Fig. 1. The design of the first Swedish NFI (1923–1929). Delineated areas indicate counties with year of inventory and pattern within areas visualizes distance between belts and their direction.
| Table 1. An overview of the design of the Swedish NFI at different time points. | ||
| Period | Design | Coverage |
| 1923–29 | Sampling of temporary belts 10 m wide | County-wise |
| 1938–52 | Sampling of temporary belts combined with temporary plots positioned along the center line of the belt | County-wise |
| 1953–72 | Sampling of temporary tracts, i.e. a cluster of plots where the plots are positioned along the sides of a rectangle with varying side length depending on stratum | Whole country, 1/10th annually |
| 1973–82 | Sampling of temporary tracts, i.e. a cluster of plots where the plots are positioned along the sides of a rectangle with varying side length depending on stratum | Whole country, 1/5th annually |
| 1983–92 | Sampling of temporary and permanent tracts. Permanent tracts re-measured every 5th year | Whole country, 1/5th annually |
| 1993–02 | Sampling of temporary and permanent tracts. Varying re-measurement interval | Whole country, varying from 1/10th to 1/5th annually |
| 2003– | Sampling of temporary and permanent tracts. Permanent tracts re-measured every 5th year | Whole country, 1/5th annually |
Fig. 2. The design of the Swedish NFI from 1923 onwards (T = temporary, P = permanent). The squares
are tracts (clusters of sample plots) with side-length 300–1800 m, and the circles are sample plots.
Fig 3. Changes in sample plot design from 1983 onwards for permanent (above) and temporary plots (below).
| Table 2. New and modified variables introduced in the Swedish NFI in 2003 for improved data related to sustainable wood-production. | ||
| New or modified variable from 2003 | Description | Method |
| Diameter on thickest branch (below 2 m of height) | Measured on sub-sample trees | Measurement with a slide (vernier) caliper |
| Presence of abrupt bend | Assessed on sub-sample trees | Measurement |
| Presence of long bend | Assessed on sub-sample trees | Ocular assessment |
| Height and crown height measurement | Measured on sub-sample trees | Registered in 0.1 m classes instead of 0.5 m classes |
| Height of stump | Measured on stumps | Measurement with a ruler |
| Objective elk-damage inventory (ÄBIN) | Assessment of damage/no damage caused by elk-grazing | Assessed on individual trees on sample plots (r = 3.5 m) |
| Stand damage | Assessment of the type of stand damage including cause of damage for existing stands, or previous stand if ruined due to damage | Assessed on sample plots (r = 20 m) |
| Tree damage | Assessment on sub-sample trees | Assessed on sub-sample trees separately for crown-, stem-, cambium- and root damages |
| Table 3. New and modified variables introduced in the Swedish NFI in 2003 for improved data on biodiversity and wildlife. | ||
| New or modified variable from 2003 | Description | Method |
| Presence of traces from woodpeckers | Presence/absence registration | Assessment on sub-sample trees and on dead wood objects |
| Presence of Polyporus fungi | Presence/absence registration including species | Assessment on sub-sample trees and on dead wood objects |
| Assessment of vegetation on dead trees and logs | Assessment of coverage | Assessment on dead wood objects |
| Assessment of distance to the ground | Measurement of distance to ground | Measurement on logs with a ruler |
| Additional class of decomposition on dead wood: Newly dead | Assesment of decomposition class | Assessment on dead wood objects |
| Bark-coverage on dead trees and logs | Assessment | Classes 0–100% |
| Ant-hills | Presence of ant-hills | Measurement of diameter and height |
| Large trees and retention trees (abandoned 2008) | Presence of large trees (definition see Fig. 3) | Registration of species and measurement of dbh |
| Presence of ground- and bottom flora | Short list of species (22 species or species groups) | Performed on 2 sub-plots (r = 0.28 m) Height above ground recorded for lichens. Flowers/berries counted on plants of Vaccinium vitis-idea and V. myrtillus |
| Crown cover | Vertical projection of tree crowns in %. Over-coverage not considered | All living trees included, bushes not included |
| Area of land-use class | To fulfill international reporting where minimum area is often included | Area based on map- and ocular studies registered |
| New sampling design for measurement of dead wood | Point of germination or thickest end defined as point of inclination | All lying objects included if point of inclination is within the sample plot, i.e. part outside plot included |
| Inventory within reserves | Ordinary field work also on plots within National parks and Nature reserves (excluded before 2003) | Identical sampling scheme as for plots outside these areas |
| Performed forestry measures registered also on unproductive forestland | Before 2003 only registered on productive forestland | Identical methods to those used for plots located on productive forestland |
| Registration of cause of felling | If felling of trees are registered on a plot, also cause is registered | Three categories: Normal felling, Clearing after severe damage, Nature conservation |
| Modified procedures for registration and assessment of tree-layers | Maximum three layers, presence of all occurring tree species in % of total number of stems or basal area (depending on height) | Regardless of how small proportion a tree species amount to, it´s occurrence is indicated registering 1% |
| Stand-attributes also registered on unproductive forestland | Stand-age, mean height, basal area, tree species composition | Identical methods to those used for plots located on productive forestland |
| Forest stands suitable for selective cutting | Included as a separate cutting class | - |
| Number of occurrences of elk-droppings | Counted (r = 3.5 m). Before 2003 r = 5.0 m | - |
Fig. 4. Outline of the Swedish NFI reporting and analysis system. View larger in new window/tab.