La mayoría de los bosques del planeta, exceptuando, quizá, el cinturón más húmedo del trópico, han sufrido perturbaciones recurrentes por incendios, desde hace miles de años. Sin embargo, en el último siglo, la combinación de factores socio-económicos y ambientales han alterado la frecuencia y distribución de incendios en casi todos los ecosistemas forestales. Esta mala distribución del fuego ha conllevado la acumulación de este elemento perturbador en ecosistemas poco adaptados a su presencia (e.g. bosques tropicales húmedos), mientras que otros ecosistemas han sufrido los efectos de las políticas de supresión de incendios (e.g. bosques templados norteamericanos). Entre las consecuencias de estas alteraciones, algunas se refieren a variaciones en el régimen de incendios, con implicaciones en términos de conservación forestal, impacto ecológico, económico y social. La presente tesis analiza la influencia de factores ambientales y socio-económicos en algunas características del régimen de incendios en ecosistemas tropicales y mediterráneos. En el ámbito tropical, la zona de estudio es el Estado mexicano de Chiapas, y los objetivos son básicamente dos: 1) caracterizar el régimen de incendios en el Estado, en términos de frecuencia de incendios, distribución, áreas y ecosistemas afectados, tipología de incendios, causalidad, y su interacción con algunos factores como el fenómeno de El Niño, la distribución de la tenencia de la tierra o la variación de las precipitaciones. 2) Analizar la influencia relativa de factores ambientales frente a factores socio-económicos, en años de condiciones climáticas normales y años de El Niño. El objetivo último era determinar variaciones en la afectación de los principales ecosistemas y listar los factores más importantes a considerar, a nivel de gestión forestal contra incendios. A nivel de ecosistemas mediterráneos, se seleccionó el incendio del Solsonés 1998, como caso estudio, siendo los principales objetivos: 3) Seleccionar la metodología de clasificación post-incendio más eficiente entre varias técnicas analizadas (teledetección y muestreo de campo). 4) Analizar la influencia de diversos factores ambientales en la formación de islas de vegetación en un gran incendio, empleando las laderas como unidad espacial. 5) Verificar la importancia de la estructura forestal y la continuidad del combustible en la heterogeneidad final de las severidades de afectación de un incendio. En relación a estos objetivos, las principales aportaciones de este estudio han sido, en lo referente a ecosistemas tropicales: La descripción de los incendios en Chiapas como mayoritariamente superficiales, afectando principalmente a estratos no arbóreos, de grandes dimensiones, de origen antrópico y con cierta propensión a afectar zonas protegidas. La aportación clave sin embargo, hace referencia a la demostración de la importancia de El Niño en la afectación de los ecosistemas tropicales húmedos, principalmente influenciado por la presencia de pastos alrededor de bosques fragmentados. El cambio de importancia relativa de los factores ambientales en años de no-ENSO frente a la mayor importancia de los factores socio-económicos en años de ENSO. También se puede remarcar el cambio de ecosistema afectado condicionado por el tipo de año (condiciones climáticas normales o extremas, ENSO o no ENSO: pino-encino versus bosques tropicales húmedos). En relación a los bosques mediterráneos, las técnicas más sencillas de teledetección resultaron las adecuadas para la identificación de islas. La formación de estas islas se ve condicionada por el tamaño y orientación y pendiente de las laderas, así como la cantidad y madurez de los rodales afectados, siendo las laderas más extensas, de orientación noroeste, de mayor pendiente, con mayores extensiones forestales y bosques más maduros (en términos de mayores tamaños), las más propicias a formar islas. Las características estructurales de los rodales fue de gran importancia para predecir la supervivencia forestal en zonas de condiciones climáticas moderadas. / The great majority of the forests of the world, excepting perhaps, the wettest belt of the tropics, have been burned over, at more or less frequent intervals, for many thousands of years. In the last century however, a combination of human and environmental factors have altered the frequency and distribution of fire, almost everywhere. This maldistribution of fire has resulted in an accumulation of this element in ecosystems not adapted to high frequencies of fire (i.e. tropical and sub-tropical areas), while other ecosystems have suffered the effects of fire suppression policies (i.e. north American temperate forests). Among the consequences of these alterations, some of them refer to variations in fire regimes, with implications in terms of forest conservation, ecological, economic and social impact. The present thesis analyses the influence of environmental and socio-economic factors for certain elements of the fire regime in tropical and Mediterranean ecosystems. In tropical areas, the study case relates to the tropical Mexican State of Chiapas, and the objectives are basically two: 1) to characterize the fire regime in the State, in terms of frequency of fires, fire distribution, areas and ecosystems affected, type of fires, causality, and their interaction with some factors like the phenomenon of El Niño, the land distribution, or the variation of rainfall values. 2) To analyse the relative influence of environmental factors versus socio-economic factors, in years of normal climatic conditions and years of El Niño. The final objective is to detect variations in the affectation of the major ecosystems and to list the most important factors to consider for forest fire management. For the Mediterranean ecosystems, the fire of Solsonés 1998 was selected as case study. Main objectives are: 3) To select the most efficient methodology for post-fire classification among several techniques: image classification and field survey. 4) To determine the influence of diverse environmental factors in the formation of vegetation islands inside a large forest fire, using "slope", as the spatial unit. 5) To verify the importance of forest structure and fuel continuity in the final heterogeneity of fire severities in a large fire. In relation to these objectives, the main contributions of this study are, with respect to tropical ecosystems: The characterization of fires in Chiapas, as in other tropical areas, mainly as superficial fires, frequently affecting non-arboreal layers. Major problems focus on large forest fires, which are responsible for the major burned areas. Fires are mainly human related and display certain propensity to affect protected zones. The key contribution nevertheless, refers to the major importance of El Niño in the affectation of humid tropical ecosystems. This is specially enhanced by the presence of cattle pasture surrounding the fragmented forests. The shift on the importance of environmental factors in years of no-ENSO versus the greater importance of socio-economic factors in years of ENSO, is also a major achievement. Moreover, shifts in ecosystem affectation have also been observed depending on the climatic conditions: pine-oak in no-ENSO years versus humid tropical forests in ENSO years. Regarding the Mediterranean forests, the simplest techniques of teledetection were the best performing ones for island identification. The formation of these islands is conditioned by the size and aspect of the slopes, as well as by the amount and maturity of the affected patches. Most extensive slopes, north-western orientations, more abrupt, larger forest extensions per slope, and more mature forests (in terms of greater sizes), are the most suitable combination of factors to form islands. This formation of islands does not have, therefore, a random distribution. Besides, the structural characteristics of the forest patches was confirmed to be of great importance to predict the forest survival in areas were fire burned under moderate climatic conditions. Larger patches and larger trees are the ones that will survive fire the best.

Thesis (M.S.)--Boise State University, 2009. / Includes abstract. Includes bibliographical references (leaves 81-91).

published_or_final_version / Botany / Doctoral / Doctor of Philosophy

This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.

No description available.

No description available.

Massive short distance spotting has been suspected of increasing the forward rate of spread of bushfires since McArthur (1967) attributed a three-fold increase in rate of spread to short distance spotting at a fire in Daylesford. However, research into spotting has generally focussed on the prediction of long distance spotting, perhaps because of its more obvious effects on suppression of bushfires. The amount of spotting that a fire generates and the distance that spotfires start from the main fire is dependent on the amount and type of bark fuel present, as this is the primary source of embers. / Existing models of fire behaviour have proposed only one model that allows spotting to influence the forward rate of spread of the main fire - the formation of pseudo fire fronts. This thesis proposes two new inl1uence mechanisms; pre-frontal burnout and the "indraught effect". Three hypotheses have been formed to test these three influence mechanisms. / As it is difficult, costly and dangerous to use high intensity fires for experimental purposes, a fire simulation model (SAROS) was developed to run on a personal computer. The SAROS model is based on the McArthur fire behaviour model (1967), with the addition of mechanisms that allow spotting to affect the forward rate of spread of the main fire. SAROS has been tested against data from fires where spotting was thought to have significantly increased the forward rate of spread, and is shown to be a reasonable model of fire behaviour. / Further experiments were carried out to test the sensitivity of the model to the input variables and the impact of each of the variables in the model on changes in forward rate of spread due to spotting. The SAROS model shows that it is possible for massive short distance spotting to increase the forward rate of spread by over 300% of the McArthur predicted rate of spread. However under the conditions where McArthur reported spotting increasing the rate of spread by a factor of three, the SAROS model accounts fbI' only around two thirds of that increase.

Thesis (M.D.)--Dept. of Psychiatry, University of Adelaide, 1990. / Typescript (Photocopy). Includes bibliographical references.

Mémoire (M.Ress.Renouv.)--Université du Québec à Chicoutimi, 1996. / Résumé disponible sur Internet. CaQCU Document électronique également accessible en format PDF. CaQCU

Thesis (MS)--Montana State University--Bozeman, 2009. / Typescript. Chairperson, Graduate Committee: Cathy L. Cripps. Includes bibliographical references (leaves 105-121).