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inputs for the timber model

clicli Member
edited September 2013 in Terrestrial Models

I have some specific questions about the production or plant table:

- Harv_mass: is it the dry or the green mass? I just have volumes, so I am transforming it into mass with the basic density of my timber. Is it correct?

- Freq_harv, T, Immed_harv: I have problems to understand how to define the temporal dimension in the table. I explain you my example: I have a natural forest being harvested in a 30yr rotation period. Each year one single parcel is logged. So in my table I have 30 rows (30 parcels) and I assign the following parameters for all the rows:
Freq_hav = 1
But the problem is that we are now in the middle of the rotation period, so a few parcels have been harvested (I have detailed data) and the rest are not (I can approximate the production with the management plan). So, should I assign Immed_harv = Y to the parcels harvested and Immed_harv = N to the future ones? How can I run the model and get the output for the past years and the future years?

- The documentation talks about an associated LULC map, is there any kind of map input apart from the parcels?

- In the documentation Price has not units associated (only (-1)). I assume it is currency/ha, am I correct?

Just a last comment. It could be nice in future versions to have the possibility to enter the timber data as volumes for those who have it.

Thanks in advance!


  • DougDoug Administrator, NatCap Staff

    The documentation does discuss LULC maps, however they are not an input to this model. I believe the discussion referring to the LULC maps is meant to indicate that the parcel shapefile that defines your timber areas can be associated with a current, past, or future LULC map.

    Unfortunately I'm not able to answer the other questions, but will get in touch with someone who can get back to you. Thanks for your patience.

    - Doug
  • Hello,

    Hopefully I can answer your remaining questions below:

    Harv_mass: I believe it will depend on what you want to value, the dry or green mass. You are correct in using the density to derive the mass from the volume (mass = density * volume). Please keep in mind the parameter for the BCEF is used to convert dry mass. So you will want to use dry mass for Harv_mass if you are going to manipulate the BCEF parameter.

    Freq_harv, T, Immed_harv: It sounds like your table parameters may not reflect the scenario you described above. The table is currently set up so every parcel is harvested annually for 30 years (T = 30, Freq_harv = 1 for every parcel). Could you please let me know if that sounds correct or should there be just a single parcel harvested each year until all 30 are rotated through?

    Price will be the currency expressed per Mg (Mg-1). I can see where the units are blank in the Data Needs section but the units are described a bit further in the User Manual for equation 1 as “Price is the market price of a Mg of timber extracted from x…”. tank you for pointing this overlook, as we will correct it in future User Manuals.

    Please let me know which set of parameters is correct for your scenario and if you need anything else.


  • clicli Member
    Thank you very much for your feedback, Doug and Brad. The questions on LULC, density and price are now clear.

    @Brad: you were right, my scenario is just a single parcel harvested each year until all 30 are rotated through. So, should it be T=30 Freq_harv=30 for all the parcels? And, then, about the meaning of Immed_harv, should I put "Y" to the parcels already harvested and "N" to the rest? Or would it be better to split the model into 2 periods (past and future)?

    Thanks in advance,

  • Hi Camino,

    Setting up the parameters in your scenario could be a bit tricky. By using T=30, Freq_harv=30 for all parcels; the model will calculate 30 years of maintenance costs on every parcel but incorrectly apply the market discount rate using either 1 year (Immed_harv=Y) or 30 years (Immed_harv=N). It sounds like you want each parcel to be discounted accordingly throughout the rotation and include annual maintenance costs over 30 years for each parcel (pesticide management, thinning, etc.). To do so, I believe you will want to run the model two times.

    For the first run, please try ignoring maintenance costs (set Maint_cost=0) for all parcels and set up each parcel so it only gets harvested once during the 30-year rotation. In this case, the first parcel would be only harvested during year 1 (T=1, Freq_harv=1, Immed_harv=N), and the next harvested parcel would be cut during year 2 (T=2, Freq_harv=2, Immed_harv=N), etc, until the last harvested parcel would be cut during the last year in the rotation (T=30, Freq_harv=30, Immed_harv=N). This should correctly account for the market discount rate for the NPV of harvested timber.

    For the second run, we will only account for 30 years of maintenance costs. Please try setting Harv_mass=0, T=30, Freq_harv=30, Immed_harv=N for all parcels and use the actual maintenance cost values. Essentially, the first run calculates the NPV of your timber without accounting for any maintenance costs and the second run calculates NPV of the maintenance costs for 30 years. The difference between the two NPV values will be the final NPV of timber production. So the final step is to just subtract the values for the second run (NPVmaintenance) from the first run (NPVtimberharvest).

    Could you please let me know if this approach seems applicable to your scenario? Hopefully, this also addresses your issue concerning past harvests as you can model the 30-year rotation in its entirety.


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