Optimal Harvesting of Age-structured Fish Populations

A generic age-structured model for optimal harvesting is formulated and analyzed. The aim is to maximize utility from the harvest, net of effort cost. Yield depends on effort, catchability, and population age structure. The recruitment function is nonlinear. The age-structured model can be viewed as a generalization of the biomass approach. Comparison with the biomass model shows that the age-structured information influences the optimal steady-state population and harvest and the qualitative features of optimal transition. Pulse fishing or interior limit cycles are possible, but the optimal solution may represent a smooth, sustainable harvest even when the model is linear in effort. Linearity assumptions do not guarantee the optimality of constant escapement. If the age distribution is dominated by young age classes, the optimal yield may be lower with higher biomass. With knife-edge selectivity, the optimal steady state may become independent of the interest rate.Fisheries, bioeconomics, optimal harvesting, age-structured models, pulse fishing, Beverton-Holt population model, endogenous recruitment., Environmental Economics and Policy, Production Economics, Public Economics, Research Methods/ Statistical Methods, Q22, Q57, C61,

Taloustieteen näkökulmia metsälakiesitykseen

Tieteen tori: Metsälakiuudistu

Economics of naturally regenerating heterogeneous forests

An economic model for naturally regenerating, heterogeneous forests is specified to yield both clear-cuts and continuous cover forestry endogenously. The model includes nonconvexities and any number of state variables but is, in its simplest form, a one-state variable problem. Clear-cuts with various rotation lengths and continuous harvesting appear as locally optimal solutions. Necessary and sufficient conditions for the local and global optimality of these two forest management types are obtained. Discounting is found to increase rotation length and to favor continuous harvesting. Initial state may determine the optimality of continuous forest cover versus clear-cuts. The relative value of large trees is an important factor in the optimality of different solutions. Analytical results are demonstrated by an empirical application.Peer reviewe

Economics of multifunctional forestry in the Sámi people homeland region

We study forestry in the Sámi people homeland to understand an ongoing conflict between conventional forestry and maintaining forests as reindeer pastures vital for indigenous Sámi livelihood. Conventional logging affects pastures by creating stand densities suboptimal to lichen growth and by decreasing old-growth forest areas, both of which are essential to reindeer survivability during the subarctic winter. Our model includes timber production, carbon sequestration, externalities on reindeer husbandry, and optimization between rotation forestry and forestry with continuous forest cover. We show that the profitability of conventional forestry relies on utilizing existing forests, an outcome we label as forest capital mining. By varying the carbon price between €0 and €60 per tCO2 and assuming a 3% interest rate, we show that continuous cover forestry, which better preserves pastures, is always optimal. A carbon price of €60 − €100 chokes off timber production. Given the present management practices and an oldgrowth forest as the initial state, the carbon choke price decreases to €14–€20. Our economic analysis on maintaining old-growth forest versus conversion to timber production is an alternative to the frequently applied approach based on carbon debts and carbon payback periods.Peer reviewe

Optimal carbon storage in mixed-species size-structured forests

We extend the study of economically optimal carbon storage to a previously unexplored forest type, mixed-species size-structured stands. The ecological model applied in the study is a transition matrix model with growth functions for boreal Norway spruce (Picea abies (L.) Karst.), birch (Betula pendula Roth and B. pubescens Ehrh.), and other broadleaves. The other broadleaved trees are assumed to have no commercial value. We maximize the sum of timber revenues and the value of carbon storage by optimizing the timing and intensity of thinnings and the potentially infinite rotation age. The optimization problem is solved in its general dynamic form using gradient-based interior point methods and a genetic algorithm. We present results for a mixed stand of Norway spruce and birch, and a mixed stand of Norway spruce, birch, and other broadleaves, and compare these to a pure Norway spruce stand. We show that carbon pricing increases stand volume by postponing harvests and limiting them to larger trees, and changes the optimal species composition by increasing the share of Norway spruce relative to birch. Further, carbon pricing incentivizes maintaining other broadleaves in the stand despite their lack of commercial value, thus increasing tree species diversity. We find that sawlog and total yields increase with carbon price. We show that the higher the number of tree species in a stand, the lower the marginal cost of carbon storage.Peer reviewe

Predation costs and compensations in reindeer husbandry

Conflicts often arise when large predators and free-ranging livestock share a common area. Various compensation schemes arc used to attempt solving these conflicts, but the costs of predation to suffering stakeholders arc often unknown. Semi-domesticated reindeer husbandry and large carnivores form one such system, where conflicts between predator conservation and the traditional livelihood are common. We apply an age- and sex-structured reindeer-lichen model to examine the effects of predation on reindeer management. Based on the previous studies we specify age- and sex-class-specific mortalities due to various predators, and study optimal reindeer husbandry under predation pressure and the costs of predation. We show that the costs of predation highly depend on the age-class-specific killing rates of reindeer by various predator species, but not on interest rate or pasture conditions. Regarding species that are more likely to kill adult reindeer in addition to calves, the total predation costs are clearly higher than the net slaughtering value of the predated animals. The decrease in steady-state yearly net income is highest for the gray wolf and lower for other predator species. Adapting to predation pressure includes increasing the size of the reindeer population in winter and changing the slaughtering age of males towards young adults, thus reducing the importance of calf harvesting. This result contrasts with the previous results from stage-structured models that do not fully include time lags related to long-living ungulate species. The costs of predation appear to be much higher in an ex post system than in a territorial compensation system, as in an cx post system herders have not adapted to the predation pressure and must search for the predated reindeer to gain compensations. Our results suggest that co-existence of a viable gray wolf population and profitable reindeer husbandry in the same area is not possible in most cases.Peer reviewe

Economics of size-structured forestry with carbon storage

We study the economics of carbon storage using a model that includes forest size structure and determines the choice between rotation forestry and continuous cover forestry. Optimal harvests may rely solely on thinning, implying infinite rotation and continuous cover forestry, or both thinning and clearcuts, implying finite rotation periods. Given several carbon prices and interest rates, we optimize the timing and intensity of thinnings along with the choice of management regime. In addition to the carbon storage in living trees, we include the carbon dynamics of dead trees and timber products. Forest growth is specified by an empirically validated transition matrix model for Norway spruce (Picea abies (L.) Karst.). The optimization problem is solved in its general dynamic form by applying bilevel optimization with gradient-based interior point methods and a genetic algorithm. Carbon pricing postpones thinnings, increases stand density by directing harvests to larger trees, and typically yields a regime shift from rotation forestry to continuous cover forestry. In continuous cover solutions, the steady-state harvesting interval and the diameter distribution of standing and harvested trees are sensitive to carbon price, implying that carbon pricing increases the sawlog ratio of timber yields. Additionally, we obtain relatively inexpensive stand-level marginal costs of carbon storage.Peer reviewe