http://creativecommons.org/licenses/by/4.0/

Natural Resources Institute Finland (Luke) owns the copyright, data protection, and other immaterial rights to this product. The Topographic Database from the National Land Survey has been utilized when making the product. This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/ or send a letter to Creative Commons, PO Box 1866, Mountain View, CA 94042, USA. When using the material, the owner of the rights to the material must be given as "©Natural Resources Institute Finland, 2023" and the name of the material must be given as "The Multi-source National Forest Inventory Raster Maps of 2021". For research use, the description of the method is in the references in the metadata element Lineage. A scientific citation practice shall be used in research use.

The first country level estimates correspond to years 1990-1994. The most

recent versions are from years 2005, 2007, 2009, 2011, 2013, 2015, 2017, 2019 and 2021. The first set of the products freely available are from year 2009. A new set

of the products will be produced biannually in the future. The map products

are in a raster format in the ETRS-TM35FIN coordinate system with a pixel

size of 16m x 16m. The products cover the combined land categories forest

land, poorly productive forest land and unproductive land. The other land

categories as well as water bodies have been delineated out using the

elements of topographic database of the Land Survey of Finland.

For the 2021 products, in total 51 833 NFI field plots were used, locating

either on forest land, poorly productive forest land or unproductive land.

The satellite images used included 7 Sentinel-2A MSI images, 6 Sentinel-2B MSI

images and 6 (3 orbits) Landsat 8 OLI images. The images were from 2021.

The field data in the 2021 products were up-dated to correspond the situation

on 31 July, 2021. The length of the up-dating period was calculated for each

field plot from the date of the field measurement to the up-dating date 31

July, 2021. The start of the tree growth was supposed to be on May 1.

The relative increment of the volume of the growing stock in a forest stand

was calculated using the models by Nyyssönen and Mielikäinen (1978) for pine

(Pinus silvestris) and spruce (Picea abies). The models for pine were used for

broad-leaved trees. The volume increments were calculated by stand layers in

case of multi-layer stands. The proportions of volumes by layers were estimated

proportionally to the quantity the basal area of the layer multiplied by the

mean height of the layer.

Regeneration cuttings on the field plots were assessed using satellite images

and, in some cases, with aerial photographs. The stand data of the plots cut

were changed to stand data for open area plots. The final volume increments

were calibrated in such a way that the volumes by tree species on July 31,

2021, was the same as that given by the regression line estimated from field

data alone when the results seemed reasonable. Otherwise the target was

determined heuristically.

For the relative height increment, diameter increment and basal area

increment, simple fixed parameter regression models were estimated using data

from the permanent sample plots of NFI10. The models were used in a similar

way as the volume models. The biomass estimates by field plots and biomass

compartments were up-dated proportionally to the volume changes.

For a cover as complete as possible from the entire country, the 2021 product has

been completed by the data estimates from the recent years. The product thus

consists of the following sub-products:

1. The estimates from 2021, based on the NFI field data from 2017-2021 updated

to 31.7.2021 and the satellite images from 2021 (99.45 % of

forest pixels),

2. The estimates from 2019, based on the NFI field data from 2015-2019 updated

to 31.7.2019 and the satellite images from 2018-2019 (0.52 % of

forest pixels),

3. The estimates from 2019, based on the NFI field data from 2013-2017 updated

to 31.7.2017 and the satellite images from 2017-2018 (0.02 % of

forest pixels),

4. The estimates from 2015, based on the NFI field data from 2012-2016 updated

to 31.7.2015 and the satellite images from 2015-2016 (0.002 % of

forest pixels),

5. The estimates from 2013, based on the NFI field data from 2009-2013 updated

to 31.7.2013 and the satellite images from 2012-2014 (0.0005 % of

forest pixels).

Data source index, MS-NFI-2021, has been added to the product to indicate

the source of the estimates.

The map form estimates were made using the improved k-Nearest Neighbour method

(ik-NN method). The value of five for k was used most frequently. The weights

of the features in the ik-NN method are sought using an optimization method

based on genetic algorithm. Coarse scale estimates of forest variables were

used as the supplementary data. The volumes by tree species groups were

selected as the variables. The purpose is to direct the selection of the

neighbours, on the average, to forests similar to the target pixel (see the

references below). The estimation was made separately for mineral soils, mires

and open bogs and fens. The stratification of both the satellite image and the

field plots were made using the topographic map data of Land Survey Finland.

The product consists of 44 theme maps in raster format plus data source index.

The themes can be grouped as follows:

The volume of growing stock is available as a total for all tree species

and broken down into tree species groups (Scots pine, Norway spruce, Birch,

Other broad-leaved trees) and into timber assortments (saw timber, pulpwood).

The volume of a tree is defined as the volume of the stem wood above stump until

the top of the tree. The volume of a tree in the field data is estimated using

the parameters measured in the field and the volume models. The unit and class

interval of the volume is 1 m3/ha in the products available for downloading.

The biomass of the growing stock has been estimated and is available by tree

species groups and by seven tree compartments. The biomass of stem and bark of

a tree is defined as the biomass of the stem above bark and above stump until

the top of the tree. The biomass of the living branches includes the biomass

of the living branches without needles or leaves. The biomass of the dead

branches includes the biomass of the dead branches possibly left in a living

tree. The foliage biomass includes the biomass of the living needles or

leaves. The biomass of stumps includes the biomass of the above and below

ground stump parts without roots. The root biomass includes the biomass of the

living roots with a diameter of at least 1 cm. The biomass of stem residual is

defined as that part of the stem biomass that can not be used as timber or

pulpwood due it size or quality.

The biomasses of the sample trees on a NFI field plot are calculated from the

living sample trees belonging to a plot using the wood density models (Repola

et al. 2007) and biomass models (Repola 2008, 2009). The biomasses of the

trees called tally trees are estimated using the estimates of the sample trees

(with more parameters measured) and the parameters of tally trees and

stands. The unit of the biomass in the maps available for downloading is 10 kg/ha.

The basal area of the growing stock on a forest stand is the cross section area

of the tree stems of a stand per hectare and measured at a height of 1.3 m.

The basal area is measured in the field for the field plot stands on forest land

and poorly productive forest land in the classes of 1 m2/ha.

The age of the growing stock on a forest stand is the weighted average of the

trees, the basal area of the tree as the weight. The age is assessed in the field

for the field plot stands on forest land and poorly productive forest land in

the classes of one year.

The mean height of the trees on a forest stand is the height of the basal

area median tree for the development classes young thinning stand or more

mature stands. It is about the same as the basal area weighted average

height. For seedling stands, the mean height is the average height of the

dominant and co-dominant seedlings. The mean height is assessed in the field

in the classes of 1 dm.

The mean diameter of trees is assessed at a height of 1.3 metres and is the

the diameter of the basal area median tree. It is about the same as the

weighted average diameter, the basal area of a tree as the weight. It is

assessed for the field plot stands on forest land and poorly productive forest

land in the classes of 1 cm.

The canopy cover of trees is the vertical projection area on the horizontal

plane of the canopies of the individual trees on a field plot (without double

counting the overlapping canopies). In NFI10, it was assessed in the field as

a shares (0-99%) on a fixed radius plot. For the NFI11 plots, it was estimated

using k-NN method and the NFI10 plot data. In North Lapland in NFI9, the

canopy cover was assessed in three categories if the plot was either on forest

land, poorly productive forest land or unproductive land. A regression model

was constructed to estimate the cover in the classes of one percent.

The canopy cover proportion of broad-leaved trees is derived from the total

cover using the basal area. However, in the seedling stands, the canopy cover

of broad-leaved trees is assessed using the shares of the stem numbers.

The theme "Land class" divides forestry land into sub-categories forest land

(pixel value 1), poorly productive forest land (2), unproductive land (3) and

other forestry land: forestry roads, forest depots, etc. Outside forestry land,

the land class describes land use. In the present themes, the combined

mask of forest land, poorly productive forest land and unproductive land is

based on the topographic database from the National Land Survey. One

of three land categories is estimated for the pixels inside the three mask

categories. The "Land Class based on FAO FRA" divides forest into four

categories based on the definition of the United Nations FAO Global

Forest Resource Assessment (FRA): forest (1), other wooded land (2),

other land (3) and other land with tree cover (4)

The main site class divides the forest land, poorly productive land and waste

land into mineral soils (1) and peatlands, and further divides the peatlands

into spruce mires (2), pine mires (3) and treeless mires (4). Both the satellite

images and the NFI field plots are stratified to mineral soils and peatlands

before analysis according to the topograhic database from the National

Land Survey. The most probable of the four NFI main site classes is

predicted for each pixel within these strata. This means that each stratum

may include both mineral soils and peatlands according to the NFI classification.

The site fertility classes are used for grouping the forest by vegetation

zones into uniform classes according to their site fertility and wood

production capacity. In national land-use classification, all stands on

mineral soil with site fertility class in 1 - 6 were classified as forest land

(1 is herb rich sites, 2 is herb rich heath forests, 3 is mesic forests, 4 is

sub-xeric forests, 5 is xeric forests, 6 is barren forests). Class 7 (rocky

and sandy soils and alluvial lands) can be forest land, poorly productive

forest land, or unproductive land, and class 8 (summit and fjeld land with

single coniferous trees) either poorly productive forest land or unproductive

land. Classes 9 (mountain birch dominated fjelds) and 10 (Open fjelds) are

poorly productive forest land or unproductive land. Both natural and drained

peatlands are classified into six site fertility classes independently of the

land class. Class 1 includes euthropic mines and fens, 2 mesothropic mires and

fens, 3 meso-oligothropic mires, 4 oligothropic mires, 5 oligo-ombothropic

mires and 6 Sphagnum fuscum dominated mires. Both the field plots and

satellite images are stratified prior the analyses into three strata, mineral

soil, pine mires and spruce mires, treeless peatland . The site fertility

class is estimated for each pixel as the most likely site fertility

class. Thus in the products, each NFI field data based category can occur

within each map based stratum.

The estimation errors at pixel level are rather high but decrease when the

area in question increases, i.e., when the area of interest consists of

several pixels. The errors vary by the themes and depend also on the actual

value in the field, for example on the volume of growing stock and the site

fertility class.

The following error estimates are based on the MS-NFI 2019 product.

The magnitude of the average errors of the volume estimates at pixel level

are presented below (SF = South Finland, NF = North Finland, min = mineral

soil, peat = peatland, m3/ha):

species group assort. SF/min SF/peat NF/min NF/peat

all all 87 67 50 39

pine all 67 51 44 30

pine saw t. 44 31 24 12

pine pulpw. 39 32 32 24

spruce all 64 43 28 19

spruce saw t. 47 30 16 10

spruce pulpw. 30 22 17 13

birch all 35 32 18 19

birch saw t. 11 7 2 2

birch pulpw. 27 26 15 17

other br. l. all 25 16 9 6

other br. l. saw t. 8 5 1 1

other br. l. pulpw. 18 11 7 5

The magnitude of the average error of the biomass estimates at pixel level are

presented below (SF = South Finland, NF = North Finland, min = mineral

soil, peat = peatland, 10 kg/ha):

tree species compartment SF/min SF/peat NF/min NF/peat

pine stem and bark 2624 1982 1711 1179

pine living branches 355 280 315 215

pine dead branches 91 74 70 51

pine foliage 118 98 108 81

pine stump 186 150 141 100

pine roots 609 470 444 295

pine stem residual 153 146 176 135

spruce stem and bark 2342 1596 1074 744

spruce living branches 511 367 319 211

spruce dead branches 95 68 46 34

spruce foliage 324 240 195 142

spruce stump 201 142 115 75

spruce roots 722 529 424 292

spruce stem residual 164 158 103 99

broad-leaved stem and bark 2127 1755 974 994

broad-leaved living branches 350 272 189 181

broad-leaved dead branches 19 16 11 11

broad-leaved foliage 75 70 55 54

broad-leaved stump 190 152 116 111

broad-leaved roots 585 505 340 342

broad-leaved stem residual 386 339 285 274

The magnitude of the average error of the estimates of the other continuous

variables at pixel level are presented below (SF = South Finland, NF = North

Finland, min = mineral soil, peat = peatland):

theme SF/min SF/peat NF/min NF/peat unit

age 26 30 47 36 a

basal area 7 7 5 5 m2/ha

mean height 52 43 38 31 dm

mean diameter 7 5 6 4 cm

canopy cover 17 17 16 15 %

canopy cover of br. l. 15 14 10 11 %

More information about the methods and the accuracies are given in the

publication: Mäkisara, K., Katila, M. & Peräsaari, J. 2022. The Multi-Source

National Forest Inventory of Finland – methods and results 2017 and 2019. Natural

resources and bioeconomy studies 90/2022, Natural Resources Institute

Finland. 73 s. http://urn.fi/URN:ISBN:978-952-380-538-5

Tietoaineistosarja

ISO19115

2003/Cor.1:2006