BG3.25 | Terrestrial microclimates
Terrestrial microclimates
Convener: Jerome Ogee | Co-conveners: Rosie A. Fisher, Jerôme Chave, Gabriel Hes
Orals
| Thu, 18 Apr, 14:00–15:45 (CEST)
 
Room N1
Posters on site
| Attendance Wed, 17 Apr, 10:45–12:30 (CEST) | Display Wed, 17 Apr, 08:30–12:30
 
Hall X1
Orals |
Thu, 14:00
Wed, 10:45
The microclimate within terrestrial ecosystems is highly heterogeneous as it responds to a multitude of local and landscape-scale factors such as foliage density, micro-topography, distance to a forest edge or a water body. This diversity of microclimates, and the potential buffering of climate extremes in the landscape, are key to understand terrestrial biodiversity and ecosystem functioning (notably carbon, water and nutrient cycling), but also ecosystem resilience and feedback onto regional climate. Despite our good understanding of the biophysical processes driving microclimate, it is still very challenging to describe and predict how microclimate varies across the landscape, and anticipate the impact of changes in climate, land use or ecosystem management.
In this session, we welcome observational, experimental and modelling studies on terrestrial microclimate, its role on biodiversity, biogeochemical cycles, ecosystem resilience and its response to climate and land use change.

Session assets

Orals: Thu, 18 Apr | Room N1

Chairpersons: Jerome Ogee, Gabriel Hes, Rosie A. Fisher
14:00–14:05
Microclimate in vegetation canopies: turbulent exchange processes
14:05–14:15
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EGU24-13191
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solicited
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On-site presentation
Gordon Bonan, Sean Burns, and Edward Patton

The influences of forests on the large-scale macroclimate are now established. Through albedo, evapotranspiration, surface roughness, and aerosols, forests influence the climate at large spatial scales. Forest influences on the local microclimate are also being recognized, and forests provide microclimatic refugia to buffer organisms against planetary warming. However, the scientific tools used to study forest influences on climate fail to account for forest microclimates. Earth system models are an important tool to inform land-use policy to mitigate planetary warming. With their big-leaf parameterization of plant canopies, however, the models are not vertically-resolved and do not simulate forest understories. Remotely sensed land surface temperature, another primary research tool to distinguish forest influences from other land cover, differs from the air temperature above and within forests. Multilayer canopy models have received renewed interest over the past several years and are a means to both improve the surface flux parameterizations and simulate vertical profiles within and above plant canopies. We present results of a comparison between the Community Land Model (CLM) multilayer canopy model and observations of air temperature, specific humidity, wind speed, and fluxes (net radiation, sensible heat, latent heat, momentum) taken at multiple heights in a walnut orchard during the Canopy Horizontal Array Turbulence Study (CHATS) from mid-March to mid-June 2007. The dataset provides a benchmark standard with which to test multilayer canopy models. Our model-data comparison highlights the potential of multilayer models to simulate the complex micrometeorology of forest canopies and also points to further research needs.

How to cite: Bonan, G., Burns, S., and Patton, E.: Modeling forest microclimates in the Earth system: a test case using the Canopy Horizontal Array Turbulence Study (CHATS) walnut orchard, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13191, https://doi.org/10.5194/egusphere-egu24-13191, 2024.

14:15–14:25
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EGU24-17152
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ECS
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On-site presentation
Julien Alléon, Catherine Ottlé, Nicolas Vuichard, Sebastiaan Luyssaert, Klara Bouwen, Jérôme Ogée, and Philippe Peylin

Intra-canopy microclimate and regional climate are two highly related components of the Earth system. On one side, intra-canopy microclimate influences strongly the ecosystem itself by regulating the vegetation/atmosphere exchanges which further influence plant dynamics, carbon sequestration and soil water dynamics. It also influences the biodiversity below the canopy by offering microhabitats or temperature buffering, and the regional climate directly by regulating the water and energy exchanges with the lowest levels of the atmosphere. On the other side, regional climate has a strong impact on intra-canopy microclimate, especially in the context of climate change, by reducing temperature gradients or by controlling the vegetation phenology. Despite this apparent strong imbrication, intra-canopy microclimates are very poorly represented in Land Surface Models (LSMs) and climate models in general, making it complicated to study their impact on climate change mitigation or the impact of climate change on the forests and their microclimates. Because of their time computing requirements, LSMs usually prefer simple models such as the “Big-Leaf” representation. However, in front of the urgent need to represent complex ecosystems and microclimates in Earth system models, first steps in this direction can be made, especially to improve the energy and water fluxes in the soil-vegetation-atmosphere continuum. This study presents recent developments made in the ORCHIDEE LSM. Two models have been implemented in ORCHIDEE in order to move from the current big leaf approach at the grid-cell scale to a representation of vertical gradients associated to the microclimate. To do so, firstly, a representation of the water flow in the soil-plant-atmosphere continuum through a hydraulic architecture model has been introduced. Secondly, a previous multi-layer energy budget representation, including turbulent vertical exchanges within the canopy, has been updated to make it operational with the current trunk of ORCHIDEE. Those two models enable a better representation of the intra-canopy leaf-atmosphere exchanges at the Plant Functional Type (PFT) level. Lastly, a representation of the sub-grid heterogeneity is also being implemented enabling a global representation of each PFT intra-canopy microclimates. This presentation will mainly focus on the multi-layer energy budget representation and its applications for different ecosystems at larger scale. Firstly, a comparison between ORCHIDEE and the forest model MuSICA (Ogée et al. (2003)) was performed over several forest sites highlighting the potential benefits as well as the difficulties of modelling the vertical gradients of temperature, wind and humidity within the canopy. Secondly, a first large scale representation of intra-canopy microclimate and its impact on ORCHIDEE energy and water budgets will be presented. Finally, opening perspectives induced by those developments in the ORCHIDEE LSM will be drawn. 

How to cite: Alléon, J., Ottlé, C., Vuichard, N., Luyssaert, S., Bouwen, K., Ogée, J., and Peylin, P.: First steps towards modelling the intra-canopy microclimate in the ORCHIDEE Land Surface Model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17152, https://doi.org/10.5194/egusphere-egu24-17152, 2024.

14:25–14:35
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EGU24-10808
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ECS
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On-site presentation
Klara Bouwen, Jean-Christophe Domec, Marie Charru, and Jérôme Ogée

Forest canopies can buffer or amplify macroclimate temperature extremes in their understory depending on structural and ecological parameters such as canopy height, canopy openness, and species composition. Forest management practices that alter these parameters have a strong impact on understory temperature extremes, with potential repercussions on forest resilience to climate change.

Physics-based microclimate models offer a means to explore the effects of forest canopy structure on understory temperatures. Compared to empirical models, they allow to extrapolate results outside the range of canopy structure and climatic conditions that have been observed so far. Although physics-based models may differ in their representation of soil-vegetation-atmosphere interactions, they all rely on a priori knowledge of meteorological data above the forest (also called climate forcing), including air temperature, relative humidity and wind speed timeseries. This raises challenges when conducting sensitivity analyses on structural parameters because canopy structure influences the microclimate not only inside and below the forest canopy but also above it. Employing the same climate forcing for all scenarios of canopy structure is thus deemed inappropriate and adjustments of climate forcing must be accounted for.

In this study, we propose a new physics-based modelling approach to perform sensitivity analyses of canopy structure on understorey microclimate that incorporates the feedback of a change in canopy structure on the climatic conditions above it. This approach relies on existing theories on the similarity of turbulent flux-gradient relationships within the atmospheric surface boundary layer between different scalars (e.g. air temperature and humidity) and wind speed, adapted to rough surfaces such as forest canopies. This approach is tested against datasets collected in various forest ecosystems across Europe and applied to explore the impact of canopy structure, in particular canopy density and clumping, on understory microclimate. Our approach will advance our understanding of the intricate relationships between canopy structure, boundary layer dynamics and microclimate, offering insights for more effective forest management strategies.

How to cite: Bouwen, K., Domec, J.-C., Charru, M., and Ogée, J.: The impact of forest canopy structure on the understory microclimate: a physics-based approach and sensitivity analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10808, https://doi.org/10.5194/egusphere-egu24-10808, 2024.

14:35–14:45
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EGU24-10235
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On-site presentation
Kim Novick, Mallory Barnes, and Pierre Gentine

Temperature and vapor pressure deficit (VPD) are fundamental drivers of plant ecophysiological function, and developing conceptual and predictive frameworks describing how photosynthesis, stomatal conductance, and transpiration respond to (and modify) these drivers is an long-standing research challenge. At the plant- and ecosystem-scale, much of our understanding of these processes has been derived by linking whole plant responses (e.g. from flux towers, sap flow, etc) to the temperature and VPD of the air measured some horizontal or lateral distance away from the plants themselves. However, thermodynamic processes frequently promote large gradients between canopy leaf and air temperatures, with tremendous variations across vertical and horizontal gradients. Here, we will synthesize observations from >100 flux towers to show that this difference can amount to 10 degrees C (or more), especially on hot summer days when heat impacts are most deleterious. The gradient between canopy and air temperature is not well explained by plant functional type, albedo, or climate, but are clearly related to canopy height and the dynamics of evapotranspiration. These profound differences in canopy versus air temperature translate into large (e.g. >5 kPa) differences between the VPD of the air and the vapor pressure differences experienced by leaves. Empirically derived sensitivities of stomatal conductance and photosynthesis to VPD are likely overestimated when the VPD of the air is used as a proxy for the vapor pressure difference experienced by plants. These biases can obscure our species-level understanding of how gas exchange responds to VPD and become especially problematic when observed sensitivities are compared with theoretical expectations or implemented in models that do not account for VPD gradients. We will conclude by discussing some strategies to limit these biases in field settings. 

How to cite: Novick, K., Barnes, M., and Gentine, P.: Large and problematic gradients in temperature and VPD in field research settings, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10235, https://doi.org/10.5194/egusphere-egu24-10235, 2024.

Microclimate in vegetation canopies: radiative exchange processes
14:45–14:55
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EGU24-10542
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ECS
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Virtual presentation
Vincyane Badouard, Philippe Verley, and Grégoire Vincent

Environmental heterogeneity occurring at small-spatial scale strongly influences the structure, composition, and functioning of tropical rainforests. Environmental filters particularly influence the establishment and survival of young individuals. The relative importance of different micro-environmental variables in shaping tree species distributions through their habitat preference and their regeneration niche however remains poorly known, due in particular to methodological limitations in the characterisation of the small-scale abiotic environment. In this study, we propose to address this knowledge gap and methodological limitation by using the latest LiDAR technology. LiDAR has already proven its ability to describe the 3D forest structure and topography on a fine scale. Forest structure and topography already allowed the prediction of important micro-climatic components for trees and notably light and associated air temperature and moisture as well as local drainage regime. LiDAR technology may also contribute to the prediction of other conditions essential to plant life: soil temperature, water and nutrient access. The LiDAR acquisition methods currently used to map forest structure have some limitations. Standard airborne laser scanning fails to describe the lower canopy in sufficient detail due to occlusion by the upper canopy. Here we explore the potential of low altitude high power laser with enhanced penetration to describe the structure of the forest understorey. We use the recorded laser pulse extinction to build a 3D model of light transmission through the canopy. We evaluate the capacity of the light transmission model to predict microclimatic variables which were monitored in the understorey for 10mo. We also derive a fine resolution digital terrain model from the airborne laser data and explore how soil characteristics covary with topographic features extracted from the DTM.

How to cite: Badouard, V., Verley, P., and Vincent, G.: Using high penetration airborne LiDAR scanning to characterise the micro-environment of dense tropical forest., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10542, https://doi.org/10.5194/egusphere-egu24-10542, 2024.

14:55–15:05
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EGU24-1767
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ECS
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On-site presentation
Emma Van de Walle, Steven De Hertog, Félicien Meunier, Kim Calders, Pieter De Frenne, Zhizhi Yang, Michiel Stock, Francis wyffels, Louise Terryn, Pieter Sanczuk, Tom E. Verhelst, and Hans Verbeeck

Studying the feedback between forest structure and the environment, particularly below canopies, is crucial for sustainable forest management, biodiversity conservation, and climate mitigation. Advanced vegetation models play a key role in unraveling the complex interaction between forest composition and environmental conditions, as these allow to understand the dynamics of ecosystems by simulating the interactions between plant species and their environment. An essential aspect necessitating refinement in these models is understanding how radiation interacts with intricate structures like forest canopies.

In this study, we employ advanced terrestrial laser scanning techniques, distributed fiber-optic, and microclimate sensors to investigate the relationships between light, microclimate, carbon cycling, and forest structure in temperate forests. In a temperate forest in Belgium, we implemented a sensor setup since March 2023. It comprises a Distributed Temperature Sensing (DTS) fiber, Temperature and Moisture Sensor (TMS) microclimate loggers, SurveyTag microclimate loggers, Photosynthetic Active Radiation (PAR) sensors, and pyranometer (direct/diffuse) light sensors along a 135 m long transect from forest edge to core. Monthly 3D terrestrial laser scanning (TLS) of the transect allowed us to quantify forest structure with high spatiotemporal resolution.

Preliminary results reveal distinct microclimate gradients along the transect and seasonal changes in forest structure in 3D space, including budding and changes in canopy volume. These findings will be used to calibrate and improve existing radiative transfer models (RTMs) to be further implemented in vegetation models. Integrating observations and model parameters in a common framework will provide breakthrough insights into the feedbacks between light, forest structure, microclimate, and their impact on the carbon cycle in temperate forests.

How to cite: Van de Walle, E., De Hertog, S., Meunier, F., Calders, K., De Frenne, P., Yang, Z., Stock, M., wyffels, F., Terryn, L., Sanczuk, P., Verhelst, T. E., and Verbeeck, H.: Quantifying and modelling feedbacks between forest structure, light, microclimate and carbon cycling in temperate forests, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1767, https://doi.org/10.5194/egusphere-egu24-1767, 2024.

15:05–15:15
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EGU24-5471
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ECS
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On-site presentation
Megan Stretton, Tristan Quaife, Phil Wilkes, and Mathias Disney

Despite terrestrial vegetation being one of the largest carbon sinks, it’s representation within weather and climate models is simple due to computational and data constraints. Whilst the representation of many processes has been improved, the absorption of light by vegetation canopies is still described using the assumption of a plane-parallel turbid medium, which is not realistic. This approach assumes randomly distributed leaves, with no horizontal or vertical variability, and a flat canopy base. However, it is widely used as it permits the radiative transfer for vegetation to be described using a two-stream model (Sellers, 1985) that can be solved analytically.

This work examines the importance of including realistic vegetation structure in photosynthesis calculations, testing the sensitivity of modelled Gross Primary Productivity (GPP) to the common turbid-media approximation by using detailed forest canopy information. We derive a methodology for calculating GPP from radiative transfer calculations from a high-resolution, computationally demanding, radiative transfer model, DART (Discrete Anisotropic Radiative Transfer). The GPP calculation  is based upon the photosynthesis scheme from the JULES (Joint UK Land Environment Simulator) land surface model. We explore the impacts of structure on GPP for six real forest canopies, from across the globe using 3D vegetation data collected using Terrestrial Lidar Scanning (TLS). The use of a 3D radiative transfer model allows us to investigate how much difference the two-stream approach introduces compared to detailed forest canopies with different levels of structure. We examine the profiles of both the absorbed radiation (fAPAR) and GPP.

Across the six forest scenes used, there is generally a reduction in GPP as more structure is introduced. However, this is particularly the case in scenes where the horizontal variation of LAI is high. Additionally, in these scenes, we find that this increase in GPP is less pronounced at low sun angles. This work suggests that consideration should be taken in incorporating horizontal variability of the vegetation within weather and climate models, particularly when identifying the effects of forests on the global carbon budget.

How to cite: Stretton, M., Quaife, T., Wilkes, P., and Disney, M.: The impact of forest canopy structure on modelled photosynthesis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5471, https://doi.org/10.5194/egusphere-egu24-5471, 2024.

Microclimate in vegetation canopies: implication for species distribution
15:15–15:25
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EGU24-13257
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Highlight
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Virtual presentation
Helena Hespanhol and the BryoMicroClim

Significant mismatches between macro- and microclimates challenge our ability to accurately estimate the climatic conditions experienced by organisms and thus to predict responses to climate change. This study aims to evaluate the relationship between macro- and microclimate for small-scale plants such as bryophytes, which are highly dependent on local environmental conditions.

To achieve this, we established a Europe-wide collaborative network of bryologists (the BryoMicroClim project), to measure the microclimate experienced by a bryophyte species. The moss Hedwigia striata, evaluated as near-threatened in Europe (Hodgetts et al., 2019), was selected as the target species. This species grows mainly in forests or rocky areas. We selected 15 sampling sites across Europe, spanning a wide range of climate conditions (Portugal, Spain, France, Belgium, Wales, Scotland, and Sweden). In each site, mostly continuous forested areas, we measured air temperature and humidity using three dataloggers (Envloggers, Environmental loggers) installed near H. striata populations. In the Iberian Peninsula, we also installed other dataloggers (BtMs, Bryolichen Temperature Moisture), specifically designed to measure ambient temperature, humidity, and water content of nonvascular cryptogams.

We used the slope and equilibrium approach (Grill et al., 2022) to infer if the microclimate temperature and relative humidity variability (as measured by the in-situ dataloggers) is buffered or amplified in relation to the macroclimate variability (from ERA5-Land and ERA5 data). We observed that microclimate temperatures were buffered or amplified depending on site conditions. As hypothesized, microclimate temperatures had a buffered variability in dense forest sites. Our results suggest that collecting bryophyte-relevant microclimate data at fine spatial resolutions and long time scales will be critical to better understand the potential vulnerability of bryophytes to climate change.

How to cite: Hespanhol, H. and the BryoMicroClim: BryoMicroClim: Collecting bryophyte-relevant microclimate data to assess the gap between macro- and microclimate , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13257, https://doi.org/10.5194/egusphere-egu24-13257, 2024.

15:25–15:35
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EGU24-4103
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Highlight
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Virtual presentation
Koenraad Van Meerbeek and Stef Haesen

In recent decades, species distribution models (SDMs) have become pivotal in forecasting how changing environmental conditions impact species distributions across space and time. Most SDMs rely on correlations, utilizing statistical or machine-learning techniques to infer links between species occurrences and their environment. Typically, these models rely on a traditional set of bioclimatic variables, often available at a coarse spatial resolution of 30 arc seconds or less. These macroclimatic data are derived through interpolating weather station data, essentially reflecting the free-air temperature conditions in open ecosystems. However, a significant portion of terrestrial life on Earth and many critical ecological processes respond to climate conditions at much finer scales beneath the canopies of trees. Neglecting this mismatch might lead to inaccurate predictions, misinterpretations, and potentially flawed conservation decisions. Hence, there's a pressing need to incorporate finer-scale microclimate data in ecological modelling to ensure more accurate assessments and informed conservation strategies.

By developing an innovative spatial machine learning model capable of quantifying the temperature buffering capacity of European forests at very fine resolutions, we crafted the ForestClim database, containing a novel set of bioclimatic variables. These variables unveil the intricate microclimatic temperature variations within forest ecosystems, marking a significant scientific breakthrough that shows promise to enhance ecological models and predictions. Furthermore, by freely sharing this data, we lower the threshold for fellow ecologists to incorporate pertinent microclimatic information into their research.

Leveraging the open-access ForestClim database, we further assessed how large-scale, gridded microclimate temperature data affect the accuracy of SDMs of European forest plant species and how their modelled environmental niches and projected geographic ranges differ from conventional SDMs. The study's findings demonstrate that SDMs based on microclimate significantly outperform their macroclimate-based counterparts. They also reveal the introduction of a systematic bias in thermal response curves when relying on macroclimate-based models, potentially leading to inaccuracies in forecasting range shifts. Furthermore, the inclusion of microclimate data in these models enables the identification of microrefugia within the landscape - areas where species can find a stable and suitable climate amid unfavourable, changing macroclimatic conditions. This newfound information holds particular significance in the realm of conservation science, as microclimate-based SDMs prove to be valuable tools for gaining insights into biodiversity conservation in the face of climate change. This is especially pertinent given the increasing policy and management emphasis on conserving refugia worldwide.

How to cite: Van Meerbeek, K. and Haesen, S.: Fine-scale microclimate data improve species distribution models of forest plant species, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4103, https://doi.org/10.5194/egusphere-egu24-4103, 2024.

15:35–15:45
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EGU24-4745
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Virtual presentation
Jonas Lembrechts and SoilTemp network

Recent research has shown that the impacts of climate change on terrestrial species distributions are more complex than expected. Species distributions are showing significant delays in responses, or have shifted in unexpected directions. Scientists have identified several mechanisms that could explain these mismatches, including slow population dynamics, habitat fragmentation, and biotic interactions that limit the spread of species. Yet, one crucial aspect remains largely overlooked: we first need relevant high-resolution baseline climate change data to accurately answer this question.

Indeed, organisms respond to microclimate change, which can differ significantly from macroclimate change. We know that local temperatures near the ground or below vegetation can be several degrees different from weather station data. However, it remains a mystery how quickly these microclimates are changing, as this depends as much on climate change as on land use changes.

In this talk, we will explore how the SoilTemp-database, a global database of more than 75,000 in-situ measured microclimate time series, can be used to improve global microclimate products and ultimately provide better estimates of microclimate change. By applying these products to improve our estimates of species distributions, we can better understand the impacts of climate change on biodiversity, crucial for adjusting biodiversity management to a rapidly changing world.

How to cite: Lembrechts, J. and network, S.: Microclimate change: the hidden driver of species redistributions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4745, https://doi.org/10.5194/egusphere-egu24-4745, 2024.

Posters on site: Wed, 17 Apr, 10:45–12:30 | Hall X1

Display time: Wed, 17 Apr 08:30–Wed, 17 Apr 12:30
Chairpersons: Gabriel Hes, Jerome Ogee, Rosie A. Fisher
X1.32
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EGU24-74
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ECS
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Gabriel Hes, Inne Vanderkelen, Rosie A. Fisher, Jérôme Chave, Jérôme Ogée, and Edouard Davin

The forest understory generally experiences temperature variations that are dampened compared to adjacent open areas (known as the “buffering effect”), allowing the development of a forest microclimate and associated ecological conditions. It is however unclear to what extent forests will maintain this buffering effect under increasing global warming. Providing reliable projections of future forest microclimates is therefore crucial to anticipate climate change impacts on forest biodiversity, and to identify corresponding conservation strategies. Recent empirical studies suggest that the buffering of air temperature extremes in forest understory compared to open land could increase with global warming, albeit at a slower rate than macroclimate temperatures. Here, we investigate the trend of this temperature buffering effect in a high-emission global warming scenario, using the process-based Land Surface Model CLM5.1. We find biome-dependant buffering trends with strongest values in tropical forests where buffering increases for every degree of global warming by 0.1 °C for maximum soil temperature, and by 0.2 °C for maximum canopy air temperature. In boreal regions, forest microclimate exhibits a strong seasonality and the effect of global warming on forest understory is less clear. This first Land Surface Model assessment of future forest microclimate highlights the specific importance of tropical forest canopies in particular, in maintaining hospitable conditions for understory species while also increasing their climate debt under global warming. Our research also illustrates the potential and limitations of Land Surface Models to simulate forest microclimate, and calls for further collaborations between Earth system modelers and ecologists to jointly question climate and biosphere dynamics.

How to cite: Hes, G., Vanderkelen, I., Fisher, R. A., Chave, J., Ogée, J., and Davin, E.: Future scenarios of forest microclimates using a Land Surface Model., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-74, https://doi.org/10.5194/egusphere-egu24-74, 2024.

X1.33
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EGU24-4647
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ECS
Ching-Hung Shih and Min-Hui Lo

Diurnal hysteresis, characterized by a time lag or phase difference between diurnal cycles of two variables, provides valuable insights into land-atmosphere interaction and ecological processes. While it is widely accepted that diurnal surface temperature and relative humidity variations are inversely locked in phase, recent studies have reported diurnal hysteresis between relative humidity and temperature. This phenomenon arises from contributions related to diurnal water vapor variation resulting from local evapotranspiration and water vapor advection from other regions. This study employed a multi-linear regression approach to quantify the phase lag time between temperature and relative humidity by distinguishing linear and non-linear contributions of diurnal temperature variation to relative humidity. Our analysis utilized data from the FLUXNET2015 dataset, which offers ecosystem-scale meteorological measurements worldwide, the HadISD dataset, providing quality-controlled surface weather data globally, and ERA5-Land, offering finer-scale and accurate land reanalysis data on a global scale, to explore the regions exhibiting diurnal hysteresis globally. Our findings reveal the presence of diurnal hysteresis between relative humidity and temperature in coastal, lakeside, and montane regions, notably in New Guinea, southwestern Arabia, the Andes, and the Himalayas. In these regions, the vapor pressure deficit (VPD) is mitigated due to the out-of-phase diurnal relationship between temperature and relative humidity, leading to a smaller underestimation bias in daily VPD when estimated by daily temperature and relative humidity. Even though lower VPD might reduce evapotranspiration in regions showing diurnal hysteresis due to decreased atmospheric demand, the non-local moisture transport provides these regions with additional water vapor. This counters the temperature rise in the morning and aids in sustaining the diurnal hysteretic relationship, maintaining the VPD mitigation in these regions. Furthermore, climate change is likely to change the diurnal hysteretic relationship, posing a threat to VPD mitigation. This study underscores the importance of identifying regions with diurnal hysteresis and highlights the potential implications of changing diurnal hysteretic relationships on local microclimates.

How to cite: Shih, C.-H. and Lo, M.-H.: The Role of Diurnal Hysteresis between Near-surface Temperature and Relative Humidity on Mitigating Near-surface Atmospheric Dryness, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4647, https://doi.org/10.5194/egusphere-egu24-4647, 2024.

X1.34
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EGU24-6794
Loren White

Connections between microclimate and ecological systems are widely recognized. Recently, the relevance of microclimate to ecological microrefugia has been highlighted in relation to endangered species and relict habitats under changing large-scale climate forcing and anthropogenic habitat losses. While truly undisturbed natural environments are rare, the broader category of non-urban vegetated land is much more widespread globally than urban surfaces. Therefore within-canopy microclimatic processes are globally important for interactions with the macroclimate. Aside from local topographic and hydrologic forcing, the structure, phenology, and behavior of vegetation canopies (forest, woodland, shrub, grassland) interact with radiative, wind, and evapotranspiration processes to modulate and drive site microclimate. To effectively sample the spatiotemporal characteristics of microclimates, it is suggested that numerical modelling, mobile transects, and surface parameters (terrain, vegetation) should be used to design measurement strategies. In particular, the very high spatial resolution of within-canopy measurements from mobile pedestrian measurements are relevant to compare spatial variations to forcing from vegetation cover, terrain, and surface moisture.

A series of microscale measurements of temperature, humidity, and radiation has been launched using a pedestrian mobile system previously developed in the CHEESEHEAD2019 field campaign, in tandem with strategically located stationary sensors over a variety of environments. The initial five sites are located in upland, floodplain, and riverine areas of Mississippi. Other sites with greater topographic relief will be investigated in Maryland and Missouri.

How to cite: White, L.: Spatial and Temporal Patterns of Vegetated Microclimates from Synergistic Mobile and Stationary Measurements, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6794, https://doi.org/10.5194/egusphere-egu24-6794, 2024.

X1.35
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EGU24-3637
Jerome Ogée, Marion Walbott, Adrià Barbeta, Emmanuel Corcket, and Yves Brunet

Riparian corridors often act as low-land climate refugia for temperate tree species in their southern distribution range. A plausible mechanism is the buffering of regional climate extremes by local physiographic and biotic factors. To test this idea, we deployed over 3 years a network of 39 microclimate sensors along the Ciron river, a refugia for European beech (Fagus sylvatica) in southwestern France. Sensor locations spread along the main geomorphological landscapes, vegetation types and microtopographic situations. Across the whole network, canopy gap fraction was the main predictor for spatial microclimatic variations. Two landscape features (elevation above the river and woodland fraction within a 300m radius) were also strong predictors, while geographical variables such as altitude or distance to the river mouth were marginally important, and mainly contributed to explain offsets in winter and spring minimum temperature. However, within the riparian forest only (canopy gap fraction < 25%, distance to the river < 150m), variations of up to -4°C and +15% in summertime daily maximum air temperature and minimum relative humidity, respectively, were still found from the plateau to the cooler, moister river banks, only ~5-10m below. Elevation above the river was then identified as the main predictor, and explained the marked variations from the plateau to the banks much better than canopy gap fraction. The microclimate measured near the river is as cool but moister than the macroclimate encountered at 700-1000m asl further east in F. sylvatica's main distribution range. Indeed, at all locations, we found that air relative humidity was much higher than expected from a temperature-only effect, suggesting that extra moisture is brought by the river. Such strong microclimatic influence of fine-scale topography and river moisture may well explain the distribution of beech trees in this riparian refugium, restricted to the river gorges where microtopographic variations are the strongest.

How to cite: Ogée, J., Walbott, M., Barbeta, A., Corcket, E., and Brunet, Y.: Decametric-scale buffering of climate extremes in forest understory within a riparian microrefugia: the key role of microtopography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3637, https://doi.org/10.5194/egusphere-egu24-3637, 2024.

X1.36
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EGU24-8229
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ECS
Johanna Lehtinen, Juha Aalto, and Miska Luoto

Microclimates have recently been emphasized for their key role in shaping local ecosystems. Their profound impact on species distributions and ecosystem dynamics are increasingly recognized. The variations in temperature, humidity, and other climatic factors within microenvironments may be important for the adaptability and resilience of diverse species. For example, in warming climate, cold-adapted species can occur and persist in cool microclimate pockets beyond their macro-climatic ranges.

In this study, we explore the spatial and temporal variations of cool microclimates at the forest-tundra ecotone, situated at 68° N latitude in the Pallas region, northern Finland. This study seeks to identify the locations and factors influencing the persistence and spatial structuring of cool microclimatic pockets. We build our study on continuous in-situ near-surface temperature measurements during peak growing season from 193 study sites, representing diverse topographical settings, soil conditions, vegetation types and land covers such as peatlands.

We generated microclimate surfaces at a spatial resolution of 10m using statistical multivariate modelling. This process allowed for the mapping of cool microclimates throughout the entire study area.

The results showed the versatility of temperature variations in the landscape. The average daily minimum temperatures in July ranged between 3.7° C and 8.8° C, whereas the average daily maximum temperatures ranged between 15.5° C and 24.5° C, respectively. During the coldest period of the day, typically nighttime, the coolest areas were open wetlands in the bottoms of valleys, whereas during the warmest period of the day, typically afternoon, the coolest areas were the shaded hill slopes with poleward aspects and characterized by coniferous forests. The cool microclimates during nighttime were strongly driven by the cold air pooling into low-elevation areas and the intense long-wave radiative cooling in treeless environments. In contrast, the daytime cool microclimates were determined by the interactive effect of low short wave-solar radiation conditions on north-facing slopes and the dense canopies of mature spruce forests. Cool microclimates exhibited connected spatial patterns both during the nighttime and daytime, but due to different driving factors, these patterns rarely overlapped.

Our results offer novel understanding on the spatiotemporal variation and drivers of cool microclimates in topographically versatile boreal-tundra ecotone. We expect this information to be important in highlighting the significance of cool microclimates for the persistence of cold-adapted species under climate change across high-latitude ecosystems.

How to cite: Lehtinen, J., Aalto, J., and Luoto, M.: Spatiotemporal variation and drivers of cool microclimates in high-latitude ecosystems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8229, https://doi.org/10.5194/egusphere-egu24-8229, 2024.

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EGU24-5277
Sandra Słowińska, Michał Słowiński, Jarosław Baranowski, Arkadiusz Bartczak, Kaja Czarnecka, Agnieszka Halaś, Anna Jarocińska, Joanna Kaczorowska, Adrian Kaszkiel, Patrycja Kowalczyk, Magdalena Kuchcik, Katarzyna Lindner-Cendrowska, and Dominika Łuców

Peatlands often function as glacial microrefugia, as shown by palaeoecological research and the contemporary occurrence of glacial species (e.g. Betula nana). The bogs and poor fens of Poland’s lowlands that we will focus on are islands of the young glacial landscape, which were mainly preserved within forests. Although microclimatic conditions have been identified as one of the most supportive factors for peatland microrefugia functioning, they have not yet been recognized on a larger scale.

In response to this need, in 2023 we initiated the MIRECLIM project, which aims to comprehensively investigate the climatic functioning of numerous mid-forest bogs and poor fens in Poland. 

As multiple feedback mechanisms influence microclimatic conditions, our research will consider meteorological conditions, peatland characteristics, conservation measures, and their surrounding environment. We will also assess the impact of peatland overgrowth due to hydrological disturbance on microclimate, the rate of organic matter decomposition, moss growth and the corresponding changes in the composition of the testate amoeba communities. These indicators serve as valuable proxies for inferring moisture dynamics of peatlands in palaeoecological research.

Our studies will be carried out in a multi-scale approach, from in situ measurements to the analysis of multispectral satellite images Sentinel-2 and Landsat. Measurements will be carried out for at least the next three years, so we encourage all interested people to participate.

One of the significant outcomes of our project will be the development of the MIRECLIM database. It will also serve as a platform to integrate the data obtained from the in situ field measurements with analysed satellite imagery. Another important aspect of our project will be to educate children and local communities about the importance of peatlands as key ecosystems for climate change mitigation, both globally and locally.

Research carried out as part of research project number 2022/45/B/ST10/03423 financed by the National Science Center in Poland.



How to cite: Słowińska, S., Słowiński, M., Baranowski, J., Bartczak, A., Czarnecka, K., Halaś, A., Jarocińska, A., Kaczorowska, J., Kaszkiel, A., Kowalczyk, P., Kuchcik, M., Lindner-Cendrowska, K., and Łuców, D.: Climatic functioning of peatlands in the context of microrefugia - the MIRECLIM project, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5277, https://doi.org/10.5194/egusphere-egu24-5277, 2024.

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EGU24-6671
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ECS
Andreas Hanzl, Karun Dayal, Kim Calders, and Cornelius Senf

Forest microclimates play an essential role in biodiversity because they buffer temperature extremes and, thus, the impacts of climate change. Yet, our understanding of the small-scale spatial variation in forest microclimate remains vague. This knowledge gap is mainly caused by existing sampling designs capturing large-scale gradients (e.g. elevation gradients, successional gradients) instead of small-scale variation within a site. To bridge this gap, we established eight 1-hectare intensive measurement sites across a diverse gradient of Central European forests, from Atlantic lowland forests in Belgium to mountain forests in Southern Germany. Each site is stocked with 16 microclimate loggers recording temperature and soil moisture on a regular grid. We further quantified forest structure within each site using terrestrial laser scanning, offering a detailed representation of plant material distribution in all three dimensions. This setup allowed us to thoroughly examine spatial variability in microclimates within and between forest types and how variations in microclimates are linked to forest structure across variable spatial scales. Our initial findings show that logger-specific linear regressions between site-average temperature and microclimate temperature had very good fits (mean R2 = 0.98, ranging from 0.85 to 1.00). The standard deviations of regression slopes per site ranged from 0.03 to 0.11 (mean of 0.06), indicating that all sites experienced substantial variation in microclimates at a spatial scale of 20 m. Higher spatial microclimate variability was thereby correlated with higher variability in forest structure. In the next step, we will predict local microclimate variation from structural predictors (i.e. plant area index, height, canopy complexity) at variable spatial scales (from 1 to 20 m), allowing for a more detailed assessment of how microclimate variability scales across space. Hence, our research provides a new and valuable perspective on forest microclimates by specifically considering small-scale spatial variability.

How to cite: Hanzl, A., Dayal, K., Calders, K., and Senf, C.: Exploring microclimate variability across spatial scales, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6671, https://doi.org/10.5194/egusphere-egu24-6671, 2024.

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EGU24-17695
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ECS
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Nathan Corroyez, Sylvie Durrieu, Jean-Baptiste Féret, and Jérôme Ogée

Refined modeling of the links between microclimate and canopy properties is needed to identify more resilient forest management practices addressing challenges raised by climate change. These practices should foster the temperature-buffering role of forest canopies, with a positive impact on multiple ecosystem services linked to biodiversity, biogeochemical cycles, and recreational services, among others.


Leaf area index (LAI) is an important input variable for state-of-the-art microclimate models. However, accurately measuring this biophysical variable in the field is challenging due to both technical and logistical difficulties. Relying on Earth observation data and processing techniques currently available appears as a promising solution to extend LAI assessment over space and time.


Standalone methods can be used to assess LAI from data acquired with different types of remote sensing sensors with advantages and limitations identified for each sensor in an operational perspective. Airborne Light Detection And Ranging (LiDAR) technology captures detailed information about forest structures at a very high spatial resolution. However, the high cost of acquisitions limits its use for monitoring LAI dynamics over extended areas. Multispectral satellite imagery provides information on vegetation properties over extended areas, with frequent revisit and fine spatial resolution. However, the signal is known to saturate with high LAI values, which prevents accurate assessment of the LAI in dense canopies. Multi-sensor approaches have the potential to help reduce the uncertainty associated with estimates of the canopy properties and alleviate the limitations of individual sensors.


Intending to improve input data for microclimate models, we developed a framework to better understand the differences between LAI estimated from either Sentinel-2 multispectral imagery or LiDAR data and further introduced a method to improve LAI assessment based on the combination of both data types. The study site is the French National Forest of Mormal, a lowland broadleaved forest located in northern France.


First, forest Plant Area Density (PAD) profiles were derived from data from a single leaf-on airborne LiDAR survey over the forest. From the profiles, Plant Area Indexes (PAI) corresponding to vegetation layers of different depths are assessed. Then we parameterized physical model inversion based on the PROSAIL model to assess LAI from Sentinel-2 canopy reflectance and optimize the correlation with LiDAR-derived PAI. Multiple strategies are currently explored to optimize this parameterization. The several sets of PAI are compared and the potential sources of discrepancies (e.g., height, cover heterogeneity) are analyzed.


In the next step, a deep learning model fusing LiDAR and Sentinel-2 data (including reflectance and higher-level products) will be developed. A domain-specific network architecture will be implemented for each data source, followed by the fusion of each network to assess the LAI. Results will be validated using digital hemispherical photographs (DHPs).


This study is part of the ANR MaCCMic project, which aims to develop new tools to help managers increase the resilience of forests and promote the ecological, recreational, and climatic services they offer.

How to cite: Corroyez, N., Durrieu, S., Féret, J.-B., and Ogée, J.: Combining LiDAR and Sentinel-2 Data to Improve Leaf Area Index Assessment in Forest and Refine Understory Microclimate Models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17695, https://doi.org/10.5194/egusphere-egu24-17695, 2024.

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EGU24-19177
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ECS
Kasper Coppieters, Hans Verbeeck, Marco Visser, Stefan Schnitzer, and Félicien Meunier

Lianas are an iconic and important feature of tropical forests. On average, they represent about 24 percent of the woody stems and they contributie significantly to the total leaf area. Their abundance increases with increasing seasonality, and they are able to keep their leaves for a longer period in the dry season. Their abundance in the neotropics has been increasing in the last decades. Lianas have a negative impact on the carbon storage of forests by reducing individual tree growth and increasing tree mortality and turnover. However, their impact on the energy balance of the forest, and the forest understory microclimate in particular, is poorly understood. To fill this gap, we installed two experimental setups in a 12-year, ongoing liana removal experiment on Gigante, Panamá. We installed 180 TOMST TMS-4 microclimate sensors in 8 removal and 8 control plots to monitor the microclimate temperature and soil moisture. Next to that, we installed  ~24 pyranometers and photosynthetic actieve radiation (PAR) sensors in a subset of two removal and two control plots, both horizontally, at 1 meter above the soil, and vertically in the canopy. Our findings revealed that lianas buffer the forest microclimate more than trees, leading to an average midday temperature reduction of 0.2°C at the soil surface (measured 15 cm above the soil). The effect increased at higher temperatures during the dry season (temperature reduction up to 0.35°C on the maximum temperature in the forest). For half of the plots, we were able to account for the impact of forest density and structure on the microclimate using simultaneously collected TLS (terrestrial laser scanning) and ALS (aerial laser scanning) data. Lianas likely reduce soil understory temperatures by reducing the amount of solar radiation that penetrates the forest canopy or by reflecting more light back into the atmosphere.

How to cite: Coppieters, K., Verbeeck, H., Visser, M., Schnitzer, S., and Meunier, F.: Lianas buffer tropical forest understories, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19177, https://doi.org/10.5194/egusphere-egu24-19177, 2024.