Britta Tietjen

• Prof. Dr.
• Professor (Full) at Freie Universität Berlin

Global biodiversity hotspots, including Mediterranean‐type ecosystems worldwide, are highly threatened by global change that alters biodiversity, ecosystem functions, and services. Some restoration activities enhance ecosystem functions by reintroducing plant species based on known relationships between plant traits and ecosystem processes. Achievi...

There is consensus that habitat loss is a major driver of biodiversity loss, while the effects of fragmentation, given a constant total habitat amount, are still debated. Here, we use a process‐based metacommunity model to show how scale‐ and context‐dependent fragmentation–biodiversity relationships can emerge from the interplay of two types of fr...

Biodiversity loss and widespread ecosystem degradation are among the most pressing challenges of our time, requiring urgent action. Yet our understanding of their causes remains limited because prevailing ecological concepts and approaches often overlook the underlying complex interactions of individuals of the same or different species, interactin...

Tropical saltmarshes share the intertidal zone with mangroves. In contrast to saltmarshes of temperate latitudes, these only occupy the uppermost niche of the intertidal zone, and are characterised by periods of severe drought and hypersalinity in the upper soil during dry seasons. Like mangroves, they show pronounced species zonation patterns alon...

The strength of biodiversity–ecosystem functioning (BEF) relationships varies within and across studies, depending on the investigated ecosystem function and diversity facet (e.g., species richness or functional composition), limiting our ability to translate BEF results into recommendations for management and conservation. The variability in BEF r...

Understanding the factors governing grassland biodiversity across different spatial scales is crucial for effective conservation and management. However, most studies focus on single grain sizes, leaving the scale‐dependent mechanisms of biodiversity drivers unclear. We investigated how climate, soil properties, abiotic disturbance, and land use in...

Temperate semi-natural grassland plant communities are expected to shift under global change, mainly due to land use and climate change. However, the interaction of different drivers on diversity and the influence of diversity on the provision of ecosystem services are not fully understood. To synthesise the knowledge on grassland dynamics and to b...

Forests in Eastern Germany are already experiencing the detrimental effects of droughts, exemplified by the severe conditions of the 2018 drought year. With climate change, such extreme events are expected to become more frequent and severe. Previous work suggests that mixed forests exhibit greater resilience against droughts than monocultures. Our...

Climate Smart Agriculture (CSA) practices play a crucial role in enhancing agricultural resilience. However, there is a need for a more comprehensive exploration of their specific impact on maize productivity under future climate change scenarios. While previous studies focused mainly on CSA effects on crop yield, a broader investigation is needed...

There is consensus that habitat loss is a major driver of biodiversity loss, while the effects of fragmentation, given a constant total habitat amount, are still debated. Here, we use a process-based metacommunity model to show how strongly scale- and context-dependent fragmentation-biodiversity relationships can emerge from the interplay of two ty...

Forage offtake, leaf biomass and soil organic carbon storage are important ecosystem services of permanent grasslands, which are determined by climatic conditions, management and functional diversity. However, functional diversity is not independent of climate and management, and it is important to understand the role of functional diversity and th...

Savannas are characterized by water scarcity and degradation, making them highly vulnerable to increased uncertainties in water availability resulting from climate change. This poses a significant threat to ecosystem services and rural livelihoods that depend on them. In addition, the lack of consensus among climate models on precipitation change m...

Savanna rangelands provide diverse communities across southern Africa with livestock and wildlife-based livelihoods, as well as extensive ecosystem services. Historical usage patterns, however, are increasingly challenged by widespread degradation. While regional- and local-scale policy initiatives have attempted to minimize damage and increase the...

Questions Soil resource heterogeneity influences the outcome of plant–plant interactions and, consequently, species co‐existence and diversity patterns. The magnitude and direction of heterogeneity effects vary widely, and the processes underlying such variations are not fully understood. In this study, we explored how and under what resource condi...

Biocrusts are ecosystem engineers in drylands and structure the landscape through their ecohydrological effects. They regulate soil infiltration and evaporation but also surface water redistribution, providing important resources for vascular vegetation. Spatially-explicit ecohydrological models are useful tools to explore such ecohydrological mech...

Forage supply and soil organic carbon storage are two important ecosystem functions of permanent grasslands, which are determined by climatic conditions, management and functional diversity. However, functional diversity is not independent of climate and management, and it is important to understand the role of functional diversity and these depend...

Under a changing climate, soil fungal communities will increasingly be subject to periods of heat stress. These periods can affect the performance of individual fungi and their competition for space and resources. Competition between fungi is strongly controlled by the exudation of inhibitory compounds, resulting in different competitive outcomes t...

Maintaining the resilience and functionality of savannas is key to sustaining the ecosystem services they provide. This maintenance is largely dependent on the resilience of savannas to stressors, such as prolonged droughts. The resilience to drought is largely determined by the interaction of herbivores and the functional composition of vegetation...

Savannas are characterized by the coexistence of two contrasting plant life‐forms: woody and herbaceous vegetation. During the last decades, there has been a global trend of an increase in woody cover and the spread of shrubs and trees into areas that were previously dominated by grasses. This process, termed bush encroachment, is associated with s...

Climate models predict the further intensification of global warming in the future. Drylands, as one of the most fragile ecosystems, are vulnerable to changes in temperature, precipitation, and drought extremes. However, it is still unclear how plant traits interact with soil properties to regulate drylands’ responses to seasonal and interannual cl...

With climate change, maize production is becoming more constrained by limited water availability especially in rainfed production systems. Climate Smart Agriculture (CSA) practices have potential to enhance water availability and water use efficiency in rainfed production systems, but their efficiencies have not been adequately investigated. The st...

Changing climatic conditions and unsustainable land use are major threats to savannas worldwide. Historically, many African savannas were used intensively for livestock grazing, which contributed to widespread patterns of bush encroachment across savanna systems. To reverse bush encroachment, it has been proposed to change the cattle-dominated land...

CONTEXT: Climate change continues to affect maize production, food security and livelihoods of smallholder farmers in most of the developing countries. Climate smart agriculture (CSA) practices can enhance agricultural production by alleviating adverse climate effects on maize productivity through improved soil moisture storage, water use efficienc...

Crop models are crucial in assessing the reliability and sustainability of soil water conservation practices. The AquaCrop model was tested and validated for maize productivity under the selected climate smart agriculture (CSA) practices in the rainfed production systems. The model was validated using final biomass (B) and grain yield (GY) data fro...

Crop models are crucial in assessing the reliability and sustainability of soil water conservation practices. The AquaCrop model was tested and validated for maize productivity under the selected climate smart agriculture (CSA) practices in the rainfed production systems. The model was validated using final biomass (B) and grain yield (GY) data fro...

In sub-humid regions, declining maize (Zea mays L.) yield is majorly attributed to unreliable rainfall and high evapotranspiration demand during critical growth stages. However, there are limited farm technologies for conserving soil water and increasing water use efficiency (WUE) in rainfed production systems amidst a changing climate. This study...

The current global rates of human impact intensification in freshwater ecosystems and their surroundings have caused an alarming loss of freshwater biodiversity and functioning across multiple trophic levels. Particularly vulnerable to anthropogenic pressures are small water bodies (SWB). However, the majority of the evidence is limited to a single...

Biogeochemical models of vegetation dynamics could potentially be used to complement empirical studies on the effect of plant species richness. A key precondition is the simulation of species coexistence. While community scale models regularly incorporate respective processes, models at the field or landscape scale used for larger scale assessments...

Changing climatic conditions and unsustainable land use are perceived as major threats to savannas worldwide. In the past, land use in African savannas was dominated by livestock-farming as one of the major economic products, which led to degraded, shrub encroached pastures in many regions. One response to this widespread degradation is a shift fro...

Ecological restoration increasingly aims at improving ecosystem multifunctionality and making landscapes resilient to future threats, especially in biodiversity hotspots such as Mediterranean‐type ecosystems. Plants and their traits play a major role in the functioning of an ecosystem. Therefore, successful restoration towards long‐term multifuncti...

Alpine grasslands on the Qinghai-Tibetan Plateau are sensitive and vulnerable to climate change and human activities. Climate warming and overgrazing have already caused degradation in a large fraction of alpine grasslands on this plateau. However, it remains unclear how human activities (mainly livestock grazing) regulates vegetation dynamics unde...

Priming, an inducible stress defence strategy that prepares an organism for an impending stress event, is common in microbes and has been studied mostly in isolated organisms or populations. How the benefits of priming change in the microbial community context and, vice versa, whether priming influences competition between organisms, remains largel...

Aim It is widely accepted that biodiversity is influenced by both niche‐related and spatial processes from local to global scales. Their relative importance, however, is still disputed, and empirical tests are surprisingly scarce at the global scale. Here, we compare the importance of area (as a proxy for pure spatial processes) and environmental h...

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Ecological restoration increasingly aims at improving ecosystem multifunctionality and making landscapes resilient to future threats, especially in biodiversity hotspots such as Mediterranean-type ecosystems. Successful realisation of such a strategy requires a fundamental mechanistic understanding of the link between ecosystem plant composition, p...

Manipulative experiments typically show a decrease in dryland biocrust cover and altered species composition under climate change. Biocrust‐forming lichens, such as the globally distributed Diploschistes diacapsis, are particularly affected and show a decrease in cover with simulated climate change. However, the underlying mechanisms are not fully...

Grassland biodiversity is vulnerable to land use change. How to best manage semi-natural grasslands for maintaining biodiversity is still unclear in many cases because land-use processes may depend on environmental conditions and the indirect effects of land-use on biodiversity mediated by altered abiotic and biotic factors are rarely considered. H...

The ecosystem-based management (EBM) philosophy draws upon the principle that holistic understanding of the system to be governed needs to guide the decision-making process. However, empirical evidence is growing that knowledge integration is still a main bottleneck for EBM decision-makers. This paper argues that transdisciplinary knowledge managem...

1. Manipulative experiments show a decrease in dryland biological soil crust cover and altered species composition under climate change. However, the underlying mechanisms are not fully understood, and long-term interacting effects of different drivers are largely unknown due to the short-term nature of the studies conducted so far. 2. We addressed...

Priming, an inducible stress defense strategy that prepares an organism for an impending stress event, is common in microbes and has been studied mostly in isolated organisms or populations. How the benefits of priming change in the microbial community context and, vice versa, whether priming influences competition between organisms, remains largel...

The continuing loss of global biodiversity has raised questions about the risk that species extinctions pose for the functioning of natural ecosystems and the services that they provide for human wellbeing. There is consensus that, on single trophic levels, biodiversity sustains functions; however, to understand the full range of biodiversity effec...

Grassland biodiversity is among the most vulnerable to land use. How to best manage semi-natural grasslands for maintaining biodiversity is still unclear in many cases because processes may depend on environmental conditions and indirect effects are rarely considered. Here we evaluate the relative importance of direct and indirect effects of grazin...

Ensuring ecosystem resilience is an intuitive approach to safeguard the functioning of ecosystems and hence the future provisioning of ecosystem services (ES). However, resilience is a multi‐faceted concept that is difficult to operationalize. Focusing on resilience mechanisms, such as diversity, network architectures or adaptive capacity, has rece...

Organisms are prone to different stressors and have evolved various defense mechanisms. One such defense mechanism is priming, where a mild preceding stress prepares the organism towards an improved stress response. This improved response can strongly vary, and primed organisms have been found to respond with one of three response strategies: a sho...

Nitrogen (N) cycling is a critical pathway by which producer, consumer, and decomposer interact with each other and with environmental circumstances simultaneously. The natural abundance composition of 15 N/ 14 N in plants and soils (termed as δ 15 N plant and δ 15 N soil), as well as the difference between them (δ 15 N soil-to-plant = δ 15 N plant...

Leaf water potential regulation is a key process in whole plant and ecosystem functioning. While low water potentials induced by open stomata may initially be associated with greater CO2 supply and a higher water flux from the rhizosphere to the canopy, they also inhibit cell growth, photosynthesis and ultimately water supply. Here, we show that pl...

The iso/anisohydry concept char- acterizes plants according to their water status regulation. Coexist- ing definitions and misconcep- tions have recently led to considerable criticism. We dis- cuss here reasons for the miscon- ceptions, and propose a robust definition of iso/anisohydry using the leaf turgor loss point to inte- grate the complex int...

Ensuring ecosystem resilience is an intuitive approach to safeguard future provisioning of ecosystem services (ES). However, resilience is an ambiguous concept and difficult to operationalize. Focusing on resilience mechanisms, such as diversity, network architectures or adaptive capacity, has recently been suggested as means to operationalize resi...

The timing regimes of precipitation can exert profound impacts on grassland ecosystems. However, it is still unclear how the peak aboveground biomass (AGB peak) of alpine grasslands responds to the temporal variability of growing season precipitation (GSP) on the northern Tibetan Plateau. Here, the temporal variability of precipitation was defined...

The biodiversity-productivity relationship is critical for better predicting ecosystem responses to climate change and human disturbance. However, it remains unclear about the effects of climate change, land use shifts, plant diversity, and their interactions on productivity partitioning above- and below-ground components in alpine grasslands on th...

Mediterranean-type ecosystems (MTEs) harbor an exceptionally high biodiversity of vascular plants. At the same time, climatic conditions in many MTE regions are projected to become both drier and hotter, and fire intervals shorter. The Interval Squeeze conceptual model integrates the potential effects of a changing climate and fire regimes on peren...

Intermittent rivers and ephemeral streams (IRES) encompass fluvial ecosystems that eventually stop flowing and run dry at some point in space and time. During the dry phase, channels of IRES consist mainly of dry riverbeds (DRBs), prevalent yet widely unexplored ecotones between dry and wet phases that can strongly influence the biogeochemistry of...

Background Biocrusts, communities dominated by mosses, lichens, cyanobacteria, and other microorganisms, largely affect the carbon cycle of drylands. As poikilohydric organisms, their activity time is often limited to short hydration events. The photosynthetic and respiratory response of biocrusts to hydration events is not only determined by the o...

1. Savanna systems exhibit a high plant functional diversity. While aridity and livestock grazing intensity have been widely discussed as drivers of savanna vegetation composition, physical soil properties have received less attention. Since savannas can show local differences in soil properties, these might act as environmental filters and affect...

III. Methods • Plant species richness and aboveground productivity were measured at ten 1.0 m 2 plots at each site. • Soil total nitrogen (STN) and phosphorus (STP) were measured at 0-20 cm layer for each plot. • Plant and soil 15 N were measured with an isotope ratio mass spectrometer. • The 15 N/ 14 N ratio of samples (R sample) was relative to t...

Precipitation and land use in terms of livestock grazing have been identified as two of the most important drivers structuring the vegetation composition of semi-arid and arid savannas. Savanna research on the impact of these drivers has widely applied the so- called plant functional type (PFT) approach, grouping the vegetation into two or three br...

A global ecological restoration agenda has led to ambitious programs in environmental policy to mitigate declines in biodiversity and ecosystem services. Current restoration programs can incompletely return desired ecosystem service levels, while resilience of restored ecosystems to future threats is unknown. It is therefore essential to advance un...

Water relations in plant communities are influenced both by contrasting functional groups (grasses, shrubs) and by climate change via complex effects on interception, uptake and transpiration. We modelled the effects of functional group replacement and biomass increase, both of which can be outcomes of invasion and vegetation management, and climat...

A sparsely-populated area (0.2 persons per km 2 land) with natural landscapes in the North Tibet (Yu et al., 2016). • Three representative grassland types, from east to west, alpine meadow, alpine steppe, and desert steppe (Li et al., 2011). • Remarkable climatic gradients of growing season temperature (GST, 4.8-8.8 ° C) and precipitation (GSP, 123...

Resilience is an important aspect of the non-linear restoration of disturbed ecosystems. Fenced grassland patches on the northern Tibetan Plateau can be used to examine the resistance and resilience of degraded alpine grasslands to grazing and to a changing climate. To examine the non-linearity of restoration, we used moderate resolution imaging sp...

Flower nectar is a sugar-rich ephemeral habitat for microorganisms. Nectar-borne yeasts are part of the microbial community and can affect pollination by changing nectar chemistry, attractiveness to pollinators or flower temperature if yeast population densities are high. Pollinators act as dispersal agents in this system, however, pollination even...

The distribution of rainfed agriculture, which accounts for approximately ¾ of global croplands, is expected to respond to climate change and human population growth and these responses may be especially pronounced in water limited areas. Because the environmental conditions that support rainfed agriculture are determined by climate, weather, and s...

Savannas are mixed tree-grass ecosystems whose dynamics are predominantly regulated by resource competition and the temporal variability in climatic and environmental factors such as rainfall and fire. Hence, increasing inter-annual rainfall variability due to climate change could have a significant impact on savannas. To investigate this, we used...

The El Niño–Southern Oscillation (ENSO) is the main driver of the interannual variability in eastern African rainfall, with a significant impact on vegetation and agriculture and dire consequences for food and social security. In this study, we identify and quantify the ENSO contribution to the eastern African rainfall variability to forecast futur...

Large scale hydrological modelling has several intrinsic difficulties. On the one hand, less accuracy is demanded and the spatial resolution can be reduced to save computational resources. However, a useful model must be calibrated and validated homogeneously across the basin, which requires good observational data. Furthermore, if gauging sta- tio...

The El Niño Southern Oscillation (ENSO), is the main driver for the interannual variability in East African rainfall with significant impact on vegetation and agriculture, and dire consequences for food and social security. In this study, we identify and quantify the ENSO contribution to the East African rainfall variability to forecast future East...

Drylands cover 40% of the global terrestrial surface and provide important ecosystem services. While drylands as a whole are expected to increase in extent and aridity in coming decades, temperature and precipitation forecasts vary by latitude and geographic region suggesting different trajectories for tropical, subtropical, and temperate drylands....

Supplementary Figures, Supplementary Tables and Supplementary References

Vegetation productivity is an essential variable in ecosystem functioning. Vegetation dynamics of dryland ecosystems are most strongly determined by water availability and consequently by rainfall and there is a need to better understand how water limited ecosystems respond to altered rainfall amounts and variability. This response is partly determ...

Drylands occur world-wide and are particularly vulnerable to climate change since dryland ecosystems depend directly on soil water availability that may become increasingly limited as temperatures rise. Climate change will both directly impact soil water availability, and also change plant biomass, with resulting indirect feedbacks on soil moisture...

Fluxes of organic and inorganic carbon within the Amazon basin are considerably controlled by annual flooding, which triggers the export of terrigenous organic material to the river and ultimately to the Atlantic Ocean. The amount of carbon imported to the river and the further conversion, transport and export of it depend on temperature, atmospher...

Ecosystem services provided by Mediterranean-type ecosystems (MTEs) are currently at risk due to global change (e.g. change in land use, nitrogen deposition, climate). Ecological restoration increasingly aims at restoring towards resilient and multifunctional landscapes. Therefore, we require a fundamental understanding of the link between ecosyste...

Information on human indoor exposure is necessary to assess the potential risk to individuals from many chemicals of interest. Dynamic indoor and human physicologically based pharmacokinetic (PBPK) models of the distribution of non-ionizing, organic chemical concentrations in indoor environments resulting in delivered tissue doses are developed, de...

Any regular interaction of land and river during flooding affects carbon pools within the terrestrial system, riverine carbon and carbon exported from the system. In the Amazon basin carbon fluxes are considerably influenced by annual flooding, during which terrigenous organic material is imported to the river. The Amazon basin therefore represents...

The present-day vegetation in the tropics is mainly characterized by forests worldwide except in tropical East Africa, where forests only occur as patches at the coast and in the uplands. These forest patches result from the peculiar aridity that is linked to the uplift of the region during the Late Cenozoic. The Late Cenozoic vegetation history of...

East Africa hosts a striking diversity of terrestrial ecosystems, which vary both in space and time due to complex regional topography and a dynamic climate. The structure and functioning of these ecosystems under this environmental setting can be studied with dynamic vegetation models (DVMs) in a spatially explicit way. Yet, regional applications...