Diekmann, Martin
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Item-typ:Veröffentlichung, Phenotypic trait variation in forest herbs along environmental gradients in the context of climate change(2014-07-22); ; ; Temporal and spatial environmental variation affects every organism in manifold ways. Especially for sessile life forms like plants it poses a big challenge to deal with fluctuations in their environment, since they are hardly able to quickly escape unfavourable conditions. Recently, it has been shown that the combination of several human-induced, rapid changes in the environment (known as global environmental change) represents large novel selective pressures to which plants need to respond and possibly adapt. Amongst others, the rapid world-wide increase in temperature is assumed to have major ecological and evolutionary consequences being a major threat to species diversity. Hence, it is of great importance to get deeper knowledge about the ability of plant species to react to environmental changes, especially in climate. One way of plant populations to avoid extinction is tracking the shift in climate either in time or space (e.g. shifts in phenology or to higher latitudes / altitudes). Such a response, however, may be impeded by low migration rates of many species and / or current human-induced habitat fragmentation (possibly combined with reduced genetic variation in fragmented populations). Thus, the ability of plant species to adapt themselves to new climatic conditions, via a combination of adaptive and non-adaptive phenotypic plasticity, genetic diversity or local adaptation, may provide an alternative vital strategy for their survival and long-term persistence. To examine the response of plant species to different environmental conditions, fitness-related plant functional traits are commonly used. So far, the variability of these traits within a species (i.e. intraspecific variation), however, has been mostly neglected. Still, there is recent awareness that i) intraspecific variation may differ substantially across different scales (among regions, between populations, within populations or even within individuals) and ii) that it may reflect the general potential of a species' ability to adapt to a new environment via phenotypic plasticity, genetic diversity or local adaptation. Therefore, the major objective of this study was to enlighten patterns and underlying causes of intraspecific variation within and among populations of temperate forest under-storey herbs with regard to different environmental conditions and climatic variation in particular. The forest understorey comprises mainly specialist species, which may be notably threatened by global change due to their low migration rates and colonization success. These species may thus especially rely on their ability to adjust themselves to a changing environment. Overall, phenotypic responses differed between species and plant functional types used in this study. Therefore, impacts of global change on different species are likely diverse and will potentially strongly affect forest community structures. Further research integrating experimental studies and examination of numerous species in natural plant communities and especially the consideration of several (human-induced) environmental changes is required to allow generalization and more explicit prospects for specific species. In summary, this thesis emphasizes the importance of taking intraspecific variation into account when using plant functional traits as proxies for species performance related to environmental variation.Dissertation310 149 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Hedgerows in agricultural landscapes as a habitat for forest plant species(2009-07-09); ; ; In many countries of the world the landscape today is dominated by agri- and silvicultural land, whereas the former natural habitats, such as forests, have largely been destroyed or reduced in size and quality. As a consequence, many herbaceous forest plant species are endangered, especially in the intensively used farming landscapes of Central Europe. Hedgerows, common elements of rural landscapes, partly offer a similar environment as forests. They have been proposed as habitat and conservation corridor for woodland herbs, but their importance for the survival of these species is still not clear. In this study the value of hedgerows for the conservation of forest plant species was examined with special attention paid to the influencing factors mainly responsible for the occurrence of these herbs. Selected for study was an agricultural used region with a highly fragmented forest cover and a relatively dense hedgerow network in the hinterland of Bremen, a city in north-western Germany.The first objective of this study was to survey the hedgerows for the occurrence of forest specialists and to determine which factors are influencing their distribution. In the study region almost a quarter of all found herbaceous species (43 of 173) could be classified as typical woodland plants. Endangered species were found more often in forests than in the adjacent hedgerows. Averaged across species there was a predominant effect of environmental factors on the occurrence of forest species in hedges. Forest herbs were favoured by low nutrient and light availability and a close distance to nearby woodland. A further objective was to test the suitability of the habitat hedgerow for the survival of five selected forest species (Adoxa moschatellina, Anemone nemorosa, Circaea lutetiana, Polygonatum multiflorum and Stellaria holostea) with common occurrence in hedges. The comparison of several life-history attributes (as a measurement of plant fitness) between the habitat types forest and hedgerow resulted only in few differences, which show no consistent patterns across species. Adoxa, Anemone and Polygonatum performed equally well in hedgerows and forests, whereas Stellaria appeared to have a higher fitness in hedgerows. In contrast, Circaea showed a higher reproduction under forest conditions. However, performance of these species was mainly influenced by light and soil water availability.The survey of forest-hedgerow transects for changes in forest species richness and frequency revealed a strong negative relationship with species number and distance from the forest edge. This was assumed to be an indication for the conservation corridor function of hedgerows for these species. However, almost a quarter of the forest species of the surrounding forests were not able to spread within hedgerows. Hedgerow age was not influencing the number of species, but older hedgerows showed a smaller variation in species composition. Furthermore, woodland species with high frequencies in forest-hedgerow transects had comparatively high Ellenberg values for light, and were mostly associated with seed dispersal by wind or animals.The last objective was to examine the suitability of a set of ecological and life-history variables, reported to have some effect on the occurrence of woodland species, predicting the occurrence of forest herbs in hedgerow networks throughout Europe. The single factor light availability had a stronger relationship to the frequency of forest herbs of a tested hedgerow network than the chosen set of variables. It is likely that the regional pool of woodland species is more influential for the species composition of the tested hedgerow network than other variables. The investigation of changes in environmental conditions and species composition along a climate gradient across Europe resulted in some differences, which are mainly explained by changes in climate. Hedgerows in more continental areas showed species compositions indicating drier and less acid soils and had lower proportions of chamaephytes and wintergreen species. In sum, climatic differences together with variations in the regional forest species pool have an important effect on the woodland species composition of hedgerows.In conclusion, hedgerows of north-western Germany provide for the majority of woodland herbs a suitable habitat and they help them to survive in an otherwise hostile environment most probably by increased connectivity between habitat patches. Endangered forest species seemed, in contrast, to be restricted to (ancient) forests and not to thrive in hedgerows. Further analyses have to consider the regional pool of forest species, which was found to be most decisive for the species composition of hedgerow networks.Dissertation275 161 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Long-term vegetation change in semi-natural grasslands – disentangling trends from pseudo-turnover(2024-07-08); ; ; Grasslands cover a significant part of the Earth’s surface and support a large proportion of its biodiversity. Despite their importance, species-rich grasslands have been severely decimated and degraded over the past century. Resurvey studies can provide the necessary knowledge of current developments in grasslands to enable effective conservative action. Many insightful resurveys have been conducted in recent decades, however, grassland ecosystems have been under-represented in these studies. Data collected during fieldwork often contains a significant amount of noise due to inaccuracies in the data collection, inappropriate study design, and random variation in species composition. In the methodological part of this thesis, we aim to contribute to disentangling signal from noise in resurvey studies. Specific resurvey studies in Nardus grasslands and calcareous grasslands were conducted. We introduced the concept of “baseline turnover” to measure the extent of vegetation changes that occur regularly due to stochastic fluctuations in species composition. It is an important factor to consider when attempting to distinguish signal from noise in studies of vegetation change. With an article on the statistical phenomenon of “regression to the mean”, we aimed to raise awareness of this potential pitfall in the statistical analysis of resurveys and longitudinal experiments. A resurvey of Nardus grasslands in western Germany confirmed the trend of soil pH increase in acidic soils. However, the widespread eutrophication of Nardus grasslands was only weakly pronounced. We believe that this is due to the exceptionally consistent management of annual mowing over the previous 30 years. The initial survey of calcareous grasslands in Lower Saxony, Germany, confirmed that particularly warm and dry microclimates have had a positive effect on the characteristic species in the past. In the resurvey, the vegetation showed clear signs of the severe drought that had occurred. This can be interpreted as a warning that sites that previously favoured typical calcareous grassland species may develop conditions that are too extreme in the future.Dissertation136 172 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, The vegetation of hedgerows in changing agricultural landscapes - past and present patterns(2022-07-11); ; ; Hedgerows, a prominent landscape element across the oceanic regions of Western and Central Europe, separate agricultural fields and offer near-natural wooded habitat for a variety of plant and animal species. The majority of today’s hedgerows were created in the 18th and 19th centuries during the Enclosure Acts, when a shortage of wood led to the planting of hedgerows as living fences. To keep them healthy and stock-proof, the hedgerow’s shrub layer needed to be regularly managed, with the management technique employed depending on regional traditions. The intensification of agriculture taking place over the past several decades changed the European cultural landscape - with severe consequences for its biodiversity and ecosystem functioning. Hedgerow management was increasingly neglected and large parts of the European hedgerow network were removed during the land consolidation of the 1960s to 1980s. Since then few new hedgerows have been planted, leaving fragmented habitats and a cleared landscape. When managed properly, hedgerows provide important ecosystem services, such as linking otherwise isolated habitats, reducing erosion by wind and water, and protecting adjacent fields and cattle from strong weather conditions. Today, hedgerows are valued for their ecological and amenity functions and are protected in most European regions. This thesis studies the vegetation of hedgerows and which factors influence their biodiversity. The patterns found were analysed on different temporal as well as spatial scales to include past and present effects, e.g. of management, agriculture, landscape structure and climate. We demonstrated that hedgerows provide a diverse habitat for various plant species, but are under considerable threat by agricultural intensification, habitat loss and climate change. Nature conservation efforts and appropriate management, however, can preserve hedgerows as key elements for the biodiversity in agricultural landscapes.Dissertation459 419 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Species' responses along environmental gradients on different spatial scales(2015-05-19); ; ; The abundance of species on Earth varies greatly - while some occur all over the globe, others can only exist in very distinct regions. Trying to explain the reasoning behind the temporal and spatial variation in the commonness and rarity of species has a long history in ecology and yet, many pieces are still missing to complete the puzzle. This thesis investigates species' responses to changing environmental gradients and asks in how far niche characteristics can be used to predict species' range sizes at different spatial scales. We worked with herbaceous species from semi-natural grasslands as well as deciduous forests, focusing especially on their reactions to abiotic conditions (soil pH, nutrients and light). We could show that the breadth of resources used by species (especially regarding soil pH), as well as their tolerance limits, are reliable predictors for their rarity and commonness across different spatial scales. Furthermore, we believe that niche properties can provide guidelines for conservation decisions, especially concerning the selection of suitable habitats for the reintroduction of species. This is a particularly important task to preserve the world s biodiversity in today s ever changing environments.Dissertation356 131 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Ökologie und Biologie gefährdeter Stromtalpflanzen(2009-12-08); ; ; In Central Europe, more than 100 vascular plant species are exclusively or predomi-nantly confined to the basins of large rivers: the so-called river corridor plants. As the natural habitats along the rivers have been destroyed and degraded by the regulation of watercourses, the building of dikes, land reclamation and agricultural intensification, they may account for an above-average proportion of endangered species. Due to the fragmentation of their habitats, many populations are small and highly isolated and this may threaten the viability of populations. The degree and the way in which species are impacted can vary between species or groups of species, respectively, depending on their traits, such as their distribution pattern or their life-form. The aim of this study was therefore to find a general pattern reflecting the fragmentation effects on perennial river corridor plants and to advise conservation measurements for these species. The study was carried out in the highly fragmented floodplains of the Weser and Elbe systems in North-western Germany.The first objective of the study was to assess the effects of habitat fragmentation on the extinction of populations and the changes in population sizes of four endangered perennial river corridor plants: Euphorbia palustris, Pseudolysimachion longifolium, Sanguisorba officinalis und Senecio paludosus. High extinction rates of small populations (≤ 25 individuals) could be identified as the most probable cause for the decline of the species studied while the isolation of populations had no effect. Sudden environmental stochasticity induced by human activity, such as land reclamation, changes in land use, or utilization of pesticides, may have led to extinction in the short-term. If conditions stay unchanged, nearly all of the surveyed populations will have become in less than 120 years. This also includes the large populations (> 100 individuals) even though they have a much higher chance of survival or even growth to a size of 1000 individuals and more.In a next step, we analyzed whether the negative effects of habitat fragmentation would reduce reproduction in fragmented populations of Euphorbia palustris, Lathyrus palustis, Pseudolysimachion longifolium, Sanguisorba officinalis and Senecio paludosus and would thus lead to extinction of populations in the long-term, too. Reproductive success of all species studied was reduced in small but not always in isolated populations. This is possibly due to limited pollination and/or the loss of genetic variation. In a following investigation on E. palustris, the loss of genetic variation in small populations was, however, not clearly confirmed and this was probably caused by the longevity of the species.Overall, the effects of habitat quality, such as light availability, soil parameters and parameters of the surrounding vegetation, on the survival and the reproduction of the species studied were considerably less pronounced compared to the effects of population size. However, the recruitment of populations of E. palustris was determined by gaps in the vegetation and a relatively high content of organic matter in the soil, both indicating abundant winterly floodings. Consequently, most populations are static and aged since they are completely cut off from the dynamics of the river due to the construction of dikes.Further investigations on E. palustris over three years showed, that the relationships between reproductive success, population size, genetic variation, and habitat quality varied depending on the weather conditions of each growing season. Thus, studies concerning the impact of habitat fragmentation on the fitness of plant populations should preferably be based on surveys conducted over several consecutive years. In conclusion, river corridor plants are highly threatened by habitat fragmentation and will be further on the decline throughout the study area. The following management measures based on the findings of this study should be included in a conservation plan of this species group to stop or reverse this development: increase of population area and sizes, improvement of the connectivity between populations, re-attachment of habitats to natural river dynamics, utilisation of restored flood plains for reintroduction or introduction of species.Dissertation335 556 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Lokale Muster Pflanzlicher Artenvielfalt(2006-07-26); ; ; SummaryPlant species diversity varies in different plant communities over a wide range of spatial scales. In this study the local variation of species richness along gradients of productivity, environmental factors, environmental heterogeneity and disturbance were analysed in different plant communities. The documented patterns were compared to theoretical models and relationships as observed in previous studies. Multiple models to predict plant diversity were developed. The vegetation data was assessed in grassland and decideous forests of Northern Germany using a standardised method. For all study sites productivity level, chemical soil properties, relative light availability in forests, environmental heterogeneity and management intensity in grassland were determined. Furthermore, several studies in forests, grassland, sand meadows and mires were compiled and reviewed on their relationship of pH and species richness. For statistical analysis mainly univariate and multiple regressions were appliedThe following results were documented: 1) Plant diversity peaks corresponded to forests, grassland, mires and sand meadows with intermediate pH. 2) A unimodal model described best the relationship between species richness and productivity in deciduous forests with a large productivity gradient at different scales, while negative linear correlations were predominant in grassland communities. 3) Generally, multiple models explained more of the variation in species richness than univariate models. 4) Models comprising productivity, pH, heterogeneity in light intensity, C/N ratio, soil Calcium content as well as on smaller plots average light availability resulted in the highest predictive abilities for species numbers in forests. 5) In grassland communities the effect of current meadow use and management history in determining species richness dominated, whereas productivity and chemical soil properties had only a weak relationship with plant diversity. 6) Plant diversity increased with heterogeneity in light availability in forests, while intermediate heterogeneity in pH maintained highest species numbers. 7) Peaks of heterogeneity in light availability corresponded to moderately productive deciduous forests. 8) The patterns of plant diversity were scale-dependent with different factors dominating at varying scales.Dissertation385 163 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Species response curves and niche quantification of vascular plants in the context of reintroduction(2018-01-15); ; ; The current loss of biodiversity is one of the most disastrous threats to the earth's biosphere. To save plants from extinction, it is important to understand the relationship between species and their environment, identify the drivers of species distributions and rarity, and develop conservation techniques based on sound ecological knowledge. The present thesis shows that soil factors play a major role in plant species distribution and rarity, as well as in practical conservation techniques, such as plant reintroduction. Both, the limits of ecological niches and soil microbes are important factors in conservation, which deserve more attention in future studies of rare plant species. Reliable predictions of species responses to environmental changes and widely applicable conservation techniques are needed to save endangered species from extinction.Dissertation355 151 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Langfristige Veränderungen von Flora und Vegetation des Grünlandes in der Dümmerniederung (Niedersachsen) unter dem Einfluss von Naturschutzmaßnahmen(2011-08-16); ; ; Wet grasslands represent endangered ecosystems which since the 1950ies have severely decreased in area and habitat quality, especially in the fen areas of northern Germany. Since the 1980ies, large efforts have been undertaken to restore these grasslands. These measures are considered as very difficult because of the irreversible degradation of the peaty soils by melioration and intensive agricultural usage. The effects of re-wetting including temporal inundation and of the impoverishment in nutrients on wet grasslands have been extensively studied. There is also vast experience about the effects of experimental management techniques. However, there is a lack of long-term studies spanning 15 years or more. The surroundings of lake Dümmer (western Lower Saxony) have been rich in wet grasslands. Here, large vegetation surveys were made around 1950 just before the start of melioration, as well as during the period of intensive agricultural use and during the still ongoing process of restoration since the early 1990ies. These vegetation data are accompanied by land use data, mappings of target species and permanent plot surveys conducted since the mid 1990ies. On the whole, these data are unique for Germany and allow an examination of the restoration-driven successional dynamics under changing environmental conditions as well as of the development of species richness. These results also allow us to evaluate the possibilities and limits of large-scale restoration of species-rich wet grasslands. The data analysis included spatial analysis with a Geographic Information System, phytosociologial table work, ordination of vegetation plots with Detrended Correspondence Analysis and an ecological interpretation with the help of Ellenbergs indicator values. Calthion meadows and Agrostis canina grasslands were the most common vegetation types around 1950, but severely decreased after melioration. Molinion meadows and Nardetalia communities completely disappeared. Restoration management caused a pronounced change in vegetation: arable land, new-sawn grasslands and Elymus repens grasslands disappeared, while flood grasslands and Carex acuta sedge fens increased in abundance. Reeds with Phalaris arundinacea and Glyceria maxima almost developed periodically. The ongoing nutrient impoverishment allowed Agrostis canina grasslands to re-settle, resulting in an increase of species typical for small-sedge fens. Differences in site factors, especially in nutrient contents, between the present and historical conditions appear to have considerable effects on the distribution of many species, but are less obvious in the actual distribution of certain vegetation types. Nearly all plant species that are listed in the Red data book of Lower Saxony and that were noticed in the study area in recent times as well as the target species of conservation increased in abundance and spread out over large parts of the study area following restoration. Some highly rare species which were extinct in the study area and its surroundings for many years re-established most likely via long-distance dispersal, namely Bromus racemosus, Dactylorhiza incarnata and D. majalis. The occurrence of target species was positively influenced by a high level of re-wetting and nutrient impoverishment, whereas land use proved to be less important. Most species appear to be able to deal with either mowing or grazing, or a combination of both. Only few target species like Oenanthe fistulosa and Senecio aquaticus that need a comparatively high level of nutrients showed a slight decrease in abundance during recent years. The populations of Caltha palustris stabilized in size and were not affected negatively by long-time inundation. Finally, some species which are problematic for land use increased in abundance in response to restoration, especially Deschampsia cespitosa and the toxic plant Equisetum palustre. The species richness of the wet grasslands has shown a steady linear increase, and there are no indications for a weakening of this trend. Heavily degraded peaty soils showed significantly lower species numbers than less degraded peat. In conclusion, extensive restoration efforts cannot guarantee success in re-establishing species-rich wet grasslands with endangered target species, but in this study they had strongly positive effects on total species richness and on the abundances of most target species. Main factors of success are large-scale, consequent impoverishment, ongoing usage of the grasslands and an adjustable rewetting. The level of peat degradation was determined as a major limit of restoration success. A low level can enable the restoration of more or less species-rich grassland and a recolonisation of a couple of target species, a lot of them endagered.Dissertation573 319 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Dynamics of the vegetation in oak forests in Northwest Germany - Effects of environment and management(2019-07-02); ; ; The main aim of this thesis is to detect and understand long-term changes of the vegetation in the four oak forest types occurring in NW Germany. The following main questions were addressed: (1) How has the vegetation of Alluvial hardwood oak forests, Thermophilious oak-hornbeam forests, Sub-atlantic oak-hornbeam forests and Acidophilous oak forests changed over the past decades? (2) What are the drivers of the changes in the vegetation in these oak forests? (3) Do the observed changes and the drivers differ between the different oak forest ecosystems?Dissertation404 186