Quantifying the target state of forest stands managed with the continuous cover approach – revisiting Möller's “Dauerwald” concept after 100 years
16/07/2020
Continuous cover forestry is often considered a management alternative to age-class forestry, in closer compliance with economic as well as societal demands. It is further thought to provide forest stands of high stability and resilience under conditions of climate change. The guiding principle for the stand structure of continuous cover forestry systems is to create managed forest stands that are multi-layered and hence of high structural diversity. Past studies of both these characteristics have been mostly qualitative. Here we used data from terrestrial laser scanning (TLS) to quantify differences in stand structure between forests managed for decades according to the continuous cover concept and forests managed otherwise. We found that the vertical distribution of plant material in the continuous cover stands was relatively homogeneous and similar to the vertical distribution found in primary European beech forests. We also found that the structural complexity of continuous cover forests was significantly higher than that of even-aged monocultures of Scots pine and Norway spruce. Based on these findings, a scaled index was developed that quantifies structural attributes of TLS point clouds and can significantly distinguish continuous cover forests from even-aged forests. This index may be a useful tool to quantify the difference in structure of a given continuous cover forest stand from a “target structure”, meaning the theoretical structure describing an ideal continuous cover forest.
Optimizing continuous cover and rotation forestry in mixed-species boreal forests
01/05/2020
We study the management of mixed-species boreal forests and tree species composition in a stand-level economic-ecological, size-structured model. The model includes ecological tree species interaction, a detailed harvesting cost module, optimal harvest timing, and optimization between continuous cover and rotation forestry. Optimization is solved applying a tri-level structure, in which the optimal rotation is the highest-level, harvest timing the middle-level, and thinning intensity the lowest-level problem. Given realistic regeneration costs and a 3% interest rate, continuous cover forestry is optimal and may include up to a 40% fraction of broadleaves. A low interest rate and low regeneration cost together with the presence of light-demanding Scots pine favours rotation forestry. Eurasian aspen decreases the bare land value but is optimal to fell without utilization only when it has no commercial value. Overyielding in terms of cubic metre output does not reveal the economically preferable species combination. Managing single-species stands by removing naturally regenerated other species decreases the economic outcome by 35-44%. Felling noncommercial trees without utilization shows that the economically optimal solution avoids “high-grading”. Maintaining the number of large-diameter trees beyond the level that maximize profitability implies only minor losses. Omitting thinning decreases the bare land value up to 73%.
Mixed Boreal Harvesting Economics Stand StructureGrowth dynamics of the Norway spruce and silver fir understory in continuous cover forestry
05/02/2020
The conversion to uneven-aged, mixed-species stands represents one possible way to mitigate the consequences of disturbances in Norway spruce forests in Central Europe. A better understanding of the establishment and growth dynamics of the understory can contribute to a more effective conversion process. Here we investigate the structure of understory, light climate and growth of natural regeneration of Norway spruce and silver fir in two forest stands undergoing conversion to continuous cover forestry. Stand-wise forest inventory was conducted in 1993 and 2013. The natural regeneration was surveyed, and the light conditions and inter-tree competition were quantified in 51 sample plots established across the stands in 2013. Our results suggest that the diffuse radiation strongly affects the height growth of fir and spruce natural regeneration. We do not confirm the effect of local sapling density on the regeneration dynamics. The results further show that fir trees grow faster than spruce under less intensity of diffuse light. Most of the spruce and fir trees reached the upper limit of the lower overstory (DBH 12 cm) at approximately 50 years of age. Thus, more substantial reductions in stand density can lead to a well-differentiated structure in less than five decades. To control the prospective representation of spruce and fir in mixed-species forests undergoing the conversion, managing of light conditions is crucial.
Transformation Conifer Stand Structure