Dead wood

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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 [1]. 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
Vt = volume at time t,
t0 = year when the tree died,
Vt0 = 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 measured

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.

Effect of clear cutting of the presence of dead wood

When clear cutting a stand there is a significant risk that much of the dead wood will be destroyed by harvesting machines.

If you control table parameter Enable Decomposition due to Final Felling is True (default), a certain (fixed) proportion of the dead wood volume in decay class 0, 1, 2 and 3 is assumed being destroyed and moved to class 4.

See ControlTable Dead wood for more settings related to Enable Decomposition due to Final Felling.

Proportion standing and downed dead wood

For each decay class, the proportion of the dead wood volume that consists of standing trees and downed 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 and 1 61%
2 30%
3 9%
4 2%

In the results, there is no separation of standing and downed dead wood per decay class.


Default decay class distribution

If you import data on dead wood occurrence, but only for the total and not per decay class, a default distribution is assumed, based on Swedish NFI data:

Decay Class Proportion of total dead wood (%)
0 13
1 17
2 20
3 23
4 27

Carbon concentration per decay class

Values are given as percentage (%) of dead wood dry matter. Based on Sandström et al. 2007 (Table 10)[1]. Concentrations are close to 50 % but varies a between decay classes and species. At the time of writing, only data for pine and spruce was available, and therefore the concentration for other species was set to 50 %, for all decay classes.

Decay Class Pine, Contorta and Larch Spruce Birch (and other species)
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

References

  1. 1.0 1.1 Sandström, F., Petersson, H., Kruys, N., & Ståhl, G. (2007). Biomass conversion factors (density and carbon concentration) by decay classes for dead wood of Pinus sylvestris, Picea abies and Betula spp. in boreal forests of Sweden. Forest Ecology and Management. Volume: 243, Number: 1, pp 19-27. http://pub.epsilon.slu.se/8937/1/sandstrom_et_al_120612.pdf