Showing papers by "Ernst Detlef Schulze published in 2019"

Arthropod decline in grasslands and forests is associated with landscape-level drivers

Abstract: Recent reports of local extinctions of arthropod species1, and of massive declines in arthropod biomass2, point to land-use intensification as a major driver of decreasing biodiversity. However, to our knowledge, there are no multisite time series of arthropod occurrences across gradients of land-use intensity with which to confirm causal relationships. Moreover, it remains unclear which land-use types and arthropod groups are affected, and whether the observed declines in biomass and diversity are linked to one another. Here we analyse data from more than 1 million individual arthropods (about 2,700 species), from standardized inventories taken between 2008 and 2017 at 150 grassland and 140 forest sites in 3 regions of Germany. Overall gamma diversity in grasslands and forests decreased over time, indicating loss of species across sites and regions. In annually sampled grasslands, biomass, abundance and number of species declined by 67%, 78% and 34%, respectively. The decline was consistent across trophic levels and mainly affected rare species; its magnitude was independent of local land-use intensity. However, sites embedded in landscapes with a higher cover of agricultural land showed a stronger temporal decline. In 30 forest sites with annual inventories, biomass and species number—but not abundance—decreased by 41% and 36%, respectively. This was supported by analyses of all forest sites sampled in three-year intervals. The decline affected rare and abundant species, and trends differed across trophic levels. Our results show that there are widespread declines in arthropod biomass, abundance and the number of species across trophic levels. Arthropod declines in forests demonstrate that loss is not restricted to open habitats. Our results suggest that major drivers of arthropod decline act at larger spatial scales, and are (at least for grasslands) associated with agriculture at the landscape level. This implies that policies need to address the landscape scale to mitigate the negative effects of land-use practices. Analyses of a dataset of arthropod biomass, abundance and diversity in grassland and forest habitats in Germany for the period 2008–2017 reveal that drivers of arthropod declines act at the landscape level.

Radar vision in the mapping of forest biodiversity from space

Abstract: Recent progress in remote sensing provides much-needed, large-scale spatio-temporal information on habitat structures important for biodiversity conservation. Here we examine the potential of a newly launched satellite-borne radar system (Sentinel-1) to map the biodiversity of twelve taxa across five temperate forest regions in central Europe. We show that the sensitivity of radar to habitat structure is similar to that of airborne laser scanning (ALS), the current gold standard in the measurement of forest structure. Our models of different facets of biodiversity reveal that radar performs as well as ALS; median R² over twelve taxa by ALS and radar are 0.51 and 0.57 respectively for the first non-metric multidimensional scaling axes representing assemblage composition. We further demonstrate the promising predictive ability of radar-derived data with external validation based on the species composition of birds and saproxylic beetles. Establishing new area-wide biodiversity monitoring by remote sensing will require the coupling of radar data to stratified and standardized collected local species data.

Genomic landscape of the global oak phylogeny

Abstract: O_LIThe tree of life is highly reticulate, with the history of population divergence buried amongst phylogenies deriving from introgression and lineage sorting. In this study, we test the hypothesis that there are regions of the oak (Quercus, Fagaceae) genome that are broadly informative about phylogeny and investigate global patterns of oak diversity.nC_LIO_LIWe utilize fossil data and restriction-site associated DNA sequencing (RAD-seq) for 632 individuals representing ca. 250 oak species to infer a time-calibrated phylogeny of the worlds oaks. We use reversible-jump MCMC to reconstruct shifts in lineage diversification rates, accounting for among-clade sampling biases. We then map the > 20,000 RAD-seq loci back to a recently published oak genome and investigate genomic distribution of introgression and phylogenetic support across the phylogeny.nC_LIO_LIOak lineages have diversified among geographic regions, followed by ecological divergence within regions, in the Americas and Eurasia. Roughly 60% of oak diversity traces back to four clades that experienced increases in net diversification due to climatic transitions or ecological opportunity.nC_LIO_LIThe support we find for the phylogeny contrasts with high genomic heterogeneity in phylogenetic signal and introgression. Oaks are phylogenomic mosaics, and their diversity may in fact depend on the gene flow that shapes the oak genome.nC_LI

Landscape-Scale Mixtures of Tree Species are More Effective than Stand-Scale Mixtures for Biodiversity of Vascular Plants, Bryophytes and Lichens

Abstract: Tree species diversity can positively affect the multifunctionality of forests. This is why conifer monocultures of Scots pine and Norway spruce, widely promoted in Central Europe since the 18th and 19th century, are currently converted into mixed stands with naturally dominant European beech. Biodiversity is expected to benefit from these mixtures compared to pure conifer stands due to increased abiotic and biotic resource heterogeneity. Evidence for this assumption is, however, largely lacking. Here, we investigated the diversity of vascular plants, bryophytes and lichens at the plot (alpha diversity) and at the landscape (gamma diversity) level in pure and mixed stands of European beech and conifer species (Scots pine, Norway spruce, Douglas fir) in four regions in Germany. We aimed to identify compositions of pure and mixed stands in a hypothetical forest landscape that can optimize gamma diversity of vascular plants, bryophytes and lichens within regions. Results show that gamma diversity of the investigated groups is highest when a landscape comprises different pure stands rather than tree species mixtures at the stand scale. Species mainly associated with conifers rely on light regimes that are only provided in pure conifer forests, whereas mixtures of beech and conifers are more similar to beech stands. Combining pure beech and pure conifer stands at the landscape scale can increase landscape level biodiversity and conserve species assemblages of both stand types, while landscapes solely composed of stand scale tree species mixtures could lead to a biodiversity reduction of a combination of investigated groups of 7 up to 20%.

Water deficiency (drought)

Abstract: This chapter first explains why plants have a greater demand for water than animals. Following a look at the physico-chemical properties of water, the water potential concept is introduced, which is used to analyse the movement of water into and through plants. Most plant species have to maintain a hydrated state; that is, they are homoiohydric. After temperature, precipitation is the most dominant environmental factor determining the distribution of vegetation at the global scale. Plants respond to fluctuations in water supply with a range of mechanisms, which are discussed at the molecular level in this chapter. These include adjustment of osmotic potentials, regulation of the stomatal aperture, and modulation of resistance to water flow by aquaporins—water channels residing in cellular membranes. Also, a plant actively modulates its growth, depending on water availability. The water status is sensed by a plant in an unknown fashion and is translated into adequate responses. These are predominantly mediated by the phytohormone abscisic acid. The corresponding signal transduction events are explained in this chapter. The final section discusses two photosynthesis variants that are characterized by higher water use efficiency and therefore represent adaptations to water scarcity. Both C4 photosynthesis and crassulacean acid metabolism photosynthesis have evolved independently many times and are of major ecological importance. Evolutionary trajectories can be postulated that illustrate how complex traits can arise in distinct steps.

Sapwood biomass carbon in northern boreal and temperate forests

Abstract: Aim Information on the amount of carbon stored in the living tissue of tree stems (sapwood) is crucial for carbon and water cycle applications. Here, we aim to investigate sapwood-to-stem proportio ...

Plant traits are poor predictors of long-term ecosystem functioning

Abstract: Earth is home to over 350,000 vascular plant species1 that differ in their traits in innumerable ways. Yet, a handful of functional traits can help explaining major differences among species in photosynthetic rate, growth rate, reproductive output and other aspects of plant performance2–6. A key challenge, coined “the Holy Grail” in ecology, is to upscale this understanding in order to predict how natural or anthropogenically driven changes in the identity and diversity of co-occurring plant species drive the functioning of ecosystems7, 8. Here, we analyze the extent to which 42 different ecosystem functions can be predicted by 41 plant traits in 78 experimentally manipulated grassland plots over 10 years. Despite the unprecedented number of traits analyzed, the average percentage of variation in ecosystem functioning that they jointly explained was only moderate (32.6%) within individual years, and even much lower (12.7%) across years. Most other studies linking ecosystem functioning to plant traits analyzed no more than six traits, and when including either only six random or the six most frequently studied traits in our analysis, the average percentage of explained variation in across-year ecosystem functioning dropped to 4.8%. Furthermore, different ecosystem functions were driven by different traits, with on average only 12.2% overlap in significant predictors. Thus, we did not find evidence for the existence of a small set of key traits able to explain variation in multiple ecosystem functions across years. Our results therefore suggest that there are strong limits in the extent to which we can predict the long-term functional consequences of the ongoing, rapid changes in the composition and diversity of plant communities that humanity is currently facing.

Thermal balance of plants and plant communities

Abstract: This chapter focuses on the physical basis of the exchange of solar energy. As an introduction to the topic, the energy balance of the atmosphere is explained, followed by a section on the microclimate near the ground surface. It is the exchange of energy that determines the temperature near the ground as modified by biotic and abiotic factors. On the basis of the understanding of climate drivers near the Earth’s surface, the energy balance of a leaf is discussed, which mainly involves adaptations of the leaf surface to absorb or reflect solar energy and a balance of sensible and latent heat transfer. Plants are adapted to cope with climate extremes on the basis of modifications in their physical energy transfer.

The climate mitigation potential of managed versus unmanaged spruce and beech forests in Central Europe

Abstract: The European Union (EU) has promised to cut its energy consumption by 20% by 2020. As a result, the use of petroleum products has continually decreased, and the use of renewable energy sources has increased. For the EU as a whole, however, the use of wood for energy has been fairly constant, even if its use has increased in several countries, for example, in the Nordic countries, the United Kingdom (UK), and Germany. As the consumption grows, the demands are increasingly met by imports of wood pellets, especially in countries with small forest areas such as Denmark and the UK, but also in Germany. Even if the forest area is increasing in many European countries, the land use change for urban development and nature conservation efforts have furthermore reduced the contribution of the forest sector in some countries. Given this situation, this chapter analyzed how managed and unmanaged temperate forests of the deciduous broad-leaved European beech (Fagus sylvatica) and the evergreen coniferous Norway spruce (Picea abies) species, to see how these forests can best help to mitigate climate change by storage of carbon in the forest and substitution of fossil intensive materials. The assessment was based on yield tables, wood assortment tables, deadwood and product-decay functions, and on the measured growth data from managed and unmanaged forests. All results are expressed as wood volume (m3/ha) that either store carbon or is made available for substitution through harvesting. The time frame is based on a suggested natural life cycle of unmanaged forest which is 230 years for beech and 350 years for spruce. In such time frames, the mitigation effect by storage is approximately zero for unmanaged forests, as the produced biomass is subject to natural mortality and input to deadwood pools that decompose and return the CO2 to the atmosphere. In unmanaged forests the mean volume stock over 350 years was 324±252 m3/ha for beech and 406±295 m3/ha for Norway spruce. For managed forests, there are, in the same time frame, also no or only minor storage effects in the long term, unless substantial changes take place in forest management or wood use. But it is also important to protect these stocks and the stocks of wood products, which together were 543 m3/ha for managed beech and 624 m3/ha for managed spruce, and of these, 279 and 342 m3/ha are stored in the forest, respectively. The forest management effect only becomes apparent through substitution effects for fossil intensive materials and the fossil fuels. In this context the role of wood energy and products is complex. Only some wood residues substitute the fossil energy and only some products substitute materials with high energy cost. Products are a transient pool of wood, which is feed by forest harvest, and which loses wood during processing and after consumption for energy or other use. The total supply of wood for energy is 1177 m3/ha over 230 years in beech (5.1 m3/ha/year) and of 3395 m3/ha over 350 years in spruce (9.7 m3/ha/year). Thus the contribution for climate change mitigation is larger for coniferous than for broadleaved species, and managed forests contribute more than unmanaged forests to storage. The implications of nature conservation, land use change are discussed, together with various options for improving incentives for forest management through international greenhouse gas accounting systems, which must still avoid double accounting.

Interactions Between Plants, Plant Communities and the Abiotic and Biotic Environment

Abstract: In this chapter, the interactions between plants, plant communities and the abiotic and biotic environment are described. First, we discuss how plants with their specific traits influence their environment, including their effects on climatic conditions, on the weathering of bedrock and on topography, as well as on the development and characteristics of soils. The second section deals with interactions among plants, including positive, neutral and negative ones, which can result in symbiosis, facilitation, commensalism, parasitism or competition. A special focus lies on competition and its consequences for coexistence among different plant species and for plant community structure and diversity. This section ends by highlighting the relevance of plant–plant interactions for practical applications, such as the use of indicator values and ecograms, which are based on the ecological niche concept. The third section describes interactions between plants and animals. We first classify plant–animal interactions by looking at the evolutionary effects of such interactions on both groups and present the evolutionary history of biological interactions and the concepts of coevolution and adaptation. The following sections elaborate in detail on specific plant–animal interactions, namely herbivory, carnivory, pollination, seed dispersal and mycorrhiza. The chapter ends with a description of the effects of abiotic environmental conditions on these biological interactions.

Dynamic global vegetation models

Abstract: In this chapter, dynamic global vegetation models (DGVMs) are described. These models mathematically represent the global biosphere and are also able to model vegetation dynamics, that is, the transient development of vegetation composition and structure. First, an overview of current DGVMs and their structure is given. Then the representation of major biogeochemical cycles (carbon, water and nutrients) is explained. Moreover, the concept of plant functional types in models is introduced and applied to scale up from plant to global communities. How to represent disturbances and land-use change is also explained. Furthermore, current shortcomings and challenges in developing a predictive understanding of the terrestrial biosphere are discussed, in particular in terms of available input data from global observations and ecosystem experiments. This knowledge is then used and applied to both past and future climate conditions.

Global change and terrestrial ecosystems

Abstract: In this chapter, global change and its impacts on terrestrial ecosystems are discussed. First, land use and land-use change are introduced, focusing on agriculture and forestry, in terms of both their characteristics and their consequences for the biogeochemistry of terrestrial managed ecosystems. Then these changes in land use are linked to observed and predicted climate change, which is described in detail, that is, radiative forcing of greenhouse gases, global warming, global dimming and brightening. Moreover, both the responses of terrestrial ecosystems to climate change and the feedbacks of terrestrial ecosystems on climate are discussed. Changes in global biodiversity are illustrated as well. The last section contains a discussion of global political agreements that have been put in place to address these global ecological challenges of land degradation, climate change and biodiversity.

Approaches to study terrestrial ecosystems

Abstract: In this chapter, different approaches to the study of terrestrial ecosystems are introduced. The chapter is organised in two main parts: observations and experiments. For both of these general approaches, many examples are given from around the globe, introduced by typical research questions and illustrated with photos. Observations can be done at the level of whole ecosystems, either as single-site studies or as multisite studies within large networks, often using new technologies to measure variables of interest or to access tall canopies. Transects and chrono-sequences are introduced and critically discussed. Grid-based inventories and applications of remote sensing techniques complement the observational approaches. Natural experiments—that is, sudden disturbances and slow continuous forcing—are also discussed. On the other hand, experiments can be carried out by manipulating pools and processes, and also by manipulating environmental conditions. Examples range from transplant and space-for-time experiments to fertilisation and irrigation trials and to roof and free-air carbon dioxide enrichment experiments. The relevance of appropriate controls and the existence of hidden treatments are discussed. Biodiversity experiments are explained in detail, as are experiments of management and changes in land cover. To conclude this chapter, artificial ecosystems are introduced and their benefits are explored.

Spatial Distribution of Plants and Plant Communities

Abstract: In this chapter we describe the spatial patterns of plant species and communities that developed over time. Together with Chap. 17, it underlines the significance of dynamics in space and time for a thorough understanding of biotic interactions within ecosystems. In the first section, we describe the different types of propagule dispersal and explain the importance of safe sites and seed banks for successful plant establishment. Depending on the effectiveness of dispersal vectors and on habitat requirements, plant species may be widespread (cosmopolites) or—owing to slow dispersal and specific demands—live only within small regions (endemics). The following section discusses general aspects of vegetation geography. Species with similar characteristics and habitat requirements may coexist in areas with comparable environmental conditions and belong to one area type (floristic element, geoelement). In the next section, we deal with species–area relationships and present the classical equilibrium theory of island biogeography. On the basis of this theory, many models were developed to better understand how plants become established on islands. Some of these models regard islands not only as terrestrial areas surrounded by the sea but also as, for example, forest “islands” within an otherwise tree-free matrix. Finally, we discuss two kinds of general vegetation models: (1) stochastic models, which possess some inherent randomness, and (2) deterministic models, which are fully determined by parameter values and initial conditions (i.e. intensity of competition, habitat diversity, degree of disturbances).

Biogeochemical fluxes in terrestrial ecosystems

Abstract: In this chapter, the major biogeochemical fluxes in terrestrial ecosystems are presented: water, carbon, nitrogen and cation fluxes. The relevance and interactions of all these fluxes are explained, and then their special features discussed, with an additional focus on land management. In the first section, water fluxes in terrestrial ecosystems are elaborated, both conceptually and mathematically. The different component fluxes of an ecosystem water budget are introduced, with a clear focus on the ecosystem scale, although leaf and tree scales are also addressed. Evapotranspiration at these different scales is the core process presented, including its radiative and physiological controls, illustrating the link between water and the energy budgets of an ecosystem. The responses of ecosystems to drought are illustrated. In the second section, carbon fluxes are the main topic. Analogously to the water section, first, the different component fluxes of an ecosystem carbon budget are introduced, ranging from photosynthesis to soil carbon turnover and carbon losses via fire or management. In addition, environmental drivers and their impacts on the carbon fluxes in terrestrial ecosystems are presented. Special attention is given to the decomposition and stabilization of organic matter, but also to net ecosystem production and net biome production and, thus, carbon sinks and sources. Moreover, also methane and other biogenic volatile organic compounds are introduced. In the third section, nitrogen fluxes are explored, focusing on plant–microbe interactions. Impacts of atmospheric N deposition and N fertilization are discussed. In the fourth section, cation fluxes are introduced. Examples include chronosequences of weathering and soil acidification.

General Themes of Molecular Stress Physiology

Abstract: In this chapter we introduce stress as an ever-present condition of plant life. The various strategies used by plants to cope with fluctuating environmental conditions are defined. An understanding of molecular stress physiology is facilitated by differentiating the responses of an individual (acclimation) from evolutionary processes at the population and species levels (adaptation). Stress tolerance and avoidance reactions of a plant involve a number of common features independent of the type of stress: sensing of environmental or internal changes, long-distance transfer of information between organs and tissues, signal transduction cascades at the cellular level, transcriptional control and the occurrence of oxidative stress. The essential role of model systems in elucidating the molecular mechanisms underlying these processes is explained. Another integral part of stress responses is the modulation of growth, that is, a change in resource allocation in favour of stress resistance. A second major strategy, besides stress resistance, that enables a plant to survive and reproduce in a particular environment is escape from unfavourable conditions. Escape is possible through the anticipation of seasonal changes and the timing of key developmental transitions, such as germination, in response to environmental factors. Anticipation is made possible by the biological clock and photoperiodism. Both are molecularly understood quite well now and are discussed here alongside the winter memory of plants and possible trans-generational stress memory phenomena.

Development of plant communities in time

Abstract: In this chapter we show that the development of plant communities in time must be known if we want to understand their actual floristic and structural composition. The first section describes the development of plants during earlier geological times, where temporal vegetation dynamics were largely influenced by tectonic and climatic events. In particular, the worldwide periodic fluctuations between cold and warm periods in the Pleistocene led to strong vegetation changes and resulted in spatial separations of different vegetation types. Today, intended or unintended human influences on vegetation are becoming increasingly important, leading to changes in vegetation structure, composition and the loss of plant species, as well as to a growing number of invasive species. We exemplify these aspects by discussing anthropogenic influences on vegetation in more detail for the Mediterranean, Saharan and tropical environments. In the following section, we present general aspects of temporal vegetation dynamics, including primary succession and secondary succession following more or less natural or human-made disturbances. Examples are given for mosaic cycles, cohort dynamics and the carousel model. We discuss different plant strategy models, which can be related to successional dynamics (r and K, CSR, resource-ratio, facilitation-tolerance-inhibition). The final section deals with aspects of ecological stability and the influence of disturbances, introducing the concepts of resistance, resilience, robustness, variability and persistence of plant communities.

Global Biogeochemical Cycles

Abstract: In this chapter, the major global biogeochemical cycles (carbon, water, nitrogen and sulphur) are introduced in relation to environmental drivers as well as LU. To understand the interactions of the global biosphere with management and biogeochemistry, first, the global distribution of terrestrial ecosystems is presented, both based on climatic zones as well as on management. Then the major biogeochemical cycles of carbon, water, nitrogen and sulphur are explained, elaborating on the identity and the magnitude of the respective pools and fluxes, their interactions, but also on their major disturbances related to global change. Finally, the concept of ecosystem services is described.

Adverse soil mineral availability

Abstract: This chapter covers our molecular understanding of how plants acquire growth-limiting mineral nutrients and cope with the presence of potentially toxic elements in the soil. Plants rarely experience an ample supply of all 14 essential elements, which have to be taken up from an exceedingly complex system, the soil. Strategies to meet this challenge include tightly controlled nutrient uptake and the plasticity of root architecture. Nutrient status and external availability are constantly monitored and translated into changes in uptake capacity and root morphology. Symbioses are of major importance for plant nutrient acquisition. Mycorrhizae and nitrogen fixation are described in separate sections with respect to the molecular processes involved in partner recognition and establishment, as well as nutrient exchange. The final sections of the chapter elaborate on the mechanisms allowing adapted plants to thrive even when normally toxic concentrations of mostly non-essential elements such as sodium and aluminium are present in the soil. Large areas around the globe are affected by either salinization or the availability of aluminium because of low soil pH. Resistance is often mediated by exclusion of the element or sequestration in vacuoles. Finally, the rare ability of some plant species to hyperaccumulate metals in spite of their toxicity is introduced as an example of plant adaptation to extremely stressful environments.

Approaches to Model Processes at the Ecosystem Level

Abstract: In this chapter, approaches to modelling processes at the ecosystem level are presented. A classification of ecosystem models is provided. The five main classes of models are as follows: physiological, biogeochemical, gap, biogeophysical and dynamic global vegetation models. After this overview, a general ecosystem carbon model is introduced. Plant ecophysiological and biogeochemical processes are represented in mathematical terms (vectors and matrices), from carbon dioxide uptake to carbon allocation to carbon turnover in soils. In addition, the effects of environmental factors on these processes are modelled. Two models are then discussed in more detail: a simple vegetation-soil model and the eight-pool model of Luo and Weng. Furthermore, highly relevant model parameterization problems are addressed, that is, the role of inputs and cycling rates in ecosystem carbon storage, residence and response times, as well as disturbance effects.

Springtime Bark-Splitting of Acer pseudoplatanus in Germany

Abstract: A large-scale regional event of springtime bark-splitting in Acer pseudoplatanus was observed in Germany in May 2018, where bark dissected from the wood. In young trees, an average of about 30% of the circumference was affected by cracks that were up to 8 m long. The damage occurred on the south-facing side of the trees after a warm period in March, followed by an extreme cold spell and warm temperatures. In this study, we investigated the possible causes of this damage. The damage occurred in the expanding xylem with cambial cells remaining in the bark. These cells-initiated growths of new, bark-based stems. The unprotected xylem was attacked by several fungi and wood-boring bark beetles. The mode of damage-recovery suggested that this event will eventually lead to a frost-scar-like structure in the future that will not totally heal, because the new stems attached to the old bark were in the process of forming new bark. Due to the increase in variation of springtime temperatures observed over the past 40 years, such damage may become more common in the future.