM = 1),  '''grad_thin''', '''alpha_rdi_upper''', '''beta_rdi_upper''' are used to calculate RDI as long as the stand has not reached self-thinning. 
+Depending on whether a stand is managed or not, the initial number of trees is calculated in a different way (see stomate_prescribe.f90). For managed stands (FM = 2, 3 and 4) '''alpha_rdi_upper''' and  '''beta_rdi_upper''' are used to calculate a dynamically changing RDI. For unmanaged forest (FM = 1),  '''grad_thin''', '''alpha_rdi_upper''', '''beta_rdi_upper''' are used to calculate RDI as long as the stand has not reached self-thinning. For better model performance the parameter '''grad_thin''' should be made PFT-dependent (see ticket #686)