The private and public insurance value of conservative biodiversity management

The ecological literature suggests that biodiversity reduces the variance of ecosystem services. Thus, conservative biodiversity management has an insurance value to risk-averse users of ecosystem services. We analyze a conceptual ecological-economic model in which such management measures generate a private benefit and, via ecosystem processes at higher hierarchical levels, a positive externality on other ecosystem users. We find that ecosystem management and environmental policy depend on the extent of uncertainty and risk-aversion as follows: (i) Individual effort to improve ecosystem quality unambiguously increases. The free-rider problem may decrease or increase, depending on the characteristics of the ecosystem and its management; in particular, (ii) the extent of optimal regulation may decrease or increase, depending on the relative size of private and external effects of management effort on biodiversity; and (iii) the welfare loss due to free-riding may decrease or increase, depending on how biodiversity influences ecosystem service provision; it increases, unless higher biodiversity greatly decreases the variance of ecosystem services. --biodiversity,ecosystem services,ecosystem management,free-riding,insurance,public good,risk-aversion,uncertainty

The economic insurance value of ecosystem resilience

Ecosystem resilience, i.e. an ecosystem’s ability to maintain its basic functions and controls under disturbances, is often interpreted as insurance: by decreasing the probability of future drops in the provision of ecosystem services, resilience insures risk-averse ecosystem users against potential welfare losses. Using a general and stringent definition of “insurance” and a simple ecological-economic model, we derive the economic insurance value of ecosystem resilience and study how it depends on ecosystem properties, economic context, and the ecosystem user’s risk preferences. We show that (i) the insurance value of resilience is negative (positive) for low (high) levels of resilience, (ii) it increases with the level of resilience, and (iii) it is one additive component of the total economic value of resilience.ecosystem, economic value, insurance, resilience, risk, risk preferences

The relationship between intra- and intergenerational ecological justice. Determinants of goal conflicts and synergies in sustainability policy

The guiding principle of sustainability is widely accepted in today´s international policies. The principle contains two seperate objectives of justice with regard to the conservation and use of ecosystems and their services: (1) global justice between different people of the present generation ("intragenerational justice"); and (2) justice between people of different generations ("intergenerational justice"). Three hypotheses about the relationship between these objectives are logically possible and are, in fact, held in the political and scientific discourse on sustainable development: independency, facilitation and rivalry. Applying the method of qualitative content analysis we evaluate political documents and the scientific literature on sustainable development by systematically revealing the lines of reasoning and determinants underlying the different hypotheses. These determinants are the quantity and quality of ecosystem services, population development, substitutability of ecosystem services by humanmade goods and services, technological progress, institutions and political restrictionssustainable development, ecosystem services, intragenerational justice, intergenerational justice, ecological justice, sustainability research

The coherent scattering function in the reptation model: analysis beyond asymptotic limits

We calculate the coherent dynamical scattering function S_c(q,t;N) of a flexible chain of length N, diffusing through an ordered background of topological obstacles. As an instructive generalization, we also calculate the scattering function S_c(q,t;M,N) for the central piece of length M < N of the chain. Using the full reptation model, we treat global creep, tube length fluctuations, and internal relaxation within a consistent and unified approach. Our theory concentrates on the universal aspects of reptational motion, and our results in all details show excellent agreement with our simulations of the Evans-Edwards model, provided we allow for a phenomenological prefactor which accounts for non-universal effects of the micro-structure of the Monte Carlo chain, present for short times. Previous approaches to the coherent structure function can be analyzed as special limits of our theory. First, the effects of internal relaxation can be isolated by studying the limit $N \to \infty$, M fixed. The results do not support the model of a `Rouse chain in a tube'. We trace this back to the non-equilibrium initial conditions of the latter model. Second, in the limit of long chains $(M = N \to \infty)$ and times large compared to the internal relaxation time $(t/N^2 \to \infty)$, our theory reproduces the results of the primitive chain model. This limiting form applies only to extremely long chains, and for chain lengths accessible in practice, effects of, e.g., tube length fluctuations are not negligible.Comment: 35 pages revtex style, 9 figures, submitted on January 5, 2002, references updated. Phys. Rev. E, to appea

The coherent scattering function of the reptation model: simulations compared to theory

We present results of Monte Carlo simulations measuring the coherent structure function of a chain moving through an ordered lattice of fixed topological obstacles. Our computer experiments use chains up to 320 beads and cover a large range of wave vectors and a time range exceeding the reptation time. -- We compare our results (i) to the predictions of the primitive chain model, (ii) to an approximate form resulting from Rouse motion in a coiled tube, and (iii) to our recent evaluation of the full reptation model. (i) The primitive chain model can fit the data for times t \gt 20 T_2, where T_2 is the Rouse time of the chain. Besides some phenomenological amplitude factor this fit involves the reptation time T_3 as a second fit parameter. For the chain lengths measured, the asymptotic behavior T_3 ~ N^3 is not attained. (ii) The model of Rouse motion in a tube, which we have criticized before on theoretical grounds, is shown to fail also on the purely phenomenological level. (iii) Our evaluation of the full reptation model yields an excellent fit to the data for both total chains and internal pieces and for all wave vectors and all times, provided specific micro-structure effects of the MC-dynamics are negligible. Such micro-structure effects show up for wave vectors of the order of the inverse segment size. For the dynamics of the total chain our data analysis based on the full reptation model shows the importance of tube length fluctuations. Universal (Rouse-type) internal relaxation is unimportant. It can be observed only in the form of the diffusive motion of a short central subchain in the tube. -- Finally we present a fit formula which in a large range of wave vectors and chain lengths reproduces the numerical results of our theory for the scattering from the total chain.Comment: 26 pages, 12 figure

Segment Motion in the Reptation Model of Polymer Dynamics. I. Analytical Investigation

We analyze the motion of individual beads of a polymer chain using a discrete version of De Gennes' reptation model that describes the motion of a polymer through an ordered lattice of obstacles. The motion within the tube can be evaluated rigorously, tube renewal is taken into account in an approximation motivated by random walk theory. We find microstructure effects to be present for remarkably large times and long chains, affecting essentially all present day computer experiments. The various asymptotic power laws, commonly considered as typical for reptation, hold only for extremely long chains. Furthermore, for an arbitrary segment even in a very long chain, we find a rich variety of fairly broad crossovers, which for practicably accessible chain lengths overlap and smear out the asymptotic power laws. Our analysis suggests observables specifically adapted to distinguish reptation from motions dominated by disorder of the environment.Comment: 38 pages in latex plus 8 ps figures, submitted to J. Stat. Phys. on September 18, 1997, please note part II on cond-mat/971006

Segment Motion in the Reptation Model of Polymer Dynamics. II. Simulations

We present simulation data for the motion of a polymer chain through a regular lattice of impenetrable obstacles (Evans-Edwards model). Chain lengths range from N=20 to N=640, and time up to $10^{7}$ Monte Carlo steps. For $N \geq 160$ we for the central segment find clear $t^{1/4}$-behavior as an intermediate asymptote. The also expected $t^{1/2}$-range is not yet developed. For the end segment also the $t^{1/4}$-behavior is not reached. All these data compare well to our recent analytical evaluation of the reptation model, which shows that for shorter times (t \alt 10^{4}) the discreteness of the elementary motion cannot be neglected, whereas for longer times and short chains (N \alt 100) tube renewal plays an essential role also for the central segment. Due to the very broad crossover behavior both the diffusion coefficient and the reptation time within the range of our simulation do not reach the asymptotic power laws predicted by reptation theory. We present results for the center-of-mass motion, showing the expected intermediate $t^{1/2}$-behavior, but again only for very long chains. In addition we show results for the motion of the central segment relative to the center of mass, where in some intermediate range we see the expected increase of the effective power beyond the $t^{1/4}$-law, before saturation sets in. Analysis and simulations agree on defining a new set of criteria as characteristic for reptation of finite chains.Comment: 19 pages in latex plus 13 ps figures, submitted to J. Stat. Phys. on September 18, 199

The Private and Public Insurance Value of Conservative Biodiversity Management

The ecological literature suggests that biodiversity reduces the variance of ecosystem services. Thus, conservative biodiversity management has an insurance value to risk-averse users of ecosystem services. We analyze a conceptual ecological-economic model in which such management measures generate a private benefit and, via ecosystem processes at higher hierarchical levels, a positive externality on other ecosystem processes at higher hierarchical levels, a positive externality on other ecosystem users. We find that ecosystem management and environmental policy depend on the extent of uncertainty and risk-aversion as follows: (i) Individual effort to improve ecosystem quality unambiguously increases. The free-rider problem may decrease or increase, depending on the characteristics of the ecosytsem and its management; in particular, (ii) the size of the externality may decrease or increase, depending on how individual and aggregate management effort influence biodiversity; and (iii) the welfare loss due to free-riding may decrease or increase, depending on how biodiversity influences ecosystem service provision.biodiversity, ecosystem services, ecosystem management, free-riding, insurance, public good, risk-aversion, uncertainty

Managing increasing environmental risks through agro-biodiversity and agri-environmental policies

Agro-biodiversity can provide natural insurance to risk-averse farmers by reducing the variance of crop yield, and to society at large by reducing the uncertainty in the provision of public-good ecosystem services such as e.g. CO2 storage. We analyze the choice of agro-biodiversity by risk-averse farmers who have access to financial insurance, and study the implications for agri-environmental policy design when on-farm agro-biodiversity generates a positive risk externality. While increasing environmental risk leads private farmers to increase their level of on-farm agro-biodiversity, the level of agro-biodiversity in the laissez-faire equilibrium remains ineciently low. We show how either one of two agri-environmental policy instruments can cure this risk-related market failure: an ex-ante Pigouvian subsidy on on-farm agro-biodiversity and an ex-post compensation payment for the actual provision of public environmental benefits. In the absence of regulation, welfare may increase rather than decrease with increasing environmental risk, if the agroecosystems is characterized by a high natural insurance function, low costs and large external benefits of agro-biodiversity.agro-biodiversity, ecosystem services, agri-environmental policy, insurance, risk-aversion, uncertainty

Ecological-economic viability as a criterion of strong sustainability under uncertainty

Strong sustainability, according to the common definition, requires that different natural and economic capital stocks have to be maintained as physical quantities separately. Yet, in a world of uncertainty this cannot be guaranteed. To therefore define strong sustainability under uncertainty in an operational manner, we propose to use the concept of viability. Viability means that the dierent components and functions of a dynamic, stochastic system at any time remain in a domain where the future existence of these components and functions is guaranteed with suciently high probability. We develop a unifying and general ecological-economic concept of viability that encompasses the traditional ecological and economic notions of viability as special cases. It provides an operational criterion of strong sustainability under conditions of uncertainty. We illustrate this concept and demonstrate its usefulness by applying it to livestock grazing management in semi-arid rangelands.capital (natural and economic), ecological-economic systems, ecosystem services, funds, stocks, sustainability, uncertainty, viability