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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Ecological responses to climate variability in west Cornwall

Kosanic, Aleksandra January 2014 (has links)
Recent (post-1950s) climate change impacts on society and ecosystems have been recognised globally. However these global impacts are not uniform at regional or local scales. Despite research progress on such scales there are still gaps in the knowledge as to 'what' is happening and 'where'? The goal of this study addresses some of these gaps by analysing climate variability and vegetation response at the furthest south westerly peninsula of the United Kingdom. This research is focused on West Cornwall (South West England) - an area dominated by a strong maritime influence. The first part of this PhD research analysed archive and contemporary instrumental data in order to detect any trends in climate variability. The weather data was retrieved from the Met Office archive for Camborne 1957-2010 and Culdrose 1985-2011 stations; Trengwainton Garden (1940-2010), and from the Royal Cornwall Polytechnic Society, for Falmouth (1880-1952) and Helston (1843-1888). The data showed positive trends in mean annual and maximum temperature with the largest trend magnitude in the 20th and 21st century. Seasonal temperature change varies locally with the highest increase in autumn spring and summer. Precipitation trends were only positive for the 19th century for Helston. Correlation between precipitation data and North Atlantic Oscillation (NAO index) was negative, however the opposite result was detected when the NAO index was correlated with temperatures. Surprisingly, return period analysis showed a decrease in the frequency and intensity of extreme precipitation events post 1975 for Camborne and Trengwainton Garden stations. The second part of this study analysed changes in vegetation distribution in West Cornwall using historical and contemporary vegetation records. Historical vegetation records were used from the Flora of Cornwall collection of herbarium records and contemporary vegetation records which were available online, containing mainly the 'New Atlas of British and Irish flora'. Data sets were geo-referenced using ArcGIS in order to analyse changes in species geographical distribution pre and post-1900. Analysis showed that historical vegetation records can be used to assess any changes in geographic distributions of vegetation. Analysis for the area of West Cornwall showed a loss of range for 18 species, for 6 species this loss was larger than 50% of the area, and there was no change in overall range area for 10 species. Ellenberg values and environmental indicator values showed that they can be used as an indicator of environmental change, showing a decrease in species with lower January temperatures. Analysis also showed an increase in moderate wetter species, where species with extreme low and high precipitation environmental indicator values showed a greater loss. Furthermore species with a higher requirement for light showed a loss as well as species with lower nitrogen values. To analyse the loss of species at the local scale, West Cornwall was divided into three areas (North Border Cells, Central West Cornwall Cells and South Border Cells). The highest loss of 11 species was detected for South Border Cells, where the loss for Central West Cornwall Cells was 6 and for North Border Cells 8 species. It was found that 17 species were experiencing loss on different local sites. For 9 of these 17 species, change at the local scale was different to the national scale change at the individual species level, group level and habitat level. Furthermore, the whole area of West Cornwall lost two species post-1900, with a different loss locally. This showed that species could be protected locally in appropriate microclimate refugia, which will be of benefit for the preservation of regional identity ecosystem services and overall genetic pool of the species.
2

Träd och buskar i kantzoner : en undersökning av kanteffekter i några av östersjöregionens skogar

Jernberg, Kersti January 2011 (has links)
Around the world, forests are generally being fragmented and as plant populations decline in both sizeand number of individuals, the genetic variation will also decrease whitch in the end leads to totalextinction of the plant. In this paper, I wanted to investigate what specific species of trees and shrubsyou usually find in the edge and core habitats in some of the forests in the Baltic Sea region. I alsowanted to identify the edge effects and their sources and finally compare the results between thedifferent regions.The data sources used are derived from the ongoining research project Landscape structures, patterns ofbiodiversity and conservation strategies in the Baltic Sea region by Kari Lehtilä, Patrik Dinnétz ochTiina Vinter who have made a record of all herbaceous plant species in four randomly chosen forestregions situated around the Baltic Sea: Estonia, Skåne, Södermanland and Germany. I made statisticalanalyses, using the computer program R, concerning the distribution of species in the edge habitats ofthe forests as well as in the core habitats. I performed generalized linear models and then variationanalyses with the factors light and biomass in order to investigate wether edge effects might appear dueto these factors. I also used the ecological characteristics – Ellenberg indicators – light, soil pH andnitrogen performing linear regression models. I then compared the results – within the regions but alsobetween them.As the results showed great variancy both within the regions and between them no general explanationto the edge effects could be affirmed. The Ellenberg analyses showed no difference between the species,i. e. the ecological characteristics could not explain why some species were associated to edge habitatsand some were not. All four regions had in common that the greatest biodiversity were to be found inthe edge habitats, which is characteristical for a habitat in an early successional state. Due to the thefeatures of the forests, the specific species that received the label ”edge species” or ”core species” werenot always mutual in all regions. For example Quercus robur turned out to be a typical forest species inGermany while in Estonia it was strongly associated to edge habitats and in this investigation one mightdiscuss later states of successions in Germany rather than stronger edge effects in Estonia.
3

How former arable fields with permanent grazing differ from managed semi-natural pastures in Sweden

Galin, Isolde January 2019 (has links)
New farming needs and innovations have, over time, led to changes in land use. Arable fields have been turned into pastures and semi-natural pastures into arable fields. Due to the ecological value of continually grazed semi-natural pastures in Sweden the aim of this study is to find out how former arable fields that are permanently grazed differ from semi-natural pastures. In this study I selected appropriate semi-natural pastures from a national monitoring program on seminatural- pastures and meadows. Plots continuously grazed were compared with grazed plots on former arable fields. Pair-wise differences in the Ellenberg indicator values Light (L), Soil moisture (F), soil pH (R) and soil nitrogen (N), vertical coverage of trees, bushes and vegetation, species richness and species composition were tested. Except for species composition there were only small differences between former arable fields that are permanently grazed and semi-natural pastures. That means former arable fields can with time and grazing gain many of the values continuously grazed semi-natural pastures have.
4

Biologie a stanovištní nároky ohroženého druhu stepníka Eresus moravicus (Araneae: Eresidae)v Česku / Biology and habitat requirements of endangered ladybird spider Eresus moravicus (Araneae: Eresidae) in Czechia

KREJČÍ, Tomáš January 2012 (has links)
The ladybird spider Eresus moravicus is one of our most endangered spiders. It is therefore necessary to know its habitat requirements and have at least basic knowledge of its biology to design an appropriate management to protect sites of its natural occurrence. Phytocenological analysis was made at each site and the outcomes were evaluated based on the Ellenberg´s indicator values. Also slope and exposure, litter layer and the quantity of rubbel were measured on the localities. Individuals were taken from burrows for the measurement of the prosoma length (investigation of the length of the life cycle). Exuviae were collected from the same burrows for measurement of the prosoma length. From these data the number of instars was determined. Prey remains were taken at most of those sites from 5?10 burrows and determined. Offsprings from several maternal burrows were taken, counted and weighted (research of fecundity of females). Weight of offsprings is important also in terms of their dispersion ability. The offsprings ability to balloon was investigated experimentally in laboratory conditions. The ladybird spider Eresus moravicus occurs in warm regions with high intensity of irradiation, mostly on the southern and southwestern slopes. Sites are characterized by poor herbaceous vegetation without trees and shrubs and by a thin layer of humus. Female lives for four years and the male for three years. The number of instars can reach to 13. Beetles (Coleoptera) are the most importent prey, the importent component of food are ants (Formicidae), too. Eresus moravicus has more offsprings than Eresus sandaliatus and Eresus kollari, more eggs in the cocoon than E. kollari and heavier offsprings than E. kollari and E. sandaliatus. In offsprings of E. moravicus and E. kollari pre-ballooning behavior of two types was observed: "tip-toe" behavior and "drop and swing" behavior.
5

Změny vegetace vlhkých luk ve Slavkovském lese / Vegetation changes of wet meadows in Slavkovský les

Šimák, Martin January 2018 (has links)
This thesis focuses on the changes of vegetation of the wet meadows in Slavkovský Les during past decade. It uses data on vegetation gained from 100 permanent plots. By the analysis of the species composition and diversity it aims to elucidate the changes of the wet meadows over the last ten years. It aims to define, which are declining and which are becoming more common. Applied management should have a great impact on the observed vegetation changes so its effect is studied in the thesis as well. The knowledge of the suitable management should lead to conservation of the local biodiversity. The abiotic environmental factors are important as well as they can influence the species composition. These factors were studied by the application of Ellenberg indicator values on the species present in the study. These changes were compared in time and in a combination of time with a management type. Thus, we should be able to say how the environment has changed in the past decade and whether the type of management has any effect on the changes. Furthermore, the thesis explores whether changes in species composition over time may be explained by species traits. The results indicate that the species diversity and composition have indeed changed during the past decade. Apparently, the higher amount of...
6

Vegetational and landscape level responses to water level fluctuations in Finnish, mid-boreal aapa mire – aro wetland environments

Laitinen, J. (Jarmo) 09 September 2008 (has links)
Abstract Gradient, which is largely considered to be related to water level in mires, is referred to as a microtopographic mud bottom to carpet to lawn to hummock level gradient or the hummock level to intermediate level (lawn) to flark level gradient. The relationship of this vegetation gradient to various physical water level characteristics was studied. The general classification used in the present summary paper divides the aro vegetation of the inland of Northern Ostrobothnia into two main groups: (a) treeless fen aro vegetation (Juncus supinus, Carex lasiocarpa, Rhynchospora fusca, Molinia caerulea) and (b) heath aro vegetation (Polytrichum commune). The first group (a) was divided into fen aro wetlands with an approximately10 cm peaty layer at most and into aro fens with a peat layer thicker than 10 cm. The treatment of the water level gradient was divided into three main groups. (1) The mean water level correlated with mire surface levels (microtopographic gradient) within mires with slight water level fluctuations and partly within mires with considerable water level fluctuations. (2) Three habitat groups could be distinguished on the basis of the range of water level fluctuation i.e. mires with slight water level fluctuations, mires with considerable water level fluctuations and the aro vegetation with extreme water level fluctuations. (3) The timing of water level fluctuations indicated that there are different types of patterns within aro wetlands, the seasonal pattern being mainly a response to yearly snow melt and the several-year-fluctuation pattern being related to the regional groundwater table fluctuation in mineral soils (heath forests). A link was suggested between the stability of the water regime and peat production in local aapa mire – aro wetland environments. From the point of view of peatland plants the direction of variation from a stable to an unstable water regime in aapa mire – aro wetland environments represents a transition towards more and more harsh ecological conditions, partly forming a gradient through natural disturbance. A qualitative functional model was provided for the mire – aro wetland systems of Northern Ostrobothnia. The model supposes differences in the characteristics of peat between two functional complexes within a mire system. Finally, the model for local mire – aro wetland systems was converted to a general from: diplotelmic (acrotelm) mires were divided into two subtypes (diplotelmic water stabilization mires, diplotelmic water fluctuation mires) and the relationship of those subtypes to percolation mires and seasonal wetlands was considered.
7

Observed changes in mountain vegetation of the Alps during the XXth century - Role of climate and land-use changes

Bodin, Jeanne 18 March 2010 (has links) (PDF)
La végétation herbacée est un bon indicateur des conditions environnementales. Pour cette raison, elle a souvent été utilisée pour mettre en évidence les changements environnementaux causés par les actions humaines, tels qu'eutrophisation, dépôts atmosphériques acides, changements de l'usage des sols ou de la pression d'herbivorie. Depuis peu, on s'intéresse aux effets des changements climatiques sur les écosystèmes en général, et sur la végétation en particulier. Le choix des zones d'étude s'est naturellement porté sur la montagne, car le gradient thermique induit par le relief (-0,56°C pour 100 mètres d'altitude) y est mille fois plus élevé qu'en plaine le long du gradient latitudinal. D'autre part, les zones de montagne sont soumises à une urbanisation et une pression agricole moindre qu'en plaine, limitant ainsi les obstacles à la migration des espèces. Ces deux arguments font des régions de montagne une zone privilégiée pour l'étude de la réponse migratoire précoce de la végétation aux changements climatiques. Jusqu'ici, les études effectuées se sont focalisées pour la plupart sur la limite supérieure des espèces, ou sur de petites zones géographiques, ou bien encore sur des zones où il est difficile de dissocier les effets du réchauffement de ceux des changements d'usage des sols, qui se produisent eux aussi à grande échelle. Une partie de cette thèse est consacrée aux milieux forestiers montagnards, dans lesquels l'effet du pastoralisme est réduit. D'autre part, une méthode basée sur la modélisation des changements de la réponse de la végétation au gradient d'altitude est développée, permettant le rééchantillonnage sur placettes non-permanentes, et ainsi d'étendre l'utilisation de données anciennes à des séries de relevés non géolocalisés. En s'appuyant sur cette méthode, deux caractéristiques de la végétation ont été analysées : la position de l'optimum d'espèces prises individuellement d'une part (données de l'Inventaire Forestier National dans les montagnes méditerranéennes du sud-est de la France), et les changements de la valeur indicatrice des communautés végétales d'autre part (vallée de la Maurienne, France). Par ailleurs, on a étudié les déplacements à long terme de la limite inférieure des espèces dans la vallée de la Bernina (Suisse), pour tester si la réponse des espèces en limite inférieure, peu étudiée jusque là, est identique à celle en limite supérieure de leur distribution. Enfin, on a étudié l'évolution de la flore d'une zone très localisée, mais par ailleurs protégée des migrations d'espèces par une large barrière physique constituée par deux glaciers (Nunatak Isla Persa, Bernina, Suisse) permettant de s'affranchir totalement des effets potentiels d'autres perturbations anthropiques concomitantes. Dans ces différentes études, les intervalles de temps entre chaque inventaire ou échantillonnage varient de 14 ans à un siècle. Chacun des cas étudiés montre une remontée des espèces en altitude : remontée moyenne de +12,6 m/décennie des optimums de 175 espèces forestières dans les montagnes méditerranéennes, communautés des forêts de Maurienne évoluant vers une végétation plus thermophile à une altitude donnée équivalent à une remontée moyenne de +29.6m/décennie, retrait de la limite inférieure des espèces en Bernina de +5,6 m/décennie, arrivée d'espèce d'étages inférieurs sur le nunatak Isla Persa. Mais d'autres phénomènes expliquant la réponse observée de la végétation sont clairement mis en cause dans cette étude : fermeture et maturation du couvert forestier relativement plus importante à basse altitude dans les montagnes méditerranéennes, eutrophisation importante de la végétation en vallée de la Maurienne probablement due à l'augmentation du trafic routier, probable fragmentation de l'habitat ou dispersion par les randonneurs en Bernina. Ces perturbations anthropiques directes jouent à des échelles de temps et d'espace comparables à l'effet anthropique indirect du changement climatique. Il est donc primordial de les prendre en compte dans les changements de végétation observés, avant de conclure à un effet du réchauffement climatique seul.
8

Adventivní odnožování krátkověkých rostlin v přírodních populacích / Adventitious sprouting of short-lived plants in natural populations

MALÍKOVÁ, Lenka January 2011 (has links)
Disturbance is one of most important selective factor causing removal of plant biomass. Man-made habitats are characterized by strong and unpredictable disturbances, providing bare soil surface colonized by plants with short life cycle. Populations of the short-lived plants are, however, vulnerable to the strong disturbance removing all stem parts with reserve axillary meristems in the case it occurs before plant flowering and fruiting. Nevertheless, 2 % of annual and 14 % of biennial plants are able to overcome meristem limitation by adventititous sprouting from hypocotyle or/and roots. This thesis is composed of four original studies describing the occurrence of adventitious sprouting in natural populations of 22 monocarpic weeds of Central Europe and one species in Indonesia. The studied phenomenon was analyzed in relation to various environmental factors and plant traits in the field and in experimental conditions.
9

Vegetation succession in old fields at broad landscape scales / Vegetation succession in old fields at broad landscape scales

JÍROVÁ, Alena January 2012 (has links)
This thesis is focused on succession in old fields in Central Europe. Repeated sampling, analysis of surrounding vegetation and soil measurements were conducted in the Bohemian Karst Landscape protected area. Samples from the Doupovské hory Mountains and the rest of the Czech Republic were added to discover basic principles of old field succession at the larger scale of landscapes.
10

Long term restoration effects : Effects of restoration measures on restoration success in nature reserves in acidic fen, buffered fen, dry heather, wet heather, and wet grassland in Drenthe, Netherlands

Nyström, Erika January 2020 (has links)
Habitat degradation, fragmentation and loss are important factors causing loss in biodiversity and red listed species, and restoring habitats is essential in preventing this. However, there is a limited knowledge of the long term effects of restoration measures. This study focuses on analysing the long term restoration success of restoration measures carried out in a restoration program between the 1980's and early 2000's in locations of acidic fen, buffered fen, dry heather, wet heather, and wet grassland. The aim of the restoration program was to diminish the effects on ecosystems that were influenced by eutrophication, acidification, and dehydration. The locality species composition and Ellenberg values of nitrogen (EVN), moisture (EVM) and pH levels (EVpH) are analysed, by using previous and current restoration success scores from 54 locations in the province of Drenthe in the Netherlands. The dependence of restoration success score and Ellenberg values on change over time, habitat type, restoration method and EVN, EVM and EVpH are analysed. Restoration success depended on habitat type, with wet heather having significantly higher success compared to wet grasslands. The change in score over time, however, did not vary among habitats. Restoration success did not depend on restoration method(s), nor did change in restoration success. Ellenberg values varied among habitat types, and EVM changed significantly over time in dry heather, but was not significantly related to restoration success score. In conclusion, wet heather was shown to be doing quite well, but could benefit from additional restoration. Acidic fen, buffered fen, dry heather, and wet grassland have all shown poor long term restoration effects, indicating an overall need for further restoration measures. The results also highlight the importance of further studies into the effect of long term restorations, especially focused on finding successful restoration methods, and the importance of detailed data gathered in the field.

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