An aging population? A century of change among Swedish forest trees

Abstract

We describe a century of change in Swedish forest using trees sampled for age, diameter, volume and species by the Swedish National Forest Inventory (NFI). Changes in the structure of the tree population since 1923 are described and related to changes in policy. During the first part of the study period, policy aimed at restoring the growing stock and productivity of forest areas, but with methods that changed over time. In the last 30 years, a new forestry policy was introduced, which included restoring the diversity of tree populations, on the assumption that this will also promote biodiversity. Over the last century, and on a national scale, the volume of timber had doubled, tree sizes had increased, older trees had become more common, even more so for broadleaf species in southern Sweden. The volume of today's protected forests has almost tripled, indicating reduced light, water, and nutrients for understory vegetation. We also considered two regional cases. The sparsely populated county of Norrbotten, which was the last region in Sweden to be exploited for forestry in the 1890s, had many old pines and many old but small spruces in 1926. These were reduced in the following decades, first by selective high-grading and then by extensive clear-cutting. After a change in policy around 1990, the negative trends levelled out. In densely populated south-central Sweden, forests have long been used for grazing, timber, fuelwood and charcoal production. During the last century, the volume of timber had tripled, older trees and broadleaves have become more abundant.