Economic consequences of altered survival of mixed or pure Norway spruce under a dryer and warmer climate

Abstract

The ecological consequences of climate change on forest ecosystems have been intensively studied in forest science. In contrast, studies on the economic performance of important tree species that investigate the financial impact of growing those species as monocultures or mixed stands are scarce. We use climate-sensitive survival probabilities to account for natural risk of tree mortality, as well as risk of fluctuating timber prices, to assess the financial performance of spruce and beech stands, pure and mixed, in the context of portfolio theory. We also compare the influence of changing climate to the impact of silvicultural options that forest owners can use to influence financial consequences: pruning spruce and avoiding planting by allowing beech to regenerate naturally. Results show that stands of pure spruce are affected by climate change through reduced mean annuities and increased standard deviation of these annuities. Admixing beech into the stands lowers this shift; by analyzing the displacement vector, we found that 7% share of beech halves the shift and a share of 49% beech reduces the length of the trajectory to 20–25%. However, the changes in risk detected for stands of spruce are relatively low compared to the influence of the silvicultural actions pruning or planting. A sensitivity scenario assuming reduced timber yields for spruce, due to climate change, and slightly increased timber yields for beech resulted massive losses in economic return in stands containing spruce. However, the economic return of spruce-dominated stands was still much higher than that of beech-dominated stands. A small admixture of beech in a spruce-dominated stand led to a comparable economic return compared to a spruce monoculture under all scenarios, with a lower level of risk.