Rafael Poyatos

CREAF Centre for Ecological Research and Forestry Applications | CREAF · CREAF Centre for Ecological Research and Forestry Applications

Temperate forests and Mediterranean woodlands of the northern hemisphere are dominated by the tree species in the Pinaceae and Fagaceae families. A recent increase in the dominance of Fagaceae has been reported worldwide, related to changes in management and disturbance regimes. Contrasting ecological strategies between the two families can also me...

Transpiration from vegetation accounts for about two thirds of land evapotranspiration (ET), and exerts important effects on of global water, energy, and carbon cycles. Resistance-based ET partitioning models using remote sensing data are one of the main methods to estimate global land transpiration, overcoming the limitation by the sparse distribu...

Frequent observations of higher mortality in larger trees than in smaller ones during droughts have sparked an increasing interest in size-dependent drought-induced mortality. However, the underlying physiological mechanisms are not well understood, with height-associated hydraulic constraints often being implied as the potential mechanism driving...

This scientific commentary refers to ‘Contrasting stem water uptake and storage dynamics of water-saver and water-spender species during drought and recovery’ by Martín-Gómez et al. (doi: 10.1093/treephys/tpad032). Drought is a key stress factor determining plant distribution and functioning (Woodward 1987). Because climate change is causing warmer...

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

While the eddy covariance (EC) technique is a well-established method for measuring water fluxes (i.e., evaporation or 'evapotranspiration', ET), the measurement is susceptible to many uncertainties. One such issue is the potential underestimation of ET when relative humidity (RH) is high (>70%), due to low-pass filtering with some EC systems. Yet,...

Temperature rise and more severe and frequent droughts will alter forest transpiration, thereby affecting the global water cycle. Yet, tree responses to increased atmospheric vapour pressure deficit (VPD) and reduced soil water content (SWC) are not fully understood due to long‐term tree adjustments to local environmental conditions that modify tra...

Transpiration is a key process driving energy, water and thus carbon dynamics. Global transpiration products are fundamental for understanding and predicting vegetation processes. However, validation of these transpiration products is limited, mainly due to lack of suitable data sets. We propose a method to use SAPFLUXNET, the first quality‐control...

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...

Plain Language Summary Forests comprise the largest share of Earth's vegetated surface area and play an integral role in its hydrological cycle. Forests transfer moisture from below the surface to the atmosphere via transpiration, affecting surface moisture budgets and weather patterns at local‐to‐regional scales. Our ability to accurately predict...

We aim to identify the importance of vapour pressure deficit (VPD), soil water content (SWC) and photosynthetic photon flux density (PPFD) as drivers of tree canopy conductance, which is a key source of uncertainty for modelling vegetation responses under climate change. We use sap flow time series of 1858 trees in 122 sites from the SAPFLUXNET glo...

While the eddy covariance (EC) technique is a well-established method for measuring water fluxes (i.e., evaporation or 'evapotranspiration’, ET), the method is susceptible to many uncertainties. One such issue is the potential underestimation of ET when relative humidity (RH) is high (>70%), due to low-pass filtering with some EC systems. The influ...

Terrestrial evaporation (E) is a key climatic variable that is controlled by a plethora of environmental factors. The constraints that modulate the evaporation from plant leaves (or transpiration, Et) are particularly complex, yet are often assumed to interact linearly in global models due to our limited knowledge based on local studies. Here, we t...

Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur and most terrestrial species reside. Here, we...

Heatwaves exert disproportionately strong and sometimes irreversible impacts on forest ecosystems. These impacts remain poorly understood at the tree and species level and across large spatial scales. Here, we investigate the effects of the record-breaking 2018 European heatwave on tree growth and tree water status using a collection of high-tempor...

The exchange of multiple greenhouse gases (i.e., CO2 and CH4) between tree stems and the atmosphere represents a knowledge gap in the global carbon cycle. Stem CO2 and CH4 fluxes vary across time and space and is unclear which are their individual or shared drivers. Here we measured CO2 and CH4 fluxes at different stem heights combining manual (biw...

Minimum water potential (Ψ min ) is a key variable for characterizing dehydration tolerance and hydraulic safety margins (HSMs) in plants. Ψ min is usually estimated as the absolute minimum tissue Ψ experienced by a species, but this is problematic because sample extremes are affected by sample size and the underlying probability distribution. We c...

Plant transpiration links physiological responses of vegetation to water supply and demand with hydrological, energy, and carbon budgets at the land–atmosphere interface. However, despite being the main land evaporative flux at the global scale, transpiration and its response to environmental drivers are currently not well constrained by observatio...

The regional variability in tundra and boreal carbon dioxide (CO2) fluxes can be high, complicating efforts to quantify sink‐source patterns across the entire region. Statistical models are increasingly used to predict (i.e., upscale) CO2 fluxes across large spatial domains, but the reliability of different modeling techniques, each with different...

Tree water use is central to plant function and ecosystem fluxes. However, it is still unknown how organ‐level water‐relations traits are coordinated to determine whole‐tree water‐use strategies in response to drought, and whether this coordination depends on climate. Here we used a global sap flow database (SAPFLUXNET) to study the response of wat...

Research in environmental science relies heavily on global climatic grids derived from estimates of air temperature at around 2 meter above ground1-3. These climatic grids however fail to reflect conditions near and below the soil surface, where critical ecosystem functions such as soil carbon storage are controlled and most biodiversity resides4-8...

Understanding how water use and drought stress in woody plants change in relation to compositional, structural and environmental variability of mixed forests is key to understand their functioning and dynamics. Observational and experimental studies have so far shown a complex array of water use and drought stress responses to species mixing, but p...

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...

Plant transpiration links physiological responses of vegetation to water supply and demand with hydrological,energy and carbon budgets at the land-atmosphere interface. However, despite being the main land evaporative flux at the global scale, transpiration and its response to environmental drivers are currently not well constrained by observations...

We apply and compare three widely applicable methods for estimating ecosystem transpiration (T) from eddy covariance (EC) data across 251 FLUXNET sites globally. All three methods are based on the coupled water and carbon relationship, but they differ in assumptions and parameterizations. Intercomparison of the three daily T estimates shows high co...

We apply and compare three widely applicable methods for estimating ecosystem transpiration (T) from eddy covariance (EC) data across 251 FLUXNET sites globally. All three methods are based on the coupled water and carbon relationship, but they differ in assumptions and parameterizations. Intercomparison of the three daily T estimates shows high co...

Potential land‐climate feedbacks in subarctic regions, where rapid warming is driving forest expansion into the tundra, may be mediated by differences in transpiration of different plant functional types. Here we assess the environmental controls of overstorey transpiration and its relevance for ecosystem evapotranspiration in subarctic deciduous w...

Evaporation (E) and transpiration (T) respond differently to ongoing changes in climate, atmospheric composition, and land use. It is difficult to partition ecosystem-scale evapotranspiration (ET) measurements into E and T, which makes it difficult to validate satellite data and land surface models. Here, we review current progress in partitioning...

The article was published without the submitted data availability statement linking readers to a public repository.

Evaporation (E) and transpiration (T) respond differently to ongoing changes in climate, atmospheric composition, and land use. Our ability to partition evapotranspiration (ET) into E and T is limited at the ecosystem scale, which renders the validation of satellite data and land surface models incomplete. Here, we review current progress in partit...

Tree stems exchange CO2, CH4 and N2O with the atmosphere but the magnitudes, patterns and drivers of these greenhouse gas (GHG) fluxes remain poorly understood. Our understanding mainly comes from static-manual measurements, which provide limited information on the temporal variability and magnitude of these fluxes. We measured hourly CO2, CH4 and...

Key message Below-crown hydraulic resistance, a proxy for below-ground hydraulic resistance, increased during drought in Scots pine, but larger increases were not associated to drought-induced defoliation. Accounting for variable below-ground hydraulic conductance in response to drought may be needed for accurate predictions of forest water fluxes...

Drought is a key driver of vegetation dynamics, but plant water‐uptake patterns and consequent plant responses to drought are poorly understood at large spatial scales. The capacity of vegetation to use soil water depends on its root distribution (RD). However, RD is extremely variable in space and difficult to measure in the field, which hinders a...

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...

The ubiquity of missing data in plant trait databases may hinder trait-based analyses of ecological patterns and processes. Spatially explicit datasets with information on intraspecific trait variability are rare but offer great promise in improving our understanding of functional biogeography. At the same time, they offer specific challenges in te...

Aboveground plant activity influences fine roots and rhizosphere activity, which is reflected on soil respiration (SR). However, it is still unclear and poorly understood the nature of plant activity control over SR, especially under drought conditions. We studied the plant activity-SR relationship at different timescales in a water-limited mixed M...

The ubiquity of missing data in plant trait databases may hinder trait-based analyses of ecological patterns and processes. Spatially-explicit datasets with information on intraspecific trait variability are rare but offer great promise in improving our understanding of functional biogeography. At the same time, they offer specific challenges in te...

Drought is a situation of water deficit of a system, compared to normal conditions. Operational definitions of drought (i.e., those used to identify specific drought events) change depending upon the system under consideration, but they have been historically restricted to climatic, agricultural, hydrologic, and socioeconomic systems. From an ecolo...

Transpiration from the Amazon rainforest generates an essential water source at a global and local scale. However, changes in rainforest function with climate change can disrupt this process, causing significant reductions in precipitation across Amazonia, and potentially at a global scale. We report the only study of forest transpiration following...

Plant transpiration is the main evaporative flux from terrestrial ecosystems; it controls land surface energy balance, determines catchment hydrological responses and influences regional and global climate. Transpiration regulation by plants is a key (and still not completely understood) process that underlies vegetation drought responses and land...

How forests cope with drought-induced perturbations and how the dependence of soil respiration on environmental and biological drivers is affected in a warming and drying context are becoming key questions. The aims of this study were to determine whether drought-induced die-off and forest succession were reflected in soil respiration and its compo...

Understanding how ecosystems functioning may respond to increments of temperature and climatic variability is crucial in the global change context. We studied the plant-and-soil interaction in a mixed Mediterranean forest where several drought events since 1990’s have resulted in Scots pine defoliation and mortality, with a subsequent replacement b...

Figure S1. Twenty‐day moving average of daytime VPD and soil water content. Whereas VPD peaked at about 1.3–1.45 in 2010–2011 and 2013, it reached approximately 2 at the end of August 2012 (DOY 239), and was already 1.48 on during the sampling period. This shows a persistently high evaporative demand condition during August 2012. The three grey are...

Different functional and structural strategies to cope with water shortage exist both within and across plant communities. The current trend towards increasing drought in many regions could drive some species to their physiological limits of drought tolerance, potentially leading to mortality episodes and vegetation shifts. In this paper, we study...

Drought limits tree water use and growth of Mediterranean trees. However, growth and water use strategies are rarely addressed simultaneously across species and drought conditions. Here, we investigate the link between stem diameter variations and sap flow in four co-existing Mediterranean trees (Pinus halepensis Mill., Quercus pubescens Willd., Qu...

Understanding physiological processes involved in drought-induced mortality is important for predicting the future of forests and for modelling the carbon and water cycles. Recent research has highlighted the variable risks of carbon starvation and hydraulic failure in drought-exposed trees. However, little is known about the specific responses of...

Drought-related tree die-off episodes have been observed in all vegetated continents. Despite much research effort, however, the multiple interactions between carbon starvation, hydraulic failure and biotic agents in driving tree mortality under field conditions are still not well understood. We analysed the seasonal variability of non-structural c...

Understanding physiological processes involved in drought-induced mortality is important for predicting the future of forests and for modelling the carbon and water cycles. Recent research has highlighted the variable risks of carbon starvation and hydraulic failure in drought-exposed trees. However, little is known about the specific responses of...

Tree transpiration is regulated by short-term physiological adjustments and long-term shifts in hydraulic architecture in response to fluctuating evaporative demand and water supply. Despite the tight interdependence of plant water loss and carbon uptake and its crucial implications for plant growth and survival under drought conditions, the underl...

Aim Mediterranean terrestrial ecosystems serve as reference laboratories for the investigation of global change because of their transitional climate, the high spatiotemporal variability of their environmental conditions, a rich and unique biodiversity and a wide range of socio‐economic conditions. As scientific development and environmental pressu...

Plant function requires effective mechanisms to regulate water transport at a variety of scales. Here, we develop a new theoretical framework describing plant responses to drying soil, based on the relationship between midday and predawn leaf water potentials. The intercept of the relationship (Λ) characterizes the maximum transpiration rate per un...

The Vallcebre research catchments are located in a Mediterranean mountain area (Pyrenean range, NE Spain). These catchments were originally covered by Quercus pubescens Willd. and deforested for agricultural use in the past. Nowadays they are covered by mesophyle grasses with spontaneous afforestation by Pinus sylvestris L. In this context, differe...

Drought-induced decline is affecting Pinus sylvestris populations in southern Europe, with very little impact on the more drought-tolerant Quercus pubescens. Although multiple studies have investigated interspecific differences in water use and growth strategies, the link between these two processes and how they vary within drought-exposed populati...

SOSTENIBILIDAD EN ESPAÑA 2011 327 l Observatorio de la Sostenibilidad de España (OSE) ha preparado el presente capítulo espe-cial sobre bosques, en el marco de su Informe Sostenibilidad en España 2011, con ocasión de la celebración del Año Internacional de los Bosques. La Asamblea General de Naciones Unidas acordó en 2006 celebrar en 2011 este impo...

Background/Question/Methods Plants are able to survive and function under extremely variable environmental conditions, including dramatic changes in soil water availability and atmospheric evaporative demand. This could not be achieved without powerful regulatory mechanisms at a variety of organizational and time scales, which allow plants to mod...

Drought stress is known to limit tree patterns of water use and radial growth in Mediterranean-type ecosystems. However, both processes are rarely dealt with in combination in multi-species studies. Here, we combine sap flow measurements with automatic band dendrometers in order to assess year-round water use strategies and stem radius growth of fo...

Drought stress is known to limit tree patterns of water use and radial growth in Mediterranean-type ecosystems. However, both processes are rarely dealt with in combination in multi-species studies. Here, we combine sap flow measurements with automatic band dendrometers in order to assess year-round water use strategies and stem radius growth of fo...

Drought‐induced defoliation has recently been associated with the depletion of carbon reserves and increased mortality risk in Scots pine ( Pinus sylvestris ). We hypothesize that defoliated individuals are more sensitive to drought, implying that potentially higher gas exchange (per unit of leaf area) during wet periods may not compensate for thei...

Unravelling the role of structural and environmental drivers of gross primary productivity (GPP) and ecosystem respiration (R eco) in highly heterogeneous tundra is a major challenge for the upscaling of chamber-based CO2 fluxes in Arctic landscapes. In a mountain birch woodland-mire ecotone, we investigated the role of LAI (and NDVI), environmenta...

El pino albar (Pinus sylvestris) es uno de los árboles más ampliamente distribuidos del mundo. Pese a su gran plasticidad ecológica, numerosos estudios muestran que su capacidad de resistir la sequía se está viendo superada en diversas zonas, especialmente en la cuenca mediterránea, donde se halla el límite meridional de su distribución. El present...

Forests at northern high latitudes are experiencing climate-induced changes in growth and productivity, but our knowledge on the underlying mechanisms driving seasonal CO2 fluxes in northern boreal trees comes almost exclusively from ecosystem-level studies on evergreen conifers. In this study, we measured growing season whole-branch CO2 exchange i...