The Swedish Forest Agency uses a model for calculating annual gross and net felling. The model is based on consumption statistics, import and export statistics, stocks statistics and data on felled but not removed whole trees. The consumption statistics consist of consumption of sawlogs, pulpwood roundwood for energy purposes (fuelwood) and other roundwood consumption.
The survey is part of Sweden's official statistics and has product number JO0312.
The annual statistics include preliminary and final felling statistics expressed in cubic metres standing volume (m3sk, the trunk volume above the stump including top and bark but excluding branches) and net felling in the unit cubic metres solid volume excluding bark (m3f ub). The gross felling is presented by county and the net felling by assortment of stemwood. The statistics also include a forecast for the current year's gross felling.
The statistics also consist of felling data from the SLU (Swedish University of Agricultural Science) National Forest Inventory. These statistics refer to information on felled and thinned area and the distribution of felling by tree species. SLU National Forest Inventory's data is based on a sample-based inventory and the data are reported as five-year averages.
The trunk volume above the stump including top and bark but excluding branches.
The trunk volume except bark, top and branches.
Total felled trunk volume above stump, including both removed trunks and felled trunks not removed from the forest. Usually expressed in m³sk.
Total felled trunk volume above the stump, excluding not removed felled whole trees. Expressed in m³sk.
Total felled trunk volume above the stump, excluding bark, tops and not removed felled whole trees and not removed stem parts. Expressed in m3fub.
Sawlogs are rough logs from trees that will be sawn to sawnwood products. The category includes roundwood for beams, sleepers, and veneer sheets of softwood. As of 2018, even roundwood for industrial production of timber piles, posts, veneer sheets and matches of hardwood are reported under the category of sawlogs.
Pulpwood is roundwood used to produce pulp and in the next step paper and board products. As of 2018, roundwood to produce fiberboard is reported in the pulpwood category.
Fuelwood refers to stemwood used for energy purpose. Fuel wood includes traditional firewood used in for example detached houses and chips made of stemwood used in heat and power plants.
Other wood consists other assortments than sawlogs, pulpwood and fuelwood. Before 2018, the category consisted of roundwood for production of props, posts, charcoal, veneer sheets and matches of hardwood, wood wool, mining timber and agricultural timber excluding sawlogs. As of 2018, we do not include roundwood for the industrial production of timber piles, posts, veneer sheets and matches made of hardwood or fiberboard in the category. See sawlogs and pulpwood.
Felling where the stand density is lowered below 0.3. The purpose is usually to achieve new forest (regeneration felling).
Thinning of forests with removals of trees.
Stand management thinning of young forests without actual removal of trees.
Harvesting of seed trees and other trees not included in final felling, thinning and pre commercial thinning.
Individual private owners, estates and not limited companies (sole trader).
The State, state-owned companies, other public owners, private-sector limited companies and other private owners such as religious associations including the Swedish Church, privately owned foundations and funds, profit and non-profit associations, profit driven community groups.
Forest land which, according to established criteria, can produce at least, an average, one cubic metre standing volume per hectare and year.
This includes productive forest land, bogs, mountains, mountains, mountain coniferous forests, fields, natural pasture and other land (such as roads, power lines and storage sites).
Developed areas including urban areas such as parks, industrial sites and various facilities with other use than forestry.
How we do the statistics
The Swedish Forest Agency's harvesting model
The Swedish Forest Agency uses a top-down model for calculating annual gross and net felling. The model is based on consumption statistics, import and export statistics, stocks statistics and data on felled but not removed whole trees.
The consumption statistics consist of the forest industry roundwood consumption (sawlogs and pulpwood), consumption of roundwood for energy purposes (fuelwood) and other roundwood consumption. We adjust consumption data with data on imports and exports of roundwood and changes in stocks to calculate the net felling.
Finally, we calculate the gross felling by adding the net felling and data on felled trees that have been felled but not removed. The calculated gross felling is then distributed by county based on timber measurement data from Biometria.
During the second half of the year, the Swedish Forest Agency also makes a forecast for gross felling for the current year. We use the gross felling model for this, but instead of actual roundwood consumption, this is based on expected consumption. The expected consumption is based on forecasts to produce solid-wood products and pulp in the forest industry and forecasts in the energy sector. We use conversion factors to estimate how much wood is expected to be used for the forest industry's forecasted production.
Consumption of roundwood in industry
Data on the consumption of roundwood in the forest industry comes from an annual survey conducted by Biometria (formerly SDC). Biometria compiles data on the consumption of roundwood and other wood raw materials in the wood fiber industry and the wood mechanical industry. This refers to sawmills, pulpmills and board industries. As of 2018, also match manufacturers and pole industries are included in the survey.
Data on the roundwood consumption in small-scale sawmills (which consume less than 2,000 m3 roundwood per year) is based on the latest sawmill inventory and updated assessment by the Swedish sawmill association Småsågarnas Riksförbund.
Fuelwood
Since 2013, we have obtained the data on roundwood for energy purposes from the Swedish Energy Agency's study "Production of unprocessed wood fuels". Data for previous years are based on data from Forest Impact Assessments 1999. As of 2013, the data on firewood include not only firewood used in detached houses, but also firewood consisting of stemwood chips used in larger energy plants.
Other roundwood
Other roundwood refers to wood other than sawlogs, pulpwood and fuelwood. The figures are based on an older assessment. As of 2018, we do not include roundwood for industrial production of timber piles, posts, veneer sheets and matches made of hardwood or fiberboard in the category.
Foreign trade of roundwood
The Swedish Forest Agency uses data from Statistics Sweden's foreign trade statistics.
Stock change
The data comes from the Swedish Forest Agency's survey Stocks of softwood sawlogs, pulpwood and pulp chips. We calculate the change in stocks of softwood sawlogs and pulpwood as closing stocks at year-end minus opening stocks at the beginning of the year. No information is available on stocks of hardwood sawlogs, so we do not adjust for changes in stocks of hardwood sawlogs.
Felled but not removed whole trees
Data on felled whole trees not removed is part of the gross felling. We calculate the annual volume of felled whole trees not removed based on the ratio between a five-year average of trees not removed according to the Swedish National Forest Inventory and a five-year average of the Swedish Forest Agency's net felling.
Gross felling by county
From 2022, we use wood measurement data from Biometria and supplementary data from the Swedish Energy Agency regarding felling for firewood use in detached houses to distribute the annual gross felling by counties and country regions. Before 2022, information from Swedish Forest Agency's survey on silvicultural activities was used instead.
Felling according to the Swedish National Forest Inventory (RT)
SLU National Forest Inventory's felling estimates are based on an inventory of a sample of Sweden's land area. The felling is estimated from stumps on sample plots where trees have been felled. The stump inventory involves the registration of all stumps from the last felling season with a diameter of at least 5 cm. The felling season is between the dates of bud opening during the previous and current inventory year. In addition to the measurement of stumps from felled trees, the type of felling and all other data registered on the National Forest Inventory's sample plots are stated.
Reliability of statistics
In the gross felling model, the Swedish Forest Agency strives to use the best available input data sources. Several different data sources are used and the reliability of the statistics is linked to the uncertainties in these data sources. If we use incorrect values, it has a direct impact on the result in the gross felling model. The calculated gross felling volume can be both overestimated and underestimated.
At present, there are sampling errors estimates for felled but not removed whole trees and for parts of the firewood statistics. In addition to sampling errors, there may be systematic errors. Therefore, it is not possible to estimate the magnitude of the total error in the calculations. The following is a description of various uncertainties that we can see in the sources used.
Import and export of roundwood
The gross felling calculation is sensitive to the accuracy of statistics on trade in roundwood. Increased imports can reduce the need for domestic wood in industry and thus harvesting. Over the years, we have used official foreign trade statistics from Statistics Sweden in the gross felling calculation. Statistics Sweden report data on imports and exports of roundwood in the unit cubic metres (m3f). Based on an interview survey in 2021 to those who provided information on import and export of roundwood to Statistics Sweden, we assume that the unit is under bark (m3fub).
Statistics Sweden's statistics for foreign trade within the EU are based on a sample survey in which companies monthly report how much they have imported and exported. Trade for companies not included in the survey is modelled by Statistics Sweden. Foreign trade with countries outside the EU is recorded in mandatory customs declarations that form input to Statistics Sweden's statistics. As far as the Swedish Forest Agency knows, Statistics Sweden does not conduct extensive quality checks of reported values.
Also, Biometria collect data on imported roundwood consumed in the wood fibre and wood mechanical industry. The data at Biometria is in unit m3fub.
For 2022, Biometria reports an import of roundwood of 6.3 million m3fub while Statistics Sweden reports a preliminary import of 6.5 million m3fub, i.e. a difference of about 0.2 million m3fub. However, the data are not fully comparable as changes in stocks of imported wood are not considered in Biometria's data. For the years 2017–2022, the differences between Biometria's and Statistics Sweden's total imports of roundwood have varied from -0.5 to +0.5 million m3fub.
Stocks of roundwood
The Swedish Forest Agency conducts a stock survey with the aim to measure stocks of coniferous sawlogs, pulpwood and wood chips on four occasions per year. The survey captures all purchasing companies, pulp industries and major sawmills. Up to and including 2018, we examined a sample of sawmill companies with a turnover of between SEK 5 and 50 million. As of 2018, all these companies are also included in the survey. As of 2020, we include only companies with a turnover greater than SEK 20 million. In case of non-response, we use imputation.
Historically we have underestimated the stock of sawlogs by roadside. Statistics from 2022 show that it could be about 200,000 m3sk for 2021. This underestimation affects gross fellings by not including any change in stocks of this stock in the gross felling calculation for 2021.
Biometria's survey to the sawmill, pulp and board industry
Data from Biometria are based on a survey to sawmills (which consume more than 2,000 m3fub roundwood per year) and to the pulp and board industry. As of 2018, they include the manufacture of poles and matches in the survey. As of 2020, data for sawmills and other wood mechanical industries are based on administrative survey data from Biometria's timber accounting system (VIOL), while they still collect data for the pulp industry via questionnaires.
From 2020, wood consumption data in sawmills and other wood mechanical industries refer to the measured volume. The data thus includes volumes measured during the year but in stock at sawmills at the end of the year. When calculating gross felling, this is considered through a correction based on the Swedish Forest Agency's inventory statistics for sawlogs.
Measured volumes of sawlogs can include deliverable logs that the sawmill chooses to resell. Biometria adjusted for 414,000 m3fub resold volumes in 2022. The volumes may have been higher, which in that case means an overestimation of wood consumption and gross felling.
Data on the raw material consumption of small sawmills (which consumed less than two thousand m3fub sawlogs per year) derive from the latest sawmill inventory conducted in the early 2000s and an updated assessment by the sawmill association Småsågarnas Riksförbund (representing sawmills with a small production). In total, roundwood consumption in small sawmills amount to around 650,000 m3fub per year.
Fuelwood
The Swedish Energy Agency's study on unprocessed wood fuels consists of several different studies. A total survey of the Swedish Wood Fuel Association's member companies and a selection of other companies. Also included are firewood data from the survey of the energy use of detached houses. The survey has a high response rate. Coverage errors and measurement errors may occur.
The Swedish Forest Agency converts the data presented to m3fub with conversion figures of 2.04 MWh/m3f (stemwood chips), 2.05 MWh/m3f (tree chips) and 2.25 MWh/m3f (fuelwood) and 0.88 m3fub/m3f. It is possible that we overestimate the bark volume, it disappears in the handling of the wood. The Swedish Forest Agency's recalculation may thus mean that we underestimate the volume of fuelwood. The conversion rates between energy measures (MWh) and volume measures (m3f) are also a source of uncertainty.
In the case of chips from whole trees, the calculations assume that 50 percent of the total weight of a tree that is 15 cm in diameter is stemwood. This is a rough estimate as the proportion of stemwood is higher in larger trees and lower in smaller ones. Chips from whole trees account for a low proportion (about 3 percent) of the total firewood felling, which is why uncertainty has a marginal impact on the total felling of firewood.
Gross felling by county
The Swedish Forest Agency calculates the annual gross felling by county and country regions based on timber measurement data from Biometria and supplementary data on wood use in detached houses from the Swedish Energy Agency. Before 2022, the gross felling by county was calculated based on data from the Swedish Forest Agency survey on silvicultural activities. For uncertainty reasons, the statistics were reported as three-year averages.
Biometria's information refers to roundwood of domestic origin that have been measured in the first business transaction step and that have been managed in Biometria's timber accounting system. The Swedish Energy Agency's information refers to estimate of the firewood use by county, which is obtained through a survey to owners of detached houses.
A compilation of the data from Biometria and the Swedish Energy Agency shows that these together make up a substantial proportion of the total net harvesting. The summary shows that of the total net felling, 93 percent was managed within Biometria's system, and that 4 percent can be referred to firewood use according to the Swedish Energy Agency's information. The remaining 3 percent (approx. 2 million m3fub) consists of volumes measured and managed outside Biometria's system and statistical differences. In the calculation we assume that the remaining part has the same distribution by county as Biometria's data.
The Swedish National Forest Inventory's estimate of gross felling
The statistics in tables 03–06, 08 and 10 in the Swedish Forest Agency's statistical database come from SLU National Forest Inventory. The Swedish National Forest Inventory's estimates of five-year averages for gross felled volume for the whole of Sweden have a mean error of about 4 percent. At certain time intervals, estimates of statistical uncertainty are made. In addition to random errors, there are systematic errors, among other things caused by undetected stumps from felled trees. Studies have shown that the stump inventory underestimates the felled volume by about 7 percent, an error for which it is compensated in the calculations. No corresponding systematic errors in the estimates of harvested area have been proven. When analyzing the control assessment conducted at the National Forest Inventory, it has been found that the seasonal assessment and classification of harvesting measures have a high degree of accuracy.
Since 2003, the model-calculated felling has on four occasions (2006, 2007, 2014 and 2015) been just within or slightly outside the Swedish National Forest Inventory's estimates when the margin of error is considered. A 95% confidence interval does not mean that the true value is always within the range. For the most recent period (2017–2021), the model-calculated felling is below the estimates of the Swedish National Forest Inventory by 4.6 percent (4.5 million m3sk). The difference is within the margin of error for the National Forest Inventory estimate. However, the periods are not fully comparable as the Swedish Forest Agency's model calculation refers to the calendar year and the National Forest Inventory to the harvesting season.
In addition to differences caused by sampling errors and periodicity, there are differences caused by differences in methods and data sources. As previously described, the Swedish Forest Agency's calculation model is based on several sources, of which each has known and unknown uncertainties. The advantage of the model calculation, unlike the National Forest Inventory, is that it has a higher timeliness in that it gives an annual estimate, and that already the year after the reference year, and that it provides a forecast for the current year. The calculation model is also based on production, foreign trade, energy and stocks statistics, which provides good comparability and compatibility with several other statistical areas.
One advantage of the National Forest Inventory's felling estimates is that the National Forest Inventory has quality control of the entire statistical production chain, from field inventory to calculations, and that the survey has been conducted with the same method for a long time. It thus provides reliable statistics for the long-term development of felling and is comparable with other official statistics from the Swedish National Forest Inventory.
The estimates of the Swedish National Forest Inventory are important from a quality point of view for the annual model-calculated gross felling statistics and over a longer period the two estimates should follow each other.
Development work for better quality
In 2019 and 2020, the Swedish Forest Agency and the Swedish National Forest Inventory conducted a joint quality study of the two gross felling models. The study resulted in conclusions that formed the basis for development work to improve the quality of input data to the Swedish Forest Agency's gross felling model.
In 2021, as part of the development work, Statistics Sweden investigated whether import and export data of roundwood refer to cubic metres under or on bark. Another development work completed in 2022 concerned the conversion factor between solid measure under bark (m3fub) and cubic metres standing volume (m3sk). The revision of the conversion factor meant that the previous conversion factor of 1.2 between the units m3fub and m3sk was revised to 1.188. The statistics have been revised since 2000 to take account of the new conversion factor.
Average harvested area for final fellings
Average area for final fellings greater than or equal to 0.5 hectares is based on the Swedish Forest Agency's register for felling notifications and registered information on felling linked to these notifications. Completed felling is registered within the Swedish Forest Agency's supervisory activities with the support of remote sensing-based methods where satellite images taken at various times are compared to identify and delimit fellings. The operations are comprehensive, but there are uncertainties, and these can partly be assessed by comparing the harvested area according to this register and the SLU National Forest Inventory's estimates of final felled area.
The estimates of the National Forest Inventory exceed the Swedish Forest Agency's register by 28 percent for the latest five-year average. The Swedish Forest Agency's register only includes fellings larger than or equal to 0.5 hectares. The estimates of the National Forest Inventory also include the area covered by smaller fellings. But there are also other potential explanations for differences between these two sources of statistics. This may involve technical differences in measurement of how the harvested area is delineated, that fellings over 0.5 hectares have been missed in the Swedish Forest Agency's register, and that there may be random variations in the National Forest Inventory's estimates. It has not been possible to clarify how much of the total difference that consists of different partial explanations.
