Christoforos Pappas

University of Patras | UP · Department of Civil Engineering

Goals of the poster: 1) To assess the annual pattern of NEE at the near-coastal Aleppo pine ecosystem in Greece, 2) To upscale CO2 fluxes at the total forest area, basedon a Copernicus LAI product. Our methodology for upscaling the Eddy C fluxes at the ecosystem level for the entire forest was quite reliable, as the estimations were close (somewha...

We tested how adult pine trees age and understory vegetation density affect C sequestration at a coastal, natural Aleppo pine forest in Chalkidiki, Greece. ➢ C sequestration declines with increasing Aleppo pine age, but it increases with denser understory shrub vegetation. ➢ Climate-smart forest management at low-elevation mediterranean pine fores...

Mediterranean regions are heavily exposed to wildfires that can result in devastating casualties and infrastructure damage. Greece has been particularly affected by wildfires during recent years and the accurate mapping of the fire-exposed areas is essential. This can enhance our process understanding on such natural hazards, also supporting practi...

The structural analysis of cultural heritage buildings, including their monitoring and maintenance, requires accurate 3D models of the structure, especially when these monuments are threatened (e.g., anthropogenic and natural disturbances). However, monuments such as castles and monasteries often lack such construction plans. Structure from motion...

The area of Western Greece and the Peloponnese region show land deformations that can be triggered, for example, by seismic activity (e.g., Corinthian Gulf faults) and environmental factors (e.g., heavy rainfall). Land subsidence observed during the recent years within the Campus of the University of Patras in Northwestern Peloponnese confirms thes...

Trees remain sufficiently hydrated during drought by closing stomata and reducing canopy conductance (Gc) in response to variations in atmospheric water demand and soil water availability. Thresholds that control the reduction of Gc are proposed to optimize hydraulic safety against carbon assimilation efficiency. However, the link between Gc and th...

Forest phenological dynamics shape the underlying biogeophysical processes and impact the carbon balance from the seasonal to inter-annual time scales. Disentangling the phenological phases of the forest components (e.g., overstory and understory), could provide novel insights on ecosystem response to climate change. This quantitative description i...

The increasing effects of climate and global change oblige ecosystem-based management to adapt forestry practices to deal with uncertainties. Here we provide an overview to identify the challenges facing the boreal forest under projected future change, including altered natural disturbance regimes, biodiversity loss, increased forest fragmentation,...

Partitioned estimates of the boreal forest carbon (C) sink components are crucial for understanding processes and developing science-driven adaptation and mitigation strategies under climate change. Here, we provide a concise tree-centered overview of the boreal forest C balance and offer a circumpolar perspective on the contribution of trees to bo...

Forests account for nearly 90 % of the world's terrestrial biomass in the form of carbon and they support 80 % of the global biodiversity. To understand the underlying forest dynamics, we need a long-term but also relatively high-frequency, networked monitoring system, as traditionally used in meteorology or hydrology. While there are numerous exis...

Les arbres, les scientifiques, les artistes et leurs instruments perçoivent l'écoulement de l'eau. Les arbres prennent des risques pendant la saison de croissance soit en augmentant leur transpiration (ou flux de sève), soit en se restreignant. Les vaisseaux se dilatent, se contractent. L'eau est tirée vers le haut, du sol vers l'air, en passant pa...

Árboles, científicos, artistas y sus instrumentos perciben cómo fluye el agua. Los árboles asumen riesgos durante la temporada de crecimiento ya sea aumentando la transpiración (flujo de savia) o conteniéndola. Las venas se expanden y se contraen. El agua es arrastrada hacia arriba desde el suelo al aire, pasando por los troncos de los árboles. Per...

Drought legacies in radial tree growth are an important feature of variability in biomass accumulation and are widely used to characterize forest resilience to climate change. Defined as a deviation from normal growth, the statistical significance of legacy effects depends on the definition of “normal”—expected growth under average conditions—which...

Studies of tree water source partitioning have primarily focused on the growing season. However, little is yet known about the source of transpiration before, during, and after snowmelt when trees rehydrate and recommence transpiration in the spring. This study investigates tree water use during spring snowmelt following tree's winter stem shrinkag...

Sapwood characteristics, such as sapwood area as well as thermal and hydraulic conductivity, are linked to species-specific hydraulic function and resource allocation to water transport tissues (xylem). These characteristics are often unknown and thus a major source of uncertainty in sap flow data processing and transpiration estimates because bulk...

The ability of forests to withstand, and recover from, acute drought stress is a critical uncertainty regarding the impacts of climate change on the terrestrial carbon (C) cycle, but it is unclear how drought responses scale from individual trees to whole forests. Here, we assembled a dataset of tree-ring chronologies co-located within the footprin...

We present here the project and the experimental design in addition to presenting the first data from the dendrometers. An important drought in late summer 2021 caused a significant increase in tree water deficit and a premature cessation of growth in August 2021. The results of this project will help evaluate future boreal forest resilience to cli...

Uncertainties surrounding tree carbon allocation to growth are a major limitation to projections of forest carbon sequestration and response to climate change. The prevalence and extent to which carbon assimilation (source) or cambial activity (sink) mediate wood production are fundamentally important and remain elusive. We quantified source-sink r...

Ecological research, just as all Earth System Sciences, is becoming increasingly data-rich. Tools for processing of “big data” are continuously developed to meet corresponding technical and logistical challenges. However, even at smaller scales, data sets may be challenging when best practices in data exploration, quality control and reproducibilit...

A comprehensive assessment of the tree growth/climate relationship was undertaken to better understand the potential impacts of climate change on the growth dynamics of four widespread and common boreal tree species, namely jack pine (Pinus banksiana), black spruce (Picea mariana), eastern larch (Larix laricina), and trembling aspen (Populus tremul...

Monitoring of forest response to gradual environmental changes or abrupt disturbances provides insights into how forested ecosystems operate and allows for quantification of forest health. In this chapter, we provide an overview of Smartforests Canada, a national-scale research network consisting of regional investigators who support a wealth of ex...

Groundwater is a key water resource in semiarid and seasonally dry regions around the world, which is replenished by intermittent precipitation events and mediated by vegetation, soil, and regolith properties. Here, a climate reconstruction of 4500 years for the Jerusalem region was used to determine the relation between climate, vegetation, and gr...

The boreal forest is a major contributor to the global climate system, therefore, reducing uncertainties in how the forest will respond to a changing climate is critical. One source of uncertainty is the timing and drivers of the spring transition. Remote sensing can provide important information on this transition, but persistent foliage greenness...

Vegetation optical depth (VOD) retrieved from microwave radiometry correlates with the total amount of water in vegetation, based on theoretical and empirical evidence. Because the total amount of water in vegetation varies with relative water content (as well as with biomass), this correlation further suggests a possible relationship between VOD a...

Integration of Earth system data from various sources is a challenging task. Except for their qualitative heterogeneity, different data records exist for describing similar Earth system process at different spatiotemporal scales. Data inter-comparison and validation are usually performed at a single spatial or temporal scale, which could hamper the...

Our understanding of the source of transpiration and how phenological and hydrological processes affect tree water use are based mainly on temperate and tropical zones. In cold regions, as trees emerge from winter dormancy, tree water storage refilling sinks large volume of water. Understanding the timing of snowmelt, tree water storage refilling,...

A key ecophysiological measurement is the flow of water (or sap) along the tree's water‐transport system, which is an essential process for maintaining the hydraulic connection within the soil–plant–atmosphere continuum. The thermal dissipation method (TDM) is widespread in the scientific community for measuring sap flow and has provided novel insi...

Vegetation optical depth (VOD) retrieved from microwave radiometry correlates with the total amount of water in vegetation, based on theoretical and empirical evidence. Because the total amount of water in vegetation varies with relative water content (as well as with biomass), this correlation further suggests a possible relationship between VOD a...

Tree growth is an indicator of tree vitality and its temporal variability is linked to species resilience to environmental changes. Second‐order statistics that quantify the cross‐scale temporal variability of ecophysiological time series (statistical memory) could provide novel insights into species resilience. Species with high statistical memory...

The boreal biome accounts for approximately one third of the terrestrial carbon (C) sink. However, estimates of its individual C pools remain uncertain. Here, focusing on the southern boreal forest, we quantified the magnitude and temporal dynamics of C allocation to aboveground tree growth at a mature black spruce (Picea mariana)-dominated forest...

Climate change can reduce surface-water supply by enhancing evapotranspiration in forested mountains, especially during heatwaves. We investigate this ‘drought paradox’ for the European Alps using a 1,212-station database and hyper-resolution ecohydrological simulations to quantify blue (runoff) and green (evapotranspiration) water fluxes. During t...

The extent, timing and duration of seasonal freeze/thaw (FT) state exerts dominant control on boreal forest carbon, water and energy cycle processes. Recent and on-going L-Band (≈1.4 GHz) spaceborne missions have the potential to provide enhanced information on FT state over large geographic regions with rapid revisit time. However, the low spatial...

We used four years of sap flow measurements to elucidate intra‐ and inter‐specific variability of gs in Larix decidua Mill. and Picea abies (L.) Karst along an elevational gradient and contrasting soil moisture conditions. Site‐ and species‐specific gs response to main environmental drivers were examined, including vapour pressure deficit, air temp...

Contents Summary 652 I. Introduction 652 II. Discrepancy in predicting the effects of rising [CO2] on the terrestrial C sink 655 III. Carbon and nutrient storage in plants and its modelling 656 IV. Modelling the source and the sink: a plant perspective 657 V. Plant‐scale water and Carbon flux models 660 VI. Challenges for the future 662 Ack...

The reliable partitioning of the terrestrial latent heat flux into evaporation (E) and transpiration (T) is important for linking carbon and water cycles and for better understanding ecosystem functioning at local, regional and global scales. Previous research revealed that the transpiration-to-evapotranspiration ratio (T/ET) is well constrained ac...

Mountain ecosystems are experiencing rapid warming resulting in ecological changes worldwide. Projecting the response of these ecosystems to climate change is thus crucial, but also uncertain due to complex interactions between topography, climate and vegetation. Here, we performed numerical simulations in a real and a synthetic spatial domain cove...

Decoupling the integrated microwave signal originating from soil and vegetation remains a challenge for all microwave remote sensing applications. To improve satellite and airborne microwave data products in forest environments, a precise and reliable estimation of the relative permittivity (ε=ε′-iε′′) of trees is required. We developed an open-end...

Trees play a key role in the global hydrological cycle and measurements performed with the thermal dissipation method ( TDM ) have been crucial in providing whole‐tree water‐use estimates. Yet, different data processing to calculate whole‐tree water use encapsulates uncertainties that have not been systematically assessed. We quantified uncertainti...

Water stress has been identified as a key mechanism of the contemporary increase in tree mortality rates in northwestern North America. However, a detailed analysis of boreal tree hydrodynamics and their interspecific differences is still lacking. Here we examine the hydraulic behaviour of co-occurring larch (Larix laricina) and black spruce (Picea...

Decoupling the integrated microwave signal originating from soil and vegetation remains a challenge for all microwave remote sensing applications. To improve satellite and airborne microwave data products in forest environments, a precise and reliable estimation of the relative permittivity (𝜺 = 𝜺’ – i 𝜺’’) of the trees is required. We developed an...

Evapotranspiration (ET) is a key component of the water cycle, whereby accurate partitioning of ET into evaporation and transpiration provides important information about the intrinsically coupled carbon, water, and energy fluxes. Currently, global estimates of partitioned evaporative and transpiration fluxes remain highly uncertain, especially for...

Terrestrial ecosystem processes, and the associated vegetation carbon dynamics, respond differently to hydrometeorological variability across timescales, and so does our scientific understanding of the underlying mechanisms. Long-term variability of the terrestrial carbon cycle is not yet well constrained and the resulting climate–biosphere feedbac...

Elevated atmospheric CO2 concentrations are expected to enhance photosynthesis and reduce stomatal conductance, thus increasing plant water use efficiency. A recent study based on eddy covariance flux observations from Northern Hemisphere forests showed a large increase in inherent water use efficiency (IWUE). Here, we used an updated version of th...

A large variability (35–90%) in the ratio of transpiration to total evapotranspiration (referred here as T:ET) across biomes or even at the global scale has been documented by a number of studies carried out with different methodologies. Previous empirical results also suggest that T:ET does not covary with mean precipitation and has a positive dep...

Boreal forests cover vast areas of the permafrost zones of North America and changes in their composition and structure can lead to pronounced impacts on the regional and global climate. We partition the variation in regional boreal tree cover changes between 2000 and 2014 across the Taiga Plains, Canada, into its main causes: permafrost thaw, wild...

Ecosystem functioning is monitored worldwide over several decades. However, a comparative in-depth characterization of the temporal variability of essential ecosystem processes, such as for example carbon assimilation and respiration is still lacking. The intra-annual (sub-diurnal, diurnal, and seasonal) variability of these processes can be well d...

Vegetation and the water cycles are inherently coupled across a wide range of spatial and temporal scales. Water availability interacts with plant ecophysiology and controls vegetation functioning. Concurrently, vegetation has direct and indirect effects on energy, water, carbon, and nutrient cycles. To better understand and model plant–water inter...

Plant trait diversity in many vegetation models is crudely represented using a discrete classification of a handful of ‘plant types’ (named plant functional types; PFTs). The parameterization of PFTs reflects mean properties of observed plant traits over broad categories ignoring most of the inter‐ and intraspecific plant trait variability. Taking...

An expression that separates biotic and abiotic controls on the temporal dynamics of the soil moisture spatial coefficient of variation Cv(θ) was explored via numerical simulations using a mechanistic ecohydrological model, Tethys-Chloris. Continuous soil moisture spatio-temporal dynamics at an exemplary hillslope domain were computed for six case...

The coarse-grained spatial representation of many terrestrial ecosystem models hampers the importance of local scale heterogeneities. To address this issue, we combine a range of observations (forest inventories, eddy flux tower data, remote sensing products) and modeling approaches with contrasting degrees of abstraction. The following models are...

Data-gaps are ubiquitous in hydrometeorological time series and filling these values remains still a challenge. Since datasets without missing values may be a prerequisite in performing many analyses, a quick and efficient gap-filling methodology is required. In this study the problem of filling sporadic, single-value gaps using time-adjacent obser...

The coarse-grained spatial representation of many terrestrial ecosystem models hampers the importance of local scale heterogeneities. To discuss this issue, we combine a range of observations (forest inventories, eddy flux tower data, remote sensing products) and modeling approaches which allow us to investigate the role of local climate, topograph...

Missing values in hydrometeorological time series is a commonplace and filling these values remains still a challenge. Since datasets without missing values may be a prerequisite in performing many statistical analyses, a quick and efficient gap-filling methodology is required. In this study the problem of filling sporadic gaps of time series using...

[1] Dynamic vegetation models have been widely used for analyzing ecosystem dynamics and their interactions with climate. Their performance has been tested extensively against observations and by model intercomparison studies. In the present analysis, Lund-Potsdam-Jena General Ecosystem Simulator (LPJ-GUESS), a state-of-the-art ecosystem model, was...

Dynamic Global Vegetation Models (DGVMs) are widely used for analyzing forest growth dynamics and possible biophysical and biogeochemical feedbacks to climate. Their performance has been typically tested against flux tower and forest inventory observations and by model intercomparison studies. In the present analysis the parameterization of LPJ-GUE...

Dynamic vegetation models have been widely used for analyzing ecosystem dynamics and climate feedbacks. Their performance has been tested extensively against observations and by model intercomparison studies. In the present study, the LPJ-GUESS state-of-the-art ecosystem model was evaluated with respect to its structure, hypothesis, and parameteriz...

Dynamic global vegetation models (DGVMs) have been widely used for analysing ecosystem dynamics and their interactions with climate through energy, carbon and water fluxes. In the present study we investigate the sensitivity of LPJ-GUESS model. This is a state-of-the-art ecosystem model, which combines a DGVM (Lund-Potsdam-Jena, LPJ) with a more de...

Being a group of undergraduate students in the National Technical University of Athens, attending the course of Stochastic Methods in Water Resources, we study, in cooperation with our tutors, the infilling of missing values of hydrometeorological time series from measurements at neighbouring times. The literature provides a plethora of methods, mo...