Research team

Expertise

My research aims to understand how terrestrial ecosystems function, especially to improve the ecosystem models used to simulate climate change. My expertise is strong for temperate deciduous forests and heath tundra. The ecosystem processes I study are primarily: plant growth, phenology (the seasonal plant life events), biomass production, plant-nutrient interactions and ecosystem-atmosphere CO2 exchange. I work at annual and seasonal scale, with a special emphasis on autumn processes. I study both the aboveground and belowground components of the ecosystem, but particularly leaves and stem. The organisms I focus are mainly trees and shrubs.

Eco-physiological dynamics behind the inter-tree bud-burst timing variability in temperate deciduous forests. 01/10/2023 - 30/09/2026

Abstract

Bud-burst is a crucial phenological event in deciduous trees, as it controls the start of the growing season, water uptake and the tree energy balance. However, current models do not predict bud-burst timing accurately. One reason for this is related to the inter-tree variability in bud-burst timing, which is generally overlooked. Earlier research highlighted the correlation between inter-tree variability in bud-burst timing and the inter-tree variability in the previous year's autumn phenology and tree size. Yet, we currently do not know the eco-physiological bases behind these dynamics. My project tackles the new hypothesis that inter-tree variability in bud-burst timing in deciduous forests is driven by inter-tree variability in non-structural reserves of carbon and nitrogen. Moreover, as bud-burst timing and reserve dynamics are species-specific and affected by local climate, these dynamics are expected to vary spatially. I will target populations of beech, oak and birch within the temperate oceanic European zone, with the majority of the research taking place in Belgium. The results obtained will be integrated into the model ORCHIDEE, strongly improving predictions of bud-burst timing in deciduous forests. The newly developed version of ORCHIDEE will be used to make simulations of long-term forest growth and carbon stocks. My project will thus fundamental understanding of tree functioning, which is essential to assess forests' ecosystem services.

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  • Research Project

Global Ecosystem Functioning and Interactions with Global Change. 01/01/2023 - 31/12/2029

Abstract

Ecosystems sustain society by providing natural resources and socio-economic services. Understanding their functioning is thus vital for accurate projections of, among others, global climate and food production and prerequisite to drawing up policies for sustainable management of the planet. This proposal therefore aims at creating the scientific breakthroughs needed to make major advances in understanding of several critical processes that determine the functioning of ecosystems and their interactions with ongoing changes in climate and in resource availabilities. The overarching, long-term goal is to understand ecosystem functioning sufficiently well so that we can, in collaboration with modelling groups, confidently project how ecosystem functioning and services will change in the near and distant future. To pursue this goal, the following four research lines will be prioritized when allocating the Methusalem funding: 1. Obtaining a quantitative understanding of plant carbon allocation to growth, energy production (respiration), and nutrient acquisition (fine roots, root exudation, root symbionts). 2. Improving insight in, and measurements of, biomass production. 3. Better understanding soil carbon dynamics and sequestration. 4. Understanding spatial and temporal variation in carbon and greenhouse gas balances at ecosystem to regional scale and attribution to drivers. In each of these research lines, we aim to understand the mechanisms underlying the global and local spatial variation as well as those underlying the long-term trends and short-term temporal patterns. Focus is on how Global Changes (climate change including extreme events, increasing atmospheric CO2 concentration, nitrogen deposition, etc.) are affecting ecosystem processes and functioning. Many projects will be conducted with the research group of the Methusalem Chair at the University of Hasselt as prioritized partners.

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  • Research Project

Historical trends and future projections of global biomass production of terrestrial ecosystems based on their natural and anthropogenic drivers. 01/10/2022 - 30/09/2026

Abstract

Biomass production (BP) is a key process of terrestrial ecosystems that provides essential natural resources to our society such as food, fibers, timber and fuel. Moreover, BP is a key component of the global carbon cycle and, as such, it crucially influences our climate. Intensive research on BP is carried out worldwide since the 1960s. However, we still lack harmonized global databases and accurate models to elucidate the natural and anthropogenic drivers of BP and, as a consequence, we are still not able to produce historical trends and future projections of global BP. In this project, we will fill these knowledge gaps by addressing four detailed objectives: (1) determine the environmental- and anthropogenic drivers of BP for the major terrestrial biomes (e.g. boreal forests, temperate croplands, arid grasslands), (2) build empirical relationships (equations) to estimate BP at biome- and planetary level, (3) use these relationships to improve a typical dynamic global vegetation model (DGVM) and (4) use the improved model to produce global BP estimates for the past, current and future, spanning from 6000 BC (before agriculture) to 2050. Objective 1 and 2 will be achieved using a new global BP database which will extend a previous smaller database produced by the team of the PI. Objective 3 and 4 will be met using the DGVM ORCHIDEE, which is the land surface component of one of the climate models (IPSL) used to produce the IPCC climate scenarios. The new insights, data and tools that will be delivered by the project will, on the one hand, advance our understanding of terrestrial ecosystems and their human influence and, on the other hand, provide BP projections that will help preparing our society to the challenges brought by global change.

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  • Research Project

The Flanders Forest Living Lab: a semi-automated observatory for multi-scale forest ecological functioning. 01/06/2022 - 31/05/2026

Abstract

The European Green Deal relies on healthy forests to remove carbon (C) from the atmosphere, stabilize the water cycle and provide sufficient biomass for the future bioeconomy. The Flanders Forest Living lab realizes a specific breakthrough in the assessment of these crucial ecosystem functions, at spatial scales ranging from the individual tree to the entire forest. The Living Lab is situated in an ICOS flux-tower observatory, that currently already provides a permanent assessment of ecosystem scale CO2-fluxes, evapotranspiration and respiration. To date however, no technique is available to study the function of individual trees, at daily resolution, across a forest. achieving this is the groundbreaking objective of this new infrastructure. Its specific equipment allows for crucial realistic simulation of the water-, energy- and carbon fluxes by advanced vegetation models at spatial scales matching those of satellite imagery products, thereby creating new possibilities for applications such as automated precision forestry management, fire prevention and worldwide carbon budget quantifications. The new infrastructure involves an UAV and a set of linked validation sensors. Observations are steered by artificial intelligence, in order to be able to adapt the flight pattern to the fluctuating source area of the flux-tower, and in order to proactively adapt to specific weather patterns and potentially interesting ground-sensor observations.

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  • Research Project

Impact of the conversation from evergreen coniferous to deciduous broadleaf forest on ecosystem carbon stocks and storage (domain De Mik, Brasschaat). 01/12/2020 - 30/11/2021

Abstract

Study focused on the influence of the conversion from evergreen coniferous to deciduous broadleaf forest on carbon stocks and storage. Two stands (in domain De Mik, Brasschaat) will be investigated / compared: (i) old pine forest with standard management, and (ii) a young oak stand planted in a part of the pine forest. The research involves field and lab work. All the ecosystem carbon stocks will be measured (trees, understory, litter and soil). Information about the management is provided by the local ANB forester. Expected results: data from all carbon stocks of the two forest stands studied, from which the influence of different forest management on the carbon storage (climate mitigation) of forests can be deduced.

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  • Research Project

Impact of forest management on ecosystem carbon storage in Scots pine stands (domain De Inslag, Brasschaat) 01/12/2020 - 30/11/2021

Abstract

Study focused on the influence of forest management on carbon storage in Scots pine stands. Two stands (in domain De Inslag, Brasschaat) will be investigated / compared: (i) seldomly thinned old pine forest, and (ii) frequently thinned old pine forest with new plantings (oaks). This research involves field and lab work. All carbon stocks of the ecosystem will be measured (trees, understory, litter and soil). Data about management are provided by the local ANB ranger. Expected results: data from all carbon stocks of the two forest stands studied, from which the influence of different forest management on the carbon storage (climate mitigation) of forests can be deduced.

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  • Research Project

Towards a better model representation of vegetation autumn phenology of temperate -zone deciduous trees. 01/10/2020 - 30/09/2023

Abstract

Autumn phenological events (e.g. leaf senescence) signal the end of vegetation activity in deciduous trees and alter their albedo, thereby exerting a strong control on various ecological processes and climate feedbacks. Predicting their timing with high accuracy is a prerequisite for better understanding the climate-ecosystem interactions. Modeling autumn phenology at larger spatial and temporal scales remains challenging, because the processes behind autumn phenological events are not well understood. Previous experimental studies have not resulted in a strong consensus on the relationship between environmental cues and leaf senescence. Most of current phenological models regarded temperature and/or photoperiod sum as the primary predictors, but have neglected the impact of other, recently discovered cues, such as nutrient limitation and drought extremes. In this project, the applicant seeks to: i) set up a database covering the records extracted from phenological observation networks as well as metrics derived from eddy covariance and remote sensing-based measurement. ii) evaluate current models at multiple spatial scales. iii) develop a new mechanistic/semimechanistic model that considers recently discovered environmental cues and allows improved model structures. The applicant will also couple this newly developed phenology model with a state-of-the art dynamic global vegetation model to improve its predictive capacity of ecosystem carbon balances.

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  • Research Project

A game-changing perspective on intra-seasonal wood formation dynamics using high-resolution X-ray Computed Tomography to elucidate leaf senescence and autumn dynamics of temperate deciduous trees in Europe. 01/01/2020 - 31/12/2023

Abstract

Intra-seasonal wood formation is still understudied because the measuring method (analysis of cellular anatomical traits) is labour-intensive and requires important manual skills. The last phase of wood formation (lignification) has been particularly neglected, resulting in a lack of understanding of tree autumn dynamics. UAntwe -PLECO and UGent-Woodlab will join forces (in collaboration with dr. Fonti, WSL, as key advisor) to address two objectives: (1) develop a new method to study wood formation based on high resolution X-ray Computed Tomography (XµCT) and (2) use the new method to test, at continental scale, the hypothesis that leaf senescence is triggered when wood formation ceases in autumn or, in case of factors limiting growth in summer, when a fixed day of the year is reached (photoperiodic threshold). The first objective will be met by (i) automating the XµCT process, (ii) identifying the degree of lignification, (iii) assessing intra-seasonal wood traits such as cell size and wall thickness etc., and (iv) implementing a time-lapse scanning on small living trees. The second objective will be achieved by analyzing data of leaf senescence and wood formation of the 10 most common deciduous species in Europe along several transects of varying environmental conditions (e.g. photoperiod, temperature, drought). Overall, the project will start a new direction for the study of wood formation and will elucidate autumn dynamics of deciduous temperate trees.

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  • Research Project

Towards a better model representation of vegetation autumn phenology of temperate -zone deciduous trees. 01/10/2019 - 30/09/2020

Abstract

Autumn phenological events (e.g. leaf senescence) signal the end of vegetation activity in deciduous trees and alter their albedo, thereby exerting a strong control on various ecological processes and climate feedbacks. Predicting their timing with high accuracy is a prerequisite for better understanding the climate-ecosystem interactions. Modeling autumn phenology at larger spatial and temporal scales remains challenging, because the processes behind autumn phenological events are not well understood. Previous experimental studies have not resulted in a strong consensus on the relationship between environmental cues and leaf senescence. Most of current phenological models regarded temperature and/or photoperiod sum as the primary predictors, but have neglected the impact of other, recently discovered cues, such as nutrient limitation and drought extremes. In this project, the applicant seeks to: i) set up a database covering the records extracted from phenological observation networks as well as metrics derived from eddy covariance and remote sensing-based measurement. ii) evaluate current models at multiple spatial scales. iii) develop a new mechanistic/semi-mechanistic model that considers recently discovered environmental cues and allows improved model structures. The applicant will also couple this newly developed phenology model with a state-of-the art dynamic global vegetation model to improve its predictive capacity of ecosystem carbon balances.

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  • Research Project

Unraveling winter sleep to understand spring reactivation: improved understanding of leaf out phenology in temperate deciduous trees by gaining insight in environmental controls of bud dormancy. 01/01/2019 - 31/12/2022

Abstract

By affecting the uptake of carbon and the transpiration of water by forests, tree phenology also influences local weather and long-term climate change. Studying spring phenology of temperate trees is thus more than just a biologist's hobby. Despite a wealth of observations of the date that leaves appear in spring, this process is still not fully understood. Leaf out can occur at very different moments in spring, despite similar spring weather. Part of the reason is that spring leaf out is only the end point of an entire winter of bud responses to cold temperatures, to warm temperatures, and to changes in day length. To fully understand the climatic controls over spring phenology, and thus to be able to produce models that can accurately predict future changes in spring phenology, insight is needed into what happens during the long winter, when buds are apparently asleep. This project focuses on just that: what happens during the bud's resting phase that makes them more or less responsive to warmer spring temperatures. We will conduct two large experiments in which temperature and day length will be altered, and throughout the entire winter season monitor changes in gene expression, in metabolite concentrations, and in depth of dormancy. The ultimate aim is to advance insight in spring phenology, but also to identify genes or metabolites that could give information on the state of dormancy during winter, and thereby on the bud's sensitivity to spring warming. -

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  • Research Project

Research in the domain of plant- and vegetation ecology 01/12/2018 - 30/11/2023

Abstract

Funding for research on plant growth, which is determined both by plant ecophysiology (e.g. photosynthesis, respiration, stress responses) and ecology (e.g. biotic and abiotic interactions). In particular, we will deal with the ecological relationships between plant growth and its environmental and climatic drivers, and how plant growth shapes the ecosystem productivity and the exchange of matter and energy between the ecosystem and the atmosphere. The findings will be important to model the functioning of terrestrial ecosystems and improve our assessment and projections of global climate change.

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  • Research Project

Determination of the drivers of the onset of autumn leaf senescence in temperate deciduous forests: the relationship between leaf dynamics, tree growth and photoperiod. 01/10/2018 - 30/09/2022

Abstract

Leaf phenology is a key component in the functioning of temperate deciduous forests. The environmental cues for bud-burst in spring are well known, but little is known about the cues controlling the timing of leaf fall in autumn. Leaf fall is the last stage of leaf senescence, a process which allows trees to recover leaf nutrients. We urgently need to understand the controls timing leaf senescence to improve our projections of forest growth and climate change. I propose a new general paradigm of the onset of leaf senescence, hypothesizing that leaf senescence is triggered by the cessation of tree growth in autumn. I expect that: (i) in the absence of growth-limiting environmental conditions, tree growth cessation directly controls leaf-senescence onset, and (ii) in the presence of growth-limiting conditions, photoperiod controls leaf-senescence onset – this prevents trees from starting to senesce too early. Here, we test these hypotheses for mature individuals of four major forest tree species (Fagus sylvatica, Quercus robur, Betula pendula and Populus tremula) growing in natural stands in Belgium, at fertile and infertile sites and in control and fertilized/irrigated treatments. We will monitor leaf senescence and tree growth at each stand. Leaf senescence will be derived from seasonal measurement of chlorophyll, performed with chlorophyll meters and spectrophotometrically. Tree growth will be derived from (i) microscopic analysis of seasonal cambial activity in stem, branches and coarse roots, and (ii) analysis of fine root seasonal elongation with the minirhizotron system. Field-work will be performed for up to three growing seasons. The results will be combined (together with data on photoperiod, climate and environment) to datasets from the LEAF-FALL project and other European studies from the literature to produce the 'European forest database of leaf senescence and seasonal tree growth'. The combination of our experimental data and of this database will allow testing the research hypotheses, both at site and at continental level. Overall, the aim is to solve the conundrum of the timing of leaf senescence in temperate deciduous trees and provide a new interpretation of the relationship between leaf senescence, tree growth and environment, which will be a key to improve projections of forest biomass production and climate change. Concurrently, novel insights on tree growth will be provided, in particular on the seasonal growth of coarse roots, which has never been reported up to date for angiosperm species.

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  • Research Project

What makes leaves fall in autumn? A new process description for the timing of leaf senescence in temperate and boreal trees (LEAF-FALL). 01/02/2017 - 31/01/2024

Abstract

Leaf phenology is a key component in the functioning of temperate and boreal deciduous forests. The environmental cues for bud-burst in spring are well known, but little is known about the cues controlling the timing of leaf fall in autumn. Leaf fall is the last stage of leaf senescence, a process which allows trees to recover leaf nutrients. We urgently need to understand the controls timing leaf senescence to improve our projections of forest growth and climate change. I propose a new general paradigm of the onset of leaf senescence, hypothesizing that leaf senescence is triggered by the cessation of tree growth in autumn. I expect that: (i) in the absence of growth-limiting environmental conditions, tree growth cessation directly controls leaf-senescence onset; and (ii) in the presence of growth-limiting conditions, photoperiod controls leaf-senescence onset – this prevents trees from starting to senesce too early. I will test these hypotheses with a combination of: (i) manipulative experiments on young trees - these will disentangle the impact of photoperiod from that of other factors affecting tree growth cessation, namely: temperature, drought and soil nutrient availability; (ii) monitoring leaf senescence and growth in mature forest stands; (iii) comparing the leaf senescence dynamics of four major tree species (Fagus sylvatica, Quercus robur, Betula pendula and Populus tremula) in four European locations spanning from 40º to 70º N; and (iv) integrating the new paradigm into a model of forest ecosystem dynamics and testing it for the major forested areas of Europe. The aim is to solve the conundrum of the timing of leaf senescence in temperate and boreal deciduous trees, provide a new interpretation of the relationship between leaf senescence, tree growth and environment, and deliver a modelling tool able to predict leaf senescence and tree growth, for projections of forest biomass production and climate change.

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  • Research Project

Global assessment of terrestrial biomass production and of its determinants. 01/10/2015 - 30/09/2018

Abstract

The biomass production (BP) of terrestrial ecosystems is a fundamental ecological process and a key ecosystem service. In fact, BP represents the supply of food, fibers and wood to our society and the carbon (C) accumulated annually on the Earth's land, which is a crucial determinant of the global C cycle and climate. Biomass production has been widely investigated and BP estimates are available from 'direct' (field-level) measurements at hundreds of experimental sites worldwide. However, global analyses of BP dynamics are limited or largely based on 'indirect' BP estimates from remote sensing, which have high resolution but low accuracy. Here, I aim to fill the critical knowledge gaps on global BP dynamics (1) by providing robust BP estimates for all major terrestrial ecosystem types (e.g. forests, grasslands, croplands, wetlands, tundra, deserts) and for the entire Earth's land, and (2) by elucidating which are the key global drivers of BP (e.g. plant traits, climate, site fertility, soil water content or management activities). In addition, the study will compare the performance of direct and indirect methods to assess global BP dynamics and clarify features and weaknesses of both approaches. These tasks will be accomplished by using a new, unique, database of direct BP estimates, that I recently compiled, and remote sensing BP estimates from MODIS.

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  • Research Project

Carbon allocation in terrestrial ecosystems: exploring universal scalars across biomes. 01/10/2012 - 30/09/2015

Abstract

The biomass production efficiency (BPE) is the fraction of carbon assimilated through photosynthesis that is used to produce plant biomass. BPE is particularly relevant to evaluate the feedback of terrestrial ecosystems to the greenhouse effect. This study will provide BPE estimates for major world's biomes (e.g. grasslands, forests, croplands, wetlands), reveal the environmental drivers of BPE, and explore the relationship between BPE and ecosystem carbon sequestration. In particular, we hypothesize that BPE is positively related to soil fertility and that such relationship holds across biomes. Plant communities are more productive in richer soils because less non-structural carbohydrates are needed belowground (for roots symbionts and root exudates) to facilitate nutrient acquisition. Thus, the better the nutrient status, the larger is the carbon available for biomass production and sequestration in the ecosystem. We will test these hypotheses with a new global biome database with hundreds of experimental sites worldwide and a mesocosm experiment focused on typical temperate biomes (e.g. grasslands).

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  • Research Project