The whole of Finland has been laser-scanned once, and the second round has already started. Based on laser scanning, data on forest resources in forests of each owner is available in the Finnish Forest Centre’s Metsään.fi service.
Many have asked why is the National Forest Inventory (NFI) based on data collected by the Natural Resources Institute Finland (Luke) needed in addition to this data. Would not a single method for collecting forest resources data be enough in a country like Finland?
NFI was established a hundred years ago to produce national and regional statistics in particular. From the very beginning, it has been considered important that data collection is based on appropriate and tested methods, and that data is known to be reliable.
Yrjö Ilvessalo, professor who started the first inventory, even went so far as to say that data on the average volume of trees is of no value unless it is accompanied by an estimate of the reliability of this data. Verified reliability is still a matter of honour when it comes to NFI.
Laser scanning data works best when making decisions at a forest and estate level, and NFI in national and regional decision-making. Even though results based on both sets of data can now be calculated at a municipal level, for example, the methods still have different strengths and uses.
In addition to reliability data, NFI’s most significant strength is that new results can be obtained annually over the whole of Finland, and the method ensures that there are no systematic over- or under-estimates in the results.
Another strength is the amount of measured data: more than a hundred variables are measured over each test area. When these are brought together, the resulting time series can be used to monitor the sustainability of forest use and the use of trees as carbon sinks, as well as to estimate future felling potential.
On the other hand, the strength of the laser scanning method lies in that forest data is so accurate that owners can make decisions on felling and management measures.
However, neither method guarantees that data summarised at a municipal level, for example, would not include systematic errors. They may come as a result of updates to tree growth and felling data.
Then again, updates are necessary because laser scanning data continues to be collected roughly every five years. This data is not generated into any time series, at least not yet.
As remote sensing advances, the two inventory methods may approach each other even more but, at present, two separate methods are truly necessary.
Picture on top of the page: Erkki Oksanen, Luke
Published in Finnish in Maaseudun Tulevaisuus newspaper on 22 of March 2021