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Mountain spruce forests in Central Europe decline under storms and bark beetle calamities driven by climate change. A stabilisation by planting rare or missing tree species is expensive and requires funding. A funding policy should mitigate climate change and support biodiversity. The goal of this study was to identify a conversion strategy of even-aged spruce-dominated forest stands to uneven-aged mixed stands with spruce (Picea abies (L.) H.Karst.), beech (Fagus sylvatica L.), and fir (Abies alba Mill.). A simultaneous nonlinear optimisation of the number of planted trees and harvested trees per species and per period schedules stand treatments aiming to maximise the long-term financial outcome. Planting modelling extends a density-dependent stand-level matrix transition model based on diameter classes with an age-class-based model for artificial regeneration. An optimal conversion strategy was applied for five funding policy schemes, each for five initial states representing different stages of age and species composition typical for spruce forest conversion in the mountain zone of the Western Carpathians. Only 50% and higher funding of planting costs for the minor/missing fir and beech species facilitates a substantial increase of their shares in stand volume. Funding decreases the volume failure due to mortality. Funding increases the standing and harvested volume, which mitigates climate change by increasing the carbon sequestration. Funding causes unintended effects on ecosystem services by lowering harvest diameters, decreasing the volume of less profitable beech, and temporarily reducing the stand density aimed at supporting plantings and their diameter increments. [ABSTRACT FROM AUTHOR]

Abstract: A new modeling approach which combined survival probabilities for spruce with financial optimization showed a considerably reduction in financial risk in spruce (Picea abies [L.] Karst.) stands with an admixture of a 20% proportion of beech (Fagus sylvatica L.). The admixture enhanced the stability of the spruce component against natural hazards, such as storm or insect damage. Here, these new survival investigations were integrated into a bio-economic modeling approach called silvicultural economics. A new failure model which includes the benefits of ecological interactions for decreasing hazard risk for spruce was developed. The modeling technique is based on Monte-Carlo-Simulation and on simultaneous portfolio optimization of management strategies under risk. Area proportions were allocated as decision variables to each tree species and to regeneration harvests at various points in time in order to achieve the maximum financial return given a predefined, acceptable risk. The simultaneous optimization led to a mixed – and, through long regeneration periods – to an uneven-aged forest stand, for almost all predefined risk-levels. In addition, for a selection of possible even-aged tree species compositions, a stand-level mixture (including the species interactions of the new model) was compared with the same species proportion at the stand level, but consisting of two separated parts of spruce and beech (thus excluding species interactions). For all even-aged and interacting mixtures that were investigated, a higher expected return and a lower financial risk were achieved when compared to the identical even-aged mixture proportions without interactions. When the timing and distribution of regeneration harvests was also optimized (as opposed to using a clear-cut strategy) there was a slight loss in financial return, but the reduction in risk was even greater, given the same tree species proportion – especially in cases with a low beech admixture. Compared to the simulation which excluded the stabilizing effect of beech on spruce, the variant with interacting tree species allowed for higher spruce proportions and shorter regeneration cycles for the same acceptable risk. [Copyright &y& Elsevier]