Initialisation of the stand
Initialisation of the ForGEM model means that initial values are assigned to the model's principle state variables of the ordinary differential equations which are numerically integrated by the NSM software package during the simulation.
The user has the following options to initialise a forest stand in Forgem:
- measuring the values of the state variables in a particular stand
- generating a forest stand based on statistics obtained from one or more forest stands
- selecting a stand from the Synthetic European Forest Structure Database (SEFS) and using the statistics available in SEFS of the selected stand to generate a forest stand
The latter option allows the user to select a forest stand at any location in Europe at the 1x1km grid scale, and thus apply the ForGEM model at the European scale without the need of additional initialisation.
Initialisation by measuring a stand
In principle, all state variables of the ForGEM model can be measured in a forest. However, minimally height, stem volume and diameter at breast height (dbh) are required.
Initialisation by statistically generating a stand
The Generate function in ForGEM allows the user to statistically generate a forest stand based on minimally tree density, average height and average dbh.
Variability between individual trees in the stand can be based on:
- observed coefficient of variation (CV) of these variables
- user defined values of the CV for each of the three stand variables
- the default value in Generate function for the CV of xx % to avoid that all trees are exactly the same.
The other state variables are derived from tree density, tree height and dbh based on the empirical relationships
Age of the tree is estimated from its [height], using the age-height relationship (Richards curve) of the highest site class available for Dutch conditions (Jansen et al., 1996). This will in most cases yield an underestimation of the age. This is deemed acceptable as age is only used in ForGEM to determine age-dependent mortality, which will be overruled by competition and harvest effects for the simulations foreseen.
Age is estimated on the individual heights and thus varies per individual tree.
In case age is given for the NFI plot, it is assumed to be the same for all trees in a cohort.
Simulation plots are 100x100m.
One plot may contain several cohorts, which are differentiated by tree species and/or height.
Initialisation by stand selection from national forest inventory database and statistically generating a stand
The procedure is to select a forest stand from a database that contains the data from a national forest inventory, and using the forest statistics from that database to generate the initial stand for ForGEM.
- tree species
- tree density (stem number ha-1)
- average height (m)
- average dbh (cm)
- basal area (m2/ha)
- stem volume (m3/ha)
Only tree density, average height and average dbh are used to initialise the stand, however, the other variables can be used to check the consistency between variables in the generated stand.
The user should provide the co-ordinates (longitude and latidute) for a specific location in Europe, corresponding to grid cells used in the Inter-Sectoral Impact Model Intercomparison Project (ISI-MIP).
The user can provide additional search criteria:
- the selected plot contains prescribed tree species
- plots selected from the SEFS database lie within a prescribed radius from the requested location. This selection of SEFS plots allows the possibility to select an azimuth sector.
If no location search criteria is specified, a random NFI plot is drawn according to the procedure for the Synthetic European Forest Structure Database i.e. using the forest inventory region as a basis. The user gets the original information of the selected plot, plus the number of plots that were selected given the search criteria.
PM: we still need to decide if we do the consistency checks or not, and if we then still can use the additional information such as minimum and maximum diameter at breast height (DHB) or age
Derivation of additional parameters The tree species map (Brus et al., 2012) is used to determine the flow of seed from outside the simulated area, for all tree species. [describe exact implementation]
Brus, D.J., Hengeveld, G.M., Walvoort, D.J.J, Goedhart, P.W., Heidema, A.H., Nabuurs, G.J., Gunia, K., 2012. Statistical mapping of tree species over Europe. European Journal of Forest Research 131(1): 145-157.
Hengeveld, G.H.M., Schelhaas, M.-J., Heidema, N., (in prep). Synthetic European Forest Structure Database.
Jansen, J.J., Sevenster, J., Faber, P.J. (eds.), 1996. Opbrengsttabellen voor belangrijke boomsoorten in Nederland. IBN Rapport 221, Hinkeloord Report No 17. 240 pp.
Hengeveld, G. M., G.-J. Nabuurs, M. Didion, I. Van den Wyngaert, A. P. P. M. Clerkx, and M.-J. Schelhaas, 2012. forest management map of European forests. Ecology and Society 17(4): 53.
Wosten et al., 1999. Development and use of a database of hydraulic properties of European soils. Geoderma,90(3-4).
Wosten, J.H.M., Pachepsky, Y.A. and Rawls, W.J., 2001. Pedotransfer fuctions: bridging the gap between available basic soil data and missing soil hydraulic characteristics. Journal of Hydrology,251(3-4).
Metzger, M. J., Brus, D.J. , Bunce, R.G.H. , Carey, P.D. , Goncalves,J. , Honrado, J.P. , Jongman,R.H.G. , Trabucco, A. , Zomer, R., 2013. Environmental stratiﬁcations as the basis for national, European and global ecological monitoring. Ecological Indicators 33:26-35.
- National Forest Inventories dataset
- National Forest Inventories dataset