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Abstract
The purpose of this study was to develop models for estimating yields of
lumber grades and by-products of individual Scots pine (Pinus sylvestris L.)
stems using stem and crown dimensions as explanatory variables. The next
stage will be combining models to simulation-optimization framework to
optimize forest management at the stand level using climate change
mitigation effect as an objective function when also material and energy
substitution benefits of wood products are taken into account.
Two separate data sets were used as a material for analysis: 1) Simulated
data set generated by the process-based growth model, PipeQual, which
provides information about stem form and branch properties. The model
was used to predict the 3D structure of Scots pine stems in thinning regimes
of varying intensity and rotation periods and 2) detailed measured empirical
data set. The stems were sawn using the WoodCim sawing simulator and the
yields and grades of the individual sawn pieces, as well as by-products,
were recorded. The sawn timber pieces were classified on A, B, C and Dgrades
for side and center boards separately (Finnish export rules). Byproducts
were pulpwood, sawmill chips, sawdust and bark.
The response variables were formulated as proportions of the total volume
of each stem. Multinomial logistic regression models were fitted to the both
data sets. Models fitted to the real stems data set was found more accurate
and the dead branch height, diameter at the breast height and the natural
logarithm of the diameter at breast height was found the best combination of
the explanatory variables. The models were tested in the generated data set
and found to overestimate the quality in medium fertile stands.
The developed approach integrates forest management, its implications to
the quality of raw wood and sawn wood conversion chain. The models can
be used in stand management optimization for comparing different
management options e.g. on the value-added basis from the sawmill’s point
of view or climatic benefits of wood products.