Stochastic viability and dynamic programming

International audienceThis paper deals with the stochastic control of nonlinear systems in the presence of state and control constraints, for uncertain discrete-time dynamics in finite dimensional spaces. In the deterministic case, the viability kernel is known to play a basic role for the analysis of such problems and the design of viable control feedbacks. In the present paper, we show how a stochastic viability kernel and viable feedbacks relying on probability (or chance) constraints can be defined and computed by a dynamic programming equation. An example illustrates most of the assertions

Réconcilier production et conservation dans les paysages agricoles: importance de l'hétérogénéité

International audienceHomogenisation of agrolandscapes is one of the causes of biodiversity loss. Agrolandscapes can be described by the proportion of land uses and their spatial arrangement. If the proportion of land uses has strong implications on the productive performance of farming systems, the spatial arrangement of land uses seems to be an important way to improve ecological performances at landscape scale with minor production loss. The objective of this study was to asses the relative effects of the proportion of land uses and their spatial arrangement on ecological dynamics. We focused on the conservation of lapwings (Vanellus vanellus) in grassland landscapes. We developed a modelling approach linking grass dynamics in grazed and mown grasslands to lapwing population dynamics. We tested contrasting landscapes composed of different pairs of land uses depending on whether they compensate or complement each other. Our results show that the proportion of land uses is the first driver of population dynamics. Spatial arrangement of land uses in the landscape is an important although secondary driver of bird population trends. Managing the spatial arrangement of land uses could therefore be an important target of conservation policies. We finally discuss the importance of heterogeneity in conciliating production and biodiversity conservation

Sustainable coalitions in the commons

It is well known that the non-cooperation among agents harvesting a renewable resource is critical for its sustainable management. The present paper gives insights on the complex balance between coalitions structure, resource state or dynamics and agents’ heterogeneity to avoid bio-economic collapses. A model bringing together coalition games and a viability approach is proposed to focus on the compatibility between bio-economic constraints and an exploited common stock dynamics. It is examined to what extent cooperation promotes sustainability. Based on the Shapley value, a measure of the marginal contribution of the users to the sustainability of the resource is proposed. It suggests that the stability of the grand coalition occurs for large enough stocks. By contrast, for lower levels of resource, the most efficient user plays the role of a dictator.Renewable resource, dynamic game, coalition, maxmin strategy, shapley value, viability kernel

From fork to fish: The role of consumer preferences on the sustainability of fisheries

The increasing consumption of seafood products raises concerns over the sustainability of marine ecosystems. We examine the role of consumer preferences on seafood demand and consequently on the sustainability of fisheries. Our analysis relies on a bio-economic model combining a demand derived from a CES utility depending on different fish species, a mixed fishery supply based on the Schaefer production function, a market equilibrium and a multispecies resource-based dynamics. Using both a steady-state approach and bio-economic viability goals, we identify analytical conditions on consumer preferences making it possible to balance biodiversity conservation with viable profits. We derive policy recommendations in terms of eco-labels for the sustainability of fisheries and the underlying seafood system. We exemplify the analytical results with the coastal fishery in French Guiana

INNOVATION RIGIDITY AND ECOLOGICALECONOMIC RECONCILIATION IN AGRICULTURE

N° ISBN - 978-2-7380-1284-5International audienceFor several decades, significant changes in bird biodiversity have been reported, especially in Europe. Agriculture, and more specifically agricultural intensification, 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 and financial incentives on both the conservation of biodiversity and farming production. We therefore develop a macro-regional model combining a community dynamics of 65 bird species impacted by agricultural land-use and an economic decision model for each French region. The ecological dynamic model is calibrated with the STOC (Time Survey of Common Birds) and AGRESTE (French land-uses) databases while the economic model relies on the optimization of the gross margin of the RICA (Network of Agricultural Accountant Information). We investigate different scenarios based on subsidies and taxes to study the impact of public policies on both biodiversity and agricultural economics. We show that simple economic instruments could be used to establish scenarios promoting economic performance and bird populations. 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. We focus here on the impact of the innovation rigidity and we show that a too big innovation ability is not necessary favourable to the biodiversity because of the inertia of the biological systems

Recovering Sustainable Fisheries

In this paper, we study recovering processes for fisheries facing crisis or over-exploitation of a marine renewable resource. We examine how to restore resource stocks and modify the economic characteristics of the fleet in order to put on a sustainable exploitation system, near of some maximal standard as the Maximum Sustainable Yield. We define the sustainability of the exploitation with respect to both economic and biological constraints. Biological constraints are bases on the definition of a minimal resource stock to be preserved in order to insure the resource regeneration. Economic constraints include a minimal size for the fleet (number of vessels, which induces a social constraint on the employment) and a minimal profit per boat. We use the viability framework to consider the favorable situations of the bio-economic system in which a sustainable exploitation is possible, i.e. viable states that make it possible to satisfy the co-viability conditions in the long run, taking into account dynamical properties of the system. Along with the definition of such favorable states, we examine transition phases to reach sustainable configurations from a crisis situation. We characterize the recovering paths studying the economic cost of limiting catches during recovery period, and the length of this transition period. The developed framework makes it possible to study the sensitivity of the various constraints on that cost and time, and to minimize either one or the other. To avoid recurrence of the over-exploitation problems, we characterize sustainable decisions associated with viable states, for the dynamical evolution of the system. It includes decisions on the effort allocated to each vessel, and decisions on the modification of the size of the fleet. We develop a global model for a single resource stock. As an illustration, we study the recovering of the Nephrops stocks in the Bay of Biscay, taking into account both conceptual and applied issues

Climate-dependent scenarios of land use for biodiversity and ecosystem services in the New Aquitaine region

The synergies and trade-offs between human well-being, biodiversity, and ecosystem services are under debate for the design of more sustainable public policies. In that perspective, there is a need of quantitative methods to compare all these outcomes under alternative policy scenarios. The present paper provides scenarios at the horizon 2053 for the New-Aquitaine region in France. They rely on spatio-temporal models derived from individual land-use choices under climate change. The models are estimated at the national level from 1993-2003 fine-scale data. We focus on farming, forestry, and urban land-uses along with bird biodiversity scores and a basket of ecosystem services namely carbon sink intensity, forest recreation, and water pollution. A ‘climate-economic adaptation’ scenario shows that climate-induced land-use worsens the negative effects of climate change on biodiversity and several ecosystem services in the long run as compared to a ‘status quo’ scenario. Another scenario with an incentive policy, based on a flat payment for pastures, slightly mitigates these negative impacts on biodiversity and water pollution. However, this turns out to be detrimental for other ecosystem services. This result confirms that the design of sustainable policies can not be limited to uniform strategies and should account for the complexity of ecosystem management

How does the economic risk aversion affect biodiversity?

The present paper analyses the role played by risk aversion in the reconciling of agricultural income and biodiversity. A bio-economic mode which articulates bird community dynamics and representative farmers selecting land uses within an uncertain macro-economic context is developed. It is spatialized and calibrated at a regional scale for France through national databases. The impact of risk aversion is assessed on economic, agricultural and ecological outputs through projections at the 2050 horizon. A high enough aversion proves sufficient to promote global bio-economic performance and multi-functional agriculture. This occurs through a diversification mechanism on regional land-uses. Spatial disparities however suggest that public incentives could be necessary to reinforce the diversification and bio-economic effectiveness.Agriculture, Aversion, Bio-economic modeling, Bird, Biodiversity, Diversification, Public good, Spatial

A Stochastic Viability Approach for Ecosystem-Based Management of Mixed Fisheries: The Case of The Bay of Biscay Demersal Fisheries

Marine scientists and stakeholders are increasingly advocating ecosystembased fishery management (EBFM). However, the way to operationalize such EBFM remains controversial. The viability approach can be a relevant modelling framework for EBFM as it accounts for dynamic complexities, uncertainties, risks and sustainability objectives balancing ecological, economic and social dimensions together with intergenerational equity. Mixed fisheries operating in the Bay of Biscay provide a challenging example to illustrate these issues. The present paper focuses on the case of the demersal fisheries catching nephrops, hake, sole and monkfish. A bioeconomic multi-species and multi-fleets model is developed to examine the capacity for the stochastic viability framework to assist in developing practical approaches to EBFM. The model integrates the dynamics of the harvested stocks with an uncertain recruitment and technical interactions through joint catches. It relies on data from ICES and IFREMER. A coviability analysis of the fish populations/fisheries system is performed to investigate how to simultaneously preserve the species (using Bpa precautionary referenced points) and guarantee economic incomes for the fleets. First results suggest that the viable harvesting intensities require a significant reduction in the effort of some fleets, as compared to reference year 2006.Keywords: Bioeconomic Analysis of Fisheries, Fish and Aquaculture Sectors Development, Fisheries EconomicsKeywords: Bioeconomic Analysis of Fisheries, Fish and Aquaculture Sectors Development, Fisheries Economic