Research team

Plant and Ecosystems (PLECO) - Ecology in a time of change

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.

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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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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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 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 team(s)

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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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 - 31/01/2023

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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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 team(s)

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.

Researcher(s)

Research team(s)

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 team(s)

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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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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