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Until recently, TASS has always started a simulation from plantation of bare ground. Even when existing stand data was available, TASS had to be manually iterated through a number of simulations with various initial conditions to try to
accurately simulate the target stand.
It is more efficient to model trees starting from their actual age than to fill in all parameters from age zero to the
starting age and then start the stand projection. As a test, we output a list of trees at age 50 and had TASS read it in, build stems and crowns, and continue processing as if the trees had been grown since age zero.
The stand reconstruction turned out to be easier than expected.
Individual tree vigour, usually assigned at planting, was computed from
the relationship between tree size and the stand mean height and
diameter or those of the top height trees. Crowns expanded as usual, to
the point of contact with competing neighbours, or to the point where
light was extinguished under neighbouring crowns. The results of this
run were then compared with those of a simulation that used the same data but reconstructed the stand from bare ground.
Comparing real with simulated stand.
The comparison showed the new process to be successful.
Limited tests of TASS producing its own trees in
mid-rotation this way have also been very successful. This method has been used in producing all of the TASS runs of the Pothole Creek stand, including trees up to 300 years old.
Research Branch contact: Ken Polsson |
