Forests are growing faster and trees are getting taller. In a recently published edition of Fakta Skog, researchers explain why.
Trees are getting taller. A 50-year-old pine or spruce is, on average, two metres taller than a similarly old tree was in the 1980s. It is a further two metres taller than a tree from the 1950s.
In Fakta Skog issue 5/2024, professor Björn Elfving and researcher Alex Appiah Mensah investigate why trees are getting taller. Says Alex Appiah Mensah:
– Our report summarises the development of tree growth during the last 40 years and compares it with other studies from around the world. This enables us to take a global view of forest growth in a time when changing practices and a changing climate affects our forest.
There are many explanations for the increased tree height, such as changing practices in forestry, a warmer climate, nitrogen emissions and increased levels of carbon dioxide in the air. Since tree height has increased equally over large regions and for multiple species, researchers hypothesize that increasing levels of carbon dioxide facilitates the water balance of trees and affects the way they grow.
The idea for the study came when then-doctorate student Alex Appiah Mensah, a researcher in forest biometrics at the department of forest resource management at SLU Umeå, met professor emeritus Björn Elfving. Professor Elfving had done extensive research on forest growth modelling in Sweden, specifically growth trends in Swedish forests between 1950 and 1993. Alex Appiah Mensah was interested in seeing how forests had developed since then. This led to a collaboration that Appiah Mensah says has enabled him to develop in both a scientific and professional sense.
In the study, Appiah Mensah and Elfving noticed that median tree height for trees of a given age had increased over time while the average growth had stayed roughly the same during the last 40 years.
– This means trees in Swedish forests have gotten taller and slimmer. The results of our report has multiple implications for site-specific forest management, says Appiah Mensah.
