### 2.2.1.3. Vegetation Structure[¶](#vegetation-structure "Permalink to this headline")

Vegetation structure is defined by leaf and stem area indices (\\(L,\\, S\\)) and canopy top and bottom heights (\\(z\_{top}\\),\\(z\_{bot}\\) ). Separate leaf and stem area indices and canopy heights are prescribed or calculated for each PFT. Daily leaf and stem area indices are obtained from griddeddatasets of monthly values (section [2.2.3.3](#surface-data)). Canopy top and bottom heights for trees are from ICESat ([Simard et al. (2011)](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/References/CLM50_Tech_Note_References.html#simardetal2011)). Canopy top and bottom heights for short vegetation are obtained from gridded datasets but are invariant in space and time and were obtained from PFT-specific values ([Bonan et al. (2002a)](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/References/CLM50_Tech_Note_References.html#bonanetal2002a)) ([Table 2.2.2](#table-plant-functional-type-canopy-top-and-bottom-heights)). When the biogeochemistry model is active, vegetation state (LAI, SAI, canopy top and bottom heights) are calculated prognostically (see Chapter [2.20](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/Vegetation_Phenology_Turnover/CLM50_Tech_Note_Vegetation_Phenology_Turnover.html#rst-vegetation-phenology-and-turnover)).

Table 2.2.2 Plant functional type canopy top and bottom heights[¶](#id16 "Permalink to this table")   
| Plant functional type
 | \\(z\_{top}\\)

 | \\(z\_{bot}\\)

 |
| --- | --- | --- |
| BES Temperate

 | 0.5

 | 0.1

 |
| BDS Temperate

 | 0.5

 | 0.1

 |
| BDS Boreal

 | 0.5

 | 0.1

 |
| C3 arctic grass

 | 0.5

 | 0.01

 |
| C3 grass

 | 0.5

 | 0.01

 |
| C4 grass

 | 0.5

 | 0.01

 |
| UCrop UIrr

 | 0.5

 | 0.01

 |
| UCrop Irr

 | 0.5

 | 0.01

 |
| Crop UIrr

 | 0.5

 | 0.01

 |
| Crop Irr

 | 0.5

 | 0.01

 |

