Dead wood

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[[::Dead wood|English]]  • [[::Dead wood/sv|svenska]]

Result variables for dead wood

The calculated occurence of dead wood volumes and carbon in dead wood is presented in the Dead Wood Results group. Occurrence of carbon in dead wood is also presented in the Carbon and Nitrogen result group.

Decay classes

The decay classes are defined according to Swedish NFI data (NEBRYTNINGSG)

Name	Value	Description
Raw	0	Wood hard. Green foliage is remaining, or vascular cambium is raw.
Hard	1	More than 90 % of the stem volume consists of hard wood. The stems is very little affected by decomposing organsims.
Slightly decomposed	2	10-25 % of the stem volume consists of soft wood.
Decomposed	3	26-75 of the stem volume consists of soft wood.
Very Decomposed	4	76-100 % of the stem volume consists of soft wood.

In Heureka the allocation of dead wood to different decay classes are based on calculated density, which depends on volume and biomass that are subject to different decay rate (see next section).

Decay rates for dead wood

Dead wood is continuously supplied from the mortality calculated. The presence of dead wood in a certain period of time is partly due to mortality during the latest period, and the decay rate of the existing dead wood in the previous period. Dead wood is classified into different decay classes depending on the calculated density . Five decay classes are reported as results, but internally in the system ten density classes are used (each accounting class divided into two subclasses) to increase the degree of detail in the decay calculations. The density is calculated as the ratio between the dead wood biomass (dry matter) and its volume. This is done for each density class (divided into species groups of spruce, pine and leaf). In every time period, a new quota is caluclated for each class, which means that the volume in a class can be transferred to a new decay class from one period to the next.

The decay functions have the following form:

where
V_t = volume at time t,
t₀ = year when the tree died,
V_t0 = tree volume when the tree died (excluding branches, stumps and roots),
a = proportion of the tree that died during the period that is collected. Note that each tree is handled as a type tree with a weight for the number of trees it represent, so "part of" a tree object may die.),
k = annual decay rate (%)

For biomass decay, the same function form is used, but "V" is substituted with "B" and another value for decay rate k is used. Parameter k is set in the Dead wood control table, parameters Decomposition Rate Biomass and Decomposition Rate Volume, respectively. Different k-values kan be set for different tree species.

Control table parameter Min Density determines at what density the dead wood is no longer discoverable or practically measurable. If the density is less than thi value the volume and biomass is removed.

Control table parameter Min Diameter (Dead wood) represents the minimum diameter for which trees to be included in the summary results, for those that used miniumum diameter as criteria, see Dead Wood Results

Control table parameter Proportion Dead Wood Collected determines whether some of the mortality is removed from the forest.

Initial dead wood

If the amount of dead wood has been inventoried, it can be loaded from the database. To accomplish this, set control table parameter Initial deadwood = Database (default).

Dead wood from stand register data

If you are using a stand register as input data there are columns available for entering the current amount of dead wood (volume per ha). There are also columns for volume in each decay class, see DeadWoodTotal, DeadWoodDecayClass1, etc. in the stand register specification. Please note that column DeadWoodDecayClass1 corresponds to result variable DeadWoodDecayClass0, column DeadWoodDecayClass2 to DeadWoodDecayClass1, and so forth. This apparent inconsistence in decay class indexing only applies to the naming of the stand register columns (originally a mistake but too late to change), in all other cases the first decay class has index 0.

Dead wood inventory

If you have an inventory of sample plots in which also dead trees and dead wood have been measured, you can add the data to the Excel sheet supplied (see Heureka Helpdoc, Import bestånd med provytor). There are specific columns for this, Status and DecayClass:

Status

0 eller 1 = Living tree. (or no value)

2 = Dead standing tree;

3 = Dead downed tree/log.

DecayClass

See DecayClass definition

Species

The species code for a dead tree is entered in the same column as för living trees. If the tree species cannot be determined the you can leave the Species-value empty or set to 0 (=Unkonwn). In that case Heureka is creating dead wood in proportion to the current species distribution of the stand.

Dead wood measured in NFI data

Dead wood is part of the Swedish NFI data and is included in those Heureka-databases to which NFI-data has been imported.

If current dead wood has not been measrued

In case you do not have access to such data but still want to assume some intiial occurrence of dead wood, statistics from the Swedish NFI can be used by setting Initial deadwood = Simulate (in control table Dead wood). You can set three different levels for this; Low, Medium or High, see Dead Wood Simulation Level paramter in control table Dead Wood.

Depending on selected lewel, a certain amount of dead wood is created as starting point (year 0). This dead wood is allocated to the decay classes with a function that is also based on the National Forest Inventory data (see below).

Deactivate usage of initial dead wood

You can always set control table parameter Initial Dead Wood = None, whether you have imported dead wood data or not. Then the amount of dead wood in year 0 will be zero in a simulation.

Påverkan av slutavverkning på förekomsten av död ved

I samband med slutavverkning finns stor risk att mycket av den döda veden förstörs av markberedning och av avverkningsmaskinerna.

Om du låter Enable decomposition due to Final Felling vara True (default), kommer en del av den döda veden som finns i klass 0, 1, 2 och 3 att nästan helt förstöras och placeras i klass 4. För klass 0-3 flyttas en lika stor andel av det som fanns i varje klass före slutavverkningen.

Decomp. Final Felling No Soil Preparation anger hur stor andel av den döda veden i klass 0-3 som förstörs (och överförs till klass 4) när beståndet slutavverkas men ingen markberedning görs. Detta är således den påverkan på den döda veden som själva slutavverkningsingreppet orsakar, och den är per default låg i förhållande till markberedningen.

Decomp. Final Felling Soil Preparation anger hur stor andel av den döda veden i klass 0-3 som förstörs (och överförs till klass 4) av både slutavverkningsingreppet och markberedningen, då markberedning görs.

Decomp. Set-Asides No Soil Preparation anger hur stor andel av den döda veden i klass 0-3 som förstörs (och överförs till klass 4) på en hänsynsyta när huvudbeståndet slutavverkas men ingen markberedning görs. Detta är således den påverkan på den döda veden som själva slutavverkningsingreppet orsakar, och den är per default låg i förhållande till markberedningen.

Decomp. Set-Asides No Soil Preparation anger hur stor andel av den döda veden i klass 0-3 som förstörs (och överförs till klass 4) på en hänsynsyta när huvudbeståndet slutavverkas men ingen markberedning görs

Standing dead trees vs. downed dead wood

For each decay class, the proportion of the dead wood volume that are standing trees and downed dead wood, respectively, is retrieved from the table below. The table is based on Swedish NFI data:

Decay class	Proportion of volume that are standing dead trees (%)
0 och 1	61%
2	30%
3	9%
4	2%

Decay class distribution

If you imported dead wood inventory data, but only the total volume and not for each decay class, Heureka is distributing the dead wood according to the table below, which is based on Swedish NFI data:

Decay class	Proportion of total volume (%)
0	13
1	17
2	20
3	23
4	27

Förekomst av kol i död ved

Förekomst av kol i död ved beräknas utifrån en given koncentration av biomassan (torrsubstans). Koncentrationerna är i stort sett 50 % men varierar något mellan trädslag och nedbrytningsklasser (Sandström m.fl. 2007 (Tabell 10). Förutom för tall och gran fanns vid skrivande stund inga uppgifter, och koncentrationen har därför satts till 50 % för övriga trädslag.

'Nedbrytningsklass	Tall, contorta och lärl	Gram	Övriga trädslag
0	50.32	49.22	50.0
1	50.52	49.17	50.0
2	51.46	49.68	50.0
3	51.46	50.81	50.0
4	52.23	51.27	50.0

I resultatredovisningen görs dock ingen särredovisning per nedbrytningsklass för stående och liggande död ved, utan dessa summeras över nedbrytningsklasser (se Resutlatvariabler nedan).