Uneven-aged or continuous cover forestry (CCF) can be simulated in Heureka by setting the Management System to "Uneven-aged (CCF)". ("Hyggesfritt" in Swedsih version), Uneven-aged management is simulated as a series of selection fellings, without any final fellings. A selection felling is by default defined as a thinning from above. There are specific setting for selection fellings. Functions for natural ingrowth are used to simulate the regeneration of new trees. In the calculation of net present value the last harvest is assumed to be repeated in perpetuity, with the same interval as between the last and second last simulated selection felling. Because of uncertainties in the growth of naturally regenerated trees, very long time horizons should be avoided, say no more than 60 years.

 

 

MgmtSystemCCF_eng

The selection of uneven-aged management is done in control table Treatment Program Generator in PlanWise and StandWise. In StandWise, you can also select it if and when you choose "Run to last period". In RegWise, the selection of uneven-aged management is done in control table Scenario Settings.

 

 

tog_minusSelection felling volume and timing in individual stands

When Management System is set to "Uneven-aged (CCF)" in PlanWise or RegWise, the execution of a selection felling is determined by the settings in section "3.2 Selection Felling" in control table Treatment Model. The selection of what trees to cut is defined in "Selection Felling Algorithm Parameters".

By default, a selection felling is executed as a thinning from above, You can find more information on the thinning form parameters on the Heureka Wiki under Thinning.

TreatmentModelSelectFelling

 

selectionFellingGuide

 

The harvested volume is based on the “least allowable volume stock after harvest intended to support forest development” according to §10 of the Swedish Forestry Act.

The volume harvested is based in the Swedish Forestry Act's  (SVL), which determines how much you may harvest before you must regenerate. The stock diagram in the Forestry Act is represented as a function in Heureka. This is parameterised with a simple regression analysis based on measured points in the published diagram. The coefficients for the curve are found under section "Selection Guide" (A0, A1, A2).

Vafter harvest = -33.75 + 6.5x + 0.1875x2

where x = mean height (according to the Forestry Act), but with some reservations in Heureka. If the mean height exceeds the site index (SIS), x is set to SIS instead. This roughly means that the remaining stock do not need to be higher than the minimum stock required at about age 100 years. In the interval 12-30, x is truncated to be within the stock diagram.

By changing the parameters, it is possible to study en "illegal" from of management. However, However, the growth prognoses are less reliable for more extreme management practices..

The size of a harvest is limited by settings of minimum and maximum allowable thinning extraction, set in the “Thinning – settings” section in the same control table. For thinning extractions, and in this case selective cutting, the min- and max-values are volume percentages, not basal area percentages as in regular thinning. The default is a thinning extraction of at least 20%.  At most 40% of the volume can be harvested in one thinning (2).

MinMaxThinningGrade

 

The harvest times are determined whether or not harvest is possible after checking the remaining volume stock, and the minimum harvest proportion (as described above). In PlanWise it is possible to vary the first time for the action, and the least allowable harvest interval, through the table Treatment Program Generator: Min Time Between Two Selections (3) denotes the minimum time allowed between two harvests, and it is 20 years by default (four five-year periods).. Selection Period Delay Max (4) denotes how much the first harvest can be delayed compared to when the harvest is first possible. This setting is included to create variation and different alternative management programs.

TpgControTableSelectionFelling

 
tog_minusHow to control the uneven-aged managed area in PlanWise

In PlanWise you can control the area where uneven-aged management should be applied in two different ways. One is to decide your self which stands that should be managed with this management system and create a forest domain for these, where uneven-aged management is the only option. Another is to let the system generate both uneven-aged and even-aged management alternatives for a larger number of stands, and let the optimization model decide in which stands uneven-aged management should be applied.

 

Example:

 

1.Create a forest domain for stands suitable for uneven-aged management. Name if for example "Spruce stands >= 80 years" and add conditions "Dominant Species = Spruce" and MeanAge >= 80", and "StandObject.EvenAgedClass" = UnevenAged.

Klicka på bilden för att förstora

 

 

2.Create a new control category called "CCF".

AddNewCC

3.In control table "Treatment Program Generator", set Management System = Uneven-aged:

MgmtSystemCCF

4.Right-click on the forest domain you created in step 1:

EditFdconnCCFcc

5.Link one or more control categories to the forest domain. If several control categories have been selected for a forest domain, alternatives will be created for each control category.

ForestDomainCC_ccf

6.If you have selected several control categories for a forest domain, you can add a constraint to the optimization model to control how how the forest domain area is distributed over the different control categories. Here is a basic examples (see more examples in chapter Optimization):
7.In the Optimization Model Explorer, add a new variable named for example "AreaCCF", and add the following definition to it:

sum <i,j> in TreatmentUnits*Alternatives with altIncluded[i,j] == 1 and trmtCategory{i,j,0] = 2 :

   area[i]*x[i,j] == AreaCCF ;

This definition says that the variable AreaCCF should equal the sum of areas for all stands that are managed with the control category number 2.

 

Note: Here we assume that the control category created in step 2-4 has number 2. To actual number may differ between different simulations, for example if you have deleted or added forest domains after you created the optimization model. To check the actual number the was used in an certain TPG-simulation, right-click the parameter called trmtCategory[i,j,t] in the model tree, choose View Definition, and select the TPG-simulation you are interested. Then a table is displayed that shows the internal numbing for the control categories:

Klicka för att förstora

8.Next, add a constraint called "MaxArealCCF", for example with the definition:

MaxAreaCCF <= 0.1 * TotalArea;

Where TotalArea is a "Formula"-parameter for the total productive area. We assume here that at most 10 % of the total area should be managed with CCF.

 
tog_minusHow to control the occurrence of uneven-aged management in RegWise

In RegWise you follow step 1-4 above for PlanWise, but in step 5 you define the proportion of the forest domain area that should be assigned to the CCF control category. You can also enter the maximum allowed

 

Example:

 

1.Create a forest domain and a control category for uneven-aged management in the same as for PlanWise above (steps 1 and 2).
2.Link the control category to the used to the domain. If you have more than one control category, enter how the forest domain's area should be distributed. In the example 80 % is assigned to Default Control Category (with even-aged management) and 20 % to a category called Selection felling, that says uneven-aged management.

RegVis_ForestDomain_ControlCat_link

3.In RegWise you can define maximum allowable harvest levels for the whole analysis (within the current domain) for thinning, selective cutting and final felling. This is done in the “Harvest levels” section of the Scenario Settings control table. Click on “Collection” to define periodic extraction levels for uneven-aged forestry. Stands will not be cut selectively if the maximum allowable harvest level is exceeded. In that case, stands are prioritized based on relative volume growth, so those with the lowest growth will be harvested first. If no values are defined, harvests are applied in all stands that meet the stand-wise criteria above. .

RegVisHarvestLevelSelection

 

4.Click the "Add"-button in the opened form to add a maximum allowed harvest level for a five-year period. Click "Adjust to number of Periods" to add a row for each period. If you set a negative value for a row, it will be treated as an empty row, and the area of selectively cut stands will be limited by “MaxProportion” (in the periods with a negative value).

RegVisMaxAnnualVolumeDialog

 
tog_minusRegeneration relies on natural ingrowth

When simulating uneven-aged forestry, Heureka is assuming that the regeneration of new trees occurs through natural recruitment or ingrowth, as it is often called nby Swedish authors (Wikberg & Elfving 2003). The ingrowth functions calculate the number of trees of each species that grow, in each period, into the tree layer or exceed 4 cm in breast height diameter.

 

The ingrowth function can be deactivated in the Regeneration section of the Production Model control table. Different tree species can also be excluded. Changes from the default values are only meant for special analyses, not for standard planning analyses.

 

ProdModelIngrowthSettings

 
<%EXTOGGLE%>Result variable Treatment = Selection (Sf)

An executed selection felling is saved as code "Sf" or "Selection" in result variable Treatment that you find in the Treatments result group.

TreatmentResultSelection
tog_minusCalculation of net present value in uneven-aged management

When calculating the net present value for uneven-aged management, the revenue from the last cutting is assumed to repeated in perpetuity, with the same interval as between the last two cuttings simulated. The last revenue is handled similarly to how the SEV component is handled when calculating the net present value for even-aged management. You can read more net present value calculation in Heureka here.

 

 

 

 

 

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