Forest management

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FORGEM


In the ForGEM model, a broad array of forest management scenarios can be composed by the user.

A forest management scenario consists of one or more subscenarios. Each subscenario is defined by a management intervention type (making gaps, thinning, sheltercut, clear cut, planting etc.). For each subscenario, the user defines when to start and to when finish the subscenario, and indicate a number of management intervention type specific parameters. E.g. gap size in case of a subscenario using the Gap making management intervention type.

It is thus possible to have different subscenarios of the same management intervention type within the same scenario. However, in such cases the subscenarios must be separated in time. For example, large gap making during the first 100 years of the simulation, followed by making small gaps during the remainder of the simulation. When a new subscenario starts, all information on the old subscenario of the same type is lost (overwritten with new values). Gaps according to the first Gap making subscenario will therefore not be effectuated as soon as a new Gap making subscenario starts.

To calculate parameters for the different management interventions, a grid is put over the simulation area. For example, the gap size in a Gap making subscenario can be defined as a fixed number of gridcells. The size of the gridcell is user-defined, or is proportionate to the area size, e.g. by indicating a number of equally sized grids.

In this section, the management intervention type specific parameters are described. For each management intervention type, first the 'Input' that the user needs to supply are listed. In the subsequent 'Implementation' section the consequences of the inputs are described. Typically, the user inputs are provided by the forest management database.

Based on the forest management module of the ForGEM model, a number of forest management approaches, indicating the most likely form of forest management at a particular location in Europe, are quantified.

Forestry links

outline of forestry

Additional planting

FORGEM

Additional planting is a management action to plant trees in an area that needs to be regenerated. It can be used to plant species immediately after a final harvest, or it can be used to enrich naturally occurring regeneration in case the density of a desired tree species is too low.

Input

Parameter List Name Explanation
PlantingSpeciesFractionList List with tree species to plant and their relative frequencies
Parameter Name Unit Explanation
cTimeSinceHarvest - Number of management intervals, as defined in General Management,

after harvest to evaluate if additonal planting is required

cLowestDensity N/100m2 Density below which additional planting will be carried out
cDesiredDensity N/100m2 Density of plants after additional planting
cUseList - code 0: let ForGEM determine species to be planted (based on dominant species in initialisation). 1: use list as defined by user

Implementation

If Additional Planting is active in combination with GapMaking, the actual density per gap is calculated. If Additional Planting is active in combination with Shelterwood or Clearcut, the actual density per management grid cell is calculated. After the time specified by cTimeSinceHarvest (expressed in number of management cycles, respectively after making a gap, after the first shelterwood cutting and after clearcut), the actual density of the regeneration is compared to cLowestDensity. If the actual density is lower, young trees are added until cDesiredDensity is reached. If cUseList is set to 0, ForGEM will plant the target species as defined at the start of the simulation (i.e. the species with the highest basal area). If cUseList is set to 1, trees will be planted according to the PlantingSpeciesFractionList.

Clearcut

Clearcut is a way of final felling, where all mature trees at the site are removed in one operation.

Input

Parameter Name Unit Explanation
cUseTargetDiameter 0-1 code 0 : use age 1: use diameter
cAge year Average age of trees when clearcut will be carried out
cTargetDiameter cm Average diameter of trees when clearcut will be carried out
cHeightCriterium fraction Fraction of maximum attainable tree height when trees will be counted

to evaluate if cutting age is reached

cSoilScarification code 0 : no soil scarification, 1 : soil scarification

Implementation

A clearcut can be triggered in two ways: either if a specific age or if a specific diameter of the trees is attained. This is defined by the user by the parameter cUseTargetDiameter. If cUseTargetDiameter equals 0, cAge will be used, otherwise cTargetDiameter is used.

During the simulation, the average age and diameter of the trees in the stand is calculated. Only trees are included that fulfill the height criterium as defined in the input (cHeightCriterium). For example, if the cHeightCriterium = 0.5, and maximum tree height is 40m, only trees exceeding 20m are included in the calculation of average height and -age. If the average age of these trees exceeds the age as defined in the input (cAge), a clearcut is carried out (but only if cUseTargetDiameter equals 0). If cUseTargetDiameter has a value larger than 0, a clearcut is carried out if the average diameter of the trees is larger than cTargetDiameter (thus any value of cAge is ignored). All trees higher than the minimum cutting height as defined in General Management are harvested. If soil scarification is to be carried out (cSoilScarification = 1), all trees are removed (so including the ones below the cutting height).

Create deadwood

Create deadwood is an approach to increase the biodiversity of a stand by increasing the amount of either upright or lying dead logs.

Input

Parameter Name Unit Explanation
cDiameterCriterium cm Minimum diameter of trees to be elegible to be selected as potential dead tree
nTreesPerHa N/ha Minimum number of large dead trees per hectare

Implementation

This routine is currently not operational.

Future tree selection

The future tree system is also called the crop tree system. A limited number of high-quality trees are selected relatively early in the rotation with the aim to form the final crop. These individual trees will be given ample space to attain large dimensions quickly. This routine consists of the selection of the crop trees, and of the thinning around the selected trees.

Input

Parameter List Name Explanation
FutureSpeciesFractionList List with tree species to select as future tree and their relative frequencies
Parameter Name Unit Explanation
cFutureTreeThinningInterval Number of management intervals, as defined in general Management,

between thinnings around future trees

cHDCriterium cm/cm Maximum height/diameter ratio that future trees should preferably have
cHeightCriterium fraction Fraction of maximum attainable tree height when trees are elegible

to be selected as future tree

cIntensity fraction fraction of basal area increment that is thinned [0-1].
cSelectTreesInterval Number of management intervals, as defined in General Management

between selection of future trees

cTargetDiameter cm Target diameter at harvest for future trees
nTreesPerHa N/ha Number of future trees per hectare to select

Implementation

If a selection of future trees is to done, all trees exceeding the user-defined height criterium (cHeightCriterium) are (pre)selected. Only trees that are not located in a known gap (as created by the gap making procedure) are eligible. Thus, the area from which future trees are selected is the total simulated area minus these known gaps. Trees with an HD-ratio less than as specified HD criterium (cHDCriterium) get a quality score of 1, all other trees are ignored (quality score = 0). From the target diameter (cTargetDiameter), the minimum required distance between trees is calculated. This distance may vary between tree species. If the required distance is not equal (because of different tree species), the average distance is taken. Distances between all pre-selected trees are calculated and compared with the minimum required distance. This results in a matrix from which neighbouring trees can be determined. A requirement of this module is that individual trees within the minimum required distance of another future tree cannot be selected.


The selection of future trees is done in two steps. First, a set of possible trees is defined, which meet the criteria of distance and height, and tree species distribution and HD-ratio as good as possible. Second, from this set the final set of future trees is selected. The two steps of future tree selection is presented in more detail below.


All trees that have been identified as a future tree in an earlier stage are pre-selected and removed from the remaining trees. For the remaining trees, a loop is done until all trees are either pre-selected or rejected. First, all trees that have no neighbours are pre-selected. Then, groups are selected that contain only trees of the same species. If such groups exist, within each group is first selected on quality, then on minimum number of neighbours (this might differ per tree within a group, since a tree can be member of more than one group) and then on the distance to the already pre-selected trees. The aim of this distance-selection criterium is to get a regular distribution of trees over the area. However, at low tree densities this criterium does not function properly yet. If still more than one tree remains, one is chosen randomly. If no tree groups exist that consist only of trees of the same species, a tree species will be selected, based on the deviation between the distribution of the currently pre-selected trees and the required distribution. Of these trees, selection is again on quality, minimum number of neighbours, distance to already pre-selected trees and then random.

The result is a set of trees that could all be selected as future trees regarding distance and height, with on average the highest quality and a species distribution that is more or less OK. If the amount of pre-selected trees is higher than the required amount of trees (nTreesPerHa), a further selection needs to be done. Firstly, all trees that were identified as future tree before are selected. Then, a loop is done over the remaining pre-selected trees. A tree species is chosen, based on the deviation between the distribution of the currently selected trees and the required distribution. Of that tree species, a selection is done on quality, then on distance to the already selected trees and then one is chosen randomly.

Selection of future trees is done as defined by cSelectTreesInterval (expressed as number of management cycles). If all future trees are still present, the selection will not change. If the number of future trees is too low, additional future trees will be selected. The number of future trees can decrease due to mortality or harvest (if the future trees exceed cTargetDiameter).


The second part of the future tree system is thinning. The frequency of thinnings is defined by cFutureTreeThinningInterval. In each thinning, future trees that exceed cTargetDiameter are removed. Then, all direct competitors from the remaining future trees are removed. A competitor is defined as a tree with a height equal to or larger than the mid of the crown of the future tree, and located within the crown projection of the future tree, in case this tree would have reached its target diameter.

removed that have an overlapping crown with one of the remaining future trees. From the remaining non-future trees, a certain share of the basal area increment (cIntensity) that has been realised since the previous thinning will be removed. The intensity is calculated over all trees removed in the stand, so including the already removed trees. This thinning starts in the grid cell with the highest realised basal area increment. Trees to be removed are selected based on the observed height diameter ratio. The tree with the highest HD ratio is removed. In case trees have equal ratios, one random tree is selected from this set. In case Genetics is active, cSpiralGrain is used as selection criterium.

Gap making

Input

Gap making is a management intervention that aims at creating space for regeneration, and/or to increase the structural heterogenity of a stand. It can be compared to a group felling system.

Parameter List Name Explanation
GapSizeFreqList List with gap sizes to make and their relative frequencies
Parameter Name Unit Explanation
cConversion code 1: all area should be a gap once (as conversion measure),

0: make gaps as regular management, not for conversion

cGapAreaToMake % percentage of total area to make gap per event.

If left open, 1/CNumberOfTimesOfGapMaking is taken.

cMaxGapSize m2 Maximum gap size to create under normal conditions
cMinGapSize m2 Minimum gap size to create under normal conditions
cMinGapWidth m Minimum gap width under normal conditions
cResetHeightCriterium fraction Fraction of maximum attainable tree height when gaps are reset

in case of non-conversion gap management, see Gap Making code.

cSoilScarification code 0 : no soil scarification, 1 : soil scarification
cThinningInterval Number of management intervals, as defined in General Management,

between thinning interventions.

nTimesOfGapMaking # Number of times to create gaps
nYoungTreesMin N/100m2 Minimum density of regeneration to be suitable to create a gap there

Implementation

If the maximum gap size (cMaxGapSize) exceeds the total area of gaps to be made per event, the maximum gap size is decreased to a value equal to the percentage to be made (cGapAreaToMake) of the total area times the total area.


A grid is put over the area (see General Management). A list is made with all possible sizes of rectangulars within the simulated area and the number of rows and columns they have. This list forms the basis for the selection of eligible gap sizes. Eligible gap sizes are defined as being larger than or equal to the minimum gap size (cMinGapSize), smaller than or equal to the largest gap size (cMaxGapSize), and larger than or equal to the minimum gap width (cMinGapWidth) (both in X and Y direction). Furthermore, a list is being kept with sizes that proved impossible to be placed in the area. These are also excluded from selection. The sizes that remain are assigned a probability, linearly interpolated according to the input list of gap sizes and frequencies (GapSizeFreqList). From these sizes with their probabilities, a random series is drawn until the area that should be cut is reached or exceeded. Then, the largest gap size from this series is selected and tried to be placed in the simulated area. If this succeeds, the next largest gap is taken and tried to be placed, etcetera. If it is not possible to place a certain gap size in the simulated area, this is marked in the aforementioned list and excluded for further selection. Then, a new series of gap sizes is randomly drawn and tried to be placed in the area, largest gap first, etcetera, until the total area to be cut is reached or exceeded, or if there are no more possible gap sizes to select from. If there are no more possibilities to select from, the user-defined criteria will be adapted. First, the minimum gap width (cMinGapWidth) is lowered. If the gridcells are not equal in the X and Y direction, it is lowered so that the new minimum gap width is still maximal below the original minimum gap width. For example, if gridcells are 5.25x5m and minimum gap width is 15m, first the number of cells in the X direction will be lowered from 3 to 2, resulting in a minimum gap width of 10.5. If lowering the minimum gap width (cMinGapWidth) is not sufficient, the minimum gap size (cMinGapSize) is lowered. To do this, the largest size just below the original minimum gap size is selected as new minimum gap size. The minimum gap width is restored to its original value, but can be decreased again if still no suitable gap location can be found.


If a gap of a certain size can be put in different places, selection criteria are needed to decide which gap will be preferred. Currently the following procedure is followed: First the total amount of light at 2m above the forest floor is calculated, assuming that the trees would have foliage according to their reserves, and light coming in as if it were July. The average amount of light per square meter is rounded to integers (this is done to avoid having only one gap, with just 0.1% more light than another gap). The gap(s) with the highest average amount of light per square meter is/are selected. The selection on maximum light mimics looking at the coverage of trees, so spots where trees do not grow dense will be selected first. If more than one possible location (or shape!) is selected, the total number of future trees that have to be harvested to make the gap is calculated. The gap(s) were the least amount of future trees have to be cut is/are selected. If future tree selection is not active, this step does not favour any gap location (there are no future trees). If more than one possibility remains, the density of regeneration (trees < 2m) per square meter is calculated. All gaps with a density higher than the user-defined minimum amount will be selected. If more than one possibility remains, the gap is chosen randomly.


The user can choose between two types of gap making, conversion or non-conversion. In case of conversion, each cell can be selected only once as a gap, and after the conversion period all parts of the stand have been a gap once. Usually the number of times of gap making (nTimesOfGapMaking) times the percentage to cut (cGapAreaToMake) will be 100%. In the case of conversion (cConversion=1), all cells that have not been selected yet as gap will be made a gap at the last time of gap making. In case of non-conversion (cConversion=0), a gap will be marked as being a gap for a certain period, after which it will be reset to non-gap and become eligible for the next gapmaking event. The gap will be reset when the dominant height of the trees in the gap exceeds the height criterium (cResetHeightCriterium) as set in the input times the average of the maximum heights of all species present in the area. Another difference between conversion and non-conversion is that the administration if gap sizes were impossible to be placed will be reset after each gapmaking event in case of non-conversion, since new cells will become available each time. Also minimum gap size is reset to the original value.

General management

Input

The general management routine determines when a "forester" is going to the forest to inspect if any management action is needed.

Parameter Name Unit Explanation
cManagementInterval year interval between management interventions
cMinimumCuttingHeight m height above which trees will be cut in clearcut, shelterwood and gap making
cMinimumHarvestDiameter cm minimum diameter that is harvested (smaller trees will be left at the site)
cLeaveDeadwoodAtHarvest fraction fraction of harvested trees to be left at the site as deadwood
cLeaveBranchesAtHarvest fraction fraction of branches from felled trees that remain at the site
cLeaveFoliageAtHarvest fraction raction of foliage from felled trees that remain at the site

Implementation

In year 1 (start of the simulation) and subsequently every Xth year (as determined by cManagementInterval), the management routine is called (in January), and all applicable management interventions are checked and applied if they satisfy their respective conditions.

cMinimumCuttingHeight defines the minimum height trees should have attained to be felled in case of the management intervention types: Clearcut, Shelterwood or Gap making. Trees below this height are considered as regeneration and will be untouched, unless these harvests are done in combination with soil scarification.

Felled trees (from any management action) with a diameter below cMinimumHarvestDiameter will be left at the site.

From the felled and harvestable trees, a certain fraction (defined by cLeaveDeadwoodAtHarvest) can be left at the site as deadwood.

From the residues generated by the harvest, the fraction of branches (cLeaveBranchesAtHarvest) and foliage (cLeaveFoliageAtHarvest) to be retained at the site can be specified. However, extraction of these harvest residues is not implemented yet.

Protect trees

The routine protect trees can be used to always leave some live (mature) trees on the site, for example for biodiversity or recreational purposes.

Input

Parameter List Name Explanation
ProtectTreesFractionList List with tree species to protect and their relative frequencies
Parameter Name Unit Explanation
cDiameterCriterium cm Minimum diameter when trees are elegible to be selected

as protected tree

cHeightCriterium fraction Fraction of maximum attainable tree height when trees are

elegible to be selected as protected tree

cTargetDiameter cm Target diameter of protected trees

(used only for distance calculation)

nTreesPerHa N/ha Number of protected trees per hectare to select

Implementation

Every management interval it is checked if the actual number of protected trees is still the same as the user-defined number (nTreesPerHa). If the number is too low, new trees are selected as protected tree using the SelectTrees routine (see also Select Future Trees). Trees are elegible if they are of sufficient height (cHeightCriterium) and of sufficient diameter (cDiameterCriterium). The species composition of the protected trees is determined by ProtectTreesFractionList. Protected trees will not be affected by any other management intervention.

Shelterwood

Shelterwood is a way of final felling, where the density of mature trees is successively decreased in a few steps. Remaining trees act as a seed source and provide shelter to the regeneration.

Input

Parameter List Name Explanation
ShelterwoodCuttingList List with ages when to carry out shelterwood cutting and to what density
ShelterwoodSpeciesFractionList List with tree species to keep as shelter tree and their relative frequencies
ShelterwoodSpeciesTargetDiameter List with the target diameter per species
Parameter Name Unit Explanation
cHeightCriterium fraction Fraction of maximum attainable tree height when trees will be counted to evaluate if cutting age is reached and which trees are eligible as sheltertree
cSoilScarification code 0 : no soil scarification, 1 : soil scarification
cUseTargetDiameter 0: shelterwood age list will be used with SpeciesFractionList. 1: target diameter list per species will be used
cStartDensity N/ha Number of trees to retain in first shelterwood cut if specific diameter is set
cInterval Number of mangement intervals for next shelterwood felling
cEnforceInitialTargetSpecies 0: determine target species from current dominant species. 1: target species is equal to the initial dominant species
cMainSpeciesTargetPercent  % Target % of dominant species in the stand after thinning. 1-target will be distributed between remaining species

Implementation

The start of a shelterwood felling can be triggered in two ways: either by reaching a specific age of the trees, or by reaching a specific diameter of the trees. This is determined by the user by the value of the parameter cUseTargetDiameter (0: use age, 1: use diameter).

To check if a stand is ready to start a shelterwood cycle, the average age and diameter of the main stand is calculated. In this calculation, only trees are included that fulfil the height criterium as defined in the input (cHeightCriterium). For example, if the height criterium is set at 0.5, and maximum tree height is 40m, only trees higher than 20m are included. The target diameter is defined per species (ShelterwoodSpeciesTargetDiameter). The average diameter is calculated per species, and compared to the respective target. The average diameters of all species need to exceed the target diameter before shelterwood cutting can be started.

In case of age as determinant for the start of shelterwood: if the average age of these trees exceeds the first age as defined in the ShelterwoodCuttingList, the first shelterwood cutting will be carried out, to the density as specified in this list and with the relative tree species proportions as specified in the ShelterwoodSpeciesFractionList. From the list with ages, the time until the next shelterwood cutting is calculated (so not the actual age of the remaining trees is used, since this might deviate considerably due to the removal of many trees). When the time has passed, the density of trees will be reduced to the defined next density. If the desired density is 0, all remaining sheltertrees will be removed. The number of cuttings within a cycle is unlimited, but usually 2 or 3.

In case of diameter as determinant for the start of shelterwood: if the average diameter of all species is above the respective target diameter, the first shelterwood cutting will be carried out to the density as given by cStartDensity. After the number of years specified by cInterval (expressed as number of management cycles), the remaining shelter trees will be removed. In this case, only 2 cuttings are allowed.

For the selection of the trees that remain in each cutting cycle (i.e. the ShelterTrees), the SelectTrees routine is used. This routine requires a stem diameter (actual or target) to determine the minimal distance between the trees to be selected (larger trees need more space). A diameter of 100 cm is used to ensure that the trees to be retained will be far apart. All trees that are not selected and exceed the minimum cutting height as defined in General Management, are harvested. If soil scarification is carried out, all trees are removed (so including the ones below the cutting height).

Tending

Tending is the process of reducing the regeneration density, with the possibility of selecting on species composition, stem shape, growth performance and stem quality. Currently, only species composition can be selected in ForGEM.

Input

Parameter List Name Explanation
TendingHeightList List with heights when tending is carried out and to what density it should be reduced
TendingSpeciesList List with tree species to keep when tending and their relative frequencies

Implementation

Tending can only be applied in combination with either gap making, shelterwood or clearcut.

If gaps have been made (using the gap making procedure), the tree density and height for each gap are evaluated separately. Dominant height (average of the height of the 100 thickest trees per hectare) should exceed the height given in the list (TendingHeightList). For the first tending, tree density is calculated for trees larger than 2m, for further tendings, tree density is calculated for trees higher than the previous tending height.

If the actual density exceeds the specified density for that height (specified in TendingHeightList), tree density is reduced to the specified density, aiming at the desired tree species composition (as given in TendingSpeciesList). Trees to be removed within a certain species are selected randomly.

First tending will be carried out on all trees exceeding 2m. Subsequent tendings will take into account only the trees exceeding the previous tending height. Each tending will be carried out only once in a gap. Outside the gaps, for each gridcell the tree density is calculated of trees between 2m and the first tending height, between first and second tending height, etcetera. If the actual density is higher than specified for that height class, a tending will be carried out in that height class, whereby tending of the highest height class has preference. In these cells, in principle the same tending operation can be carried out more than once. Tending outside gaps simulates tending of groups of advanced regeneration in natural gaps or under the tree layer.

For clearcut and shelterwood, the same procedure is applied as the area not identified as a gap. I.e., the evaluation is done per grid cell and each grid cell can in principle receive the same tending more than once.

Thinning

Thinning is the selective removal of trees. A thinning can have many goals, among others to influence the tree species composition, to promote good-quality trees, to remove unhealthy trees or trees with low quality, to increase the growth rate, to concentrate growth on the best trees, to influence the wind stability of a stand, or to have income earlier than the final rotation length.

Input

Parameter List Name Explanation
ThinningAgeList List with tree densities to keep at certain ages (yield table thinning according to preset values)
ThinningSpeciesFractionList List with tree species to keep in thinning and their relative frequencies
Parameter Name Unit Explanation
cMethod code 1 : depending on crown space, 2 : percentage of basal area increment, 3: yield table densities
cThinningInterval Number of management intervals,as defined in General Management, between thinning interventions.
cIntensity fraction fraction of basal area increment that is thinned [0-1]. Only used in case of thinning method 2
cEnforceInitialTargetSpecies code 0: determine target species from current dominant species. 1: target species is equal to the initial dominant species
cMainSpeciesTargetPercent  % 0: tree species frequency list will be used. >0:Target % of dominant species in the stand after thinning. 1-target will be distributed between remaining species.

Implementation

Which trees to remove in a thinning and how many can be defined in many different ways. In ForGEM, 3 different ways are implemented, which can be selected using the parameter cMethod. Method 1 uses a regression between stem diameter and crown space to determine if the trees present have enough space available. Method 2 allows the user to remove a certain percentage of the realised basal area increment. Method 3 enforces a fixed density scheme according to age, for example as derived from a yield table.

In methods 1 and 2, the user can choose to use a fixed species frequency list (ThinningSpeciesFractionList) by setting cMainSpeciesTargetPercent to 0. If cMainSpeciesTargetPercent is larger than 0, the main species will get the fraction defined, while the remaning species will equally share the remaining fraction. The main species can be the one that is currently dominant (cEnforceInitialTargetSpecies=0) or the one that is identified as the most important species for this stand at the start of the simulation (cEnforceInitialTargetSpecies=1). The first option can be used to follow "natural" processes in the simulation over time.

Method 1: Each tree needs a certain amount of crown space, depending on its stem diameter. This relationship is derived from Dutch yield tables, from the situation immediately after thinning. For each tree the crown space needed is calculated. If the cumulative of these crown spaces needed exceeds the actual stand area, a thinning should be carried out. If gaps have been made, this evaluation is done per gap, otherwise per cell.

If a thinning needs to be carried out, this is done per cell. The actual species distribution is compared to the desired species distribution. The species that exceeds the desired distribution the most, is selected and one tree is removed. Then again a tree species is selected and one tree removed, until the crown space needed is lower or equal to the actual available crown space. Selection of the tree removed depends on its HD ratio (high HD ratios to be removed first). In case genetics is active, selection is done on quality of the tree (spiral grain) instead of HD ratio. In case more than one tree is selected based on quality or HD ratio, a tree is chosen randomly. Only trees exceeding 8m are included in the thinning, assuming the tending routine is used in case trees are still below 8m.

Method 2: The first time the program uses this routine, nothing is done, but the basal are per cell is recorded. For the next times, the basal area increment since the previous time period are calculated. From the previous basal area, the increment and the share of the increment to remove (as defined by cIntensity), the target basal area is calculated. As long as the current basal area is higher than the target, ForGEM locates the grid cell with the highest basal area increment and thinnes the cell to the required basal area. Removal of trees is done firstly on species, then on quality (spiral grain) if available. If more than one tree is selected for thinning, a tree is chosen randomly. Only trees exceeding 8m are included in the thinning, assuming the tending routine is used in case trees are still below 8m.

Method 3: This method resemebles a thinning from below, where tree density is reduced to a fixed number, depending on age (as defined by ThinningAgeList). The mean age of the trees present in the stand is calculated (including all trees) and rounded up to the nearest age as defined in the thinning list. If the actual density of the stand is higher than the one specified, a thinning will be carried out. In a thinning, density in each grid cell will be reduced to the required density. Trees to be removed are selected based on the lowest crown radius (if crown competition is active) or lowest stem diameter. Since tree species is ignored, this method is most suitable for mono-species stands. Only trees exceeding 2m are included in the thinning. If using method 3 for thinning, it is not advisable to use the tending routine.

Thinning - unevenaged

An unevenaged thinning regime is aimed at maintaining a certain ideal shape (exponentially decreasing) in the distribution of number of trees over the diameter classes.

Input

Parameter List Name Explanation
UnevenagedSpeciesFractionList List with tree species to keep in thinning and their relative frequencies
Parameter Name Unit Explanation
cDesiredBasalArea m2/ha
cLioucourtConstant - Ratio in stem number between diameter classes
cTargetDiameter cm Maximum desired diameter in forest
cThinningInterval # Number of management intervals, as defined in general Management, between thinnings

Implementation

The ideal distribution of trees over diameter classes is defined by the Lioucourt constant (cLioucourtConstant). If the number of trees in the highest diameter class (defined by cTargetDiameter) is N, the number of trees in the preceeding class should be N^cLioucourtConstant. The ideal number of trees per diameter class is calculated using the desired basal area after thinning (cDesiredBasalArea) and the Lioucourt constant. In a thinning, first the trees exceeding the target diameter (cTargetDiameter) will be removed. Then, for the highest diameter class, the number of trees will be reduced to match the target as calculated before. The trees that are selected are liberated from competitors as described under the Future trees intervention. Subsequently the lower diameter classes are evaluated, until the remaining basal area is lower than or equal to the desired basal area. Selection of trees to retain is done by choosing the trees with the lowest height/diameter ratio.

The frequency of application of unevenaged thinning is determined by cThinningInterval.

Overview of the user-defined parameters of the forest management module of the ForGEM model

User-defined lists for Forest Intervention Types implemented in the ForGEM model
Forest Intervention Type Parameter List Name Explanation
Additional Planting PlantingSpeciesFractionList List with tree species to plant and their relative frequencies
Gap Making GapSizeFreqList List with gap sizes to make and their relative frequencies
Protect Trees ProtectTreesFractionList List with tree species to protect and their relative frequencies
Selection of Future Trees FutureSpeciesFractionList List with tree species to select as future tree and their relative frequencies
Shelterwood Cutting ShelterwoodCuttingList List with ages when to carry out shelterwood cutting and to what density
Shelterwood Cutting ShelterwoodSpeciesFractionList List with tree species to keep as shelter tree and their relative frequencies
Tending of Regeneration TendingHeightList List with heights when tending is carried out and to what density
Tending of Regeneration TendingSpeciesList List with tree species to keep when tending and their relative frequencies
Thinning ThinningAgeList List with tree densities to keep at certain ages (yield table thinning according to preset values)
Thinning ThinningSpeciesFractionList List with tree species to keep in thinning and their relative frequencies
Unevenaged Thinning UnevenagedSpeciesFractionList List with tree species to keep in thinning and their relative frequencies



User-defined parameters for the Forest Intervention Types implemented in the ForGEM model
Forest Intervention Type Parameter Name Unit Explanation
Additional Planting cDesiredDensity N/100m2 Density of plants after additional planting
Additional Planting cLowestDensity N/100m2 Density below which additional planting will be carried out
Additional Planting cTimeSinceHarvest - Number of management intervals, as defined in General Management, after harvest to evaluate

if additonal planting is required

Clearcut cAge year Average age of trees when clearcut will be carried out
Clearcut cHeightCriterium fraction Fraction of maximum attainable tree height when trees will be counted to evaluate if cutting age is reached
Clearcut cSoilScarification code 0 : no soil scarification, 1 : soil scarification
Create Deadwood cDiameterCriterium cm Minimum diameter of trees to be elegible to be selected as potential dead tree
Create Deadwood nTreesPerHa N/ha Minimum number of large dead trees per hectare
Gap Making cConversion code 1: all area should be a gap once (as conversion measure),

0: make gaps as regular management, not for conversion

Gap Making cGapAreaToMake % % of total area to make gap per event. If not set in the database, 1/CNumberOfTimesOfGapMaking is taken.
Gap Making cMaxGapSize m2 Maximum gap size to create under normal conditions
Gap Making cMinGapSize m2 Minimum gap size to create under normal conditions
Gap Making cMinGapWidth m Minimum gap width under normal conditions
Gap Making cResetHeightCriterium fraction Fraction of maximum attainable tree height when gaps are reset in case of non-conversion gap management

(see Gap Making).

Gap Making cSoilScarification code 0 : no soil scarification, 1 : soil scarification
Gap Making cThinningInterval Number of management intervals, as defined in General Management, between thinning interventions.
Gap Making nTimesOfGapMaking # Number of times to create gaps
Gap Making nYoungTreesMin N/100m2 Minimum density of regeneration to be suitable to create a gap there
General Management cLeaveDeadwoodAtHarvest fraction fraction of harvested trees to be left at the site as deadwood
General Management cManagementInterval year Interval between management interventions
General Management cMinimumCuttingHeight m Height above which trees will be cut in clearcut, shelterwood and gap making
General Management cMinimumHarvestDiameter cm minimum diameter that is harvested (smaller trees will be left at the site)
Protect Trees cDiameterCriterium cm Minimum diameter when trees are elegible to be selected as protected tree
Protect Trees cHDCriterium cm/cm Maximum height/diameter ratio that protected trees should preferably have
Protect Trees cHeightCriterium fraction Fraction of maximum attainable tree height when trees are elegible to be selected as protected tree
Protect Trees cTargetDiameter cm Target diameter of protected trees (used only for distance calculation)
Protect Trees nTreesPerHa N/ha Number of protected trees per hectare to select
Selection of Future Trees cFutureTreeThinningInterval Number of management intervals, as defined in general Management, between thinnings around future trees
Selection of Future Trees cHDCriterium cm/cm Maximum height/diameter ratio that future trees should preferably have
Selection of Future Trees cHeightCriterium fraction Fraction of maximum attainable tree height when trees are elegible to be selected as future tree
Selection of Future Trees cIntensity fraction fraction of basal area increment that is thinned [0-1].
Selection of Future Trees cSelectTreesInterval Number of management intervals, as defined in General Management between selection of future trees
Selection of Future Trees cTargetDiameter cm Target diameter at harvest for future trees
Selection of Future Trees nTreesPerHa N/ha Number of future trees per hectare to select
Shelterwood Cutting cHeightCriterium fraction Fraction of maximum attainable tree height when trees will be counted to evaluate if cutting age is reached and which trees are eligible as sheltertree
Shelterwood Cutting cSoilScarification code 0 : no soil scarification, 1 : soil scarification
Thinning cIntensity fraction fraction of basal area increment that is thinned [0-1]. Only used in case of thinning method 2
Thinning cMethod code 1 : depending on crown space, 2 : percentage of basal area increment, 3: yield table densities
Thinning cThinningInterval Number of management intervals,as defined in General Management, between thinning interventions.
Unevenaged Thinning cDesiredBasalArea m2/ha
Unevenaged Thinning cLioucourtConstant Ratio in stem number between diameter classes
Unevenaged Thinning cTargetDiameter cm Maximum desired diameter in forest
Unevenaged Thinning cThinningInterval Number of management intervals, as defined in general Management, between thinnings