Title Abstract "Effects of tree species specific litter and root decompostition products on the mobility of cadmium and zinc in sandy soils" "Litter decomposition and fine root turnover are important within the mobilization process of metals. Hence, the goal of this project is to quantify the effects of decomposition processes of leaf litter and roots under differen tree species on the mobility of Cd and Zn, by means of the modifications in pH and percent base saturation and the different OC-fractions that will be originated during those decomposition processes" "How do tree species diversity and composition carry over their environmental legacies to future forest generations?" "Department of Environment" "The diversity and composition of the tree community influence the biotic and abiotic soil properties. Here we will study how these effects are carried over to future forest generations, affecting tree establishment, vitality, and species composition. First, we will analyse soil samples from stands varying in tree diversity and composition, both in recently established young forest and in mature forest. This allows studying the initial tree effects versus the effects when the trees have been affecting the soil for a long time, respectively. Second, we will set up pot experiments by sowing tree species in pots containing the soil originating from the young and mature forest sites and growing these seedlings for two years in a semi-controlled environment. Here, we test for possible (interactive) biotic and abiotic carry-over effects caused by tree species identity and diversity effects, by looking at the seedling performance and composition. In addition, we will also test the influence of the carry-over effects on the response of seedlings to a drought period, as summer droughts are expected to be more severe and frequent due to climate change. The results of this project are expected to provide a better understanding of the way current tree diversity has an impact on a future forest generation, which is important given the ongoing shift towards natural forest regeneration methods in forest management." "Are mixed forests more resilient to environmental change? Analysis of recent growth trends along a gradient of tree species diversity." "Bart Muys" "Forest, Nature and Landscape, Division of Forest, Nature and Landscape" "Forests provide important ecosystem services to humans. The EU renewable energy target can only be reached by massive use of forest biomass. This implies productive forests, while recent studies show climate change related decreasing growth trends. This project aims at evaluating the role of biodiversity to support the production function of forests. The hypothesis that mixed forests are more resilient to environmental change is tested by setting up the Tree Diversity Observatory, a unique platform of plots along a tree diversity gradient in Flanders and Wallonia. These plots consist of target trees of oak and beech with their neighbour trees of different species. In the Observatory tree ring cores of target trees from different age class are taken and their  eighbourhoods described. Tree rings widths are measured and provide a database of wood basal area increment. Tree rings further provide samples to analyse stable isotopes, used to build a  ata series of drought stress and nitrogen deposition. In order to evaluate overall recent growth trends and to separate effects of species diversity and functional diversity from other covariates,  Fixed models are fitted to the tree ring series. To test for higher resilience to environmental changes in forests with higher tree diversity, mixed models for growth response to these stress factors are built for separate pointer years, comparing extreme and consequent years with normal years. The detected diversity effects are then further interpreted in terms of their ecological drivers, and recommendations for forest management are formulated." "Are mixed forests more resilient to climate change? Analysis of recent growth trends along a gradient of tree species diversity." "Forests are biodiversity hotspots worldwide with a large share of terrestrial biodiversity being linked to forested landscapes. However, deforestation, forest degradation and fragmentation lead to an increasing rate of species extinctions and loss of biodiversity. Recent research brings ever more evidence that this biodiversity crisis is not just an ethical problem, but a potential threat to ecosystem functioning and the services they can deliver. Until now, however, the relationships between biodiversity and ecosystem functioning in forests have been largely unexplored. The main objective of this proposal is to lay the foundation for the long-term quantification of the effects of tree species diversity on forest ecosystem functioning and services in a unique, large-scaled tree diversity experiment at Zedelgem (West Flanders). This experiment is part of the largest experimental platform in ecosystem research worldwide, specifically designed to elucidate the functional significance of forest biodiversity. We aim (i) to install porous cup lysimeters in the field for quantification of nutrient leaching to groundwater, (ii) to buy basic equipment for preliminary treatment and extraction of soil samples and (iii) to perform basic measurements for quantification of the point of departure and short-term influence of tree diversity on ecosystem properties by taking soil samples and measurements of tree survival and vitality. " "Trees in the urban jungle: modelling the impact of tree planting strategies on urban overheating" "Hans Verbeeck" "Department of Environment" "Urban green infrastructure provides a multitude of ecosystem services. Among others, it contributes to climate regulation through shade provisioning and transpiration. City trees are a key component in this climate regulation. A good understanding of these benefits is required to contribute to green infrastructure management and to make cities more resilient against climate change. The current knowledge on the spatially explicit quantification of cooling of urban trees, as well as differences between tree species, fails to answer related questions. The aim of this project is to contribute to a better understanding of cooling effects of urban trees. State-of-the-art techniques such as Terrestrial LiDAR Scans (TLS) will be used to identify relevant functional and structural tree characteristics that will be used to develop allometric relations. By improving an existing microscale climate model we will better assess the cooling effects of urban trees. This is achieved by modelling the effects of shading and transpiration of urban trees while taking the surrounding urban environment and their interactions into account. The ultimate goal is to create a prototype of a decision-making tool for urban tree implantation, species selection and management to maximise cooling." "Tree hydraulic functioning under changing climate regimes" "Department of Plants and Crops, Department of Applied ecology and environmental biology" "An increase in average air temperatures, associated with an increase in frequency and duration of heat waves, rising levels of atmospheric CO2 concentration [CO2], and alterations in precipitation patterns, resulting in more frequent and intense drought periods, have been predicted throughout this century. Changing climate regimes have a major impact on plant growth and physiology, resulting in widespread tree mortality, but these climate-induced effects are still poorly understood. In this project, we aim at determining the effects of elevated temperature (including heat waves) and [CO2], either alone or in concert with drought, on tree seedling growth and hydraulic functioning. Two indigenous tree species, Populus tremula and Quercus robur, will therefore be grown in treatment chambers under different conditions in temperature, [CO2] and soil water availability. State-of-the-art plant sensors, combined with discrete physiological measurements and thermal imaging, will be used to bridge the important knowledge gap about tree hydraulic functioning under changing climate regimes. With this project we aim to answer outstanding questions on tree seedling strategies to survive drought and (extreme) heat stress under ambient and elevated [CO2] by adapting wood anatomical traits and hydraulic function. This is of vital importance for policy makers and forest managers in order to make thoughtful decisions to ensure maximum resilience of Flemish forests in a changing climate." "Improving the vitality and productivity of forests on poor sandy soils by introducing rich-litter species." "Bart Muys" "Forest, Nature and Landscape" "The provision of forest ecosystem services heavily depends on the ecosystem function of nutrient cycling, in which the belowground ecosystem compartment plays a fundamental role. An essential pathway in such nutrient cycling is the return of nutrients to the soil via leaf litterfall. Although much soil ecological research has been executed throughout the years, our understanding of the mechanisms underlying belowground functioning remains partial, most likely due to the complexity and opacity of this nurturing underworld. In this thesis we aimed at contributing to such understanding in relation to leaf litter effects of different tree species. First, we sought to disentangle the interactions at the plant-soil interface and evaluate how abiotic and biotic factors underlie the context-dependency of litter effects. Second, this thesis further explores the concept of admixing rich litter species as a management measure to restore acidified sandy forest soils.The first objective was addressed in two fundamental Chapters (2 and 3). Chapter 2 shows that the impact of forest conversion differs depending on the edaphic context, here a pedogenic threshold in soil acid buffering. We found that upon conversion from broadleaved mixed forest to Norway spruce monoculture, a shift in soil buffering domain occurred, triggering multiple concurrent changes including the build-up in the litter layer, an increase in acidity, a pronounced decrease in microbial functional diversity and earthworm biomass, a collapse of base saturation and even a change in the way carbon is sequestered. Subsequently we illustrated how burrowing earthworms can reinforce litter effects in some soils but not in others, using a dataset of European forests. The existence of a positive feedback loop in which burrowing earthworms maintain their own niche – by promoting turnover rate in the forest floor, thereby increasing topsoil pH and creating suitable living conditions for themselves – was evidenced for acidic forest soils. As most of our world’s forests are located on soils vulnerable to acidification, the regulation by pedogenic thresholds (Chapter 2) and the pivotal role of earthworms (Chapter 3) should be taken into account in future research efforts and when making forest management decisions, so that the typical context-dependent conclusions could be supported by more mechanistic and spatially explicit understanding.In the second, more applied, part of this thesis (Chapter 4, 5 and 6) we built further on the concept of admixing rich litter species as a forest management measure to restore degraded forest soil systems, particularly those located on Pleistocene sandy deposits. In Chapter 4, we re-defined litter quality for West-European forests on Pleistocene aeolian deposits: rich litter is leaf litter that has high concentrations of calcium, magnesium and potassium and thereby promotes earthworm abundance and fast nutrient cycling. We found a negligible impact of leaf litter C/N ratio on the forest floor and belowground acidity status, which could be linked to the overload of nitrogen already present in the studied systems due to the high N-deposition in the region. Moreover, we identified which rich litter species have potential to counteract soil acidification, improve the soil nutrient status and promote fast nutrient cycling and corresponding organic matter turnover. Chapter 5 illustrates, in laboratory conditions, that admixing rich litter of black cherry with poor litter of pedunculate oak may promote the decomposition of oak itself via synergistic effects. Finally, Chapter 6 illustrates that when rich litter is admixed in-situ, large shares of high-quality litter (and thus tree admixture) are needed to have a considerable impact on the soil chemical status. This translates into high amounts of rich litter tree species admixture in terms of share in the basal area (>30%).Further research is needed to evaluate whether, where and when the improved nutrient availability in the soil, as a consequence of rich litter admixture, feeds back to aboveground nutrient uptake and improved vitality of the overall ecosystem. Additionally, future studies should take into account root litter input, next to leaf litter, and further translate the process of nutrient cycling to soil carbon sequestration.Taken together, this research shows the pervasive impact litter quality can have on belowground functioning and how site conditions (soil type) and earthworm activity can modulate that impact. Its outcomes also emphasize the potential for forest managers to use tree species selection (as a function of litter quality) for steering belowground functioning and counteracting soil acidification processes. Which could, in turn, affect the services provided by the aboveground forest ecosystem compartment." "Mining the extraordinary regeneration potential of Marchantia polymorpha to increase regeneration of crop species" "Lieven De Veylder" "Department of Plant Biotechnology and Bioinformatics" "The plant lineage displays an unrivalled regeneration capacity that not only restores damaged tissue but can also give rise to whole plant bodies. Unfortunately, many economically and ecologically important species display a poor regeneration potential. E.g., many elite tree species are recalcitrant to routine propagation by stem cuttings. In agricultural species, the capacity to regenerate is even worse, as most cereals, including important food crops such as rice and maize, tend to be recalcitrant to plant regeneration. Within this project, we aim to exploit the remarkably regeneration potential of the bryophyte Marchantia polymorpha to address these problems. Recently, I contributed to the identification of the MpERF15 transcription factor as a conserved key factor controlling plant regeneration. MpERF15 has a profound effect on the plant’s metabolome, including the production of oxylipins that through a positive feedback loop drive proliferation and regeneration. However, the genes and metabolites operating downstream of the oxylipins remain unknown. To this end, I will perform comparative transcriptomic and metabolomic experiments between wild -type with regeneration-deficient Marchantia thalli. Selected candidate genes and metabolites will be systematically screened for their potential to increase the rooting potential of the poplar hybrid Populus tremula x alba, as well as their potency to increase the transformation efficiency of the maize B104 inbred line." "Modelling the effects of extreme droughts on forest ecosystem functioning - Towards climate smart forestry" "Koenraad Van Meerbeek" "Forest, Nature and Landscape" "Recent rapid changes in natural disturbance regimes are documented in many forest ecosystems across the world, with climate change being a prominent driver of this trend. Especially extreme drought events push forests beyond their limits. Since climate change will make droughts more frequent, more intense and longer in the future, it is of great importance to gain a better understanding of the effects of extreme droughts on forests. This study aims to achieve this goal by using advanced computer models to combine data from satellites and field monitoring networks. First, the effects of the tree species diversity on the impact droughts have on forests will be studied. Using this knowledge the study will then assess the suitability of the current and projected climate for species currently used in Belgian forestry as well as new species that are not yet used in Belgium. The results from this research project will be directly valuable to forest managers, therefore, we will communicate the results clearly to the forestry sector through, among other methods, a user-friendly tool for forest managers. Our research will also serve as a starting point for more specified research towards the application of new tree species in forestry. The overall goal is to provide information to allow the forestry sector to move to climatesmart practices." "Effects of tropical rainforest disturbance on gene flow, genomic diversity and introgression in understory trees: the case of Coffea canephora in the Congo basin." "Olivier Honnay" "Ecology, Evolution and Biodiversity Conservation, Plantentuin Meise, ILVO-Instituut voor Landbouw-, Visserij-, Het AfricaMuseum, Universiteit Gent" "Tropical rainforests cover only 7% of the earth’s surface, but they are by far the richest biomes in terms of vascular plant diversity. To ensure the resilience and long-term stability of tropical rainforests, fostering the regeneration of the occurring woody plant species is critical. Yet, crucial aspects of gene flow, including pollination and seed dispersal, have become strongly jeopardized through ongoing large-scale anthropogenic disturbances of tropical forests. Furthermore, many crop wild relatives from tropical forests face the risk of hybridization with planted cultivars. The general objective of this project is to study the population genetic structure, gene flow and the pollination and frugivorous communities in Robusta coffee, a tropical rainforest understory shrub, in the Congo Basin. Comparing coffee populations from regions that differ in their degree of anthropogenic pressure, will enable us to investigate the potential threats from anthropogenic interferences. To this end, we will combine (i) state of the art genomic tools to quantify genetic diversity and gene flow, (ii) observations of pollinator communties and frugivores, and (iii) experimental work."