Changes between Version 59 and Version 60 of Documentation/TrunkFunctionality4

Timestamp:

2020-10-23T18:15:34+02:00 (4 years ago)

Author:

luyssaert

Comment:

--

Documentation/TrunkFunctionality4

@@ -220 +220 @@
 
 === Leaf area ===
-XXX
+Describes r6908. There is no longer a parameter for maximum LAI in the trunk. Given that LAI is likely the key variable that links the biogeochemistry to the biophysics of ORCHIDEE it deserves some background information. LAI is now calculated as a prognostic variable and is the net result of growth, allocation and turnover. 
+ 
+
+=== Leaf longevity and turnover ===
+Describes r6908. The impact of within-season leaf turnover (thus the turnover between plant_status = icanopy and isenescent) can be monitored by two variables: LEAF_TURN_AGEING_c and LEAF_M_MAX_c. When expressed as percentage the within season turnover (thus due to ageing) varies between 0 and 30% for trees and reaches 100-150% for grasses. This seems to be acceptable. See the documentation on the wiki for some additional background on this issue.
+
+Because of the way leaf_age_crit is calculated there is an apparent conflict between the prescribed longevity and observed longevity. The prescribed longevity is used to calculate the leaf_age_crit (as a function of climate). Half the value of leaf_age_crit is used as the threshold to start within season leaf turnover. So the simulated longevity is less than the prescribed longevity …
+
+An example longevity_leaf = 400, leaf_age_crit = 300 at 25 C, 400 at 15 C and 600 at 5 C. Note that turnover starts when leaf age is half this value. Thus at 150 days in the tropics … which is still too high but not as bad as it looks like.
+
+For grasses the prescribed longevity was 7 times longer than the observed. Even with the climate and the leaf_age_crit complexities we will never match the observed longevity.
+
+The observed longevity suggests an annual within season turnover of 100 to 200%. This is what we get if we decrease longevity_leaf but with such a turnover it is almost impossible to achieve realistic LAI’s unless we increase NPP/GPP (which seems to improve several aspects of growth).
+
+! longevity_leaf is a prescribed parameter for the longevity of a 
+    ! typical leaf/needle at the average temperature for that PFT. For
+    ! PFTs where a large range in longevity has been observed, this is
+    ! accounted for in the calculation of leaf_age_crit. Leaf_age_crit is 
+    ! thus the location-specific longevity. It the age of a leaf/needle
+    ! exceeds crit_leaf_age, leaf turnover will start (see stomate_turnover).
+
+=== Leaf and roots ===
+
 
 === Litter decomposition ===