Seedling cohort establishment, growth and competition
The reproduction of trees is described by:
- the maximum production of seeds by an individual tree
- the variability of the production of seeds between years
- the seed dispersal distance
- survival and fraction of viable seeds.
Details can be found in (Kramer 2004; Kramer et al. 2006).
A model of seedlings establishment, growth and competition has been developed. The model is based on the necessary trade-offs between detailed representation of seedling dynamics and the computational efficiency necessary to run the model for areas of several hectares, and thus possibly model an extremely large number of seedlings. Seedling dynamics are generally not modelled in "gap models" of the JABOWA or FORET family (Price et al. 2001), including individual-tree spatial-explicit models like SORTIE (Pacala et al. 1996;Pacala, Canham, & Silander, Jr. 1993), with exception of the model FORGRA (Jorritsma, van Hees, & Mohren 1999).
In the ForGEM model, seedlings are modelled as cohorts distributed over a fixed-area subset (grid) of the simulation area. A cohort comprises all the seedlings establishing in the plot over one year which share the same set of ecophysiological traits.