Changes between Version 81 and Version 82 of Documentation/TrunkFunctionality4

Timestamp:

2021-02-18T11:51:37+01:00 (3 years ago)

Author:

mmcgrath

Comment:

Adding a section about vegetation height

Documentation/TrunkFunctionality4

@@ -222 +222 @@
 Describes r6614. All biomass harvest is recorded in a harvest variable '''harvest_pool''', this variable also stores the mass and dimensions of the harvest/mortality (absolute numbers thus accounting for the pixel area!). Related variables were introduced: '''harvest_type''', '''harvest_cut''', and '''harvest_area'''. Wood product pools and fluxes from wood and biomass decomposition are calculated in a separate module dedicated to wood use. The dimension of the wood use pools were externalized and can be changed to better address regional differences when aiming for regional simulations. The default 1, 10 and 100 year pools were replaced by 2, 17 and 50 years which is closer to the reality for Europe. For most parts of the world a 100 year wood pool is very optimistic. 
 
+=== Height (of vegetation) ===
+Describes r7089.  Vegetation height is dynamic; as the PFT (in particular forests) grow, the height will grow through the allocation.  When multiple circumferences classes are used, height has an impact on where the carbon goes.  Due to intra-stand competition, more carbon gets allocated to taller circumference classes.  Disturbances can change the average stand height.  Self-thinning is a natural process in which small trees die because they are out-competed for resources.  Environmental mortality is another natural process in which larger trees are killed as they are assumed to be more sensitive to environmental stress.  Windthrow is an (optional) process which will disproporationally impact taller trees.  In runs using forest management (not currently the default), forests can be thinned from above or below.  Forests thinned from above lose tall trees to harvest, while those thinned from below lose small trees.  Both actions change the average height of the stand.
+
+Vegetation height has an impact on roughness height (aerodynamic properties of the surface).
+
+PFTs are prescribed by choosing the height of the saplings, which determines initial biomass through allometric relations.
+
+Two variables are output for each PFT: "HEIGHT", which is the average height of the vegetation (averaged across all circumference classes), and "HEIGHT_DOM", which is the dominant height (the height of the largest circumference class).  A switch was introduced in r7083 which allows one or the other to be used in the calculation of the roughness height.
 
 === Land cover change (with age classes) ===