Dynamic optimization methods have become increasingly important over the last years in economics. Within the dynamic optimization techniques employed, optimal control has emerged as the most powerful tool for the theoretical economic analysis. However, there is the need to advance further and take account that many dynamic economic processes are, in addition, dependent on some other parameter different than time. One can think of relaxing the assumption of a representative (homogeneous) agent in macro- and micro-economic applications allowing for heterogeneity among the agents. For instance, the optimal adaptation and diffusion of a new technology over time, may depend on the age of the person that adopted the new technology. Therefore, the economic models must take account of heterogeneity conditions within the dynamic framework.This thesis intends to accomplish two goals. The first goal is to analyze and revise existing environmental policies that focus on defining the optimal management of natural resources over time, by taking account of the heterogeneity of environmental conditions. Thus, the thesis makes a policy orientated contribution in the field of environmental policy by defining the necessary changes to transform an environmental policy based on the assumption of homogeneity into an environmental policy which takes account of heterogeneity. As a result the newly defined environmental policy will be more efficient and likely also politically more acceptable since it is tailored more specifically to the heterogeneous environmental conditions. Additionally to its policy orientated contribution, this thesis aims making a methodological contribution by applying a new optimization technique for solving problems where the control variables depend on two or more arguments --- the so-called two-stage solution approach ---, and by applying a numerical method --- the Escalator Boxcar Train Method --- for solving distributed optimal control problems, i.e., problems where the state variables, in addition to the control variables, depend on two or more arguments.Chapter 2 presents a theoretical framework to determine optimal resource allocation over time for the production of a good by heterogeneous producers, who generate a stock externalit and derives government policies to modify the behavior of competitive producers in order to achieve optimality. Chapter 3 illustrates the method in a more specific context, and integrates the aspects of quality and time, presenting a theoretical model that allows to determine the socially optimal outcome over time and space for the problem of waterlogging in irrigated agricultural production. Chapter 4 of this thesis concentrates on forestry resources and analyses the optimal selective-logging regime of a size-distributed forest.

La gestió de xarxes és un camp molt ampli i inclou molts aspectes diferents. Aquesta tesi doctoral està centrada en la gestió dels recursos en les xarxes de banda ampla que disposin de mecanismes per fer reserves de recursos, com per exemple Asynchronous Transfer Mode (ATM) o Multi-Protocol Label Switching (MPLS). Es poden establir xarxes lògiques utilitzant els Virtual Paths (VP) d'ATM o els Label Switched Paths (LSP) de MPLS, als que anomenem genèricament camins lògics. Els usuaris de la xarxa utilitzen doncs aquests camins lògics, que poden tenir recursos assignats, per establir les seves comunicacions. A més, els camins lògics són molt flexibles i les seves característiques es poden canviar dinàmicament. Aquest treball, se centra, en particular, en la gestió dinàmica d'aquesta xarxa lògica per tal de maximitzar-ne el rendiment i adaptar-la a les connexions ofertes.En aquest escenari, hi ha diversos mecanismes que poden afectar i modificar les característiques dels camins lògics (ample de banda, ruta, etc.). Aquests mecanismes inclouen els de balanceig de la càrrega (reassignació d'ample de banda i reencaminament) i els de restauració de fallades (ús de camins lògics de backup). Aquests dos mecanismes poden modificar la xarxa lògica i gestionar els recursos (ample de banda) dels enllaços físics. Per tant, existeix la necessitat de coordinar aquests mecanismes per evitar possibles interferències. La gestió de recursos convencional que fa ús de la xarxa lògica, recalcula periòdicament (per exemple cada hora o cada dia) tota la xarxa lògica d'una forma centralitzada. Això introdueix el problema que els reajustaments de la xarxa lògica no es realitzen en el moment en què realment hi ha problemes. D'altra banda també introdueix la necessitat de mantenir una visió centralitzada de tota la xarxa. En aquesta tesi, es proposa una arquitectura distribuïda basada en un sistema multi agent. L'objectiu principal d'aquesta arquitectura és realitzar de forma conjunta i coordinada la gestió de recursos a nivell de xarxa lògica, integrant els mecanismes de reajustament d'ample de banda amb els mecanismes de restauració preplanejada, inclosa la gestió de l'ample de banda reservada per a la restauració. Es proposa que aquesta gestió es porti a terme d'una forma contínua, no periòdica, actuant quan es detecta el problema (quan un camí lògic està congestionat, o sigui, quan està rebutjant peticions de connexió dels usuaris perquè està saturat) i d'una forma completament distribuïda, o sigui, sense mantenir una visió global de la xarxa. Així doncs, l'arquitectura proposada realitza petits rearranjaments a la xarxa lògica adaptant-la d'una forma contínua a la demanda dels usuaris. L'arquitectura proposada també té en consideració altres objectius com l'escalabilitat, la modularitat, la robustesa, la flexibilitat i la simplicitat.El sistema multi agent proposat està estructurat en dues capes d'agents: els agents de monitorització (M) i els de rendiment (P). Aquests agents estan situats en els diferents nodes de la xarxa: hi ha un agent P i diversos agents M a cada node; aquests últims subordinats als P. Per tant l'arquitectura proposada es pot veure com una jerarquia d'agents. Cada agent és responsable de monitoritzar i controlar els recursos als que està assignat. S'han realitzat diferents experiments utilitzant un simulador distribuït a nivell de connexió proposat per nosaltres mateixos. Els resultats mostren que l'arquitectura proposada és capaç de realitzar les tasques assignades de detecció de la congestió, reassignació dinàmica d'ample de banda i reencaminament d'una forma coordinada amb els mecanismes de restauració preplanejada i gestió de l'ample de banda reservat per la restauració. L'arquitectura distribuïda ofereix una escalabilitat i robustesa acceptables gràcies a la seva flexibilitat i modularitat. / Network management is a wide field including many different topics. This thesis focuses on resource management of broadband networks that have the mechanisms for performing resource reservation, such as Asynchronous Transfer Mode (ATM) or Multi-Protocol Label Switching (MPLS). Logical networks can be established by using Virtual Paths (VP) in ATM or Label Switched Paths (LSP) in MPLS, which we call generically Logical Paths (LP). The network users then use these LPs, which can have pre-reserved resources, to establish their communications. Moreover, LPs are very flexible and their characteristics can be dynamically changed. This work focuses, in particular, on the dynamic management of these logical paths in order to maximise the network performance by adapting the logical network to the offered connections.In this scenario, there are several mechanisms that can affect and modify certain features of the LPs (bandwidth, route, etc.). They include load balancing mechanisms (bandwidth reallocation and re-routing) and fault restoration (utilisation of backup LPs). These two mechanisms can modify the logical network and manage the resources (bandwidth) of the physical links. Therefore, due to possible interferences, there is a need to co-ordinate these mechanisms. Conventional resource management, using a logical network, performs a centralised recalculation of the whole logical network periodically (e.g. every hour / day). This brings the problem that the logical network readjustments do not happen when a problem occurs. Moreover, there is a need of maintaining a centralised network overview. In this thesis, a distributed architecture, based on a Multi-Agent System (MAS), is proposed. The main objective of this architecture is to perform joint resource management at a logical network level, integrating the bandwidth reallocation and LP re-routing with pre-planned restoration and spare bandwidth management. This is performed continuously, not periodically, when a problem is detected (an LP is congested, i.e. it is rejecting new user connections because it is already saturated with user connections) in a completely distributed way, i.e. without any central network overview. Therefore, the proposed architecture performs small rearrangements in the logical network and thus it is continuously being adapted to the user demands. The proposed architecture also considers other objectives, such as scalability, modularity, robustness, simplicity and flexibility. The proposed MAS is structured in two layers of agents: The network Monitoring (M) agents and the Performance (P) agents. All these agents are situated at different network nodes, where the computing facilities are. There is one P agent and several M agents on every node. The M agents are subordinated to the P agents, therefore the proposed architecture can be seen as a hierarchy of agents. Each agent is responsible for monitoring and controlling the resources they are assigned to. We have performed several experiments, using a connection level distributed simulator of our own design. The results show that our architecture is capable of performing the assigned tasks of detecting congestion, dynamic bandwidth reallocation and re-routing in a co-ordinated way with the pre-planned restoration and the spare capacity management. The distributed architecture offers a suitable scalability and robustness due to its flexibility and modularity.