Journal Article

Tree line shifts in the Swiss Alps: Climate change or land abandonment?

Zimmermann, Niklaus E., Gehrig-Fasel, Jacqueline, Guisan, Antoine

2007

Overview

Questions: Did the forest area in the Swiss Alps increase between 1985 and 1997? Does the forest expansion near the tree line represent an invasion into abandoned grasslands (ingrowth) or a true upward shift of the local tree line? What land cover / land use classes did primarily regenerate to forest, and what forest structural types did primarily regenerate? And, what are possible drivers of forest regeneration in the tree line ecotone, climate and/or land use change? Location: Swiss Alps. Methods: Forest expansion was quantified using data from the repeated Swiss land use statistics GEOSTAT. A moving window algorithm was developed to distinguish between forest ingrowth and upward shift. To test a possible climate change influence, the resulting upward shifts were compared to a potential regional tree line. Results: A significant increase of forest cover was found between 1650 m and 2450 m. Above 1650 m, 10% of the new forest areas were identified as true upward shifts whereas 90% represented ingrowth, and we identified both land use and climate change as likely drivers. Most upward shift activities were found to occur within a band of 300 m below the potential regional tree line, indicating land use as the most likely driver. Only 4% of the upward shifts were identified to rise above the potential regional tree line, thus indicating climate change. Conclusions: Land abandonment was the most dominant driver for the establishment of new forest areas, even at the tree line ecotone. However, a small fraction of upwards shift can be attributed to the recent climate warming, a fraction that is likely to increase further if climate continues to warm, and with a longer time-span between warming and measurement of forest cover. Nomenclature: Aeschimann & Heitz (1996).

• Publisher: Opulus Press Uppsala,Opulus Press,Opulus Press AB
• Subject: abandoned land / algorithms / Alps region / Altitude / Analysis / Climate change / Climate models / Climatic changes / climatic factors / Climatic tree line / ecological invasion / ecotones / Environmental aspects / Forest cover / Forest cover change / Forest dynamics / forest ecology / Forest ingrowth / forest mensuration / Forest regeneration / global warming / grasslands / Influence / land cover / Land use / Land use change / Montane forests / mountains / Moving window analysis / natural regeneration / Pixels / statistics / Switzerland / Timberline / Timberlines / treeline / Trees / Upward shift