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Institut
- Institut für Ökologie (IE) (30) (entfernen)
Assessment of forest functionality and the effectiveness of forest management and certification
(2021)
Forest ecosystems are complex systems that develop inherent structures and processes relevant for their functioning and the provisioning of ecosystem services that contribute to human wellbeing. With increasing climate change impacts, especially regulating ecosystem services such as microclimate regulation are ever more relevant to maintain forest functions and services. A key question is how forest management supports or undermines the ecosystems’ capacity to maintain those functions and services. The main objective of this thesis is the development of a concept to assess the functionality of forests and to evaluate the effectiveness of forest ecosystem management including certification. An ecosystem-based and participatory methodology, named ECOSEFFECT, was developed. The method comprises a theoretical and an empirical plausibility analysis. It was applied to the Russian National FSC Standard in the Arkhangelsk Region of the Russian Federation - where boreal forests are exploited to meet Europe's demand for timber. In addition, the influence of forestry interventions on temperature regulation in Scots pine and European beech forests in Germany was assessed during two extreme hot and dry years in 2018 and 2019. Microclimate regulation is a suitable proxy for forest functionality and can be applied easily to evaluate the effectiveness of forest management in safeguarding regulating forest functions relevant under climate change. Thus, the assessment of forest microclimate regulation serves as convenient tool to illustrate forest functionality. In the boreal and temperate forests studied in the frame of this thesis, timber harvesting reduced the capacity to self-regulate forests’ microclimate and thus impair a crucial part of ecosystem functionality. Changes in structural forest characteristics influenced by forest management and silviculture significantly affect microclimatic conditions and therefore forest ecosystems' vulnerability to climate change. Canopy coverage and the number of cut trees were most relevant for cooling maximum summer temperature in pine and beech forests in northern Germany. The Russian FSC standard has the potential to improve forest management and ecological outcomes, but there are shortcomings in the precision of targeting actual problems and ecological commitment. It is theoretically plausible that FSC prevents logging in high conservation value forests and intact forest landscapes, reduces the size and number of clearcuts, and prevents hydrological changes in the landscape. However, the standard was not sufficiently explicit and compulsory to generate a strong and positive influence on the identified problems and their drivers. Moreover, spatial data revealed, that the typical regular clearcut patterns of conventional timber harvesting continue to progress into the FSC-certified boreal forests, also if declared as "Intact Forest Landscape". This results in the need to verify the assumptions and postulates on the ground as it remains unclear and questionable if functions and services of boreal forests are maintained when FSC-certified clearcutting continues.The analysis of satellite-based data on tree cover loss showed that clearcutting causes secondary dieback in the surrounding of the cleared area. FSC-certification does not prevent the various negative impacts of clearcutting and thus fails to safeguard ecosystem functions. The postulated success in reducing identified environmental threats and stresses, e. g. through a smaller size of clearcuts, could not be verified on site. The empirical assessment does not support the hypothesis of effective improvements in the ecosystem. In practice, FSC-certification did not contribute to change clearcutting practices sufficiently to effectively improve the ecological performance. Sustainability standards that are unable to translate principles into effective outcomes fail in meeting the intended objectives of safeguarding ecosystem functioning. Clearcuts that carry sustainability labels are ecologically problematic and ineffective for the intended purpose of ecological sustainability.The overexploitation of provisioning services, i.e. timber extraction, diminishes the ecosystems' capacity to maintain other services of global significance. It also impairs ecosystem functions relevant to cope with and adapt to other stresses and disturbances that are rapidly increasing under climate change.
Traditional farming landscapes typically support exceptional biodiversity. They evolved as tightly coupled social-ecological systems, in which traditional human land-use shaped highly heterogeneous landscapes. However, these landscapes are under severe threats of land-use change which potentially pose direct threats to biodiversity, in particular through land-use intensification and land abandonment. Navigating biodiversity conservation in such changing landscapes requires a thorough understanding of the drivers that maintain the social-ecological system. This dissertation aimed to identify system properties that facilitate biodiversity conservation in traditional farming landscape, focusing specifically on birds and large carnivores in the rapidly changing traditional farmland region of Southern Transylvania, Romania. In order to identify these properties, I first examined the effects of local and landscape scale land-use patterns on birds and large carnivores and how they may be affected by future land-use change (Chapters II-V). Second, to gauge the role of particular traditional land-use elements for biodiversity I focused on the conservation value of traditional wood pastures (Chapters VI-VIII). Third, I took a social-ecological systems approach to understand how links between the social and ecological parts of the system affect human-bear coexistence (Chapters IV and IX). Bird diversity was supported by the broad gradients of woody vegetation cover and compositional heterogeneity. Land-use intensification, and hence the loss of woody vegetation cover and homogenization of land covers, would thus negatively affect biodiversity. This was especially evident from predictions on the distribution of the corncrake (Crex crex) in response to potential future land cover homogenization. Here, a moderate reduction of land cover diversity could drastically reduce the extent of corncrake habitat. Further results showed that the brown bear (Ursus arctos) would mainly be affected by land-use change through the fragmentation of large forest blocks, especially if land-use change would reduce habitat connectivity to the presumed source population in the Carpathian Mountains. Moreover, this dissertation revealed that large carnivores (brown bear and wolf, Canis lupus) may have important and often ignored roles in structuring the ecosystem of traditional farming landscapes by limiting herbivores. Wood pastures were found to have a high conservation value. The combination of low-intensity used grasslands with old scattered trees provided important supplementary habitat for different forest species such as woodpeckers and the brown bear. Worryingly, current management of wood pastures differed from traditional techniques in several aspects, which may threaten their persistence in the landscape. The majority of people had a positive perception on human-bear coexistence. The use of traditional sheep herding techniques combined with the tolerance of some shepherds to occasional livestock predation facilitated coexistence in a region where both carnivores and livestock are present. More generally, the genuine links between people and their environment were important drivers of people´s positive views on coexistence. However, perceived failures of top-down managing institutions could potentially erode these links and reduce people´s tolerance towards bears. Through the consideration of two different animal taxa, this dissertation revealed six important system properties facilitating biodiversity conservation in traditional farming landscapes. Similar proportions of the main land-use types (arable land, grassland, and forests) support species richness at the regional scale possible through habitat connectivity and continuous spill-over between land-use types. Heterogeneous landscapes can further support biodiversity through complementation and supplementation of habitat at the landscape scale. Gradients of woody vegetation cover and heterogeneity, supported biodiversity at both local and landscape scales possibly through the provision of a wide range of resources. The heterogeneous character of the landscape is tightly linked to traditional land-use practices, which also maintain specific traditional land-use elements and facilitate human-carnivore coexistence. Top-down limitation of large carnivores on herbivores possibly enhances vegetation growth and tree regeneration. The genuine links between humans and nature support human-bear coexistence, and these links may form the core of people´s values and sustainable use of natural resources.
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.
Through the expansion of human activities, humanity has evolved to become a driving force of global environmental change and influences a substantial and growing part of natural ecosystem trophic interactions and energy flows. However, by constructing and building its own niche, human distance from nature increased remarkably during the last decades due to processes of globalization and urbanization. This increasing disconnect has both material and immaterial consequences for how humans interact and connect with nature. Indeed, many regions across the world have disconnected themselves from the productivity of their regional environment by: (1) accessing biological products from distant places through international trade, and (2) using non-renewable resources from outside the biosphere to boost the productivity of their natural environment. Both mechanisms allow for greater resource use then would be possible otherwise, but also involve complex sustainability challenges and lead to fundamentally different feedbacks between humans and the environment. This dissertation empirically investigates the sustainability of biophysical human-nature connections and disconnections from a social-ecological systems perspective. The results provide new insights and concrete knowledge about biophysical human-nature disconnections and its sustainability implications, including pervasive issues of injustice. Through international trade and reliance on non-renewables, particularly higher-income regions appropriate an unproportional large share of global resources. Moreover, by enabling seemingly unconstrained consumption of resources and simultaneous conservation of regional ecosystems, increasing regional disconnectedness stimulates the misconception of decoupling. Whereas, in fact, the biophysically most disconnected regions exhibit the highest resource footprints and are, therefore, responsible for the largest environmental damages. The increasing biophysical disconnect between humans and nature effectively works to circumvent limitations and self-constraining feedbacks of natural cycles. The circumvention of environmental constraints is a crucial feature of niche construction. Human niche construction refers to the process of modifying natural environments to make them more useful for society. To ease integration of the chapters in this thesis, the framework paper uses human niche construction theory to understand the mechanisms and drivers behind increasing biophysical disconnections. The theory is employed to explain causal relationships and unsustainable trajectories from a holistic perspective. Moreover, as a process-oriented approach, it allows connecting the empirically assessed states of disconnectedness with insights about interventions and change for sustainability. For a sustainability transformation already entered paths of disconnectedness must be reversed to enable a genuine reconnection of human activities to the biosphere and its natural cycles. This thesis highlights the unsustainability of disconnectedness and opens up debate about how knowledge around sustainable human niche construction can be leveraged for a reconnection of humans to nature.
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.
Rangelands are the most widespread land-use systems in drylands, where they often represent the only sustainable form of land-use due to the limited water availability. The intensity of the land-use of such rangeland ecosystems in drylands depends to a large extent on the climatic variability in time and space. Rangeland systems are seriously threatened by climate change, because climate change will alternate the availability of water in time and space. This dissertation therefore deals with the question which role climatic variability plays for the effects of grazing on vegetation in dry rangelands. The relatively intact steppes in central Mongolia were chosen as a model system. They are characterised by low precipitation and high climatic variability in the south (100mm annual precipitation), and comparatively high precipitation and low climatic variability in the north (250mm). The effects of grazing on vegetation on 15 grazing transects were investigated along the climatic gradient. The central elements were the plant species and their abundances on 10m x 10m areas, for which functional characteristics such as height, affiliation of functional groups or leaf nutrients were recorded. The main hypothesis of this dissertation is that grazing has a greater impact on vegetation communities with increasing rainfall. To test this hypothesis, three studies were carried out. In a first study, the research group found that the vegetation communities in the dry area differ strongly along the climatic gradient, while the plant communities in the wetter area differ more strongly along the grazing gradient. The results of the second study suggested that this difference can be explained by a functional environmental filter that becomes weaker from south to north as the niche spectrum increases. The third study has shown that this is likely a function of the higher availability of resources, which at the same time leads to higher grazing pressure, therewith stressing the vegetation especially in years with droughts. In summary, the author concludes that the climate gradient also represents an environmental filter that filters species for certain characteristics, thus having a significant influence on the vegetation. Climatic variability influences the effect of grazing on vegetation, which is particularly problematic where the grazing intensity is high and the species are less adapted to strong climatic fluctuations. Future scenarios predict increasing productivity and therefore increasing livestock density. This may lead to an increase in floristic and functional diversity across the climate gradient, but also to increasing grazing effects and therefore threads for overgrazing. Increasing climatic variability is likely to intensify this thread, especially in the moister regions, whereas the dry rangelands are likely to be more resilient due to the adaptation of the plants to non-equilibrium dynamics.
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.
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.
Climate change and atmospheric deposition of nitrogen affect biodiversity patterns and functions of forest ecosystems worldwide. Many studies have quantified tree growth responses to single global change drivers, but less is known about the interaction effects of these drivers at the plant and ecosystem level. In the present study, the authors conducted a full-factorial greenhouse experiment to analyse single and combined effects of nitrogen fertilization (N treatment) and drought (D treatment) on 16 morphological and chemical response variables of one-year-old Fagus sylvatica seedlings originating from eight different seed families from the Cantabrian Mountains (NW Spain). Drought exerted the strongest effect on response variables, reflected by decreasing biomass production. However, D and N treatments interacted for some of the response variables, indicating that N fertilization has the potential to strengthen the negative effects of drought (with both antagonistic and amplifying interactions). For example, combined effects of N and D treatments caused a sevenfold increase of necrotic leaf biomass. The authors hypothesize that increasing drought sensitivity was mainly attributable to a significant reduction of the root biomass in combined N and D treatments, limiting the plants' capability to satisfy their water demands. Significant seed family effects and interactions of seed family with N and D treatments across response variables suggest a high within-population genetic variability. In conclusion, the findings indicated a high drought sensitivity of Cantabrian beech populations, but also interaction effects of N and D on growth responses of beech seedlings.
Der hochwassergebundene Sedimenteintrag ist Motor der Bodenbildung in Auen. Der mit dem Sedimenteintrag einhergehende Schadstofftransport in die flussbegleitenden Auen ist Ursache für die Akkumulation von Schadstoffen in den aquatischen und semiterretrischen Systemen. Er wirkt in weiten Teilen der Elbauen nicht nur einschränkend auf die landwirtschaftliche Nutzung des Grünlandes sondern beeinträchtigt daneben auch weitere Schutzgüter, wie z. B. Habitate und Lebensgemeinschaften. Diese Arbeit hatte das Ziel, die Steuergrößen des Sediment- und Schadstoffeintrags anhand von langjährig erhobenen Messdaten zu untersuchen und gleichzeitig die zeitliche und räumliche Verbreitung ausgewählter Schadstoffe als Baustein eines belastungsangepassten Auenmanagements aufzuklären. Dafür wurden eigene Daten über Hochflutsedimente und Böden ebenso ausgewertet wie Daten anderer Autoren. Außerdem lag ein Schwerpunkt der Arbeit in der kombinierten Auswertung von Zeitreihen der Sedimentbelastung von Gewässern und von Auenböden, die eine Grundlage für das Verständnis des elbespezifischen Belastungsmosaiks von Böden mit Schwermetallen und Dioxinen/Furanen darstellt. Zunächst erfolgte eine detaillierte Recherche und Analyse der retentionsfördernden Eigenschaften der Elbauen. Es wurden abschnittsspezifische Flächengrößen, Landnutzungsunterschiede und Flächenbetroffenheiten bei unterschiedlichen Hochwasserzuständen herausgearbeitet. Mit Hilfe der darauf aufbauenden, datenbasierten Analysen über ereignisbezogene Sedimenteinträge in die Elbauen konnten wesentliche Steuergrößen des Sedimenteintrags identifiziert werden. Die Distanz der Standorte zur Elbe ist die wesentliche Kenngröße, sodass die größten Sedimenteinträge in Flussnähe stattfinden. Darüber hinaus ist die Höhe des Sedimenteintrags abflussabhängig. Auf dieser Grundlage wurde ein Ansatz zur Berechnung des großräumigen Sedimenteintrags entwickelt, mit dessen Hilfe die Retentionsfunktion der Auen im Abfluss- und Stofftransportgeschehen der Elbe abgeschätzt werden konnte. Die Sedimentretention der Elbauen hatte im Betrachtungszeitraum zwischen 2003 und 2008 einen Anteil von 7 bis 30 % an den Jahresschwebstofffrachten in Hitzacker. Die Analysen von verschiedenen Zeitreihen der Sediment- und Bodenbelastungen mit Schwermetallen, Arsen sowie Dioxinen/Furanen verdeutlichte, dass die Stoffgruppen ganz unterschiedliche Belastungsentwicklungen durchlaufen haben. Der Schwerpunkt der Dioxinkontamination in Sedimenten und Böden trat in den 1950er bis 1960er Jahren auf, während Metalle im Allgemeinen erst später Belastungsmaxima zeigten. Allerdings konnte mit dem Pb/Zn-Verhältnis ein Metallmuster identifiziert werden, mit dessen Hilfe auch in Oberböden auf der Basis von Metalldaten auf Dioxinbelastungen geschlossen werden konnte. Darüber hinaus wurde unter Kenntnis der spezifischen Belastungshistorien mittels Kategorisierung der Standorteigenschaften Höhenlage, Distanz, Bioturbation und Sedimenteintrag ein Erklärungsschema zur Vorhersage von räumlichen Schadstoffmustern für ausgewählte Metalle und Dioxine/Furane entwickelt. Sowohl die Untersuchungen zum Sedimentationsgeschehen als auch zur Aufklärung des Belastungsmosaiks in den Elbauen ließen Ableitungen von Maßnahmenvorschlägen zur Förderung der Sedimentationsdynamik, des Hochwasserschutzes, zur schadstoffspezifischen Verbesserung der Bodenbelastung als auch zur belastungsangepassten Landnutzung zu.