Multiple Use Management of Tropical Forests: On the Superiority of Land Use Specialization

One of the debates in tropical forest management centers on how to manage these resources for multiple uses. In fact, although the need to account for multiple values in forestry decisions is widely recognized, its implications for forest management are not clear. In particular, how is multiple-use to be achieved? Should management for multiple values be adopted on each forest management unit? Or should multiple use be attained at the landscape level, for example by dividing the landscape into units and manage each unit for a dominant use (e.g., timber production, conservation, etc.)? In tropical forest settings, where multiple use is often attained with less intensive harvesting and at the expenses of bringing larger – often virgin – areas into production, the circumstances under which multiple-use management is superior to dominant-use remain unclear. Past scholarly work has pointed to some circumstances under which dominant use may be superior to multiple (joint) use. The empirical significance of these circumstances has been quantified only in limited temperate settings. In this paper, we review two circumstances that are likely to yield to a non-convexity in the forest production set: the existence of large fixed costs associated with the production of one good (e.g., timber); and the existence of inefficiencies in the timber production process. The empirical significance of such circumstances is evaluated with the aid of a simulation model developed for a lowland tropical forest in peninsular Malaysia. Results suggest that, for certain benefits associated with forest diversity, specialized use (separation of conservation and timber production processes) is likely to be a strategy superior to multiple use.tropical forests, multiple use, specialization, non-convexities, biodiversity, carbon storage

Promoting better logging practices in tropical forests

The study presented in this paper tests the empirical significance of several common recommendations for promoting better logging practices in tropicalforests: in particular, making concession agreements longer, linking renewal of those agreements to logging practices, and using performance bonds to encourage compliance with logging regulations. It assesses how these recommendations affect both the economics of timber harvesting and the provision of environmental benefits. With regard to the latter it focuses on carbon sequestration and biodiversity. It also examines the effects of timber fees and discount rates on economic and environmental outcomes. The study focuses on two aspects of logger behavior: choice of logging technology and compliance with prescribed minimum diameter cutting limits. The study analyzes loggers'decisions about technology and cutting limits in two scenarios: (i) the repeated harvesting of a given forest stand (virgin forest for the initial harvest, second growth forest for subsequent harvests), which occurs at a time delay of several decades (the cutting cycle); and (ii) the sequential harvesting of an annual series of different forest stands with identical characteristics (all virgin). The former gets at issues of sustainable forest management, while the latter gets at the mining of virgin timber stocks. In this way, the study examines both the long-run and short-run dynamics of logger behavior. The paper is organized as follows. The authors begin by describing the models of forest growth and logger behavior that comprise the simulation model. The description of the forest growth model includes the indicators used to predict the environmental impacts of logging, and the description of the model of logger behavior includes the regulatory instruments analyzed. Next, they present and discuss the simulation results, dealing with repeated harvesting and sequential harvesting in turn. In the final section the report highlights the principal conclusions that can be drawn from these results.Forests and Forestry,Environmental Economics&Policies,Water Conservation,Silviculture,Agribusiness,Environmental Economics&Policies,Agricultural Trade,Agribusiness,Forestry,Silviculture

Marine refrigeration plants for passenger ships:Low-GWP refrigerants and strategies to reduce environmental impact

This paper is devoted to the evaluation of the use of low-GWP refrigerants in marine provision plants for cruise ships.We present the state of the art of current refrigeration plants, and we identify ammonia (NH3), carbon dioxide (CO2), and the HFOs R1234yf and R1234ze(E) as the most promising low-GWP refrigerants adequate for the marine refrigeration systems considered in the paper. Single-stage, two-stage and cascade plant configurations are examined, and the performances of the different alternatives are evaluated through simulations. The results are analyzed, and the performances are compared with those of the current systems with R407f: in the comparisons we consider COP, volumetric capacity, safety and environmental impact.We conclude that switching from current technologies to systems using low-GWP refrigerants entails a worsening of the performances in at least one of the areas considered. Moreover, we observe that the reduction of the GWP value of the refrigerants is not an effective strategy to diminish the total environmental impact of the refrigeration systems considered

Frenamento magneto-rotazionale ed evoluzione delle pulsars nel piano P-Pdot

Attraverso un semplice modello di frenamento magneto-rotazionale che consideri anche il progressivo allineamento tra l’asse di rotazione e l’asse del dipolo magnetico in una pulsar, con un tempo caratteristico τA di 10 milioni di anni, è possibile riprodurre in modo soddisfacente attraverso simulazioni Monte Carlo la distribuzione delle pulsars isolate nel piano P − Pdot e l’evoluzione temporale della popolazione. In questo quadro, l’evoluzione di una pulsar è formata dalla successione di due fasi: la prima in cui la sorgente si sposta quasi linearmente nel piano log P −log Pdot (in analogia con quanto previsto se l’angolo tra l’asse di rotazione e l’asse di dipolo resta costante) ed una seconda in cui il periodo rimane sostanzialmente invariato mentre la derivata del periodo decresce portando la stella di neutroni sotto la soglia di osservabilità. Tali conclusioni rimangono sostanzialmente invariate implementando anche il decadimento del campo magnetico se il tempo scala è dello stesso ordine di τA. Al contrario, il caso in cui l’allineamento e il decadimento magnetico avvengono su scale di tempo diverse è sfavorito perché porta le pulsars ad essere non rilevabili troppo velocemente.ope

Stima del diametro di un grafo con il framework Apache Spark(TM)

Il tema centrale di questo lavoro è l’analisi e l’implementazione dell’algoritmo HADI per la stima del diametro e del diametro effettivo dei grafi. Per migliorare le prestazioni di HADI faremo uso di Spark, un nuovo framework per il calcolo distribuito che si presenta come molto più efficiente rispetto ad Hadoop. Dalla nuova implementazione di HADI, abbiamo ottenuto un incremento delle prestazioni fino a un ordine di grandezza rispetto all'algoritmo originaleope