Optimal detection strategies for an established invasive pest

We model optimal detection of sub-populations of invasive species that establish ahead of an advancing front. For many invaders, eradication of the main population is an untenable goal, yet it may be possible to treat and eradicate emerging sub-populations once these sub-populations are detected. We embed a dynamically optimal post-detection management plan of sub-populations into a model of optimal detection effort determination and find that optimal detection effort depends, in part, on the distance from the main front: locations closer to the front with shorter management horizons enjoy lower reductions in overall cost from intervention. The uninfested landscape is divided into two zones, characterized by different dynamically optimal management plans: a suppression zone and an eradication zone. In the suppression zone, optimal detection effort increases with distance from the front. At the distance where the suppression zone yields to the eradication zone, optimal detection effort plateaus at its maximum level.     

Sufficient conditions applied to an optimal control problem of resource management

The purpose of this paper is twofold. First, by solving an interesting problem in the theory of exhaustible resources, it is exemplified how direct sufficiency conditions should properly be used in optimal control problems. The motivation for this aspect of the paper is the almost complete negligence in the economic literature of dealing properly with sufficiency conditions. Second, an important point in the discussion of J. Aarrestad (Scand. J. Econom., 81 (1979), 522–565) is supplemented.     

Environmental amenities and optimal agricultural land use: The case of Israel

This paper evaluates the effectiveness of changing land allocation among crops as a mechanism for increasing net-social benefits, where production profits and amenity values are augmented. A positive mathematical programming model is calibrated and applied to 43 regions in the northern part of Israel, using a crop-discriminating amenity-value function. Changes in land allocation increase net-social benefits by 2.4% nationwide and by up to 15% on the regional level, where in some regions the net-social-benefits-increase/profit-loss ratio exceeds 20. Therefore, the results indicate that a policy encouraging amenity-enhancement of agricultural land use is warranted, provided that it is implemented on a regional scale, rather than as a comprehensive nationwide-enforced program.     

Some sensitivity aspects of optimal control calculations for economic systems

In this paper we consider the problem of minimizing a quadratic welfare cost function constrained by a linear macro-econometric model. First we formulate the optimal control problem in a suitable form and specify the solution. Then we consider the sensitivity of the optimal control to changes in the targets and the weights of the welfare cost function. It is shown that the targets should not be selected without reference to the selection of the weights. Next, some simulation experiments, comparing open-loop versus closed-loop controls, are briefly reported on. The effects of changes in the lag structure are also mentioned.     

Computation of non-linear continuous optimal growth models: experiments with optimal control algorithms and computer programs

In this paper we discuss the use of optimal control methods for computing non-linear continuous optimal growth models. We have discussed various recently developed algorithms for computing optimal control, involving step-function approximations, Runge–Kutta solutions of differential equations, and we suggest that the discretization approach is preferable to methods which solve first-order optimality conditions. We have surveyed some powerful computer programs by : , and for computing such models numerically. These programs have no substantial optimal growth modelling applications yet, although they have numerous engineering and scientific applications. A computer program named by is developed in this study. Results are reported for computing the Kendrick–Taylor optimal growth model using and programs based on the discretization approach. References are made to the computational experiments with and . The results are used to compare and evaluate mathematical and economic properties, and computing criteria. While several computer packages are available for optimal control problems, they are not always suitable for particular classes of control problems, including some economic growth models. The -based and , however, offer good opportunities for computing continuous optimal growth models. It is argued in this paper, that optimal growth modellers may find that these recently developed algorithms and computer programs are relatively preferable for a large variety of optimal growth modelling studies.     

Optimal control of an invasive species with imperfect information about the level of infestation

The presence of invasive species is often not realized until well after the species becomes established. Discovering the location and extent of infestation before the invasive species causes widespread damage typically requires intensive monitoring efforts. In this paper, we analyze the problem of controlling an invasive species when there is imperfect information about the degree of infestation. We model the problem as a partially observable Markov decision process in which the decision-maker receives an imperfect signal about the level of infestation. The decision-maker then chooses a management action to minimize expected costs based on beliefs about the level of infestation. We apply this model to a simple application with three possible levels of infestation where the decision-maker can choose to take no action, only monitor, only treat, or do both monitoring and treatment jointly. We solve for optimal management as a function of beliefs about the level of infestation. For a case with positive monitoring and treatment costs, we find that the optimal policy involves choosing no action when there is a sufficiently large probability of no infestation, monitoring alone with intermediate probability values and treatment alone when the probability of moderate or high infestation is large. We also show how optimal management and expected costs change as the cost or quality of information from monitoring changes. With costless and perfect monitoring, expected costs are 20–30% lower across the range of belief states relative to the expected costs without monitoring.     

Technical efficiency analysis correcting for biases from observed and unobserved variables: an application to a natural resource management project

This article brings together the stochastic frontier framework with impact evaluation methodology to compare technical efficiency (TE) across treatment and control groups using cross-sectional data associated with the MARENA Program in Honduras. A matched group of beneficiaries and control farmers is determined using propensity score matching techniques to mitigate biases stemming from observed variables. In addition, possible self-selection arising from unobserved variables is addressed using a selectivity correction model for stochastic frontiers recently introduced by Greene (J Prod Anal 34:15?C24, 2010). The results reveal that average TE is consistently higher for beneficiary farmers than the control group while the presence of selectivity bias cannot be rejected. TE ranges from 0.67 to 0.75 for beneficiaries and from 0.40 to 0.65 for the control depending on whether biases were controlled or not. The TE gap between beneficiaries and control farmers decreases by implementing the matching technique and the sample selection framework decreases this gap even further. The analysis also suggests that beneficiaries do not only exhibit higher TE but also higher frontier output.     

Bioeconomic modeling for control of weeds in natural environments

When a weed invasion is first discovered a decision has to be made on whether to attempt to eradicate it, contain it or do nothing. Ideally, these decisions should be based on a complete benefit-cost analysis, but this is often not possible. A partial analysis, combining knowledge of the rate of spread, seedbank longevity, costs of control and techniques of economic analysis, can assist in making a good decision. This paper presents a decision model to determine when immediate eradication of a weed should be attempted, or more generally whether weed control should be attempted at all. The technique is based on identifying two ‘switching points’: the invasion size at which it is no longer optimal to attempt eradication but where containment may be an option; and the invasion size at which it becomes optimal to apply no form of control at all. The model is applied to a woody perennial weed in a natural environment. The results show that seedbank longevity is the main constraint on the maximum eradicable area and spread rate is the main constraint on the maximum containment area. Stochastic simulations are undertaken to derive probability distributions of costs which are than used to evaluate the effect of budget constraints on areas that can be eradicated. We find that, in the absence of a budget constraint, it may be desirable to eradicate invasions from areas as large as 8000 ha, but when budget constraints typical of those faced by agencies in Australia are introduced, feasible eradicable areas are less than 1000 ha.     

Bio economic modeling for a sustainable management of biodiversity in agricultural lands

For several decades, significant changes in farmland biodiversity have been reported in Europe. Agriculture is a major driver of these modifications. Taking into account these environmental impacts, agriculture nowadays aims at a more sustainable way of producing which would reconcile its economic and ecological functions. The objective of this paper is to give insights into the impact of public policies on both conservation of biodiversity and farming production. We develop a macro-regional model combining community dynamics of 34 bird species impacted by agricultural land-uses and an economic decision model. The ecological dynamic model is calibrated with the STOC (French Breeding Bird Survey) and AGRESTE (French land-uses) databases while the economic model relies on the gross margins of the FADN (Farm Accountancy Data Network). We investigate the scenario based on subsidies and taxes. We show that simple economic instruments could be used to establish scenarios promoting economic performances and bird populations. It is pointed out how the sustainability of the policies is sensitive to the ecological and economic indicators used by the planner. The bio-economical analysis shows several solutions for the ecology-economy trade-off. These results suggest that many possibilities are available to develop multi-functional sustainable agriculture.     

An options based bioeconomic model for biological and chemical control of invasive species

The management of non-native invasive species is a complex but crucial task given the potential for economic and environmental damages. For many invasions the development of socially optimal control strategies requires more than is offered by the single-species, single-control models that have dominated this area of research. We develop a general stochastic optimal control framework that accommodates multiple interacting species while accounting for uncertainty in the temporal population dynamics. This extension to the current line of bioeconomic control models allows for the design of optimal integrated pest management strategies that utilize both chemical and biological controls in an environment of uncertainty and irreversibility. We demonstrate the benefits of combining chemical and biological controls in long term management strategies through a case study of the hemlock wooly adelgid (Adelges tsugae) infestation in the eastern United States. In this application we find that the introduction of natural predators is usually sufficient to manage the infestation, though chemical insecticides can play an important role when detection of the infestation is delayed or when the biological control agent does not sufficiently increase mortality of the invasive species.     

The industrial implications of an optimal reflationary mix for the British economy

This paper derives an optimal reflationary mix for the next decade and comments on the industrial implications of this policy. The discussion is based on simulations of the multisectoral dynamic model of the UK economy developed by members of the Cambridge Growth Project. The results suggest that the concentration on macroeconomic policy alone may be misguided and that instruments which attack the roots of Britain's industrial problems should receive more attention. The paper also demonstrates that the optimal control procedure is a reliable tool for steering an economy towards a desired target trajectory and that this is feasible for very large econometric models.     

Poverty and the management of natural resources: A model of shifting cultivation

It is frequently asserted in the environment/development literature that severe poverty causes the neglect of worthwhile investments, resulting in deforestation and other resource degradation. While microeconomic theory does suggest a relationship between poverty and the evaluation of investments, the environmental impact is not so simple. This paper develops a dynamic theory of “shifting cultivation,” with special attention to an environmental impact variable: the length of time a given field is cultivated before a shift to the next. The model indicates that poverty reduction will lead in some ways to accelerated extraction of a natural resource, but also to a longer extraction period. The results therefore provide support for claims of an indirect environmental benefit from the primary goal of alleviating rural poverty. The impact of discount rates, prices, and other parameters are also explored.     

Eco-efficient choice of cropping system for reducing nitrate-N leaching in an agricultural watershed

Eco-efficiency analysis framework was used to evaluate joint economic and environmentally optimal N application rates for alternative cropping systems managed in a watershed in Atlantic Canada. Eco-efficiency indexes were estimated as the ratio of economic returns from N fertilizer application to groundwater-N leaching associated with crop production. Trade-offs between crop yield and associated reduction in groundwater-N leaching were also estimated. Data for the analysis were generated using the soil and water analysis tool modeling, and allowed for evaluating crop yield and groundwater-N leaching effects for a given crop in rotations assumed to be managed at varying N fertilizer application rates. The cropping systems evaluated included: (i) corn-based cropping systems involving corn–corn–alfalfa–alfalfa–alfalfa (CCAAA, and CCCAA) rotations; (ii) potato-based cropping systems involving potato–corn–barley–potato–corn (PCBPC and PBWPC); and (iii) vegetable-horticulture cropping system involving potato–winter wheat–carrot–corn. Cropping systems were compared under conventional tillage (CT) and no-till (NT) systems. Estimated eco-efficient N fertilizer rates were substantially lower than current provincial nutrient management plan (NMP)-recommended rates, and estimated maximum economic rate of nitrogen fertilizer. However, the actual amounts depended on the crop and rotation system. CCAAA-CT was the eco-efficient choice of rotation system among the corn-based cropping systems considered. Similarly, PCBPC-CT was the eco-efficient choice among the potato-based production systems. In addition, when the NMP-recommended N rate was replaced by the eco-efficient rate for the vegetable horticulture cropping system, the eco-efficient cropping system shifted from a rotation involving CT to a NT system.     

Carbon sequestration and farm income in West Africa: Identifying best management practices for smallholder agricultural systems in northern Ghana

The interest in agricultural soils as global storage of carbon has increased in recent years, along with the prospect of farmers' participation in payment schemes under the Clean Development Mechanism of the Kyoto protocol. Thus, a better understanding of agricultural practices that can increase soil carbon and enhance the livelihoods of farmers is necessary, particularly in smallholder farming systems of West Africa. This study evaluates different crop management strategies both by their capacity to sequester carbon in agricultural soils and by their contribution to household income. A case study in Wa, Upper West Region of Ghana is used to test 48 different cropping strategies by means of a crop simulation model and a household-level multiple-criteria optimisation model. Each cropping strategy is evaluated after a 20-year simulation period by its capacity to accrue carbon in the soil, by its economic performance at the plot-level, and by its contribution to the farm income with and without carbon payments. A set of best management practices that concomitantly increase soil carbon and farm income are identified and classified by their cost of investment.     

Spatial economic analysis of early detection and rapid response strategies for an invasive species

Economic impacts from invasive species, conveyed as expected damages to assets from invasion and expected costs of successful prevention and/or removal, may vary significantly across spatially differentiated landscapes. We develop a spatial–dynamic model for optimal early detection and rapid response (EDRR) policies, commonly exploited in the management of potential invaders around the world, and apply it to the case of the Brown treesnake (Boiga irregularis) in Oahu, Hawaii. EDRR consists of search activities beyond the ports of entry, where search (and potentially removal) efforts are targeted toward areas where credible evidence suggests the presence of an invader. EDRR costs are a spatially dependent variable related to the ease or difficulty of searching an area, while damages are assumed to be a population-dependent variable. A myopic strategy in which search only occurs when and where current expected net returns are positive is attractive to managers, and, we find, significantly lowers present value losses (by $270 m over 30 years). We find further that in the tradeoff between search costs and damages avoided, early and aggressive measures that search some high priority areas beyond points of entry even when current costs of search exceed current damages can save the island more ($295 m over 30 years). Extensive or non-targeted search is not advised however.