Regional Implications: timber yield and conservation concerns
Our results imply that the composition of mid-altitude, monospecific spruce forests will become increasingly mixed over the coming decades under rapid high-altitude warming (Beniston, Diaz and Bradley 1997).P . abies comprises the majority of roundwood timber supply in many European countries, with population sizes bolstered by continental reforestation efforts since the 1950s and a longstanding preference for Picea lumber over products from mixed-deciduous forests (Fanta 1997). Picea is increasingly regarded as an unsustainable timber-species choice, due to high drought susceptibility and worsening spruce beetle outbreaks (Hanewinkel et al. 2013). In these cool-humid Carpathian Picea forests, moisture sensitivity is somewhat higher in southern locations, but the majority of these sites have actually increased in productivity over 1980-2010 (Schurman et al. 2019). However, our results imply that managers in the region wishing to maintain monospecific Picea stands will battle against improved growing conditions for species like Fagus sylvatica that are likely to outcompete Picea .
The Carpathians are among Europe’s most ecologically pristine ecoregions. In fact, sampling within fragments of primary forest throughout the Carpathians provided the rare opportunity to study a naturally occurring low-altitude range limit of Picea abies in Europe, where intense management has otherwise led to an artificial proliferation of Picea at low altitudes. The unique structural characteristics of these monospecific Picea forests, for example, disturbance patches generated by spruce beetle outbreaks, are crucial habitat elements for multiple species of high conservation value (Mikolaš et al. 2017). Critically, alpine areas conducive to monospecific Picea forests are shrinking, and the likely encroachment of low altitude tree species implies major changes to the variety of habitats found in these forests (Dirnböck et al. 2011). Determining whether species associated with monospecific spruce forests can adapt to forthcoming changes in forest composition emerges as a critical conservation priority.