Spatio-temporal patterns of birch regrowth in a Western Norwegian treeline ecotone

Abstract

The study investigates spatio-temporal patterns of birch regrowth in a mountain valley in which intensive livestock grazing was formerly practised. Vegetation changes were identified through analysis of three sets of aerial photographs. The results of GIS analyses, one-way ANOVA and PCA showed that regrowth patterns are complex. In the early phase of succession, grazing history has a strong impact on where new forest establishes, both at a distance from the seasonal farmsteads where grazing intensity prior to abandonment was highest, and close to previously existing forest. Sprouting is most likely to be the dominating regeneration strategy in this early phase. In a later phase of succession, the impact of grazing history on forest distribution patterns decreases, as exemplified by the increasing distance from existing forest. The largest amounts of birch forest then establish in warm locations with moderate moisture. Protection against wind appears to be important for birch establishment.

Keywords:

• Aerial photographs
• Betula pubescens ssp. czerepanovii
• maritime climate
• mountains
• seasonal farming

Acknowledgements

Thanks are due to Sebastian Eiter for help during fieldwork, and to Timo Ikola and Hanne Gro Wallin for technical support for the production of orthophotos. Ole Reidar Vetaas and Anders Bryn contributed with discussions of statistical issues and the latter additionally with valuable comments on the manuscript. Kjell Helge Sjøstrøm kindly helped to prepare Figure 1. Thanks are also due to three anonymous reviewers for their valuable feedback.