When is it optimal to eradicate a weed invasion?
When a weed invasion is discovered a decision has to be made as to 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. Partial analysis, combining knowledge of the demographics of the weed and economic techniques, can assist in making the best decision. This paper presents a general conceptual model to decide when eradication of a weed should be attempted. Decision rules are derived based on a few parameters that represent the rate of spread, the cost of controlling the invasion, and the cost of damage caused by the invasion. These decision rules are then used to identify the 'switching point' - the invasion size at which it is no longer optimal to attempt eradication. The decision rules are used to estimate the optimal duration of the eradication effort depending on the current size of the invasion. Sensitivity analysis is undertaken and the possibility of characterising an invasion based on five parameters is discussed.
Applying search theory to determine the feasibility of eradicating an invasive population in natural environments
The detectability of invasive organisms influences the feasibility of eradicating an infestation. Search theory offers a framework for defining and measuring detectability, taking account of searcher ability, biological factors and the search environment. In this paper, search theory concepts are incorporated into a population model, and the costs of search and control are calculated as functions of the amount of search effort (the decision variable). Simulations are performed on a set of weed scenarios in a natural environment, involving different combinations of plant longevity, seed longevity and plant fecundity. Results provide preliminary estimates of the cost and duration of eradication programs to assist in prioritising weeds for control. The analysis shows that the success of an eradication program depends critically on the detectability of the target plant, the effectiveness of the control method, the labour requirements for search and control, and the germination rate of the plant.
Mariculture of giant clams, 'Tridacna crocea' and 'T. derasa': management for maximum profit by smallholders in Solomon Islands
The International Center for Living Aquatic Resources Management (ICLARM) has demonstrated that coastal village communities in Solomon Islands can successfully farm giant clams. The production technology is simple and does not require a large capital investment. The main inputs are clam seed, labour and time. Labour is used for activities such as planting, cleaning, thinning and harvesting. In this paper, a bioeconomic model is used to explore optimal farm management for two species of giant clam fanned for the aquarium and seafood markets. The theoretical basis for this analysis is found in the economic theory of optimal forestry exploitation. Optimal management involves finding the combination of the decision variables and the cycle-length that maximises a stream of discounted profits. The decision variables considered here are husbandry which relates to cleaning, and the frequency with which thinning is undertaken. The optimal cycle-length is determined for both a single clam harvest and multiple harvests for various management scenarios. The labour requirements for these management scenarios are identified for the multiple-harvest case and input substitution between optimal combinations of labour and cycle-length is investigated. Results indicate that profits are maximised for both species when husbandry is excellent and labour usage is most intensive. Thinning is only necessary for seafood clams for which the optimal cycle-length is longer. Village farmers may not be profit maximisers however, and labour spent on giant-clam farming takes them away from other activities. Rather than investing more labour and harvesting the clams earlier, a village farmer with other objectives may devote less labour and harvest the clams later, and spend more time on other activities. In general, these results are consistent with extension advice provided to village farmers by ICLARM. Optimal solutions were found to be very stable when incorporated into global optimisation routines and sensitivity analysis of a wide range of parameter values.
Postharvest losses at the farm level and its economy-wide costs: the case of the maize sector in Mozambique
With increasing population and demand for food, reducing food loss and waste is one of the greatest challenges worldwide. Current estimates point to over 1 billion tons of food lost and wasted worldwide, though nearly 10 percent of the global population is suffering from undernourishment and food insecurity. In Mozambique, about one-quarter of the population suffers from undernourishment and food insecurity. Estimates from FAO point to postharvest losses of maize in Mozambique at about 3.69 to 7.92 percent; this is less than one-fifth of the on-farm losses reported by other authors. In this study, an Equilibrium Displacement model is used to assess the economy-wide impact of postharvest losses of maize at the farm level. The impact of a 3 percent postharvest loss is tested. Results suggest that even this very conservative percentage of postharvest losses has a direct annual net cost of around $USD 28 million for both farmers and consumers domestically. This is equivalent to over 1 percent of the national budget. It is also higher than the average cost of food aid programs received over the last three years. Therefore, reducing postharvest losses of maize along with other interventions is crucial to achieve sustainable development and economic growth.
Evaluating Apple Orchard Management using a Bioeconomic Model
Managers of deciduous perennial fruit crops must consider both biological and economic relationships in determining orchard design and life-time orchard management strategies. Orchardists require a good understanding of the many environmental, physiological and horticultural factors that influence tree growth, fruit production and fruit quality. Of particular importance in apple-tree management is knowledge of how the growing environment and horticultural manipulation of past years affect current and future growth habits and productivity of the tree. In addition to understanding biological factors that influence apple-tree productivity, a diverse range of orchard systems are currently available to orchardists. Each system, consisting of a particular combination of cultivar, rootstock, tree spacing and training method, has implications for fruit quality, quantity and ultimately profit. A dynamic simulation model of apple orchard production is developed in this research, and used to investigate a range of issues of relevance to the commercial apple orchardist. The model is developed in a bioeconomic framework and consists of biophysical and economic components. The biophysical component describes the vegetative and reproductive physiology of an apple tree, factors affecting the quantity and quality of apples produced and interrelationships between these factors. The economic component describes the costs and revenues associated with each orchard system from planting to maturity.
Economic evaluation of the management of bitou bush ('chrysanthemoides monilifera' subsp. 'rotundata'(DC.) T.Norl.) to conserve native plant communitites in New South Wales
The bitou bush ('Chrysanthemoides monilifera' subsp. 'rotundata' (DC.) T.Norl.) Threat Abatement Plan (TAP) aims to reduce the impacts of bitou bush on biodiversity in New South Wales. This is the first weed TAP in Australia and so its effectiveness in conserving threatened biodiversity, as well as its cost of implementation, must be examined to determine if this new approach should be adopted as a template for managing the biodiversity impacts of other major weed species. We therefore consider the question 'is the TAP a good investment in relation to protecting biodiversity'? We combine the costs of implementing the TAP with conservative, published estimates of the benefits of protecting biodiversity, to calculate the benefit-cost ratios of the investment. The ratios indicate that the benefits of the TAP exceed the costs under a wide range of economic conditions. While this result supports the approach, the cost of implementation should be analysed over the five years relative to the biodiversity outcomes in order to determine the ex post benefit of the TAP.
Simulating the impact of fertiliser strategies and prices on the economics of developing and managing the Cicerone Project farmlets under climatic uncertainty
The application of fertilisers to pastures in the high rainfall regions of southern Australia has contributed to large increases in carrying capacity following the widespread adoption of the practice since the late 1940s. Recently, large shifts in the worldwide demand for fertiliser inputs have lead to large rises in the cost of fertiliser inputs. These increasing costs have significant potential ramifications on the future management of soil fertility and its interaction with the persistence and profitability of sown pastures, especially during periods of climatic uncertainty. Adynamic pasture resource development simulation model was used to investigate the implications of fertiliser rates and costs on the efficient management of soil fertility under climatic uncertainty. The framework also allowed the investigation of how the management of soil fertility interacts with the utilisation of pasture resources through different stocking rates. In the application of this method to the Cicerone Project farmlets case study, fertiliser input costs were found to influence the optimal combination of fertiliser inputs and stocking rate. Analyses of the dynamic interaction between fertiliser application and cost, stocking rate and the persistence of desirable species enabled the identification of the most risk-efficient strategies. The implications for grazing industries in the high rainfall regions of southern Australia are discussed.
A Stage Matrix for 'Miconia calvescens' in the Wet Tropics of Australia: Implications for Management
A stage matrix for 'Miconia calvescens' under Australian conditions is presented in this paper. The matrix contains eight stages - new seeds, seed bank, four juvenile stages, and two adult stages - reflecting the growth habit of 'M. calvescens' in tropical Australia, where it takes at least four years for a plant to reach maturity and where there are large differences in seed production between small and large adults. Life cycle analysis of the stage matrix is undertaken to give details of important events in the growth of this species, including age-specific survival and fecundity. Sensitivity and elasticity analyses are used to indicate the relative contributions of life stages to population growth. This information can be useful in planning control programs.
Carbon-accounting methods and reforestation incentives
The emission of greenhouse gases, particularly carbon dioxide, and the consequent potential for climate change are the focus of increasing international concern. Temporary land-use change and forestry projects (LUCF) can be implemented to offset permanent emissions of carbon dioxide from the energy sector. Several approachesto accounting for carbon sequestration in LUCF projects have been proposed. In the present paper, the economic implications of adopting four of these approaches are evaluated in a normative context. The analysis is based on simulation of Australianfarm–forestry systems. Results are interpreted from the standpoint of both investors and landholders. The role of baselines and transaction costs are discussed.
Benefits and costs of deforestation by smallholders: Implications for forest conservation and climate policy
Deforestation is a leading cause of biodiversity loss and an important source of global carbon emissions. This means that there are important synergies between climate policy and conservation policy. The highest rates of deforestation occur in tropical countries, where much of the land at the forest frontier is managed informally by smallholders and where governance systems tend to be weak. These features must be considered when designing policies to reduce emissions from deforestation such as REDD +. Deforestation is often accompanied by fires that release large amounts of carbon dioxide. These emissions are especially high in the case of peatlands which contain thick layers of carbon-rich matter. In this paper we derive marginal abatement cost (MAC) curves using data from a farmer survey in Sumatra, where rates of peatland deforestation are high. Comparing these results with farmers' stated willingness to accept payment not to clear forest to establish oil palm suggests that REDD + policies may be more expensive than MAC estimates suggest The extent to which this is true depends on the types of soils being deforested.