Forest expansion as explained by climate change and changes in land use: a study from bergen, western norway

Abstract

Extensive forest expansion has taken place across Europe during recent decades. Forest expansion is also a major trend in orway, with an annual increase of about 24.6 million m³ during 2007–11. Similar trends were found in the study area at t Fløyen, ergen, western orway. Two types of forest expansion were discovered: expansion of alien coniferous tree species from plantations and spontaneous expansion of native etula pubescens. Historical data on livestock grazing and climate were used to detect possible drivers of forestation. Forest expansion started in the 1970s, in a period when average uly temperatures were lower than the period before. This is an indication that forest expansion was triggered by another cause than increasing summer temperatures. The area used to be heathland for livestock pasture but grazing came to an end around 1900. The area is well below the upper alpine forest limit and forestation should be expected when grazing ceased. The reason why forestation started so late is that neighbouring areas were also deforested. Forestation took place when trees planted in the 1950s began to produce seeds from the 1970s. During the twentieth century birch colonized steep slopes and still continues to do so in abandoned pastures. A distinct increase in uly temperatures was found since 2000, which may increase the speed of future forest expansion. This will cause a substantial increase in uptake and storage of carbon, and will decrease the need for afforestation of new open land as suggested by some governmental bodies.

Key words:

• forestation drivers
• climate change
• land‐use change

Acknowledgements

We want to thank the Fulbright program for their generous grant, which enabled the first author to study in Bergen for a year and complete this research. We also want to acknowledge useful comments from the reviewers.

Additional information

Notes on contributors

Ruth Penniston

Ruth Penniston, Department of Geography, University of Bergen, Norway, Fosswinckelsgt. 6, N‐5006 Bergen, Norway

Email: [email protected]

Anders Lundberg

Anders Lundberg, Department of Geography, University of Bergen, Norway, Fosswinckelsgt. 6, N‐5006 Bergen, Norway

Email: [email protected]