Switzerland’s changing wood resources: trends from 40 years of NFI

The Swiss National Forest Inventory (NFI), with its series of measurements spanning almost 40 years, collects representative data on the Swiss forest. Launched in 1983, the NFI has since surveyed more than 6600 permanent plots and over 80 000 trees on a regular network. We are using the interim results of the fifth inventory (NFI5; surveys 2018/22, i.e. five out of nine measurement years) published in May 2023 to present the long-term trends in terms of growing stock, increment, harvesting and mortality over all the inventories for Switzerland and the biogeographical regions. On a national scale, the growing stock increased steadily between NFI1 (1983/85) and NFI4 (2009/17), with a trend towards an increase in the stock of broadleaved trees. Since then, the stock has remained more or less constant at 420 ± 5 million cubic meters. Half of this stock is found in the biogeographical regions of the Plateau and the northern slopes of the Alps. Since NFI2 (1993/95), the stock has been decreasing in the Plateau biogeographical region and increasing steadily in almost all the other regions. The Jura biogeographical region is an exception: the interim results of NFI4-NFI5 show for the first time a clear decline in growing stock and a corresponding increase in mortality (in the NFI: stemwood volume of trees that died naturally or disappeared between two inventories but were not removed for forestry). While harvesting amounts have remained relatively constant throughout Switzerland since the NFI1, at between 7 and 7.5 million m3 per year, mortality has varied greatly, both between biogeographical regions and over time. As a result of the severe winter storms of 1999/2000, the drought years from 2018 onwards and the bark beetle damage that followed, both between LFI2 and LFI3 and between LFI4 and LFI5 30–40% of loggings were sanitary fellings. This monitoring serves as a basis for forest management adapted to climate change. The NFI is therefore an important database for science, politics, forest owners, industry and the authorities.