Cambios en los usos y cubiertas del suelo y los efectos en la vulnerabilidad en las comarcas de montaña de Cataluña. Del rol del fuego como herramienta de gestión a los incendios como amenaza

Fire is one of the oldest and most efficient tools for managing land use in the Pyrenees and has contributed to shaping a landscape of great cultural and ecological diversity. Human actions affecting land cover have introduced certain changes that affect the role and our perception of forest fires, converting them from one of the normal processes of nature into a serious threat to ecosystems and to society. This study addresses the question: what specific changes in the Pyrenees have led to the current perception of forest fire as a risk or threat? Using GIS and statistical analysis, we conducted a quantitative assessment of land cover changes and we reviewed the forest fires that have occurred in the counties (comarques) of the Catalan Pyrenees between 1993-2007, in terms of seasonality and some characteristics of the territory as altitude, slope and orientation. The results shows that: a) land cover change tend to forestry and a more homogeneous landscape; b) most surface burned occurred in bush and clear forest, what is a sign of the trend of forest transition; c) there is a concentration of fires in winter ahead of summer and are located in accessible areas.En los Pirineos el fuego ha sido una de las herramientas más antiguas y eficientes de la historia de la gestión de los usos del suelo y ha contribuido a dar forma a un paisaje de una gran diversidad. La acción humana sobre la cubierta del suelo ha introducido algunas modificaciones, de forma que los incendios forestales han dejado de ser un proceso más del sistema natural para convertirse en una grave amenaza para los ecosistemas y para la sociedad. Utilizando técnicas SIG y análisis estadístico se cuantifican los cambios en las cubiertas del suelo y se hace una diagnosis de los puntos de ignición ocurridos en las comarcas de montaña del Pirineo catalán durante el periodo 1993- 2007, en función de la estacionalidad y algunas características del territorio como la altitud, la pendiente y la orientación. De esta forma se pretende aportar argumentos que ayuden a dar respuesta a la pregunta ¿qué ha cambiado en el Pirineo para que los incendios actualmente constituyan un riesgo? Los resultados indican que: a) los cambios en las cubiertas del suelo tienden al recubrimiento arbóreo y a un paisaje forestal más homogéneo; b) la mayoría de incendios que queman mayor superfície empiezan en zonas de matorral y bosque claro, lo cual supone una muestra de la tendencia a la transición forestal después del abandono de las actividades tradicionales en las áreas de montaña c) los incendios se concentran en invierno y se localizan en zonas accesibles

Landscape dynamics and fire activity since 6740 cal yr BP in the Cantabrian region (La Molina peat bog, Puente Viesgo, Spain)

A lack of paleobotanic studies with adequate resolution and multiproxy approaches has limited proper discussion of vegetation dynamics in Cantabria and of the role of fires in the configuration of the plant landscape during the Holocene in the northwest part of the Iberian peninsula. The pollen diagram of La Molina peat bog in Puente Viesgo (43 ‹15 Œ38 N.3 ‹58 Œ37 W; ETRS89), located at 484 m.a.s.l., and the study of its sedimentary charcoals allowed the acquisition of a continuous and thorough fire sequence for the last 6 700 cal yr BP and an understanding of its relationship to the forest. The results show the importance of human influence on the incidence and characteristics of fire activity during the different phases studied: the Neolithic, Bronze Age, Iron Age, Roman period, and Middle Ages. A synergy seems to exist between dry climate periods (especially during Bond events 3 and 4) and a greater presence of biomass. As the Holocene advances, vegetation coverage clearly tends to decrease. This study provides key elements for understanding the role of fire activity in the forest dynamics of deciduous and evergreen Quercus, Corylus, Pinus, Fagus, and Alnus and demonstrates the strongly artificialized character of the present landscape

La explotación de las cimas. Ocupación e impacto humano en las zonas alpinas de los Pirineos al final del Neolítico

En los últimos años se ha constatado arqueológicamente la presencia humana en el Pirineo axial desde inicios del Holoceno, que se incrementa especialmente durante el Neolítico. Con un escaso desfase con respecto a la cronología de las primeras ocupaciones neolíticas del Piedemonte y del Prepirineo, se han documentado diversos yacimientos en fondos de valle del área axial y en laderas entre los 1400 y los 1800 metros de altitud, ocupados desde el V y IV milenios cal ANE. Las últimas investigaciones confirman, además, un incremento del número de asentamientos durante el tercer milenio cal ANE en diversos puntos de la región central de los Pirineos en cotas que, en ocasiones, superan los 2.300 metros de altura. Paralelamente, los datos paleoambientales muestran las primeras señales de impacto humano sobre el medio, como por ejemplo descensos de las formaciones forestales o un incremento de las evidencias de las aperturas de pastos. En definitiva, parece que es a partir del final del Neolítico cuando se establece una explotación ganadera de las áreas alpinas y la franja superior de los pisos subalpinos, iniciando un proceso que ganará en intensidad durante el II milenio cal ANE. Esta presentación aborda la discusión del fenómeno del poblamiento en las zonas altas de la sierra, procurando evitar apriorismos relacionados con el determinismo medioambiental. Para eso, entendemos imprescindible la comparación y contrastación de los datos arqueológicos y la información paleoecológica, con el objetivo de entender, de forma integrada, la evolución del paisaje, de las sociedades y del impacto que éstas produjeron sobre el territorio.Peer reviewe

Negative responses of highland pines to anthropogenic activities in inland Spain: a palaeoecological perspective

Palaeoecological evidence indicates that highland pines were dominant in extensive areas of the mountains of Central and Northern Iberia during the first half of the Holocene. However, following several millennia of anthropogenic pressure, their natural ranges are now severely reduced. Although pines have been frequently viewed as first-stage successional species responding positively to human disturbance, some recent palaeobotanical work has proposed fire disturbance and human deforestation as the main drivers of this vegetation turnover. To assess the strength of the evidence for this hypothesis and to identify other possible explanations for this scenario, we review the available information on past vegetation change in the mountains of northern inland Iberia. We have chosen data from several sites that offer good chronological control, including palynological records with microscopic charcoal data and sites with plant macro- and megafossil occurrence. We conclude that although the available long-term data are still fragmentary and that new methods are needed for a better understanding of the ecological history of Iberia, fire events and human activities (probably modulated by climate) have triggered the pine demise at different locations and different temporal scales. In addition, all palaeoxylological, palynological and charcoal results obtained so far are fully compatible with a rapid human-induced ecological change that could have caused a range contraction of highland pines in western Iberia

Interacción entre clima y ocupación humana en la configuración del paisaje vegetal del Parque Nacional de Aigüestortes i Estany de Sant Maurici a lo largo de los últimos 15.000 años

The vegetation of the National Park of Aigüestortes i Estany de St Maurici is the result of an interaction between climate, plant community dynamics and the human occupation of the territory. The OCUPAproject aimed to reconstruct this interaction across the last millennia combining methods from palaeoecology and archaeology. The study focused primarily on the Sant Nicolau valley and built on the multidisciplinary analysis of the sedimentary archive of two lakes (Llebreta and Redó) and a number of archaeological sites located in shelters and outdoors. There is archaeological evidence of human presencesince 9000 yr cal BP, and a continuous record since 7500 yr cal BP. At early stages, humans transformed the surroundings of the shelters occupied and lithic tools indicate contacts with locations far away (i.e.,the Ebro plains). Since more than 3000 years ago, there has been human impact on the vegetation withoutinterruption until present. Initially, the impacts were mostly related to livestock: use of fire to open grazing lands, soil erosion and, during the medieval period, forestry and eutrophication of lakes. The agriculture impact in the lower part of the valley (e.g., Llebreta) occurred about 2100 yr ago, although some cereal grains and tools for harvesting have been found for the Neolithic. In the medieval period, the impact was higher than during the last centuries. In general, the changes in the human land use approximately follow the major changes in climate, but the specific causal link is likely related to the social and cultural dynamics of a broader territory since the Neolithic

THE TANGENT SEMICONE AND LIMITS OF TANGENT SPACES TO REAL SURFACES (Singularity theory and Differential equations)

Pyrenees; nature conservation; species distribution; lakes; forest

Dinámica climática y paisajística del Pirineo leridano durante la transición Tardiglacial¿Holoceno

El Estany de la Coma de Burg (CMB) y la turbera de Estanilles (EST) son dos registros sedimentarios que aportan información paleoambiental sobre la transición del Tardiglacial al Holoceno en el Pirineo centro‐oriental (Alto Pallars, Lleida). La comparación de los valores de materia orgánica (Loss On Ignition) de CMB con los registros polínicos de las dos secuencias (CMB y EST) indica que la LOI es más sensible a los cambios en la temperatura que en la precipitación. Los valores polínicos reflejan la sucesión de distintos paisajes, desde formaciones estépicas (Artemisia y Poaceae) hasta comunidades más o menos boscosas (Pinus, Betula y Corylus). Las 6 fluctuaciones documentadas por la LOI coinciden con las fluctuaciones de las temperaturas del Hemisferio Norte (Greenland Ice Core Project, GRIP) y marcan el Bölling, Alleröd, Dryas Reciente y el inicio del Holoceno, así como algunas fluctuaciones posteriores.Peer Reviewe

Fire history and human activities during the last 3300cal yr BP in Spain's Central Pyrenees: The case of the Estany de Burg

The study of macroscopic charcoal particles from peat bogs has led to a better understanding of climate, vegetation and fire history, and human impacts. To determine the relationship between human activities and the role of fire events in vegetation change during the last 3300. cal yr BP, we present the results of a multi-proxy approach based on the analysis of sediment characteristics, sedimentary charcoal, organic matter and pollen, as well as historical sources. This multi-proxy research permits high resolution palaeoenvironmental and fire history reconstruction of a mountain area located in the southern central Pyrenees (Spain). In the Pyrenees, fire is typically attributed to human activities since the beginning of the Bronze Age and may be correlated with slash-and-burn cultivation, metallurgy and pasturing activities. The data indicate a good linkage between high fire signals and Poaceae and Cerealia pollen, which reveals the impact of agro-pastoral practices. This study also shows two periods, 2900-2650. cal yr BP and 1850-1550. cal yr BP, for which higher frequencies of fire occurred, suggested by high arboreal pollen (AP) concentrations, and confirming the need for arboreal biomass to sustain fires. From the beginning of the Middle Ages, it seems that a change occurred in the anthropogenic use of fire, from a tool for agro-pastoral forest clearance to a means of maintaining open spaces. © 2011 Elsevier B.V.This work was supported by 1) a research grant from the Comunitat de Treball dels Pirineus (2007ITT 00001): Environmental dynamic of the Pyrenees over the past 20,000 years: A study of the impact of changes in climate and land use on forest ecosystems for the development of possible scenarios (Dinàmica ambiental pirinenca dels darrers 20.000 anys: estudi de l'impacte dels canvis climàtics i dels usos del sòl sobre els ecosistemes forestals per a l'elaboració d'escenaris prospectius) and 2) a project of the Catalan government (Generalitat de Catalunya — 2006EXCAVA00022): Archaeology of the high Pyrenees mountains.Peer Reviewe

Potential influence of Bond events on mid-Holocene climate and vegetation in southern Pyrenees as assessed from Burg lake LOI and pollen records.

10 páginas.Superimposed on the long-term climate variability attributed to orbital forcing, there are other modes of variability covering timescales from interannual to millennial throughout the Holocene. Their signatures in climate proxy archives can differ substantially because of their lower magnitude and regional diversity. However, if identified they can yield better understanding of the physical mechanisms regionally linking causes and effects. Here we describe a high-resolution record of organic matter accumulation in the sediments of Burg lake (Pyrenees, NE Iberian Peninsula), as assessed using loss on ignition (LOI), and compare it with the ice rafted debris (IRD) indexes from the North Atlantic. The LOI record indicates two main phases in the water body, a lacustrine phase as a shallow lake and a palustrine phase as a fen. The latter covers the period 2600—7200 cal. yr BP and within it there is a high coherence between LOI and IRD, which indicates submillennial climate fluctuations in the Pyrenees that can be related to the North Atlantic influence. The Burg’s LOI record suggests wetter (and occasionally colder) situations in the Pyrenees during high IRD in the Atlantic (Bond oscillations). These fluctuations would likely affect the snow covered period in the mountains (winter and spring seasons) the most, the period in which Atlantic westerlies currently have higher influence on precipitation over the Pyrenees. These climatic oscillations could have favoured Abies penetration during the mid Holocene, as evidenced by increased pollen percentages of this taxon during low IRD values (drier conditions). The pollen record also suggests potential relationships between climate and human activity as early as at mid Holocene, as human-related cereals increase during all the low IRD periods. The human signature (charcoal, cereals) becomes particularly evident at around 2800 cal. yr BP; in this oscillation Pinus overtake Abies in the conifer response to low IRD.Peer reviewe