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- Institut für Ökologie (IE) (27) (entfernen)
European species-rich grasslands are threatened both by land use intensification as well as land abandonment. The studies shown in this thesis tested the possible use of ecological knowledge to ensure hay productivity whilst maintaining diversity of grasslands, with a view to informing ecological restoration. The overall approach was to understand interactions between plants, to study diversity effects on productivity, and mainly investigate how plant functional groups that arrive first in the system can create priority effects that influence community productivity both above- and belowground. A grassland field experiment was established and monitored for four years, in order to verify the effects of manipulating the order of arrival of different plant functional groups, as well as the sown diversity level on productivity and methane yield. The overall findings were: a) sowing legumes first created priority effects aboveground (higher biomass) and belowground (lower root length), plants invested less in roots and more in shoots, b) priority effects were more consistent below than aboveground, c) sown diversity did not affect aboveground biomass, d) the order of arrival treatments indirectly affected methane yield by affecting the relative dominance of plant functional groups. Since the researchers lack information on how legumes and non-legumes interact spatially belowground, (particularly related to root foraging) a controlled experiment was performed, using two grass species and one legume. The identity and location of the neighbours played a role in interactions, and the order plants arrived modulated it. When the focal species (grass) was growing with a legume it generally equated to the same outcome as not having a neighbour. Roots from the focal species grew more toward the legume than the grass neighbour, indicating a spatial component of facilitation. Since these studies involved root measurements, a method study was also conducted to verify how comparable and accurate are root length estimates obtained from different techniques. Results showed that the use of different methods can lead to different results, the studied methods did not have the same accuracy, and the automated methods can underestimate the root length. Overall, the results allow to conclude that different groups of plants arriving before others affected above and belowground biomass, roots may be key drivers during the creation of these priority effects, and interaction outcomes between plants depended on neighbour identity and location, modulated by the order they arrive in. The results suggest that priority effects can be used by sowing different species or plant functional groups at different time to steer a community to a desired trajectory depending on the restoration goal. However, there is a need to test contingency, potential, and long term impacts of such possible tools for restoration.
The worldwide decline of plant and insect species during the last decades has far-reaching consequences for the functionality of ecosystems and their inherent processes. Pollination as one of them is an indispensable ecosystem service for human wellbeing. However, an increasing number of pollinator and plant species are threatened by multiple, interacting, and sometimes synergistic causes that are becoming a growing threat to ecosystem functioning. Given the loss of plant species diversity, it is increasingly difficult for pollinators to find food throughout the year. Therefore, this study analyses the influence of plant diversity on pollinators. The study was conducted in the course of the Jena Experiment, which is a long-term biodiversity experiment (since 2002) with 60 plant species, common to Central European Arrhenatherum grasslands. With a plant diversity gradient of 1, 2, 4, 8, 16, and 60 plant species per plot, time-series data resulted from a wide range of ecosystem processes, ranging from productivity, decomposition, C-storage, and N-storage to herbivory, and pollination. These were studied to investigate the mechanisms underlying the relationships between biodiversity and ecosystem processes. Chapter 2 studies the spatio-temporal distribution of pollinators on flowers along an experimental plant diversity gradient. In particular, the spatial pollinator behaviour was examined. Chapters 3 and 4 continues on the chemical composition of flower nectar (nectar) of various plant species. The chemical composition of the nectar was analysed for the two most important macronutrients, carbohydrates (C) and amino acids (AA), using high performance liquid chromatography (HPLC). Subsequently, their contents were analysed in terms of concentration, proportional content and the ratio of carbohydrates to amino acids (C:AA). In Chapter 3, the nectar of 34 plant species from the grasslands of the Jena Experiment was compared. In Chapter 4, nectar was investigated in the context of diversity effects on the example of the plant species Field Scabious, Knautia arvensis. It was analysed to what extent the nectar quality (nutrient content) differs between plant individuals of one species. Overall, these studies indicate how fragile plant-pollinator interactions are but also how important plant species-rich grasslands are to support plant-pollinator interactions. Increased plant species diversity is essential to ensure the availability of flowering resources throughout the year. Pollinators, such as honeybees, bumblebees, solitary bees, and hoverflies can use the niches in time and in vertical space complementarily. However, in plant species-poor grasslands there may be more niche overlaps, which is probably due to a reduced availability of resources. This points to the need to include different plant species belonging to different plant families, whose nectar may have evolved in response to morphological flower traits and metabolic pathways. Therefore plant species diversity can supply pollinators with nectar differing in carbohydrate and amino acid content and thus differing in quality. Also C-AA ratios have proven to be a useful measurement to reveal differences between plant species. In addition, C:AA ratios were not differing in nectar of K. arvensis individuals growing in different plant species richness levels, although their nectar seemed to be more attractive in mixtures with 16 plant species, likely due to higher content of essential and phagostimulatory amino acids than in plant species-poor mixtures.
Excessive fertilizer use leads to nutrient imbalances and losses of these to the environment through leaching, runoff and gaseous emissions. Nutrient use efficiency (NUE) in agriculture is often low and improving it could increase the sustainability of agricultural systems. The main aims of this thesis were to gain a better understanding of plant-soil-microbe interactions in order to improve agricultural NUEs. The studies included experimentally tested how crops respond to addition of high carbon amendments, fertilizer application rates and timing, and crop rotations. Furthermore, methods for measurement of roots were compared and a protocol for measurement of roots was developed. The first experiment simulated an agricultural field using mesocosms. In this setting, the researchers tested the effect of 4 previous crops (precrops), which either had or did not have a symbiosis with arbuscular mycorrhizal fungi (AMF)/rhizobia, on the focal crop (winter barley). They also tested the addition of high carbon amendments (wheat straw/sawdust) for immobilization of residual soil nitrogen (N) at harvest of the previous crop. Overall, the findings were that non-AMF precrops had a positive effect on winter barley yield compared to AMF precrops. Wheat straw reduced N leaching, whereas sawdust addition had a negative effect on the yield of winter barley. The second experiment tested the effect of different fertilizer (N/phosphorus (P)) application timings on plant traits grown in rhizoboxes. Overall, delaying N application had a more detrimental effect on plant biomass than delaying P application. The root system increased its root length initially due to N-deficiency, but was quickly thus N-limited that root length was relatively lower than the control group. Because of the many root related measurements in the second experiment, a step-by-step method for measuring root traits under controlled and field conditions was developed and included in this thesis. This method paper describes precisely how root traits of interest can be measured, and helps with deciding which approach should be taken depending on the experimental design. Additionally, the authors compared the bias and accuracy of several popular root measurement methods. Overall, these results highlight the importance of crop choice in crop rotations and the plasticity of root systems in relation to nutrient application. The results show high carbon amendments could reduce nitrate leaching after the harvest of crops, especially those with high risk of nitrate leaching, although they had only small impacts on yield.
The smallholder-dominated landscapes of southwestern Ethiopia support a unique biodiversity with great importance to local livelihoods and high global conservation value. These landscapes, however, are severely threatened by deforestation, forest degradation and the adverse effects of farmland management regimes. These changes have fundamentally altered the structure of the landscapes and threaten their biodiversity and ecosystem services. Managing biodiversity and related services in such rapidly changing landscapes requires a thorough understanding of the effects of land use change and the reliance of local communities on biodiversity. This dissertation examines woody plant biodiversity patterns and services and presents several recommendations regarding biodiversity and multiple ecosystem services in smallholder-dominated landscapes of southwestern Ethiopia. Using a social-ecological systems approach, the author conducted four studies on the complex interactions of local people and woody plant diversity. First, he investigated the effects of human-induced forest degradation on woody plant species. His results suggest that forest biodiversity has been affected by the combined effects of coffee management intensity, landscape context and history at the local and landscape level. Specifically, richness of forest specialist species significantly has decreased with coffee management intensity and in secondary compared to old growth forests, but increased with current distance from forest edge in both primary and secondary forests. These findings highlight the need to maintain undisturbed forest sites to conserve forest biodiversity. Second, the author examined legacy effects of past agricultural land use on woody plant biodiversity. The results show that historical distance seems to be the most important variable affecting woody plant composition and distribution in farmland sections of the landscapes. The author found evidence for immigration credits for generalist and pioneer species but not for extinction debts for forest specialist species which might be rapidly paid off in farmland. The results suggest not only an unrecognized conservation value of old farmland but also a disturbing loss of forest specialist species. To slow this trend, it is necessary to shift to a cultural landscape development approach and to restore forest specialist species in the landscapes. Third, the author evaluated the supply of potential multiple ecosystem services and the relationships between the diversity of woody plant and ecosystem service in the three major land use types, namely forests with and without coffee management and farmland. The results revealed a high multifunctionality of landscapes and showed that ecosystem services significantly increase with woody plant diversity in all types of land use. These findings suggest that the woody plant diversity and multifunctionality in southwestern Ethiopian landscapes has to be maintained. Fourth, the author explored farmers' woody plant use to assess their dependency on and maintenance of woody plants and also considered the influence of property rights and management in this context. He found that local farmers used 95 species for eleven major purposes from all major land uses across the landscapes. He also found that most of the widely used tree species regenerated successfully throughout the landscapes, including in farmland. Local people felt, however, that their property and tree use rights were limited, especially in forests, and that some of the most widely used plant species, including important timber species, appeared to have been overharvested in forests. The results suggest that many species are important for local livelihoods, but a perceived low sense of property rights also seems to adversely affect the management of woody plants, particularly in forests. By focusing on woody plants and their ecosystem services to local people, this dissertation documents a dramatic loss of native forest biodiversity and rapid changes in the cultural landscapes of southwestern Ethiopia. Overall, the findings suggest the need for preservation of intact forest sites and for cultural landscapes development to safeguard biodiversity and multifunctionality of the landscapes in the future. This, in turn, requires holistic and integrated approaches that involve local people and recognize their basic needs of woody plants and their property rights to foster the management of biodiversity and ecosystem services. Maintaining primary forests in and using cultural landscape approaches to the rapidly changing rural setting of southwestern Ethiopia would also contribute to the global effort to halt biodiversity loss.
Wood-pastures have been present in Europe for thousands of years. This form of grazed landscape, combining herbaceous vegetation with trees and shrubs, has often co-evolved with its human users into complex social-ecological systems (SES). Wood-pastures are associated with high cultural and biodiversity values and are an example of the sustainable use of resources. However, due to their often relatively labour-intensive management and low productivity, large areas of wood-pastures have been lost over the last century. The loss of these areas means not only the loss of biodiversity on both local and landscape scales, but also the loss of traditional farming and cultural heritage in some regions. Across the European Union, wood-pastures are facing different problems and are embedded in different social systems and ecological environments. Yet they are all affected by global change and common European policies. To understand the challenges for wood-pastures in a changing world, a holistic approach combining different disciplines is needed. This dissertation therefore is analyzing wood-pastures across Europe as a Social-ecological System, combining ecology and social science with the aim to identify the barriers and drivers for wood-pastures persistence into the future.
Tropical forests worldwide support high biodiversity and contribute to the sustenance of local people’s livelihoods. However, the conservation and sustainability of these forests are threatened by land-use changes and a rapidly increasing human population. This dissertation, therefore, aimed to characterize biodiversity patterns in the moist Afromontane forests of southwestern Ethiopia and to examine how biodiversity patterns are affected by land-use and land-use changes (mediated by coffee management intensity, landscape attributes and housing development) in a context of a rapidly growing rural population. To achieve this goal, the author takes an interdisciplinary approach where, first, she examined the effects of coffee management intensity on diversity patterns of woody plants and birds, spanning a gradient of site-level disturbance from nearly undisturbed forest interior to highly managed shade coffee forests. Results showed that specialized species of woody plants (forest specialists) and birds (forest specialists, insectivores and frugivores) were affected by coffee management intensity. The richness of forest specialist trees and the richness and/or abundance of insectivores, frugivores and forest specialist birds decrease with increasing levels of disturbance. Second, the author investigated the effects of landscape context on woody plants, birds and mammals. Community composition and specialist species of woody plants and birds were sensitive to landscape context, where woody plants responded positively to gradients of edge-interior and birds to gradients of edge-interior and forest cover. Further results showed that a diverse mammal community, with 26 species, occurs at the forest edge of shade coffee forests and that the leopard, an apex predator in the region depended on large areas of natural forest. A closer examination of leopard activity patterns revealed a shift in the diel activity as a response to human disturbance inside the forest, further highlighting the importance of natural undisturbed forests for leopards in the region. Together, these findings demonstrate the value of low managed shade coffee forests for biodiversity, and importantly, emphasize the irreplaceable value of undisturbed natural forests for biodiversity. Third, the researcher investigated the effects of prospective rural population growth (mediated by housing development) on the forest mammal community. Here, population growth was projected to negatively influence several mammal species, including the leopard. Housing development that encroached the forest entailed worse outcomes for biodiversity than a combination of prioritized development in already developed areas and coffee forest protection. Fourth, to understand the motivations behind high human fertility rates in the region, she examined the determinants of women fertility preferences, including their perceptions on social and biophysical stressors affecting local livelihoods such as food insecurity and environmental degradation. Fertility preferences were influenced by underlying social norms and mindsets, a perceived utilitarian value of children and male dominance within the household, and were only marginally affected by perceptions of social and biophysical stressors. The findings suggest the need for new deliberative and culturally sensitive approaches that engage with pervasive social norms to slow down population growth. Overall, this dissertation demonstrates the key value of moist Afromontane forests in southwestern Ethiopia for biodiversity conservation. It indicates the need to promote coffee management practices that reduce forest degradation and highlights that high priority should be given to the conservation of undisturbed natural forests. It also suggests the need to integrate conservation goals with housing development in landscape planning. A promising approach to achieve the above conservation priorities would be the creation of a Biosphere Reserve and to promote the ecological connectivity between the larger forest remnants in the region. Finally, this dissertation demonstrates the importance of placed-based holistic approaches in conservation that consider both proximate and distal drivers of forest biodiversity decline.
The global coffee market is connected to many sustainability issues like the persisting poverty of coffee farmers, and degrading ecosystems. Many interventions, from state-led regulation to industry-led certification processes, exist, that try to change global value chains to shift societies back on more sustainable trajectories. To this date, it is still under debate if these interventions are an effective means to change global value chains. With climate change and persisting issues of social justice as strong accelerators, calls are increasingly made for a radical transformation of global production and consumption patterns. Many frameworks try to inform research and real-world policies for a transformation of global value chains. In this dissertation, the author uses the framework of the practical, political and personal sphere proposed by O'Brien and Sygna (2013) highlighting that the interactions between these three spheres bare the greatest potential for a transformation towards sustainability. However, in this dissertation, the author argues that it is exactly at the nexus between the three spheres of transformation where barriers towards a fundamental shift of systems occur. He, therefore, uses three perspectives to bring empirical nuance to the problems that arise on the interplay between the different spheres of transformation. (1) The scientific perspective: using a systematic review of alternative trade arrangements; (2) the producer perspective: facilitating a participatory network analysis of social-ecological challenges of Ugandan coffee farmers and their adaptive management practices; (3) the consumer perspective: through the use of a German consumer survey and a structural equation model to investigate into the Knowledge-Doing-Gap end-consumers are facing. Through the results from the scientific perspective, the author is able to show that most of the research is investigating the certified market and that the effectiveness of labels rarely exceeding the practical sphere. His empirical research on the producer perspective highlights that Ugandan coffee farmers facilitate a variety of on-farm crop management (practical sphere) but their support structures rarely exceed informal exchange with neighboring communities (political sphere). Exchange with governmental actors and global traders is happening but has been assessed as not sufficient to cope with the social-ecological challenges the producers are facing. Through the results of the consumer perspective, the author is able to highlight that even though end-consumers have pro-sustainable attitudes (personal sphere) they are facing situational constraints (political sphere) that create a gap between their attitudes and the respective behavior. Using these empirical insights about drivers and barriers for a transformation he proposes that frameworks, aiming to inform research and policies, need to include two aspects: (1) the notion of a forced transformation; and (2) the translational capacity of the frameworks to create meaningful interdisciplinary discourses in different contexts. The author, therefore, propose two approaches:(1) a fourth sphere, called the "planetary force" to include the notion of a forced transformation that is already happening in different contexts, highlighted by the producer perspective in this dissertation; and (2) the consequent use of methods that create interdisciplinary exchange and rigorous testing.
In this dissertation, a multi-proxy study, which included palaeoecological, lithological, geochemical and geochronological methods, was carried out to investigate climatic and environmental changes and their interaction during the Quaternary in formerly glaciated and non-glaciated areas. The information obtained will be used to provide a better understanding of the regional stratigraphic framework and to establish broader regional terrestrial correlations within the global marine isotope stage (MIS) framework. This study was conducted on two key drillings, the Garding-2 research drill core in the German North Sea coastal area of Schleswig-Holstein and the GBY#2 archaeological core at the Gesher Benot Ya'aqov (GBY) site, in the Upper Jordan Valley in Israel. The results of this study are presented in three papers. Papers I and II focus on the study of the Garding-2 core, while the multi-proxy study of the GBY#2 core is presented in Paper III. The results of a variety of analyses conducted on the 240 m long Garding-2 sequence show interglacial-glacial cycles that are mainly controlled by variations in temperature. This sequence is composed of mainly fluvial-shallow marine sediments intercalated by muddy-peaty deposits. Based on the palynological and lithological findings, the Pliocene-Pleistocene transition was observed at 182.87 m. It is overlain by Praetiglian and the subsequent sediments of the Waalian and Bavelian Complexes. The boundary of either the second or third Cromerian Interglacial with younger sediments, which still belong to MIS 19, is marked by the last occurrence of Tsuga at 119.50 m and the development of mixed-deciduous forests. The palynologically equivalent sediments of the Bilshausen Interglacial were found below two Elsterian till layers, at 89.00 m-82.00 m. These sediments showed high and increased percentages of Pinus and Picea and scattered occurrences of Abies and Carpinus, which are similar to the features of the beginning of the Bilshausen or Rhume interglacial. An unconformity occurred at 80.29 m, at the bottom of late Holsteinian deposits, characterised by the occurrences of Fagus and Pterocarya, with low percentages of Abies and Carpinus and the absence of Buxus. These deposits are succeeded by sediments of the Fuhne cold period that shows higher percentages of NAP and occurrences of Ericales, Helianthemum and Selaginella selaginoides, which are unconformably overlain by Drenthian till at 73.00 m-71.00 m. A single peaty sample at 69.25 m with Pinus-Picea-Abies assemblage is correlated with the late Eemian Interglacial. This deposit is overlain by Weichselian glaciofluvial sediments. Middle-late Holocene sediments occurred from 20 m upwards, following a hiatus, which was caused by the Early Holocene transgression. A subsequent thin layer of marine Atlantic sediments is unconformably overlain by marine-tidal flat deposits up to 11.00 m. The first occurrence of Fagus (at 15.97 m) and Carpinus (at 15.03 m), which was optically stimulated luminescence (OSL)-dated to 3130 +/- 260 BP (at 16.22 m, Zhang et al., 2014), gives evidence for a Subboreal age for these deposits. Sandy sediments of the early Subatlantic, which were deposited between 11.00 m and the top of the Garding-2 sequence, indicate that local salt marshes, dunes and tidal flat vegetation expanded during this period. Due to regional features and the peculiarities of the local coastal environment, the expansions of Fagus and Carpinus, which are characteristic for the Subboreal-Subatlantic transition at about 2700 BP in northern Germany, are not clearly reflected in the Garding-2 pollen diagram. In the Mediterranean area, a 50 m long core of GBY#2, was drilled at the Acheulian site of Gesher Benot Ya'akov. The GBY#2 core provides a long Early-Middle Pleistocene geological, environmental and climatological record, which also enriches the knowledge of hominin-habitat relationships documented at the margins of the Hula Palaeo-lake. The sediment sequence of GBY#2 is under- and overlain by two basalt flows that are 40Ar/39Ar dated: two samples at the bottom of the core dated to 1195 +/- 67 ka (at 48.30 m) and 1137 +/- 69 ka (at 45.30 m), and another one at the top dated to 659 +/- 85 ka (at 14.90 m). With the additional chronological identification of the Matuyama Brunhes Boundary (MBB) and the correlation with the GBY excavation sites, the sedimentary sequence of GBY#2 provides the climatic history during the late part of the mid-Pleistocene transition (MPT, 1.2 Ma-0.5 Ma). Multi-proxy analyses including those of pollen and non-pollen palynomorphs, macro botanical remains, molluscs, ostracods, fish, amphibians and micromammals provide evidence for lake and lake-margin environments during MIS 20 and MIS 19. During MIS 20, relatively cool semi-moist conditions were followed by a pronounced dry phase. During the subsequent MIS 19, warm and moist interglacial conditions were characterised by Quercus-Pistacia woodlands in this area. The depositional environment changed from an open water lake during MIS 20 to a lake margin environment in MIS 19. This finding is at odds with changing climate conditions from relatively dry to moist. This discrepancy could be explained by the prograding pattern of the lake shore due to the infilling of the basin, which resulted in shallower water. Climatic changes during the Late Tertiary and the Quaternary in the high latitude regions in northwest Europe and during the Early-Middle Pleistocene in the mid latitude regions of the Middle East follow the patterns of global climatic changes, which are mainly controlled by orbital obliquity (+/-41 ka cycle) during the Early Pleistocene and by orbital eccentricity (+/-100 ka cycle) during the MPT (1.2 Ma-0.5 Ma) and the younger periods of the Quaternary. The results of this study also provide reliable evidence for long distance correlation of stratigraphic and climatic events of the Quaternary, which extends knowledge of regional and global impact of climatic fluctuations on the environment.
To counteract species loss and preserve the remaining biodiversity, with its important ecosystem functioning and services essential to human well-being, there is an urgent need to develop promising and long-term conservation strategies. In order to achieve these goals, extensive research to gain a better understanding of the general mechanisms underlying community diversity is of greatest importance. Especially, the identification of intrinsic ecological and distributional species traits is receiving increased attention in ecology and conservation biology research. Depending on the expression of their traits, species perform particular ecosystem functions and respond in a specific manner to environmental conditions. Although insects make up the largest part of animal diversity, the majority of studies on extinctions have mainly focused on vertebrates. Among invertebrates either charismatic taxa or those targeted by conservation laws have been investigated until now (e.g. butterflies or saproxylic beetles). Being highly species-rich and trait-diverse, ground beetles (Coleoptera: Carabidae) should be even more suitable for conducting trait-based analyses. Thus, using ground beetles as a model taxon, four case studies focusing on the analyses of traits form the basis of this doctoral thesis. The work of this thesis was conducted with the aim of gaining general insights on the influence of species traits on ground beetle community compositions, such as habitat occupancy and species vulnerability to extinction, for instance. An important aspect when investigating species traits is the consideration of confounding factors, such as dependent relations between the different traits. Compiling a large dataset of 555 Central European species, the author identified that dependent relations between the six tested traits of ground beetles (distribution range size, habitat specialization, body size, hind-wing morphology, breeding season and trophic level) are highly common. Across all identified dependent trait relations, the relation between body size and hind wing morphology or range size and hind wing morphology showed the strongest significant dependencies. Since the consideration of trait relations is necessary to provide reliable interpretations, all analyses of this thesis tested several traits simultaneously and considered possible trait interactions. Studies on local communities found specific traits characterizing the local species pools of certain habitat types. Here, the species pools of seven different habitat types (coastal, forest, mountain, open, riparian, wetland and special habitat) were used to determine habitat-specific trait filters. The identified traits, characteristic for certain habitat types, were in most cases in accordance with the previous findings on local communities. Across Germany, the species of frequently disturbed habitat types, namely coastal, riparian and wetland habitats were characterized by small body size, high amount of macroptery, intermediate to high habitat specialization, spring breeding, and predatory feeding behavior. The species of stable habitat types (forest, mountain, and open habitats), however, were found to be generally larger in body size and more frequently breeding in autumn, further displaying greater variations in the other traits. The gained knowledge on the habitat-specific filtering of traits improve our understanding of the organization and assembly of communities, and can thereby help to detect alterations in the habitat-specific species pool due to natural or human-induced environmental changes. Furthermore, traits can provide evidence on species occurrences and vulnerability to extinction. Three case studies of this thesis aimed to gain new insights on this topic, through the investigations on the following research questions: (1) Which traits drive species extinction risks of Central European ground beetle species? (2) How traits influence the species occurrences of 28 forest species within a large area in Central Europe? (3) Whether certain traits are related to long-term population trends of the species pool from an ancient forest in northern Germany? The results indicated, that depending on the habitat type and tested species pool, different traits prove to be good predictors for the vulnerability of species. Nevertheless, across different geographical and taxonomical scales, especially species with small range sizes and high habitat specialization faced a greater risk of extinction. Therefore, the two traits distributional range size and habitat specialization emerge as reliable predictors of ground beetles vulnerability to extinction. Interestingly, body size did not display a consistent response; while increasing body size led to higher extinction risk in riparian, wetland and open habitats and large macropterous species showed higher extinction risks across the entire species pool, smaller species showed long-term population declines in an ancient forest.
Die Entfernung von Phosphor aus Abwasser bleibt ein Forschungsthema, das in Zukunft nur an Wichtigkeit gewinnen kann. Das wird durch die Umweltauswirkungen der Eutrophierung und den Verlust eines essentiellen Nährstoffes für die Nahrungsmittelproduktion dessen Knappheit immer offensichtlicher wird, immer deutlicher. Auf Kläranlagen werden heute hauptsächlich zwei Techniken verwendet um Phosphor zu entfernen, biologisch aktive Verfahren wie das Enhanced Biological Phosphorus Removal (EBPR) Verfahren und Fällungstechniken unter Verwendung von Metallsalzen. Bei beiden Methoden gibt es gegenwärtig Schwierigkeiten wie z.B. die Instabilität des EBPR Prozesses wegen des Mangels an Wissen über die Grundlagen des Stoffwechselprozesses. Bei der Verwendung von Fällungsmitteln kommt es zu vielen Nachteilen im Zusammenhang mit der Nachbehandlung des Schlammes, bei der Entsorgung kommt es zu dem Verlust der Schlammmassen und damit auch des Phosphors aus dem Nährstoffkreislauf. Das Ergebnis dieser Forschung ist, dass es möglich ist, die Phosphorspeicherkapazität von Belebtschlamm zu erhöhen wenn dieser spezifische Anforderungen erfüllt. Diese Anforderungen werden wie folgt zusammengefasst: Die Schlammmasse muss in der Lage sein, EBPR Prozesse zu entwickeln, auch muss der Schlamm aus einem Belebungsbecken-System kommen, weil die Schlammflocken unter den Umgebungsbedingungen des Reaktors stabilisiert worden sind. Schließlich muss der Belebtschlamm aus einem Verfahren kommen, bei dem man für die Phosphorentfernung keine Metallsalze verwendet. Die erhöhte Phosphorstoffspeicherkapazität der Belebtschlammmassen in Verbindung mit der Möglichkeit den Phosphor aus dem Belebtschlamm über Rücklösung in die wässrige Phase wieder gewinnen zu können, bietet großes Potential in der Zukunft einen in der Abwasserwirtschaft geschlossenen Phosphorkreislauf zu entwickeln und so den Verlust des wichtigen Nährstoffes nachhaltig zu verhindern.
A solid knowledge about nature is essential to understand the consequences of biodiversity loss, the limitation of natural resources and the need for a sustainable development. Inspired by these challenges, the researcher investigated in her dissertation seed predation, an important ecosystem function, as part of citizen science project. As seed predation has only rarely been investigated along urban-rural gradients and to integrate the question if the background (urban vs. rural) of primary school children affects their environmental knowledge, she selected study sites in and around Lüneburg and Hamburg, in Northern Germany. In her ecological experiments, it was found that slugs are important seed predators that independently of urbanization predated about 30% of all seeds in the anthropogenically used landscapes investigated. Also, for the first time, primary school children could be integrated in a citizen science approach into this research and it could be shown that even seven year old children can record data as reliable as a scientist. Finally, the researcher investigated the native species knowledge from the children taking part as citizen scientists in her research, considering possible differences due to their urban or rural background. Contrary to her expectation, the urban or rural background had no significant effect on the species knowledge. However, the work provides a good foundation to transfer the approach of introducing a basic foundation of a taxonomical species concept in primary school to foster further understanding on biodiversity and ecosystem functions.
The timber shortage led to large scale afforestations on previously agriculturally used land in Central Europe during the 19th and 20th century. Widespread afforestation programs created recent forest ecosystems (i.e. young forest systems in terms of their development history). Despite the positive effect of increasing the forest area of Central Europe, the ecological effects of these land-use changes on forest ecosystems remain poorly understood. In order to increase the understanding of ecosystem processes in forests, an assessment of conceivable shifts in ecosystem functions caused by former land-use changes and forest management is required. By analysing aboveground growth rates of European beech (Fagus sylvatica L.) in response to environmental change drivers, such as climate extremes and nitrogen (N) deposition, the presented thesis aims to assess the role of land-use and management legacies in modulating present responses to drivers of environmental change. To this end, annual radial growth rates of individual trees were measured in mature beech stands. The investigated stands differed either in their land-use history (i.e. ancient forest sites versus recent forests) or their forest management history (i.e. managed forest sites versus short-term and long-term unmanaged forest sites). Measurements of radial growth rates were complemented by analyses of the fine root systems, soil chemical properties and crown projection areas to gain insights into the mechanisms underlying alterations in tree growth. Within the projects of the presented thesis, shifts in the climate-growth relationships driven by land-use and management legacies were analysed. In addition, land-use legacy mediated differences in the climate-nitrogen-growth relationships were assessed. The key findings are: (I) Soil legacy driven alterations in the fine root systems cause a higher sensitivity of radial increment rates to water deficits in summer for trees growing on recent forest sites than for trees growing on ancient forest sites. (II) Management legacies (in terms of tree release) enhance the sensitivity of beech’s radial growth to water deficits in spring through changes in crown sizes. (III) Interacting effects of spring water deficits and co-occurring high deposition of reactive N compounds lead to stronger radial growth declines in trees growing in ancient forests. This is likely caused by resource allocation processes towards seed production, which is, in turn, mirrored by decreasing radial growth rates. In this context, high N deposition likely boosts mass fructification in beech trees. Overall, it has been demonstrated that the ecological continuity plays a crucial role in modulating both climate sensitivity and the growth response to interacting effects of water deficits and nitrogen deposition in beech trees. The presented thesis identified a trade-off between the climate sensitivity and maximised growth rates within beech trees, depending on forest history. The results show that the growth of beech in ancient, unmanaged beech forests is less sensitive to water deficits than in recent and managed beech forests. Additionally, interacting effects of spring water deficits and N deposition likely increase the reproductive effort of beech trees, particularly in ancient forests. Thus, the results of this thesis once again underpin the uniqueness of ancient, unmanaged beech forests, whose importance for the conservation of biodiversity has been widely acknowledged. In summary, the presented thesis highlights the need to consider the "ecological memory" of forest ecosystems when predicting responses to current and future environmental changes.
The effects of habitat fragmentation and land use changes are usually studied by relating patterns of genetic diversity and differentiation to environmental factors, habitat history, landscape structure, or to a combination thereof. However, these three drivers are rarely addressed simultaneously. In addition, these studies are usually carried out in conservation-driven contexts, and therefore tend to concentrate on hyper-fragmented landscapes and on rare or endangered species. However, how habitat fragmentation and land use affect widespread species in more typical landscapes has not been fully investigated. This thesis addresses these two gaps. Abax parallelepipedus, a flightless ground beetle with low dispersal power, was used as a model species to test how environmental factors, habitat history, and landscape structure affect genetic diversity and genetic differentiation in three study regions located across Germany. Although all of the study regions represent fairly typical rural landscapes for central Europe, each consisting of a complex matrix of land uses, they differ from one another in terms of environmental factors, habitat history, and landscape structure, and thus can serve as three test cases. In the first stage of the work, the investigator identified polymorphic microsatellite loci which could potentially be used to study genetic diversity and differentiation in A. parallelepipedus. She then developed PCR and genotyping protocols for two suites of loci, in the end selecting to use the set of 14 fully multiplexed loci for the study. After having developed the needed study system, she genotyped over 3300 beetles from 142 study sites. In her investigation of how environmental factors and habitat history affect genetic diversity and genetic differentiation, and found that genetic diversity was being driven by variables that could be related to population sizes rather than by habitat history. She also did not find evidence of an influence of habitat history on the genetic differentiation patterns. Although populations of A. parallelepipedus in the past were probably smaller due to deforestation, they apparently remained large enough to prevent rapid genetic drift. In addition, the researcher carried out a landscape genetics analysis of the genetic differentiation patterns found in each of her study regions, in which she examined the relationship between genetic differentiation and landscape structure. She tested whether she could find patterns of isolation by distance, isolation by resistance, or isolation by barriers in the study regions. No effects of land use or of fragmentation were found. Based on the importance of population sizes found in the previous study, combined with the beetle's known avoidance of non-wooded areas and its inability to cross roads, the investigator concludes that although there is probably little gene flow across the study regions, large population sizes are preventing the rapid development of genetic differentiation. Models simulating the development of genetic differentiation over time in populations of different starting sizes support this conclusion.
Biodiversity loss could jeopardize ecosystem functioning. Yet, the evidences that support this demonstration have been mostly obtained in aquatic and grassland ecosystems. Howbiodiversity affects ecosystem functioning still remain largely unanswered in forests, particularly in subtropical broad-leaved evergreen forests (EBLF). Tree productivity, among a wealth of forest ecosystem functioning, is of particular interest because it reflects the carbon sink capacity and wood productivity. Biodiversity-productivity relationships have been usually investigated at community level. However, tree-tree interactions occur at small scale. Thus, local neighborhood approach may allow a better understanding of tree-tree interactions and their contributions to the effects of biodiversity on tree productivity / growth rates. This thesis aims to analyze the effects of biodiversity and the abiotic environmental factors on the tree growth rates using both local neighborhood and community-based approaches. Furthermore, tree growth rates vary among different tree species. Functional traits have been related to the species-specific growth rates to understand the effects of species identity. Therefore, I also evaluated the crown- and leaf traits to predict the interspecific difference in growth rates. For a better understanding of the mechanisms that underline the relationships of biodiversity and tree growth rates, data of high solution and along time series is required to scrutinize the tree-tree interactions. Thereupon, I evaluated the applicability of terrestrial laser scanning (TLS) in assessing the tree dendrometrics. This thesis was conducted in the Biodiversity Ecosystem Functioning (BEF)–China experiment, which is located in a mountainous subtropical region in southeast China. A total of 40 native broad-leaved tree species were planted. In the first study, I used the local neighborhood approach to analyze how local abiotic conditions (i.e. topographic and edaphic conditions) and local neighborhood (i.e. species diversity and competition by neighborhood) affect the annual growth rates of 6723 individual trees. The second study used the community approach to partition the effects of environmental factors (i.e. topographic and edaphic), functional diversity according to Rao’s quadratic entropy (FDQ) and community weight mean (CWM) of 41 functional traits on community tree growth rates. The main question of the third study was how the species-specific growth rates are related to five crown- and 12 leaf traits.
In the fourth study, I investigated 438 tree individuals for the congruence between the conventional direct field measurements and TLS measurements. It was found that tree growth rates were strongly influenced by the local topographic and edaphic conditions but not affected by the diversity of local neighborhood. In contrast, results obtained by using the community-based approach showed that FDQ and CWMs of various leaf traits rather than abiotic environmental factors had significant impact on the community means of growth rates. Tree-tree interactions already occur in early life stages of trees, which were evidenced by the significant effect of competition by local neighborhood. These findings imply that the effects of abiotic environmental factors may be more evident at local scale and biodiversity effects may vary at different spatial scales. The species-specific growth rates were found to be related to specific leaf traits but not to crown traits and were best explained by both types of traits in combination. This finding supports the niche theory and provides the evidence for using functional diversity to examine the BEF relationships. The TLS-retrieved total tree height, stem diameter at 5 cm above ground, and length and height of the longest branch were highly congruent with those obtained from direct measurements. It indicates that TLS is a promising tool for high resolution, non-destructive analyses of tree structures in young tree plantations. Being one of very few studies to incorporate the individual tree scale in examining the biodiversity-productivity relationships within the BEF researches, this thesis stresses the importance of using individual-tree based approach, functional diversity and TLS to find the evidences of explanatory mechanisms of the observed biodiversity and ecosystem functioning (e.g. tree growth rates) relationships. Biodiversity effects may evolve along the successional stages. Therefore, incorporating the interaction between biodiversity and time in analyzing BEF relationship is also encouraged.
Urban areas are prone to climate change impacts. Simultaneously the world's population increasingly resides in cities. In this light, there is a growing need to equip urban decision makers with evidence-based climate information tailored to their specific context to adequately adapt to and prepare for future climate change. To construct climate information high-resolution regional climate models and their projections are pivotal. There is a need to move beyond commonly investigated variables, such as temperature and precipitation, to cover a wider breath of possible climate impacts. In this light, the research presented in this thesis is centered around enhancing the understanding about regional-to-local climate change in Berlin and its surroundings, with a focus on humidity. More specifically, following a regional climate modelling and data analysis approach, this research aims to understand the potential of regional climate models, and the possible added value of convection-permitting simulations, to support the development of high-quality climate information for urban regions, to support knowledge-based decision-making. The first part of the thesis investigates what can already be understood with available regional climate model simulations about future climate change in Berlin and its surroundings, particularly with respect to humidity and related variables. Ten EURO-CORDEX model combinations are analyzed, for the RCP8.5 emission scenario during the time period 1970-2100, for the Berlin region. The results are the first to show an urban-rural humidity contrast under a changing climate, simulated by the EURO-CORDEX ensemble, of around 6% relative humidity, and a robust enlarging urban drying effect, of approximately 2-4% relative humidity, in Berlin compared to its surroundings throughout the 21st century. The second part explores how crossing spatial scales from 12.5km to 3km model grid size affects unprecedented humidity extremes and related variables under future climate conditions for Berlin and its surroundings. Based on the unique HAPPI regional climate model dataset, two unprecedented humidity extremes are identified happening under 1.5°C and 2°C global mean warming, respectively SH>0.02 kg/kg and RH<30%. Employing a double-nesting approach, specifically designed for this study, the two humidity extremes are downscaled to the 12.5km grid resolution with the regional climate model REMO, and thereafter to the 3km with the convection-permitting model version of REMO (REMO NH). The findings indicate that the convection-permitting scale mitigates the SH>0.02kg/kg moist extreme and intensifies the RH<30% dry extreme. The multi-variate process analysis shows that the more profound urban drying effect on the convection-permitting resolution is mainly due to better resolving the physical processes related to the land surface scheme and land-atmosphere interactions on the 3km compared to the 12.5km grid resolution. The results demonstrate the added value of the convection-permitting resolution to simulate future humidity extremes in the urban-rural context. The third part of the research investigates the added value of convection-permitting models to simulate humidity related meteorological conditions driving specific climate change impacts, for the Berlin region. Three novel humidity related impact cases are defined for this research: influenza spread and survival; ragweed pollen dispersion; and in-door mold growth. Simulations by the regional climate model REMO are analyzed for the near future (2041-2050) under emission scenario RCP8.5, on the 12.5km and 3km grid resolution. The findings show that the change signal reverses on the convection-permitting resolution for the impact cases pollen, and mold (positive and negative). For influenza, the convection-permitting resolution intensifies the decrease of influenza days under climate change. Longer periods of consecutive influenza and mold days are projected under near-term climate change. The results show the potential of convection-permitting simulations to generate improved information about climate change impacts in urban regions to support decision makers. Generally, all results show an urban drying effect in Berlin compared to its surroundings for relative and specific humidity under climate change, respectively for the urban-rural contrast throughout the 21st century, for the downscaled future extreme conditions, and for the three humidity related impact cases. Added value for the convection-permitting resolution is found to simulate humidity extremes and the meteorological conditions driving the three impacts cases.
Loss of natural and semi-natural habitat due to increasing human land use for agriculture and housing has led to widespread declines in bee pollinator diversity and abundance, which raised global concerns about the stability of pollination services. Bee population dynamics depend on floral resource diversity and availability in the surrounding landscape, and loss of plant biodiversity may thus directly impair the fitness of individual bee species. However, whether and how plant and resource diversity and availability affect foraging patterns, resource intake, resource quantity and nutrient quality and ultimately fitness of generalist social bees remains unclear. In this thesis, we placed hives of the Australian eusocial stingless bee Tetragonula carbonaria (Apidae, Meliponini) in natural habitat (subtropical forests) and two landscapes differently altered by humans (suburban gardens and macadamia plantations), varying in plant species richness, resource abundance and respective habitat patch size. Foraging patterns and resource intake were compared between landscapes in different seasons and colony growth and fitness were monitored over two and a half years. Bee foraging activity, pollen and sugar intake, diversity of collected pollen and resin resources, resource quantity (colony food stores), colony fitness (brood volume, queenand worker reproduction) and colony growth overwhelmingly increased with plant species richness in the surrounding habitat. However, plant species richness and thus bee fitness was highest in gardens, not in natural forests, as bees in gardens benefited from the continuous floral resource availability of both natural and exotic plants across seasons. In contrast, foraging rates and success, forager orientation and consequently colony fitness was largely reduced in plantations. While bees maximized diversity of collected resources, collecting more diverse resources did however not increase resource functionality and nutritional quality, which appeared to be primarily driven by the surrounding plant community in our study. Conversely, individual worker fitness (body fat and size) was not affected by available resource diversity and abundance, showing that colonies seem not to increase the nutritional investment in single workers, but in overall worker population size. This thesis consequently revealed the outstanding role of plant biodiversity as a key driver of (social) bee fitness by providing more foraging resources, even when only small but florally diverse patches are available.
Ensuring food security and halting biodiversity loss are two of the most pressing global sustainability challenges. Attempts to identify pathways have been dominated with a biophysical-technical focus that provides technical solutions to the integration of food security and biodiversity conservation. The social-political dimension, however, including equity, governance, and empowerment received little to no attention. By focusing on the poorly investigated social-political dimension, this dissertation aimed to identify governance properties that facilitate and impede the integration of food security and biodiversity conservation through an empirical case study conducted in a multi-level governance setting of southwestern Ethiopia. To address the overarching goal of this dissertation, first the author examined how the existing widely discussed food security approaches and agricultural land use framework, land sparing versus land sharing unfold in the local context of southwestern Ethiopia. The finding in this dissertation indicated that the existing global framing of food security approaches as well as frameworks around agricultural land use has limited applicability in on-the-ground realities mainly because landscapes are complex systems that consist of stakeholders with multiple and (often) conflicting interests. This was evident from the finding that local land use preference was not a matter of "either/or", but instead involved mixed features exhibiting properties of both land sparing and land sharing. Moreover, in addition to the biophysical factors embedded in the existing food security approaches and land use frameworks, stakeholders preference involved social factors such as the compatibility of land use strategy with local values and traditions, which are mainly unaccounted in the existing global frameworks. Findings in this dissertation revealed that the existing reductionist analytical framings to the issues of food security and biodiversity conservation seldom address the complexity inherent within and between food security and biodiversity conservation sectors. Second, this dissertation identified governance structural and process related challenges that influence individual as well as integrated achievements of food security and biodiversity conservation goals. The result of the study showed that the governance of food security and biodiversity conservation was characterized by a strongly hierarchical system with mainly linear vertical linkages, lacking horizontal linkages between stakeholders that would transcend administrative boundaries. Furthermore, with regard to the governance process, three key and interdependent categories of governance process challenges namely, institutional misfit, the problem of interplay, and policy incoherence influenced the achievement of individual and integrated goals of food security and were identified. Given the interdependence of these governance challenges, coupled with the complexity inherent in the food security and biodiversity conservation, attempts to achieve the dual goals thus needs an integrative, flexible and adaptive governance system Third, to understand how food security and biodiversity conservation unfold in the future, the author explored future development trajectories for southwestern Ethiopia. Iterative scenario planning process produced four plausible future scenarios that distinctly differed with regard to dominating land use strategies and crops grown, actor constellations and governance mechanisms, and outcomes for food security and biodiversity conservation. Three out of the four scenarios focused on increasing economic gains through intensive and commercial agricultural production. In contrast, one scenario involved features that are widely considered as beneficial to food security and biodiversity conservation, such as agroecological production, diversification practices, and increased social-ecological resilience. In smallholder landscapes such as the one studied here, such a pathway that promises benefits for both food security and biodiversity conservation may need to be given greater emphasis. In order to ensure the integration of food security and biodiversity conservation, recognizing their interdependence and addressing the challenges in a way that fits with the local dynamics is essential. In addition, addressing the food security-biodiversity nexus requires a holistic analytical lens. Moreover, this dissertation indicated that there is a clear need to pay attention to the governance structure that accommodates the diversity of perspectives, enable participation and strong coordination across geographical boundaries, policy domains and governance levels. Finally, this dissertation revealed opportunities to integrate food security and biodiversity through the pro-active management of social-ecological interactions that produce a win-win outcome. The win-win outcome could be achieved in a system that involve properties such as diversification and modern agroecological techniques, smallholders empowerment, emphasize adaptive governance of social-ecological systems, value local knowledge, culture and traditions, and ensure smallholders participation.
Restoration and management of abandoned, dry Continental heathland and sandy grassland communities
(2018)
Whereas heathlands in the Atlantic biogeographical region have been in the centre of interest, dry heathland communities in the Continental biogeographical region have been widely neglected. Thereby, the conservation status of both habitat types is listed as unfavourable-bad across the Continental biogeographical region. Surprisingly, no detailed studies are available on cost-efficient and sustainable restoration and management schemes to successfully restore and maintain highly degraded, long-abandoned Continental heaths and sandy grasslands, and thus, to counteract the poor conservation status of the habitat types. This shows the great need for research for the Continental biogeographical region. Thus, the present thesis provides substantial knowledge about the population dynamics of the key plant species of dry heaths Calluna vulgaris (L.) HULL by investigating key processes in the biology of the species as well as about the restoration and management of long-abandoned, dry Continental heathland and sandy grassland communities. In order to better understand the process of successful Continental heathland restoration, I analysed the reproductive potential (seed production, soil seed bank, and germination ability of seeds) of degenerate Calluna stands as well as the effects of single and combined management options on the generative rejuvenation (i.e., recruitment and survival) of Calluna. The results are based on a comprehensive three-year field experiment including the management options year-round, low-intensity cattle and horse grazing, one-time mowing and one-time shallow soil disturbances combined with greenhouse investigations on the soil seed bank content and germination ability of Calluna seeds. The results showed that even after long-term abandonment, seed production of degenerate Calluna stands and the germination ability of seeds proved to be high, being similar to Atlantic heathlands, whereas the soil seed bank is considerably reduced probably due to the dry conditions in the Continental region. In addition, low-intensity grazing with free-ranging robust breeds and the combination with one-time mowing at the beginning of the restoration process is an effective means of supporting the generative rejuvenation of this key plant species in degraded Continental heaths. The second study of this thesis focussed on the first-year establishment of Calluna in managed and unmanaged dry heaths and heaths in mosaics with dry sandy grasslands. The germination ability of seeds of different life-history phases of Calluna was analysed to determine if the predominance of the late life-history phase restricts the rejuvenation process of this key plant species. In addition, beside effects of management measures (year-round, low-intensity grazing, one-time mowing, one-time shallow soil disturbances) the author analysed the most important safe site conditions that possibly influenced the germination and the first-year survival of Calluna. The results of the study combine field experiments with growth chamber investigations. The author found that life-history phase of Calluna did not significantly affect seed germination and thus, the predominance of the degenerate life-history phase does not restrict the rejuvenation process. In addition, the results of the study revealed that grazing and thus trampling intensity must be temporarily and locally enhanced at the beginning of the restoration process of highly degraded heaths to increase safe site availability for successful Calluna establishment. Thereby, shadowing is the most important safe site condition. In the third study, the author investigated the impacts of year-round low-intensity cattle and horse grazing on the development of the highly competitive grass Calamagrostis epigejos (henceforth referred to as Calamagrostis), as well as the vegetation structure and plant species richness of long-abandoned but nutrient-poor dry heathland and sandy grassland communities, their mosaics and Calamagrostis stands. Finally, I assessed the local conservation status of the habitat types after seven years of grazing in comparison to long-abandoned sites. The results are based on a comprehensive field study on two spatial scales (plot-level: 25 square meters, macroplot-level: 1 ha). The author found that grazing successfully reduced the coverage and prevented the further spread of Calamagrostis, while simultaneously maintained or improved characteristic species richness and vegetation structure across the different nutrient-poor vegetation types over time, and thus enhanced the local conservation status of habitat types of community interest. In conclusion, the results of the studies considerably improved the understanding of dry, Continental heathland and sandy grassland restoration and management. They provide evidence that even after long-term management abandonment, year-round low-intensity cattle and horse grazing is a suitable management tool for restoring, maintaining and even improving nutrient-poor heathland and sandy grassland communities. However, at the beginning of the restoration process, additional management measures are necessary to faster restore abandoned habitats, especially highly degraded heaths.
Protected areas are an essential tool for conserving biodiversity. However, their ecological effectiveness is contested and their capacity to resist human pressures differ. This dissertation aimed to assess the ecological effectiveness of different protection levels (from strict to less strictly protected: national park, game reserve, forest reserve, game-controlled area, and unprotected areas) in biodiversity (both mega diverse butterflies and mammals), maintaining habitat connectivity, and reducing anthropogenic threats at the wider landscape in the Katavi-Rukwa Ecosystem of southwestern Tanzania. To achieve this overarching goal, the researcher employed an interdisciplinary approach. First, he analyzed butterfly diversity and community composition patterns across protection levels in the Katavi-Rukwa Ecosystem. He found that species richness and abundance were highest in the game reserves and game-controlled areas, intermediate in the forest reserves, national park and unprotected areas. Species composition differed significantly among protection levels. Landscape heterogeneity, forest cover, and primary productivity influenced species composition. Land-use, burned areas, forest cover, and primary productivity explained the richness of species and functional traits. Game reserves hosted most indicator species. Second, the author modelled the spatial distribution of six large mammal target species (buffalo Syncerus caffer, elephant Loxodonta africana, giraffe Giraffa camelopardalis, hartebeest Alcelaphus buselaphus, topi Damaliscus korrigum, and zebra Equus burchellii) across environmental and protection gradients in the Katavi-Rukwa Ecosystem. Based on species-specific density surface models, he found relatively consistent effects of protection level and land-use variables on the spatial distribution of the target mammal species: relative densities were highest in the national park and game reserves, intermediate in forest reserves and game-controlled areas and lowest in un-protected areas. Beyond species-specific environmental predictors for relative densities, the results highlight consistent negative associations between relative densities of the target species and distance to cropland and avoidance of areas in proximity to houses. Third, the author examined temporal changes in land-use, population densities and distribution of six large mammal target species across protection levels between 1991 and 2018. During the surveyed period, cropland increased. Wildlife densities of most, but not all target species declined across the entire landscape. Based on logistic regression models, target species preferred the national park over less strictly protection levels and areas distant to cropland. Fourth, he quantified land-use changes, modelled habitat suitability and connectivity of elephant over time across a large protected area network in southwestern Tanzania. Based on analyses of remotely-sensed data, cropland increased from 7% in 2000 to 13% in 2019. Based on ensemble models, distance from cropland influenced survey-specific habitat suitability for elephant the most. Despite cropland expansion, the locations of the modelled elephant corridors (n=10) remained similar throughout the survey period. Based on circuit theory, the author prioritizes three corridors for protected area connectivity. Key indicators of corridor quality varied over time, whereas elephant movement through some corridors appears to have increased over time. Overall, this dissertation underpins differences in ecological effectiveness of protected areas within one ecosystem. It highlights the need to utilize a landscape conservation approach to guide effective conservation across the entire protection gradient. It also suggests the need to enforcing land use plans and having alternative and sustainable forms for generating income from the land without impairing wildlife habitat.
The dissertation deals with the impact of nitrogen deposition on the functioning of heathland ecosystems. Special interests were the displacement of heather (Calluna vulgaris) by the purple moor-grass (Molinia caerulea) as well as the fate of nitrogen loads in dry heathland ecosystems. The results of the studies undertaken in the field and in the greenhouse are presented as five individual journal articles. The nature of nutrient limitation was studied by means of fertilisation experiments with nitrogen (N) and phosphorus for heather and purple moor-grass (Articles I and II). The impact of nitrogen deposition on the outcome of competition between these two species was analysed during a competition experiment in the greenhouse (Article III). The aim of a 15N tracer experiment was to determine the fate of nitrogen deposition as well as allocation patterns (Article IV). In addition, the response of purple moor-grass to the combined effects of nitrogen deposition and summer droughts was investigated in a second greenhouse experiment (Article V). The fertilisation experiments showed that the growth of heather as well as of purple moor-grass is predominantly limited by N (Articles I and II). However, the results of the competition experiment demonstrated that only purple moor-grass has the ability to benefit from additional N loads, which in turn gives the grass the opportunity to displace heather (Article III). Drought treatment resulted in strikingly reduced biomass production of purple moor-grass in N-fertilised pots, mainly as a result of dying aboveground biomass during dry periods (Article V). This striking susceptibility of purple moor-grass to the combination of nitrogen deposition and drought must be taken into account, when predicting future developments of dry heathlands. The results of the 15N tracer experiment showed that the investigated heath is still in an early stage of N saturation, as indicated by a high immobilisation capacity and negligible leaching losses of 15N (Article IV). The findings of the dissertation contribute to a better understanding of the processes underlying the encroachment of purple moor-grass in dry heathlands and can enhance heathland management. The results can also be used to to evaluate the current and future status of this ecosystem particularly with regard to the various stages of N saturation as well as in the determination of “Critical Loads”.