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.
Optimal Continuous Cover Forest Management with a Lower Bound Constraint on Dead Wood
16/07/2020
We analyze economically optimal continuous cover forestry with dead wood as a biodiversity indicator. We study mixed-species stands consisting of Norway spruce (Picea abies L. Karst.), birch (Betula pendula Roth.), and other broadleaves (e.g., oak Quercus sp., maple Acer sp.). The analysis is based on an economic description of continuous cover forest management using an empirically estimated size-structured transition matrix model. We use size-specific decomposition rates for dead wood, with the lower limit on total dead wood volume varying between 0 and 40 m3 ha–1. The optimization problem is solved in its general dynamic form using gradient-based interior point methods. Increasing the dead wood volume requirement affects total stand density only slightly, but increases stand heterogeneity as other broadleaves are grown in higher numbers. In addition, increasing the dead wood requirement has only a minor effect on the total felled volume, but harvests shift from timber harvests to biodiversity fellings to maintain the required dead wood volume. In the optimal steady state with a high dead wood requirement, two harvesting cohorts emerge: one for timber harvests and the other for biodiversity fellings. Increasing the dead wood requirement decreases steady-state net timber income by up to 30 percent compared to the unconstrained solution.
Janne Rämö, Aino Assmuth, Olli Tahvonen, Optimal Continuous Cover Forest Management with a Lower Bound Constraint on Dead Wood, Forest Science, Volume 66, Issue 2, April 2020, Pages 202–209,
Monitoring Mixed Harvesting EconomicsOptimizing 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 Structure