Publications des chercheurs de PSE

Cet article réexamine le problème dit du "vaisseau spatial", c'est-à-dire la définition de la population optimale sous la contrainte d'un espace de vie donné, en mettant l'emphase sur le dilemme existant entre l'ajout de nouveaux êtres et l'extension de la durée de vie d'êtres déjà existants. A cette fin, nous caractérisons, sous l'hypothèse d'un bien-être sur la vie additif à travers le temps, et d'un bien-être temporel affecté négativement par la densité de population, les préférences d'un planificateur social utilitariste sur les histoires à temps de vie égal, c'est-à-dire des histoires dont les variables démographiques sont telles qu'un nombre fini égal de périodes sont vécues au total dans chacune de celles-ci (ce nombre étant imposé par des contraintes de ressoures). L'analyse du problème du vaisseau spatial contredit des croyances répandues sur le prétendu populationnisme de l'utilitarisme classique, ainsi que sur l'antipopulationnisme de l'uilitarisme moyen. Nous étudions également l'invariance des rangements utilitaristes à l'espace total disponible pour la vie, ainsi qu'aux préférences individuelles. Enfin, nous comparons des histoires pour un vaisseau avec des populations stationnaires égales, et tentons d'accommoder l'intuition de postérité d'une population avec celle du renouvellement d'une population.

Many countries are formalizing customary land rights systems with the aim of improving agricultural productivity and facilitating community forest management. This paper evaluates the impact on tree cover loss of the first randomized control trial of such a program. Around 70,000 landholdings were demarcated and registered in randomly chosen villages in Benin, a country with a high rate of deforestation driven by demand for agricultural land. We estimate that the program reduced the area of forest loss in treated villages, with no evidence of anticipatory deforestation or negative spillovers to other areas. Surveys indicate that possible mechanisms include an increase in tenure security and an improvement in the effectiveness of community forest management. Overall, our results suggest that formalizing customary land rights in rural areas can be an effective way to reduce forest loss while improving agricultural investments.

This paper presents a first model integrating the relation between biodiversity loss and zoonotic pandemic risks in a general equilibrium dynamic economic set-up. The occurrence of pandemics is modeled as Poissonian leaps in economic variables. The planner can intervene in the economic and epidemiological dynamics in two ways: first (prevention), by deciding to conserve a greater quantity of biodiversity to decrease the probability of a pandemic occurring, and second (mitigation), by reducing the death toll through a lockdown policy, with the collateral effect of affecting negatively labor productivity. The policy is evaluated using a social welfare function embodying society’s risk aversion, aversion to fluctuations, degree of impatience and altruism towards future generations. The model is explicitly solved and the optimal policy described. The dependence of the optimal policy on natural, productivity and preference parameters is discussed. In particular the optimal lockdown is more severe in societies valuing more human life, and the optimal biodiversity conservation is larger for more “forward looking” societies, with a small discount rate and a high degree of altruism towards future generations. Moreover, societies accepting a large welfare loss to mitigate the pandemics are also societies doing a lot of prevention. After calibrating the model with COVID-19 pandemic data we compare the mitigation efforts predicted by the model with those of the recent literature and we study the optimal prevention–mitigation policy mix.

Since the 1960s, the increased availability of modern seed varieties in developing countries has had large positive effects on households’ well-being. However, the effect of related land use changes on deforestation and biodiversity is ambiguous. This study examines this question through a randomized control trial in a remote area in the Congo Basin rainforest with weak input and output markets. Using plot-level data on land conversion combined with remote sensing data, we find that promotion of modern seed varieties did not lead to an increase in overall deforestation by small farmers. However, farmers cleared more primary forest and less secondary forest. We attribute this to the increased demand for nitrogen required by the use of some modern seed varieties, and to the lack of alternative sources of soil nutrients, which induced farmers to shift towards cultivation of land cleared in primary forest. Unless combined with interventions to maintain soil fertility, policies to promote modern seed varieties may come at the cost of important losses in biodiversity.