Comparing yesterday’s forest with today’s

In the beginning of the 1900s, the state of the forest was under debate in Sweden and other Nordic countries. People experienced a forest deficiency and some meant the forest was being over-exploited. Sweden, Norway and Finland pioneered with national forest inventories based on random sampling and a Nordic collaboration began early on. Thanks to that, there are today long, complete series of data, which are unique in an international perspective.

From firewood to habitat
In the early days of the Swedish National Forest Inventory, one county at a time was surveyed by a method called “belt inventory” (bältesinventering).

‘Belt inventory is an efficient method for sparsely occurring phenomena. At the same time we get detailed historical information on the landscape’s structure, although that wasn’t the original purpose,’ says Anna-Lena Axelsson, researcher at SLU and project leader of Historical Data of the Swedish National Forest Inventory in Umeå.

As part of the project, information on paper forms is being converted into digital format which in the long run will make the information as accessible as possible.

‘This material is unique and very valuable. The next step is to study the entire time series and ask new questions to the older material. We will be able to do that, through gradually filling the data base with all the historical information.’

But comparing yesterday’s forest with today’s has its difficulties. Over time statistical design, variable content and definitions of the inventory have changed.

Anna-Lena takes firewood for example. Earlier it was interesting to know the amount of firewood present in the forest and therefore windfalls and dry trees were inventoried. Today deadwood is inventoried for other reasons, primarily for information concerning carbon storage and biodiversity.

‘Usually it’s easiest to recalculate new data to match old data and in this way harmonise the analysis, a central and very important work,’ says Anna-Lena Axelsson.

“Semi-finished” to the interested
All data from the very first forest inventory in the 1920s are soon to be entered and quality assured. The idea is that SLU will be able to provide different combinations of basic data. SLU will also develop a number of maps illustrating changes over time. Researchers and authorities are some of the interested parties waiting to study the older material.

‘We’d love to get in touch with more researchers who would like to take advantage of this material and with whom we may collaborate,’ says Anna-Lena Axelsson.