Suchergebnisse

The evergreen Mexican oak, Quercus crassifolia Bonpl. is illustrated; its distribution is given and related species are discussed. Its survival in gardens in England is noted.

SummaryThe evergreen oak, Quercus lamellosa, is illustrated. Its discovery by Francis Buchanan‐Hamilton and its ecology are described. Suggestions for its cultivation are given.

A Chinese evergreen oak, Quercus guyavifolia A. Lév., from Yunnan, and Sichuan, is illustrated and compared with related species. Its cultivation is considered.

Summary. Quercus castaneifolia C.A. Mey. is described and illustrated from a tree growing at Kew. Its habitat, distribution, variation in the wild and its relationships with similar species, are discussed. A summary of the history and conservation of some of the oldest trees at Kew is included.

10 pages, 2 figures, 26 references. We thank the Consejería de Medio Ambiente (Andalusian Government) and Felipe Oliveros, Director of Los Alcornocales Natural Park, for the facilities and support to carry out the field work. We also thank to Maite Domínguez and Carmen Navarro for field assistance. Regeneration Models were carried out by IRU, with the advice of Dr. Richard Kobe, during a short-time grant in Michigan State University. El libro referenciado ha sido publicado con motivo de Conference Proceedings: Conference held at the University of Huelva on 20-22 october, 2005. Organised bay: Departamento de Ciencias Agroforestales, Universidad de Huelva, Spain. Centro de Estudos Florestais, Universidade Técnica de Lisboa, Portugal. ; The success of natural regeneration in forests depends on the sequential and complete achievement of several connected life-history stages of tree species. The collapse of any stage results in the limitation of the overall recruitment process. In this study, we focus on several regeneration stages of the cork oak (Quercus suber) tree species: seed production, pre-dispersal and post-dispersal predation rates, and establishment of seedlings. The fieldwork was carried out at three forest plots located within Los Alcornocales Natural Park (Southern Spain) where Q. suber is dominant. We have monitored seed production of 50 adult trees during three consecutive years, estimating the proportion of crop loss due to abortions and to damage by insect larvae. We have also studied the impact of predators (rodents and large herbivores) on seed survival in different types of microsites. Finally, we have studied the effect of microsite types and environmental factors (light, soil moisture and soil compaction) on the germination of sown seeds and the subsequent emergence and survival of seedlings. Results suggest that the high acorn predation rates (both pre-dispersal and post-dispersal) and the high mortality of seedlings (during the summer drought) are main causes of limitation in the natural regeneration of Q. suber in the study area. These factors act on a microsite-depending scale, altering acorns and seedlings probability of survivorship. The scientific knowledge of natural regeneration requirements of Q. suber will help to develop ecological restoration programs in disturbed areas caused by fire, tree disease, or changes of land use. ; This study was supported by the coordinated project Heteromed (REN2002-04041-CO2). This research is part of REDBOME and GLOBIMED networks on forest ecology. ; Peer reviewed

Die Trauben-Eiche (Quercus petraea [MATT.] LIEBL.) ist ökologisch wie ökonomisch eine prägende Baumart im nordostdeutschen Tiefland. Seit längerer Zeit haben jedoch lokal bis regional drastische Vitalitätseinbußen zu Diskussionen um ihre Verwendbarkeit für den Wald der Zukunft geführt. Vor dem Hintergrund fortschreitender Veränderungen des Klimas stellen sich Fragen nach der Anpassungsfähigkeit der Baumart im Sinne der Überlebensfähigkeit, nach den Beziehungen zwischen Vitalitätszustand und Wuchsverhalten sowie nach möglichen Entwicklungstendenzen dieser Parameter. Die vorliegende Arbeit untersucht die Zusammenhänge zwischen Vitalität und Zuwachs sowie die Effekte der Witterung auf die Jahrringbreite als wesentlichem Vitalitätsindikator. Die retrospektive Analyse dieser Beziehungen dient dazu, das mögliche Verhalten des Witterungs-Zuwachs-Komplexes in der Zukunft abzuschätzen und damit die Risiken einer forstlichen Schwerpunktsetzung auf die Trauben-Eiche in Nordostdeutschland genauer zu fassen. Die Untersuchungen fußen auf zwei Versuchsflächen-Sets. Die Kernflächen K1-K5 umfassen fünf Mischbestände aus Trauben-Eichen und Kiefern (Pinus sylvestris L.) entlang eines Gradienten von Sachsen-Anhalt bis Ostpolen im Altern von etwa 110-150 Jahren auf Standorten mittlerer Nährkraft und durchschnittlicher Wasserversorgung. Dieses Set wird erweitert durch 20 Zusatzflächen im Osten bis Süden des Landes Brandenburg, ebenfalls zum größten Teil in Mischbeständen mit Kiefer. Neben den ertragskundlichen Basisaufnahmen wurden auf den Versuchsflächen Bohrkerne an Stichproben des herrschenden Bestandes entnommen. Zu allen Flächen liegen die Angaben der forstlichen Standortkartierung über die Nährkraftstufe und die Wasserversorgung sowie Zeitreihen von Tagesmitteltemperaturen und Niederschlagstagessummen vor. Als Szenariodaten werden die Medianläufe des 2-Kelvin-Szenarios mit dem Regionalisierungsmodell STAR 2 auf Grundlage des SRES-A1B-Szenarios verwendet. Zur Einschätzung der Vitalität der Trauben-Eichen in den Untersuchungsbeständen wurde 2006-2011 der prozentuale Laubverlust im Sommerzustand nach dem Standard der Waldzustandserhebungen erfasst (EICHHORN et al. 2006). Parallel wurde der Kronenzustand im Winter nach dem Schema von KÖRVER et al. (1999) beurteilt. Als Indikatoren für die Vitalität der Trauben-Eichen standen die Jahrringbreite und die Zuwachsrate ("Jahrringindex") im Mittelpunkt der Untersuchungen. Für die Zeitreihen der Jahrringbreite wurden die Parameter Autokorrelation und Sensitivität für die gesamte Zeitreihe sowie als gleitende Mittel hergeleitet und interpretiert. Im Programmpaket "CLIMTREG" (BECK et al. 2013) erfolgten anschließend die Trendeliminierung und die AR(1)-Modellierung zur Entfernung autokorrelativer Effekte aus den baumspezifischen Jahrringindex-Zeitreihen. Die Identifikation von Weiserjahren stützte sich auf die Verteilungsparameter Mittelwert und Standardabweichung der Einzelbaum-Jahrringindizes pro Jahr. Aus den individuellen Zeitreihen des Jahrringindexes wurde die mittlere bestandesbezogene Index-Zeitreihe (= Chronologie) errechnet. Zur Quantifizierung der Witterungs-Zuwachs-Beziehungen wurden die Analyse-Tools CLIMTREG (mit tagesgenauer Auflösung) sowie "bootRes" für R (monatliche Auflösung; ZANG & BIONDI 2012) verwendet, in die Daten der jeweils nächstliegenden Wetterstationen sowie Zeitreihen des mittleren Jahrringindexes eingesteuert wurden. Die Auswertungen zeigten, dass sich im Untersuchungszeitraum 2006-2011 Belaubungsgrad und Kronenstruktur für die Mehrzahl der untersuchten Bäume deutlich verbessert haben. Mit dem relativen Kreisflächenzuwachs ist die Kronenstruktur (hochsignifikant) über alle Kernflächen hinweg straffer positiv korreliert als der Laubverlust (nicht signifikant). Bei gleichem BHD sind größere Kronenflächen sowohl mit besseren Kronenstrukturwerten als auch mit einem geringeren Laubverlust gekoppelt. Der jährliche Radialzuwachs nimmt im Mittel der Kernflächen seit mehreren Jahrzehnten zu. Auf den Zusatzflächen liegen die mittleren Jahrringbreiten etwa auf Ertragstafelniveau (ERTELD 1963). Die absolut und relativ höchsten Zuwächse 2006-2011 zeigten die polnischen Kernflächen. Die Korrelationen der Jahrringindizes (JRI) mit dem Niederschlag sind etwas straffer als mit der Temperatur, aber nur selten signifikant. Die für die Vegetationsperiode berechneten Korrelationskoeffizienten sind in keinem Fall höher als die für das Gesamtjahr ermittelten. Bei der Prüfung dendroklimatologischer Zusammenhänge auf Monatsebene mit bootRes zeigen die Flächen K1 und K3 ein ähnliches Bild: Höhere Jahrringindizes sind mit überdurchschnittlichen Niederschlägen vor allem in den Wintermonaten sowie im Spätsommer bis Frühherbst des Wuchsjahres gekoppelt. Auf den übrigen Kernflächen sind die Zusammenhänge im Vergleich weniger straff. Zwischen herrschendem und beherrschtem Bestand gibt es kaum Unterschiede in der Reaktion des Jahrringindex auf die Witterung. Die Beziehungen zu den Mitteltemperaturen sind etwas schwächer ausgeprägt. Auf allen Flächen sind vorrangig kühle Spätfrühlings- und Frühsommermonate mit überdurchschnittlichen Jahrringindizes verbunden. Analysen durch moving windows zeigen für einige Flächen im Lauf der Zeit zunehmende Korrelationen zwischen Witterung und Jahrringindex. In Zusammenfassung aller Flächen ergeben sich für die zweite Hälfte der Untersuchungsperiode deutlich mehr signifikante Zusammenhänge als in der ersten. Nach den Auswertungen mit CLIMTREG führen fast überall hohe Niederschläge bei niedrigen Temperaturen im Hochsommer des Vorjahres zu überdurchschnittlichen Zuwachsraten. Außerdem fördern erhöhte Niederschlagsmengen von Ende November bis in den Februar, zum Teil auch höhere Temperaturen, die Jahrringbildung. Das dritte auffällige Intervall ist die Zeit von Anfang April bis Mitte Juli mit höheren Zuwachsraten bei niedrigen Temperaturen und überdurchschnittlichen Niederschlägen. Die Modellierung von Jahrringindex-Zeitreihen für den Szenariozeitraum 2001-2055 auf Basis unterschiedlicher Kalibrierungszeiträume ergibt in den meisten Fällen die höchsten mittleren Jahrringindizes (JRI) für das mit der zweiten Hälfte des Gesamtuntersuchungsintervalls 1951-2006 parametrisierte Modell. Im Vergleich unterschiedlicher Kalibrierungszeiträume verändern die von CLIMTREG identifizierten zuwachswirksamen Zeiträume in der Regel weder ihre Lage noch ihre Länge in wesentlichem Ausmaß. Auffällig ist jedoch, dass die Richtung der Zusammenhänge in der jüngeren Vergangenheit uneinheitlicher wird. Auf Basis der Untersuchungsergebnisse leitet die Studie Chancen und Risiken ab, die für die Trauben-Eiche unter dem Einfluss des genutzten Witterungsszenarios im Untersuchungsgebiet maßgeblich sind. Die Handlungsoptionen zum Stärken der Anpassungsfähigkeit umfassen im Wesentlichen die Steuerung der negativen und positiven Einflüsse, die dem menschlichen Einfluss zugänglich sind. Dazu gehört die Förderung der individuellen Vitalität und Elastizität durch optimal entwickelte Kronen und Wurzelsysteme. Die Mischung mit anderen Baumarten steigert die Bestandesstabilität, wobei die relative Konkurrenzschwäche der Eiche zu berücksichtigen ist. Verjüngungsmaßnahmen sollten auf die Erhaltung und Steigerung der genetischen Vielfalt ausgerichtet sein und Individuen mit überdurchschnittlicher Vitalität besonders fördern. Die Konkurrenz um Wasser kann – unter Beachtung des Risikos zusätzlicher Verdunstung –durch geringere Bestandesdichten reduziert werden. Die größten Erfolgsaussichten für diese Aktivitäten bestehen auf Standorten höherer Wasserspeicherkapazität und Nährkraft. Ein angepasstes Monitoring sollte Bedrohungen zum Beispiel durch Insektenmassenvermehrungen rechtzeitig erkennen, gegen die alle Bekämpfungsmöglichkeiten auszuschöpfen sind. Auf gesellschaftlicher Ebene ist eine umfassende Diskussion zu den Zielen und Methoden der Waldbewirtschaftung zu führen, um eine höhere Wertschätzung und Langfristigkeit gezielter Eichenförderung zu erreichen. ; Sessile oak (Quercus petraea [MATT.] LIEBL.) is an important tree species in the northeastern lowlands of Germany. The widespread introduction of the species into mature Scots pine (Pinus sylvestris L.) stands as a means of ecological forest conversion has further enhanced its relevance in forest science and management. For a few decades, however, increasing numbers of trees and stands showing a severe decline in vitality have led to critical discussions on the possible role of oaks in today's forest development strategies. The adaptive capacity of Sessile oak will be further challenged by climate change in the future. In this context, more information is needed on the relations between the vitality status and growth, including the development of these relations in the next decades. Thus, the study investigates the dependencies between annual radial increment in Quercus petraea (measured as tree-ring width, TRW) and individual-tree vitality as well as the effects of climatic variables on TRW on different temporal scales. Investigations were carried out using two sets of trial plots. The core plot sequence K1-K5 comprises five mature mixed stands of Sessile oak with Scots pine along a gradient from Saxony-Anhalt to eastern Poland. Trees are 110-150 years old and grow on sandy and partly podsolic cambisols with average water supply. A set of 20 additional plots was established in mixed oak-pine stands in Brandenburg. In addition to growth and yield data for the whole plot, increment cores were extracted from a representative sample of 20 trees per plot. Time series data of local daily mean temperatures and daily precipitation sum were provided by the Potsdam-Institute for Climate Impact Research. Data for 2007-2060 come from the median scenario of the regional climate model "STAR 2" based on the SRES-scenario A1B and assumes an increase in temperature of two Kelvin until 2060. Individual vitality was recorded from 2006 to 2011on the core plots (i) according to the European standard method for the assessment of crown condition based on defoliation percentages in summer (EICHHORN et al. 2006) and (ii) following the approach by KÖRVER et al. (1999) for crown structure classification in winter. Both methods were applied to all dominant and co-dominant oaks in the five subsequent years. Trees on the additional plots were assessed only once. Because they are regarded a reliable indicator of tree vitality, annual radial increment as expressed in tree-ring width (TRW) and the resulting growth rate (tree-ring index) are at the center of the analyses. For TRW time series the parameters autocorrelation and sensitivity were calculated both for the whole investigation period and as floating means ("moving windows"). The program "CLIMTREG" (BECK et al. 2013) was applied to eliminate long-term trends in individual TRW series by means of cubic spline functions and to minimize auto-correlation within the resulting TRI time series. Pointer years were identified on the basis of the mean and standard deviation of annual TRI distributions. Plot-specific "chronologies" were calculated as arithmetic means of all "typical" tree-specific TRI series per plot. To analyze the relations between climate and growth, the programs CLIMTREG (for daily climate data resolution) and "bootRes" for R (monthly resolution; ZANG & BIONDI 2012) were applied to local climate data and the TRI chronologies. The repeated assessments show that during the interval 2006-2011 crown condition as expressed in summer foliage as well as in crown structure has improved considerably. Crown structure values are correlated more closely to individual basal area increment than defoliation percentages. At the same DBH, trees with larger crowns exhibit a significantly better crown structure and less defoliation. Annual radial increment has been increasing on the core plots over the past decades, thus the increment level of the dominant trees is on average slightly higher than that of the first yield class in the table by ERTELD (1963). On the additional plots, mean TRW is parallel to yield table values but shows a slowly decreasing trend in a number of stands. The two core plots in Poland exhibited the highest radial increments 2006-2011, both absolutely and relatively. On the annual level, TRI time series are correlated more closely to precipitation sums than to annual mean temperatures. Except for one of the additional plots, the respective correlation coefficients are statistically insignificant. Correlations did not increase when climate parameters were calculated exclusively for the vegetation period instead of the whole year. According to dendroclimatological analyses on the monthly scale with bootRes, trees on core plots K1 and K3 respond almost similarly to climatic influences: High TRI values are related to above-average precipitation mainly during the winter months, as well as in late summer and early fall of the year of growth. On the other core plots, dependencies are less clear. The relations of TRI to monthly temperature are weaker than those to precipitation with the same ranking of plots regarding their sensitivity. The most favorable influence on TRI is exerted by cool spring to early summer months in the year of growth. Correlation patterns are very similar for both dominant and suppressed trees. Separate analyses of the first and the last half of the investigated interval show that the strength of correlations between TRI and climatic variables has been increasing over the past decades. When summarized over all plots, there were distinctly more significant correlation coefficients in the period from 1984-2006 than from 1951-1983. The analyses using CLIMTREG showed that high summer precipitation in the preceding year clearly promotes above-average TRI values. Another conspicuous climate-influenced time period ranges from late November to February with positive correlations both to precipitation and to temperature (at least partly). The third important period for TRI in most trees on the core plots starts in early April and lasts until Mid-July. During this time, high TRI values are correlated with low temperatures and high precipitation. For most of the plots, the average modeled TRI is higher if the second half of the data interval 1951-2006 is used for calibration rather than the entire interval or its first half. The results of the models based on different calibration periods do not differ very much in terms of the identified variables (i.e. length of influential period and type of climatic parameter). However, the direction of correlations becomes more variable in the more recent past. The results of this study are summarized in a number of risks and opportunities regarding future vitality and growth of Sessile oak under regional conditions. Finally, several options of silvicultural management to support vitality and growth of the species are recommended. These consist basically in promoting favorable conditions and limiting negative influences. A large crown with dense foliage and a well-developed root system are crucial conditions for individual vitality which should be strengthened for instance by reducing stand densities at an early age. Mixed stands have a higher stability towards disturbances and provide more diverse habitats for natural antagonists against defoliators. The relatively weak competitiveness of oaks should be taken into account when advocating mixed stands. Regeneration activities should enhance genetic diversity, promote phenotypes with above-average vitality, and accelerate the adaptation of the species by "assisted migration" of drought-tolerant provenances. Competition for water may be eased by lower stand densities. However, the canopy should be kept sufficiently closed to prevent excessive growth of ground vegetation or increased evapotranspiration. An adapted system to monitor forest growth and vitality should be used to technically assist the species in counteracting major insect outbreaks and other severe biotic risks as early as possible. On a more general level, productive discussions are needed between all stakeholders, interest groups, and the public on the social and political role of forests and the required level of management. This should lead to a stable social and political appreciation of forestry and provide the resources and staff necessary to cope with an uncertain future.

Forest decline is nowadays a major challenge to management and sustainability of natural ecosystems worldwide. This syndrome is a multifactorial disease influenced by several biotic and abiotic agents such as alien invasive pathogens, changes in land use and management policies, population dynamics driven by economic and politic changes, and climatic perturbations. All these factors changing due to anthropogenic influence, together with others, conformed the so-called global change. Since the 1990's decade, the oak decline has been identified as one of the most important ecological problems in Europe, affecting deciduous and evergreen Quercus species from the continental forests on Central and North Europe, to temperate forests of the Mediterranean basin. In the case of Iberian Peninsula, holm oak (Quercus ilex L.) and cork oak (Quercus suber L.) decline has been detected since the 1980's decade. These two species covered most of the forest surface of the south and central part of the Iberian Peninsula, mainly through "dehesas" and "montados" formations. This area is considered to be one of the worst affected regions in the world by climate change, worsening the effects and the consequences of oak decline in "dehesas". "Dehesas" are Mediterranean savanah-like ecosystems, which provide several economic yields and ecological services. In turn, the holm oak is the most representative tree in the Iberian Peninsula, and the main species conforming the tree layer on the Spanish "dehesas". The loss of this tree layer is a major ecological and economical constraint. The holm oak decline is mainly associated to the action of soil-borne pathogens, especially Phytophtora cinnamomi. Despite the influence of other factors in the decline, there is a strong association between root rot caused by oomycetes and the death of trees. Phytophtora cinnamomi is an aggressive alien plant pathogen widely widespread worldwide, which has been associated with the disease, die-off and death in a large list of different plant hosts. It is able to change trophic relationships with their hosts, becaming biotroph in asymptomatic hosts and hemibiotroph or necrotroph in susceptible hosts. It is considered that holm oak is the most susceptible Quercus sp. to the action of this pathogen. Additionally, other Phytophthora spp. and Pythium spp. have been recorded associated with the holm oak decline in Spain, Portugal, Italy and France. Many scientific efforts have focused to study this important hostpathogen system, obtaining great results and increasing the knowledge of the causes and effects of the interaction, improving management techniques to limit the spread and the symptoms. However, most of the reviewed works are based on empirical approaches, being the underlying mechanisms regulating the interaction between both species mostly unknown. This PhD Thesis covers part of this lack of basic knowledge, focusing on the host-pathogen interaction at histological and physiological level, and exploring the influence of the soil biota in the severity of the disease symptoms. For this purpose, the work was structured in seven chapters. Chapter 1 provides the framework in which the present PhD Thesis has been developed, and the general and specific objectives. Chapter 2 presents the methodology developed to evaluate the colonization and infection of Phytophthora cinnamomi in Quercus ilex seedling through the semi-automated quantification of pathogen structures present in histological sections of fine roots. A workflow was tuned-up testing different fixing solutions, embedding substances and staining methods, and the results allowed the clear differentiation of pathogen structures from host tissues. Furthermore, different indices based on structure location, host tissue classification and specificity of pathogen structures were evaluated to find the easiest and statistically robust indices that are able to explain the progress of the oomycete into the root. In chapter 3, inoculation experiments in growth chamber were carried out to describe the pathogenesis of the Quercus ilex-Phytophthora cinnamomi interaction. Longitudinal sections were analysed for epidermal, cortex, parenchymatous tissue of central cylinder and vascular tissue after 1, 3, 7 and 14 days after inoculation. Total oomycete structures area, intracellular structures area, extracellular structures area, and specific structures area of the pathogen were quantified. The analysis of these data results in the description of the colonization/infection cycle of the pathogen, classified in three different stages related with their trophic behaviour. Moreover, histological changes of the root tissues as a result of the presence of defence responses and the action of the pathogen were described. In Chapter 4, the differential responses of holm oak seedlings to the inoculation with P. cinnamomi, the acute drought and combination of both stressors were assessed. Six-months old seedlings were inoculated and mock-inoculated, and half of each inoculation treatment plans were subjected to acute drought meanwhile the others were well irrigated. Photosynthesis, stomatal conductance and fluorescence were measured weekly, and total biomass and biomass allocation parameters were quantified at the end of the experiment. The resulting data showed differences in the response of seedlings to drought and inoculation, and the influence of the additive effect of both stressors in the seedlings die-off. In Chapter 5, soil samples of "dehesas" were collected and total DNA was extracted and analysed through metabarcoding techniques, to evaluate the specific composition and diversity of the fungal and oomycete communities, and to study their relationship with the disease symptoms. The fungal community included a wide range of pathogens and abundance of ectomycorrhizal key taxa. Phytophthora spp. dominated the oomycete community, but the species related to root rot did not appear as the most abundant, nor were they related directly to defoliation levels. A particular Operational Taxonomic Unit (OTU) belonging to the genus Trichoderma was strongly correlated with the scarcity of pathogenic Phytophthora spp. The differences in defoliation were related to changes in the functionality of soil microbiota and diversity levels of pathogenic species. Chapter 6 presents the general discussion of the Thesis, including some aspects limiting the results of the works carried out, ad new work lines deriving from this Thesis, and finally Chapter 7 contains the conclusions of the work. Changes in roots as a consequence of P. cinnamomi inoculation, including defence responses, and the differential response identified with pathogen colonization/inoculation, leads to new insights about the causes of tree death. Holm oak responds to the attack of the pathogen, and their physiological changes differ from the ones caused by water stress, allowing the recovery of plants if no additional stress is present. Moreover, the study of soil microbiome in declined "dehesas" showed the influence of the microbial diversity in the health status of trees, and also presented new species of oomycetes and fungi that must be considered in the management of holm oak decline in Andalusian "dehesas". ; El decaimiento forestal es hoy en día uno de los mayores desafíos para el manejo y la sostenibilidad de los ecosistemas naturales en todo el mundo. Dicho síndrome es una enfermedad multifactorial en la que intervienen diversos agentes bióticos y abióticos como los patógenos invasores, los cambios en los usos del territorio y las políticas de recursos, o las perturbaciones climáticas. El cambio producido en todos estos factores debido a la influencia del hombre entre otros motivos es lo que se ha dado en llamar cambio global. Desde la década de los 90 del siglo XX, el decaimiento de los robles se ha identificado como uno de los problemas ecológicos más relevantes en Europa, afectando a masas de Quercus caducifolios y perennifolios desde los bosques continentales de Centro Europa y Norte Europa, hasta los bosques templados de la cuenca mediterránea. En el caso de la Península Ibérica, el decaimiento de la encina (Quercus ilex L.) y el alcornoque (Quercus suber L.) se identificó en los años 80 del siglo XX. Estas dos especies cubren la mayor parte de la superficie forestal del sur y centro de la Península Ibérica, principalmente formando sistemas de dehesa y "montados". Dicha área geográfica está considerada como una de las regiones a nivel mundial que se verán peor afectadas por el cambio climático, lo que agravaría las consecuencias y los efectos del decaimiento de la encina en las dehesas. Las dehesas son ecosistemas mediterráneos semejantes a la sabana, que proveen de diversos beneficios económicos y servicios ambientales. Por su parte, la encina es el árbol más representativo de la Península Ibérica, y la especie principal del estrato arbóreo de las dehesas. La pérdida de este estrato es un problema ecológico y económico de gran relevancia. El decaimiento de la encina está asociado principalmente a la acción de patógenos de suelo, especialmente Phytophthora cinnamomi. Sin olvidar la influencia de otros factores en el síndrome, existe una fuerte asociación entre la podredumbre radicular causada por los oomicetos y la muerte del arbolado. Phytophthora cinnamomi es un patógeno invasor muy agresivo, ampliamente distribuido por todo el mundo, que ha sido asociado con la enfermedad, la decadencia y la mortalidad de una larga lista de diferentes especies vegetales. Es una especie capaz de cambiar su relación trófica con el huésped, comportándose como un organismo biótrofo en huéspedes asintomáticos, y como hemibiótrofo ó necrótrofo en huéspedes susceptibles. Se considera que la encina es la especie del género Quercus más susceptible a la acción del patógeno. De forma adicional, otras especies de los géneros Phytophthora y Pythium se han encontrado asociadas con el decaimiento de la encina en España, Portugal, Italia y Francia. Para estudiar este sistema patógeno-huésped se han llevado a cabo grandes esfuerzos científicos, que han obtenido resultados muy meritorios y han incrementado el conocimiento de las causas y los efectos de la interacción, mejorando las técnicas de gestión para limitar la dispersión y los síntomas del decaimiento. Sin embargo, la mayoría de los trabajos revisados se basaron en aproximaciones empíricas, desconociéndose gran parte de los mecanismos subyacentes que controlan la interacción entre las dos especies. Esta Tesis cubre parte de esta falta de conocimiento básico, centrándose en la interacción entre el huésped y el patógeno a nivel histológico y fisiológico, así como explorando la influencia de la biota del suelo en la severidad de los síntomas de la enfermedad. Para dicho propósito, el trabajo se estructuró en 7 capítulos. El Capítulo 1 proporciona el marco teórico en el que se desarrolla esta Tesis Doctoral, así como los objetivos generales y específicos. El Capítulo 2 muestra la metodología desarrollada para evaluar la colonización e infección de Phytophthora cinnamomi en plántulas de Quercus ilex a través de la cuantificación semiautomática de las estructuras del patógeno presentes en secciones histológicas de raíces finas. El flujo de trabajo fue puesto a punto probando diferentes soluciones de fijación, sustancias de inclusión y métodos de tinción, y los resultados permitieron la diferenciación clara de las estructuras del patógeno y de los tejidos del huésped. Además, distintos índices basados en la localización y especificidad de las estructuras del patógeno y en el tejido del huésped, se evaluaron con el fin de buscar la manera más sencilla y estadísticamente robusta de explicar el progreso del oomiceto en la raíz a través de índices. En el capítulo 3, se llevaron a cabo experimentos en cámara de crecimiento para describir la patogénesis de la interacción entre P. cinnamomi y Q. ilex. Se analizaron secciones longitudinales de epidermis, córtex, tejido parenquimático del cilindro central y tejido vascular, a los 1, 3, 7 y 14 días después de la inoculación. Se cuantificó el área total de estructuras, estructuras intracelulares, estructuras extracelulares y estructuras específicas del patógeno. El análisis de estos datos proporcionó una descripción del ciclo de colonización/infección del patógeno, clasificada en tres etapas diferentes relacionadas con su comportamiento trófico. Asimismo se describieron los cambios histológicos resultantes de la presencia del patógeno o de las respuestas desencadenadas por la planta. En el capítulo 4 se analizó la respuesta diferencial de plántulas de encina ante la inoculación con P. cinnamomi, ante la sequía severa y ante ambos estreses combinados. Plántulas de seis meses de edad fueron inoculados y sometidos a falsa inoculación, y la mitad de cada uno de estos tratamientos fue sometida a sequía severa, mientras que el resto fue regada de manera óptima. Semanalmente se midieron los valores de fotosíntesis, conductancia estomática y fluorescencia, y la biomasa total así como la compartimentación de la biomasa fueron cuantificadas al final del experimento. Los datos resultantes mostraron la existencia de diferencias en la respuesta de las plántulas ante la sequía y la inoculación, así como el efecto aditivo de ambos estreses en la muerte de las plántulas. En el Capítulo 5 se colectaron muestras de suelo de dehesas y se extrajo el ADN total, que se analizó a través de técnicas de metabarcoding, con el fin de evaluar la composición específica y la diversidad de las comunidades fúngica y de oomicetos, y para estudiar sus relaciones con los síntomas de la enfermedad. La comunidad fúngica presentó una gran variedad de patógenos y abundancia de taxones clave de ectomicorrizas. Phytophthora spp. apareció como el taxón dominante dentro de la comunidad de oomicetos, pero las principales especies relacionadas con la podredumbre radicular no fueron las más abundantes, ni presentaron relación directa con los niveles de defoliación. Una unidad taxonómica operacional (OTU) particular, perteneciente al género Trichoderma, presentó correlaciones significativas con la escasez de especies patógenas de Phytophthora spp. Las diferencias en defoliación se correlacionaron con cambios en la funcionalidad de la microbiota del suelo y con los niveles de diversidad de las especies patógenas. El Capítulo 6 presenta la discusión general de la Tesis, incluyendo algunos aspectos que limitan los resultados de los trabajos realizados, y nuevas líneas de trabajo que se derivan de esta Tesis, y finalmente, el Capítulo 7 contiene las conclusiones del trabajo. Los cambios que se producen en la raíz a consecuencia de la inoculación con P. cinnamomi, incluyendo las respuestas defensivas, así como la respuesta diferencial identificada con la colonización/infección, conducen a nuevas apreciaciones sobre la causa de la muerte del arbolado. La encina responde al ataque del patógeno, presentando variaciones en la fisiología diferentes de las causadas por el estrés hídrico, las cuales permiten la recuperación de las plantas si no se superpone un estrés adicional a la inoculación. Adicionalmente, el estudio del microbioma del suelo en dehesas con decaimiento del encinar mostró la influencia de la diversidad microbiana en el estado sanitario del arbolado, así como mostró nuevas especies de oomicetos y hongos que deben tenerse en consideración en el manejo del decaimiento de las dehesas de encina en Andalucía.

Diversity patterns are governed by a complex network of interacting factors. Studies directed to disentangle the most important factors affecting diversity have frequently shown divergent results, which has encouraged a rewarding debate about the relative importance of each factor. Scale dependency has been identified as a direct cause of at least part of such divergences. However, studies with spatially-explicit measurements at different scales are costly and therefore they are relatively scarce despite their importance. Here, we present a database to disentangle the cross-scale variation in the importance of factors affecting the diversity of epiphytic bryophyte communities in Quercus dominated forests (Quercus ilex L., Quercus pyrenaica Willd. and Quercus faginea Lam.) in the North-western region of the Iberian Peninsula. We provide speciesper- site abundance information with more than 9000 entries and an environmental table containing 20 in situ measured variables at three different scales (forest, stand, and sample). The database will help to advance the research of cross-scale effects of diversity patterns while at the same time providing valuable information on the distribution of a poorly known group of organisms. ; The fieldwork was funded by the Spanish Government through grants CGL2007-61389, CGL2010-15693 and CGL2011-28857. N.G.M. was supported by a PhD grant from the Spanish Ministry of Education (grant number AP2007-00905). ; Peer reviewed

Intro -- Contents -- 1 Oaks and People: A Long Journey Together -- Abstract -- Acknowledgements -- References -- 2 An Updated Infrageneric Classification of the Oaks: Review of Previous Taxonomic Schemes and Synthesis of Evolutionary Patterns -- Abstract -- 2.1 History of Classifications of Oaks -- 2.2 Change in Criteria for Classification -- 2.3 Changing from Morphology to Molecules -- 2.4 Revised Subgeneric and Sectional Classification of Oaks -- 2.4.1 Genus Quercus -- 2.4.2 Subgenus Quercus -- 2.4.2.1 Section Protobalanus (Intermediate Oaks) -- 2.4.2.2 Section Ponticae -- 2.4.2.3 Section Virentes -- 2.4.2.4 Section Quercus (White Oaks) -- 2.4.2.5 Section Lobatae (Red Oaks) -- 2.4.3 Subgenus Cerris -- 2.4.3.1 Section Cyclobalanopsis -- 2.4.3.2 Section Ilex -- 2.4.3.3 Section Cerris -- 2.5 Infrasectional Classification: The Big Challenge -- 2.6 Fossil Record -- 2.7 Conclusion and Outlook -- Acknowledgements -- Appendix 2.1 -- References -- 3 The Fossil History of Quercus -- Abstract -- 3.1 Introduction -- 3.2 Methodology -- 3.3 Results -- 3.3.1 The Cretaceous and Paleocene record -- 3.3.1.1 North America -- 3.3.1.2 Europe and Western Asia -- 3.3.1.3 Eastern Asia -- 3.3.2 North America: Eocene through Pliocene -- 3.3.2.1 The Eocene Records -- The Early to Middle Eocene -- The Late Eocene -- 3.3.2.2 The Oligocene -- 3.3.2.3 The Neogene -- Western North America -- Eastern and Central North America -- Central America -- 3.3.3 Europe and Western Asia: Eocene through Pliocene -- 3.3.3.1 The Eocene -- 3.3.3.2 The Oligocene -- 3.3.3.3 The Neogene -- 3.3.4 East Asia: Eocene through Pliocene -- 3.3.4.1 The Eocene -- 3.3.4.2 The Oligocene -- 3.3.4.3 The Neogene -- 3.4 Biogeographical and Palaeoclimatic Implications -- 3.5 Conclusions -- Acknowledgements -- References

4 páginas, 2 figuras. ; Ultrasonic acoustic emissions were measured in Quercus ilex trees of a Mediterranean forest in Catalonia (NE Spain) each season from summer of 2004 to autumn of 2005. Acoustic emissions were maximum during hot and dry summer periods. Acoustic emissions started below 17% soil moisture, 0.85 RWC, and 2.5 MPa leaf water potential. They were negatively correlated with soil moisture and leaf water potential. The relationship between acoustic emissions and leaf water potential was the strongest, indicating that xylem tension is the most important factor inducing both cavitation (acoustic emissions) and a decrease in leaf water potential. Future increase of xylem cavitation derived from climate change may result in growth and survival limitations for this species in the drier southern limits of its current distribution. ; This research was financially supported by MEC REN2003-04871 and CGL 2004-01402/BOS grants from the Spanish Government, a Fundacio´n BBVA 2004 grant, a Catalan Government SGR2005-00312 grant, and the European project ALARM (Contract 506675, EU sixth framework programme). ; Peer reviewed