Changes between Version 27 and Version 28 of Documentation/TrunkFunctionality4

Timestamp:

2020-03-27T14:19:13+01:00 (4 years ago)

Author:

luyssaert

Comment:

--

Documentation/TrunkFunctionality4

@@ -229 +229 @@
 
 === Mortality (r6614) ===
-ORCHIDEE trunk 4 distinguished 3 types of natural mortality. The first two options are similar to those in previous version of ORCHIDEE and are set by the flag '''constant_mortality'''. If '''constant_mortality''' = y, the background mortality of a forests is calculated as a constant, prescribed fraction. In ORCHIDEE trunk 4, this fraction is given by '''residence_time''' (see also forest management).  If '''constant_mortality''' = n, the background mortality of a forest is a function of its net primary production (npp). If npp decreases, mortality will increase. 
-
-Both options have been developed but only '''constant_mortality''' = y has been tested in ORCHIDEE trunk 4. However, because of the introduction of self-thinning (the third type of natural mortality) in ORCHIDEE trunk 4, '''constant_mortality''' = y became the default setting. In ORCHIDEE trunk 4, the total mortality is the maximum of the background mortality and the mortality from self-thinning. Only if self-thinning is absent or too low, background mortality will play a role. This approach implies that when '''constant_mortality''' = y is used in combination with self-thinning, background mortality will only play a role in the first years to decade before self-thinning starts (the latest calculations of RDI - see Prescribe - the role of the background mortality has further decreased). Despite its limited use, it represents an essential process: owing to background mortality, the number of individuals decreases, the remaining individuals grow faster and thus manage to reach self-thinning in a reasonable amount of time. It needs to be tested how the interplay between background mortality and self-thinning will work out when '''constant_mortality''' = n is used.
+ORCHIDEE trunk 4 distinguishes 2 types of natural mortality: (1) explicitly considering mortality from disturbances and self-thinning, and (2) implicitly considering background mortality. Ideally, approach (1) should be further developed such that all underlying agents driving background mortality are represented in the model (i.e., gap-scale mortality, pests, disease, windthrow, etc.) such that it can replace approach (2). Two options of background mortality may be chosen: constant background mortality and dynamic background mortality. To use the first option, set the flag '''constant_mortality''' = y. The background mortality of a forests is calculated as a constant, prescribed fraction. In trunk 4, this fraction is given by '''residence_time''' (see also forest management). Otherwise set '''constant_mortality''' = n, the dynamic background mortality of a forest is a function of its net primary production (npp). If npp decreases, mortality will increase Both options have been developed but only '''constant_mortality''' = y has been tested in ORCHIDEE trunk 4. 
+
+However, because of the introduction of self-thinning in ORCHIDEE trunk 4, '''constant_mortality''' = y became the default setting. In ORCHIDEE trunk 4, the total mortality is the maximum of the background mortality and the mortality from self-thinning. Only if self-thinning is absent or too low, background mortality will play a role. This approach implies that when '''constant_mortality''' = y is used in combination with self-thinning, background mortality will only play a role in the first years to decade before self-thinning starts (the latest calculations of RDI - see Prescribe - the role of the background mortality has further decreased). Despite its limited use, it represents an essential process: owing to background mortality, the number of individuals decreases, the remaining individuals grow faster and thus manage to reach self-thinning in a reasonable amount of time. It needs to be tested how the interplay between background mortality and self-thinning will work out when '''constant_mortality''' = n is used.
 
 ORCHIDEE trunk 4 calculates the number of individuals and uses this as a criterion to initiate a stand replacing disturbance. This approach, guided by the self-thinning relationship, avoids the need for a stand-level turnover time. ORCHIDEE-CN, and ORCHIDEE-CNP still make use of stand-level turnover. Note that the meaning of residence_time is very different between the CAN branch and the trunk.  In the trunk biomass has no age and thus the residence time accounts for all forest dynamics including self-thinning, pests, diseases and windthrow. In the CAN branch, biomass does have an age and self-thinning is explicitly accounted for, hence, the residence time should be much higher as it only accounts for pest, diseases and windthrow. Even the latter is not exact because as long as those disturbances are small scale they are probably accounted for in the parametrization of self-thinning.