| 141 | | 1. Following a disturbance, tree species changes and forest management change can be prescribed or read from a map in ORCHIDEE-CAN. This code still needs to be merged into ORCHIDEE-CN-CAN. For the moment set '''lchange_species''' = n, '''read_species_change_map''' = n, and '''read_desired_fm_map''' = n |
| 142 | | |
| 143 | | 2. The calculation of wind storm damage can be activated by setting '''ok_windthrow''' to y in the run.def. This module calculated the critical wind speed of a stand taking stand and soil properties into account. If the stand is managed, the damaged trees are salvaged logged. If the stand is unmanaged the damaged trees are left on-site to decompose. The default setting for ok_windthrow is n. |
| 144 | | |
| 145 | | 3. Bark beetle outbreaks. The core of this module has been developed but needs to integrated in ORCHIDEE-CN-CAN. The bark beetle module was developed such that it interacts with the windthrow module. |
| 146 | | |
| | 144 | 1. The calculation of wind storm damage can be activated by setting '''ok_windthrow''' to y in the run.def. This module calculated the critical wind speed of a stand taking stand and soil properties into account. If the stand is managed, the damaged trees are salvaged logged. If the stand is unmanaged the damaged trees are left on-site to decompose. The default setting for ok_windthrow is n. |
| | 145 | |
| | 146 | 2. Bark beetle outbreaks. The core of this module has been developed but needs to integrated in ORCHIDEE-CN-CAN. The bark beetle module was developed such that it interacts with the windthrow module. |
| 241 | | 2 - The second possibility takes hydraulic architecture of plants into account, when calculating the plant water supply. This scheme, based on Hickler et al (2006), calculates the water supply as the ratio of the pressure difference between the soil and leaves. The plant water supply is the amount of water the plant can transport from the soil to the stomate accounting for resistance of water transport in the roots, sapwood and leaves. The resistances are inversely proportional to the conductivities in these different tissues, with the sapwood conductivity decreasing when cavitations occurs. If transpiration rates exceeds plant water supply, stomatal conductance is reduced. |
| 242 | | |
| 243 | | Moreover, as a further refinement to the hydraulic architecture, a more detailed description of the soil to root resistance has been included (now the default setting) and is activated with the flag '''OK_SOIL_ROOT'''. In the original scheme of the hydraulic architecture a tuning factor was used to calculate the soil to root resistance (PHI_SOIL_TUNE). When '''OK_SOIL_ROOT''' = y, an adjustment of the soil water potential (phi_soilroot) due to soil to root resistance is allowed. Phi_soil is weighted by the fraction of evapotranspiration supplied by each soil layer, which depends on the soil to root resistance per layer that accounts for different root properties and hydraulic conductivity. |
| | 243 | 2 - The second possibility takes hydraulic architecture of plants into account, when calculating the plant water supply. This scheme, based on Hickler et al (2006), calculates the water supply as the ratio of the pressure difference between the soil and leaves. The plant water supply is the amount of water the plant can transport from the soil to the stomate accounting for resistance of water transport in the roots, sapwood and leaves. The resistances are inversely proportional to the conductivities in these different tissues, with the sapwood conductivity decreasing when cavitation occurs. If transpiration rates exceeds plant water supply, stomatal conductance is reduced. |
| | 244 | |
| | 245 | Moreover, as a further refinement to the hydraulic architecture, a more detailed description of the soil to root resistance has been included (now the default setting) and is activated with the flag '''OK_SOIL_ROOT'''. In the original scheme of the hydraulic architecture a tuning factor was used to calculate the soil to root resistance (PSI_SOIL_TUNE). When '''OK_SOIL_ROOT''' = y, an adjustment of the soil water potential (psi_soilroot) due to soil to root resistance is allowed. Pssi_soil is weighted by the fraction of evapotranspiration supplied by each soil layer, which depends on the soil to root resistance per layer that accounts for different root properties and hydraulic conductivity. |
| 247 | | The following PFT dependent parameters are needed for the calculations accounting for plant hydraulic architecture; minimal leaf water potential '''PHI_LEAF_xx''', sapwood leaf water potential that causes 50 % loss of xylem '''PHI_50_xx''', additive tuning parameter to account for soil-root interactions '''PHI_SOIL_TUNE_xx''', maximum sapwood conductivity '''K_SAP_xx''', root conductivity '''K_ROOT_xx''', leaf conductivity '''K_LEAF_xx''', specific root lenght '''SRL_xx''', fine root radius '''R_FROOT_xx''', minimum root water potential '''PHI_ROOT_xx'''. |
| | 249 | The following PFT dependent parameters are needed for the calculations accounting for plant hydraulic architecture; minimal leaf water potential '''PSI_LEAF_xx''', sapwood leaf water potential that causes 50 % loss of xylem '''PSI_50_xx''', additive tuning parameter to account for soil-root interactions '''PSI_SOIL_TUNE_xx''', maximum sapwood conductivity '''K_SAP_xx''', root conductivity '''K_ROOT_xx''', leaf conductivity '''K_LEAF_xx''', specific root lenght '''SRL_xx''', fine root radius '''R_FROOT_xx''', minimum root water potential '''PSI_ROOT_xx'''. |
| | 250 | |
| | 251 | === Prescribe initial vegetation === |
| | 252 | 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 is 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 height was chosen because it is easy to (mentally) visualize the prescribed vegetation. In the run.def '''HEIGHT_INIT_MIN''' and '''HEIGHT_INIT_MAX''' need to be prescribed. Typical values are 2 to 5 meter. If more than one diameter class is used, '''HEIGHT_INIT_MAX''' needs to larger than '''HEIGHT_INIT_MIN'''. The larger the difference between the min and max, the more vegetation layers the canopy will be composed from. |
| | 253 | |
| | 254 | In addition the initial number of seedlings needs to be prescribed as well. For this the parameter '''NMAXTREES''' needs to be set. '''NMAXTREES''' is a critical parameter to obtain acceptable model behavior. 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 (2-3 m) the calculated number of trees could in the millions and so the GPP had to be distributed over too many individuals. |
| | 255 | |
| | 256 | The way the initial vegetation is prescribed can also be used to prescribe a mature vegetation right at the start of the simulation. One could set '''HEIGHT_INIT_MIN''' and '''HEIGHT_INIT_MAX''' to for example 15 and 20. If '''NMAXTREES''' is not adjusted, massive self-thinning will take place on the first day. It is better to set '''NMAXTREES''' to a value just below the exact self-thinning value. Prescribing mature vegetation has been tested and works but it is very sensitive. If the combination of '''NMAXTREES''', '''HEIGHT_INIT_MIN''' and '''HEIGHT_INIT_MAX''' is far from realistic the model may crash (the change in KF following the change in gap probability could result in problems in allocation) and N-feedbacks will become apparent in for example the leaf mass (likely because when mature vegetation is prescribed at the start of a run, there is not enough soil N to maintain a mature vegetation). |
