Abstract
We developed an uneven-aged forest economic decision-making framework that combines: (i) a size-structured matrix model, based on growth and mortality predictions of a dynamic process-based forest landscape model, (ii) an optimal control model that determines the dynamics of control and state variables, which in turn are defined by tree harvesting and forest stock, respectively, and (iii) a water yield function that depends on changes in the leaf area index (LAI), the latter being affected by forest management. This framework was used to simulate the effects of economic-driven harvesting decisions on water yields on a catchment of South-Western Swiss Alps when both timber and water benefits are considered. Water benefits are estimated as environmental prices considering current water demands for drinking, irrigation and hydropower production. We simulated optimal harvesting decisions given the initial forest structure at each 200 m × 200 m grid cells, a set of restrictions to harvesting, and specific species survival, recruitment and growth probabilities, all of which are affected by the stand’s LAI. We applied this model using different harvesting restriction levels over a period of 20 to 40-years, and accounting for single and joint timber and water benefits. The results suggested that at the environmental prices estimated at the catchment area, water benefits have a slight influence on harvesting decisions, but when water is accounted for, harvesting decisions would include more tree species and different diameter classes, which, in principle, is expected to favor more diverse forest structures.
Highlights
Optimization of forest resources has received considerable attention for many decades, in particular since the reintroduction of the Faustmann [1] forest optimal rotation model by PaulSamuelson [2]
Each LAI class is defined by specific leaf area index and allometric parameters [45] that relate diameter at breast height (DBH)
This section presents and discusses the results of the optimizations modeling framework. Those results include the estimation of the parameters of the forest growth matrix models (Tables 4–6, and Figure 2). This includes an interpretation of the results comparing optimal harvesting decisions and the resulting forest structures with different restriction levels to harvesting over time, and when both single or joint timber and water benefits are considered (Figures 3 and 4 )
Summary
Optimization of forest resources has received considerable attention for many decades, in particular since the reintroduction of the Faustmann [1] forest optimal rotation model by PaulSamuelson [2]. In its more generic form, the Faustmann model aims to determine the optimal length of time between tree clearcuts, considering a chain of identical even-aged tree cohorts [3]. The Faustmann model has been extended in numerous papers, serving as the base in many research and practical forestry applications, see [4] for a review. Demands for a more sustainable forestry is increasing the interest in alternative forest management practices. This is encouraging a shift back from even-aged forest management practices, based on clearcuts, to uneven-aged forest management strategies, based on selection cutting of individual trees or small groups of trees, and natural regeneration [5,6]. Uneven-aged forest management models are in general more complex than the even-aged ones. The multiple species and age classes involved in uneven-aged mixed forest stands expand
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