Estructura ecológica de los pastos de monte turolenses : análisis de las relaciones entre los factores del medio y la vegetación en un territorio de vocación ganadera

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Biológicas, leída en 1982.Fac. de Ciencias BiológicasTRUEProQuestpu

Sostenibilidad ecológica : espacios y oportunidades para un reto inaplazable

Como parte del conjunto de artículos que constituyen el tema central del presente número de Quorum, mi contribución incide sobre la sostenibilidad desde una perspectiva ecológica. Después de una primera parte de presentación de los contenidos de los artículos que siguen, se presenta un modelo para valoración multidimensional del desarrollo. El modelo consiste en un conjunto de ejes valorativos conceptualmente independientes, aunque ligados por compromisos funcionales y relaciones jerárquicas, con los que se construyen escenarios que sirven de referencia para la discusión y valoración de los procesos de desarrollo. El papel básico que reconoce para la calidad del medio natural, lo hace muy adecuado para un continente, América Latina, que destaca por su contribución a la biodiversidad del planeta. Se exponen a continuación algunas ideas sobre el concepto de integridad ecológica que inciden sobre el umbral admisible para la explotación de los recursos y algunas referencias para su estimación. Por último proponemos recomendaciones para tener en cuenta en los sobre procesos de sostenibilidad, basados en nuestra experiencia en planificación ecológica y en la cooperación universitaria en Centroamérica.As a part of the whole of papers forming the main topic of Quorums present number, my contribution deals on sustainability from an ecological perspective. Following the presentation of the main issues discussed in the papers that come afterwards, a model for development multidimensional evaluation is explained. The model consists in a conceptually independent group of evaluative axes, but related by functional trade-offs and hierarchical relationships. Scenarios useful w discuss and assess development processes can be built widí those axis. The basic role that the model recognizes for the ecosystem quality -ecological integrity-, make it as very suitable for a Continent, Latin America, that stands out for his contribution to the earth biodiversity. Following, some ideas about the ecological integrity concept and the way that it contributes to define an admissible resource exploitation threshold, are proposed. In this approach, references for the natural valué assessment are provided. Finally we suggest recommendations to bear in mind in sustainability processes. They are based both on our experience in ecological planning and the Alcalá University cooperation in Central America

The effect of environmental conditions in the duration of daily grazing itineraties of small ruminants in Northeast Portugal

The production of small ruminants (sheep and goats) in Northeast Portugal is an extensive activity, mainly based on exploitation of spontaneous resources. The shepherds direct their flocks on daily grazing itineraries over different types of resources. These itineraries vary throughout the year, in both duration and locations visited. The aim of this study is to analyse the variation of the grazing circuits in relation to the environmental conditions. The time spent by flocks on each itinerary varied from 381 to 746 minutes for goat flocks, and from 300 to 921 minutes for sheep flocks, depending on the duration of daylight. Nevertheless, other environmental conditions have an important role on the pattern of grazing circuits, such as mid-day temperature and abundance of resources

Effect of livestock grazing on combustibles decreasing in Quercus pyrenaica woodlands

Avaliou-se a biomassa herbácea em bosques de Quercus pyrenaica em dois períodos do ano (Primavera e Outono) durante três anos consecutivos (1999, 2000 e 2001), em áreas pastoreadas e não pastoreadas. Para o efeito utilizou-se o método de corte e pesagem em quadrados de 0,25m de lado em ambos os tratamentos (10 e 9 quadrados, com e sem pastoreio, respectivamente). Este procedimento repetiu-se em quatro carvalhais (Freixedelo, Sortes, Rebordaínhos e Zido) localizados em ambientes diferentes e com estrutura distinta. Os resultados mostram diferenças de biomassa acumulada entre locais, entre períodos do ano e anos, e entre os tratamentos pastoreado e não pastoreado. Comprova-se a interacção positiva entre as componentes lenhosa e animal, condição necessária para a abordagem silvopastoril na gestão destes sistemas. The herbaceous biomass was evaluated in Quercus pyrenaica woodlands in two seasons (Spring and Autumn) for three consecutive years (1999, 2000 and 2001), both in grazed and non-grazed areas. For this, we used the method of clipping and weighing, in 0.25 m side plots in both areas (10 and 9 quadrates of grazed and non-grazed land, respectively). This procedure was repeated in four black oak woodlands (Freixedelo, Sortes, Rebordainhos and Zido), all located in different environments and with different structures. The results show differences in the accumulated biomass among the various locations, seasons, years, and among the grazed and non-grazed plots. Evidence shows the positive interaction between the wood and animal components, an essential condition for the silvopastoral approach in the management of these system

Changes in spatial point patterns of pioneer woody plants across a large tropical landslide

We assessed whether the relative importance of positive and negative interactions in early successional communities varied across a large landslide on Casita Volcano (Nicaragua). We tested several hypotheses concerning the signatures of these processes in the spatial patterns of woody pioneer plants, as well as those of mortality and recruitment events, in several zones of the landslide differing in substrate stability and fertility, over a period of two years (2001 and 2002). We identified all woody individuals with a diameter >1 cm and mapped them in 28 plots measuring 10 × 10-m. On these maps, we performed a spatial point pattern analysis using univariate and bivariate pair-correlation functions; g (r) and g12 (r), and pairwise differences of univariate and bivariate functions. Spatial signatures of positive and negative interactions among woody plants were more prevalent in the most and least stressful zones of the landslide, respectively. Natural and human-induced disturbances such as the occurrence of fire, removal of newly colonizing plants through erosion and clearcutting of pioneer trees were also identified as potentially important pattern-creating processes. These results are in agreement with the stress-gradient hypothesis, which states that the relative importance of facilitation and competition varies inversely across gradients of abiotic stress. Our findings also indicate that the assembly of early successional plant communities in large heterogeneous landslides might be driven by a much larger array of processes than previously thought

Heterodinuclear TiMo and TiW complexes bridged by the (dimethylsilanediyl) dicyclopentadienyl ligand

Reactions of the tricarbonyl-molybdenum and -tungsten complexes [M(CO)3(MeCN)3] (M = Mo, W or [Mo(CO)3(mesitylene)] with equimolar amounts of [Ti(η5-Cp′){(η5-C5H3)(SiMe2)2 (C5H4)}Cl2] (Cp′ = C5H5, C5Me5) lead to the heterodinuclear compounds [Ti(η5-Cp′)Cl2{μ-[(SiMe2)2(η5-C5H3)2]}MH(CO)3]. These dinuclear complexes are isolated as single cis- and trans-isomers or as mixtures of both depending on the starting complex and the reaction conditions. The molar ratio of the two resulting isomers is controlled by thermodynamic and kinetic factors which prevent the application of stereoselective methods for some of the products. Reaction of the hydrido cis- and trans-complexes with CCl4 in CH2Cl2 allows the isolation of chloro complexes [Ti(η5-Cp′)Cl2{μ-[(SiMe2)2(η5-C5H3)2]} MCl(CO)3] of the same configuration. All of the new heterodinuclear compounds reported were characterized by their analytical composition, IR and NMR spectroscopy and the molecular structure of cis-[Ti(η5-C5Me5)Cl2{μ-[(SiMe2)2(η5-C5H3)2]}WH(CO)3] was studied by X-ray diffraction methods.Comunidad Autónoma de Madri

Nutritive value of Quercus pyrenaica Willd browse species in NE of Portugal

Quercus pyrenaica Willd (pyrenean oak) occurs in a transition between the Mediterranean sclerophyllous and the temperate deciduous forest, being one of the most abundant and characteristic oak species in the Iberian Peninsula, due our economical and biological importance and by several services produced. The aim of this study was to assess the nutritive value of key browse species of Pyrenean oak Mediterranean Ecosystems in Trás-os-Montes region (Portugal). The study was to undertake at different mature stages the evolution of chemical composition and in vitro digestibility of shrub twigs and tree leaves. The browse species evaluated were Cytisus scoparius (L.) Link, Cytisus striatus (Hill) Rothm, Cytisus multiflorus (LHér.) Sweet, Genista falcata Brot. and Quercus pyrenaica. Tree samples were formed by foliage and shrub by mixed twigs from several specimens. Hand-samples of the different species were taken along the year seasons, in five moments of the year, begin May in late spring, July in summer, and final September in autumn, December in winter and begin March in early spring. Quercus pyrenaica was sampled only during the leaf production periods in five moments too. The dates were: May, July, August, September, and October; regarding different stages of leaves: very young leaf, young leaf, mature leaf, leaf in early of senescence, senescent leaf. Species varied widely in crude protein content (CP) (10.06-22.57 gKg-1 DM), neutral detergent fibre content (NDF) (36.03-66.53 gKg-1 DM), acid detergent fibre content (ADF) (24.22-53.50 gKg-1 DM), acid detergent lignin content (6.20-15.76 gKg-1 DM) and in vitro digestible organic matter (IVOMD) (39.21-70.39 %). Cytisus sp. showed the higher CP and IVOMD values. Shrub species showed the highest nutritive value in late spring and the lowest values in autumn. Oak leaves presented a constant composition along the leaf cycle just, this pattern changed in very young leaf stages when leaves were not formed

Silyl and siloxanediyl cyclopentadienyl titanium and zirconium complexes: synthesis and reactivity. X-ray molecular structure of [Zr{η5-C5H4SiMe2(μ-OH)}(μ-Cl)Cl2]2

Chloro(dimethyl)silyl-η5-cyclopentadienyl group 4 metal complexes of the type [M(η5-C5H4Cl)Cl3] (Full-size image (<1 K)) react with thallium salts Tl(C5H4R) (R = H, SiMe3) to give mixed dicyclopentadienyl derivatives [M(η5-C5H4R)(η5-C5H4SiMe2Cl)Cl2], (M = Ti, R = H 3, R = SiMe34; M = Zr, R = H 5, R = SiMe36) in high yield. Hydrolysis of complexes 3 and 4 affords the dinuclear complexes [Ti(η5-C5H4R)Cl2]2{μ-[(η5-C5H4SiMe2)2O]}] [R = H 7, R = SiMe38) containing a siloxanyl bridge, by elimination of two equivalents of HCl. Reactions of complexes 1 with hydroxo containing reagents such as anhydrous LiOH and SiPh2(OH)2 give the derivatives [Ti(η5-C5H4SiMe2Cl)Cl2]2(μ-O)], 9 and Ti[μ-(η5-C5H4SiMe2OSiPh2-η1-O)]Cl2, 10 identified by analytical, spectrometric and spectroscopic data. Treatment of analogous complex 2 with water produces the dimeric monocyclopentadienyl zirconium trichloride adduct [Zr(η5-C5H4SiMe2OH)Cl3]2, 11. Compound 11 has been characterized by X-ray crystallography.Universidad de AlcaláConsejería de Educación de la Comunidad de Madri

Dicyclopentadienyl titanium and zirconium complexes with the double bridged bis(dimethylsilanodiyl) dicyclopentadienyl [(Me2Si)2(η5-C5 H3)2]2- ligand: X-ray molecular structure of [Ti{(SiMe2)2(η5-C5H3)2}Me2]

The reaction of the doubly bridged bis(1,1′,2,2′-dimethylsilanodiyl)-η5-dicyclopentadienyl titanium and zirconium complexes Full-size image (<1 K) with water gave the μ-oxo derivatives Full-size image (<1 K). Addition of one equivalent of M′R (M′ = MgCl, R = CH3, CH2SiMe3; M′ = Li, R = CH2CME2Ph) to toluene or diethyl ether solutions of Full-size image (<1 K) afforded the chloro alkyl derivatives [M{(SiMe2)2(η5-C5H3)2}CIR]Full-size image (<1 K). Compounds 3 and 4 reacted with [CPh3][B(C6F5)4] at −78°C in CD2Cl2 leading to the cationic species Full-size image (<1 K) as demonstrated by NMR spectroscopy. The titanium(III) and zirconium(III) serivatives [M{(SiMe2)2(η5-C5H3)2} (μ-Cl)2 (M = Ti (12), Zr (13)) were obtained by reduction of 1 amd 2 with one equivalent of sodium amalgam. The X-ray molecular structure of [Ti{(SiMe2)2(η5-C5H3)2}Me2] (3) has been determined by diffraction methods.Financial support for this research by DGICYT (Project PB92-0178-C) is gratefully acknowledged. A,M. is grateful to Consejeria Educación (CAM) for a fellowship