Below-ground response of Norway spruce to climate conditions at Mt. Brocken (Germany)—A re-assessment of Central Europe's northernmost treeline

Alpine treelines at medium high mountains are less abundant and thus have been less frequently studied than at high-elevation mountain ranges of the world. We studied mature Norway spruce stands along an extended elevation transect at Mt. Brocken (Harz Mountains, Central Germany) to analyse the altitudinal changes in climate-related growth conditions, and to evaluate the prevailing climate conditions at the treeline of medium high Mt. Brocken. A particular aim was to analyse the change in fine root biomass partitioning along the transect towards the treeline. Microclimate conditions at the treeline of Mt. Brocken were very similar to other treeline sites worldwide. Tree height and stem biomass strongly decreased from middle elevations towards the treeline. On the contrary, fine root biomass and the ratio of fine root/stem biomass strongly increased towards the treeline indicating a marked shift in carbon allocation in favour of the fine root system with elevation. A meta-analysis of literature data revealed that the elevation-related increase in dry mass partitioning to the fine root system is a general phenomenon for Norway spruce stands in northern and central European mountains. We conclude that the particularly large fine root system of Norway spruce at cold sites represents a mechanism to cope with unfavourable soil conditions such as reduced or temporally variable nutrient supply.