2.2.1. Simple Tests with the Raw Data
First, the regional data on the production and trade of industrial roundwood, wood residues, chips, and particles were examined with three relatively simple tests i–iii, described below under the questions (i)–(iii), respectively.
(i) Is the reported wood production at least as high as the reported net export (exports − imports)? If not, the region’s apparent wood consumption is negative, which signals errors in the underlying data.
The data allowed this first infeasibility check to be made for four wood categories: industrial coniferous roundwood, industrial non-coniferous roundwood, chips and particles, and wood residues.
(ii) Is the reported production of chips, particles, and wood residues (too) high compared to the production of solid wood products?
This test identifies countries where the produced number of woody by-products is considerably higher than the produced amount of the solid wood products. The test was carried out for the category of “wood chips and particles” alone and then for the total amount of by-products labeled “wood chips and particles” and “wood residues”.
If the number of by-products is much higher than the production of the principal products, there is probably something wrong in the data, despite the fact that part of the residues comes from further processing of sawnwood, veneer, and plywood to finished products, carpentry, and so on.
Typically, chips and particles are obtained as a side product of sawnwood and plywood production, and they form only part of the material obtained as by-products. Also, other types of residues, for instance sawdust, are coming out. Moreover, part of the log input in sawnwood and plywood production vanishes due to shrinking. The log input coefficient under bark in the production of solid wood products is seldom above 2 (
Table 2), in particular, when it comes to sawnwood that is more commonly produced than plywood and veneer. For these reasons, it is reasonable to expect that production of chips and particles should not exceed that of solid wood products. If the output of “chips and particles” and solid wood products were equal, it would indicate that little other material would come out from the process.
(iii) Are the apparent levels of wood use high enough for the reported production of forest industry products?
This test was done for all sawlogs and veneer logs (coniferous + non-coniferous), for pulpwood and pulpwood substitutes (coniferous pulpwood + non-coniferous pulpwood + chips and particles), and for all wood. If the assumed required minimum consumption of wood inputs exceeds the amount of their maximum availability under the rather loose requirements discussed below, it is likely that there is something wrong with the data.
• Case of sawlogs and veneer logs used for sawnwood, plywood, and veneer
In this test, the assumed minimum quantity of logs needed in sawnwood, veneer, and plywood production in a country was compared to the maximum potential volume of sawlogs and veneer logs available based on the statistics on wood harvest and trade. The test setting was cautious for the following reasons. Firstly, it was assumed that 1.5 m
3 of logs under bark are sufficient to produce one unit of sawnwood, veneer, or plywood. This coefficient can be considered somewhat low (see
Table 2). Secondly, the maximum available amount of sawlogs and veneer logs in a region was defined to include sawlog and veneer logs harvests and all industrial roundwood imports to the country, despite the fact that part of the imports can be pulpwood or roundwood for other industrial uses. Thirdly, all the exports of industrial roundwood were assumed to consist of the wood grades other than sawlogs and veneer logs.
• Case of wood material used for pulp
This test asked if there may have been enough pulpwood, chips, and particles to sustain the reported wood pulp production in a country. Again, the test was rather robust in the sense that the requirements for the data passing the test were set low. It was assumed that all pulpwood, chips, and particles potentially available in a region may have been used for pulp production, although these raw materials are also used for particle board, Medium-density fibreboard (MDF), and other panel products. Furthermore, all industrial roundwood imports were now assumed to be pulpwood, while all roundwood exports were assumed to be other wood grades. It was modestly assumed that chemical pulp requires only 3 m3, dissolving pulp 4 m3 and mechanical and semi-chemical pulp 2 m3 of wood fiber per tonne of pulp output.
• Case of all wood materials used for all products
This test added panels (particle board, Oriented strand board (OSB), MDF, etc.) to the previous set of products and asked whether the production of this new set of products could have been produced by the wood material reported to be available. A very modest (see
Table 2) wood use coefficient was applied to these panels: 1 m
3/m
3. For the other products, the minimum input coefficients described above were used. “Wood residues” were included to the available wood together with sawlogs, pulpwood, chips, and particles. The amount of wood available per country was defined to include net imports (imports − exports) and own harvests or production of these wood grades. The test compared only the total wood material reported to be available in a region to the conservatively defined aggregated demand for wood materials in the reported forest industry productions. It imposed no allocation rules based on the suitability of alternative wood grades (
Table 2) to different products.
2.2.2. Test Using Linear Programming
An LP formulation was used to improve the consistency and precision of test iii for all wood grades and products and also to identify the cases where the regional wood supply seems too high compared to the respective forest industry production. Because the exact mathematical formulation of the LP problem is space demanding, only its main principles are described here, while a complete description, including all the constraints, is provided in the
Supplementary File S2: Description of the LP model (word.doc).
The main principle of the LP program is that it aims to find input coefficients for the industrial products in
Table 1 that are as close as possible to the reference values given in
Table 2 (or the more country-specific figures) and which, when applied to the reported forest industry production data, match the consumption of various wood grades to their apparent availability (production + imports − exports) as well as possible. The objective function minimizes the sum of the various penalty variables that allow the data to be inconsistent with the rules defined.
Three levels of penalty variables for the wood input coefficients not complying with their reference values were defined: (1) a somewhat low penalty of deviation from the point estimate reference value; (2) a higher penalty for input coefficients not being within an assumed range around the reference value; and (3) the highest penalty for not even fitting in between the absolute minimum and maximum values defined for the coefficients. The default input coefficient values are given in
Table 2 but were refined as shown in the
Supplementary Materials when there was additional country-specific information available. When looking for the input coefficients, constraints (subject to penalty variables if violated) that aim to minimize year-to-year fluctuations of the input coefficients were also defined so that the technologies were assumed to be material saving. A regional input coefficient for a product in a given year that was higher than that in the previous year was penalized if there was production in both years.
Roundwood harvests were constrained to equal the harvests reported in the statistics subject to penalty variables. The calculated value for the penalty variable in a region indicated the suggested deviation from roundwood harvests from the statistics.
The program also divided the traded quantities of roundwood given in the statistics between pulpwood, sawlogs, and other industrial wood. It also divided the production of sulfate pulp, plywood and veneer, and chips and particles into coniferous and non-coniferous grades. These divisions were done so that the data become as consistent as possible with the wood use in the forest industry.
Before doing the LP test, the data showing negative apparent consumption figures for wood in test i described in
Section 2.2.1 were modified as follows:
The production volumes of wood residues and chips were increased to match with the exports.
The production volumes of other coniferous or other non-coniferous industrial roundwood were increased if the apparent consumption of coniferous or non-coniferous roundwood was negative, respectively. Such typically small adjustments were rarely needed.
Similarly, noting the inconsistencies raised by test ii, the following modifications for the data on by-product outputs were made before the LP test in order to improve their consistency with the production of the solid wood products (sawnwood, plywood, and veneer).
The production volumes for chips and particles were decreased to be at most 80% of the production of solid wood products.
The production of wood residues was reduced, if necessary, so that the resulting logs input calculated as “(sawnwood production + plywood and veneer production + chips and particles production + wood residues production)/(sawnwood production + plywood and veneer production)” is at most 2.8 m3/m3. If a country then violated test i, the exports were reduced.
Test i in
Section 2.2.1 mostly identified cases where the production of forest industry residues was too low compared to the exports, while test ii found cases where it was too high, generally. Consequently, further corrections made based on test ii seldom affected the same countries.