@misc{SzymczakBarthBendixetal., author = {Szymczak, Sonja and Barth, Johannes A. C. and Bendix, J{\"o}rg and Huneau, Fr{\´e}d{\´e}ric and Garel, Emilie and H{\"a}usser, Martin and Juhlke, Tobias R. and Knerr, Isabel and Santoni, S{\´e}bastien and Mayr, Christoph C. and Trachte, Katja and Geldern, Robert van and Br{\"a}uning, Achim}, title = {First indications of seasonal and spatial variations of water sources in pine trees along an elevation gradient in a Mediterranean ecosystem derived from δ18O}, series = {Chemical Geology}, volume = {2020}, journal = {Chemical Geology}, number = {549}, doi = {10.1016/j.chemgeo.2020.119695}, abstract = {Water availability is the most important factor for the vitality of forest ecosystems, especially in dry environments. The Mediterranean region is one of the hotspots of future climate change; therefore, data on the water cycle are urgently needed. We measured oxygen isotope compositions in creek water, precipitation, stem water, needle water, and tree-ring cellulose over one growing season to establish the relationship between isotope compositions in different compartments along a fractionation pathway. We analyzed plant material from pine trees (Pinus nigra J.F. Arn subsp. laricio (Poiret) Maire var. Corsicana Hyl. and Pinus pinaster Aiton) at five locations along an elevation gradient from sea level to 1600 m asl. We traced back the oxygen isotope composition from source to sink in tree-ring cellulose in order to identify the water sources used by the trees, and to quantify the extent of isotope fractionation processes. Our results showed that the trees used different water sources over the course of the growing season, ranging from winter snow meltwater to summer precipitation at higher sites and deep soil water reservoirs at coastal sites. Needle water enrichment was higher at higher elevation sites than at coastal locations, highlighting the importance of site-specific climate conditions on the isotopic composition values in tree material. Water availability seems to be most restricted at the highest site, making these trees most vulnerable to climate change.}, language = {en} } @misc{SzymczakHaeusserGareletal., author = {Szymczak, Sonja and H{\"a}usser, Martin and Garel, Emilie and Santoni, S{\´e}bastien and Huneau, Fr{\´e}d{\´e}ric and Knerr, Isabel and Trachte, Katja and Bendix, J{\"o}rg}, title = {How Do Mediterranean Pine Trees Respond to Drought and Precipitation Events along an Elevation Gradient}, series = {Forests}, volume = {7}, journal = {Forests}, number = {11}, doi = {10.3390/f11070758}, pages = {17}, abstract = {Drought is a major factor limiting tree growth and plant vitality. In the Mediterranean region,the length and intensity of drought stress strongly varies with altitude and site conditions. We usedelectronic dendrometers to analyze the response of two native pine species to drought and precipitationevents. The five study sites were located along an elevation gradient on the Mediterranean islandof Corsica (France). Positive stem increment in the raw dendrometer measurements was separatedinto radial stem growth and stem swelling/shrinkage in order to determine which part of the trees'response to climate signals can be attributed to growth. Precipitation events of at least 5 mm anddry periods of at least seven consecutive days without precipitation were determined over a periodof two years. Seasonal dynamics of stem circumference changes were highly variable among thefive study sites. At higher elevations, seasonal tree growth showed patterns characteristic for coldenvironments, while low-elevation sites showed bimodal growth patterns characteristic of droughtprone areas. The response to precipitation events was uniform and occurred within the first six hoursafter the beginning of a precipitation event. The majority of stem circumference increases were causedby radial growth, not by stem swelling due to water uptake. Growth-induced stem circumferenceincrease occurred at three of the five sites even during dry periods, which could be attributed tostored water reserves within the trees or the soils. Trees at sites with soils of low water-holdingcapacity were most vulnerable to dry periods.}, language = {en} } @misc{BendixAguireBecketal., author = {Bendix, J{\"o}rg and Aguire, Nicolay and Beck, Erwin and Br{\"a}uning, Achim and Brandl, Roland and Breuer, Lutz and B{\"o}hning‑Gaese, Katrin and Paula, Mateus Dantas de and Hickler, Thomas and Homeier, J{\"u}rgen and Inclan, Diego and Leuschner, Christoph and Neuschulz, Eike L. and Schleuning, Matthias and Suarez, Juan P. and Trachte, Katja and Wilcke, Wolfgang and Windhorst, David and Farwig, Nina}, title = {A research framework for projecting ecosystem change in highly diverse tropical mountain ecosystems}, series = {Oecologia}, volume = {195}, journal = {Oecologia}, number = {3}, issn = {0029-8549}, doi = {10.1007/s00442-021-04852-8}, pages = {589 -- 600}, abstract = {Tropical mountain ecosystems are threatened by climate and land-use changes. Their diversity and complexity make projections how they respond to environmental changes challenging. A suitable way are trait-based approaches, by distinguishing between response traits that determine the resistance of species to environmental changes and effect traits that are relevant for species' interactions, biotic processes, and ecosystem functions. The combination of those approaches with land surface models (LSM) linking the functional community composition to ecosystem functions provides new ways to project the response of ecosystems to environmental changes. With the interdisciplinary project RESPECT, we propose a research framework that uses a trait-based response-effect-framework (REF) to quantify relationships between abiotic conditions, the diversity of functional traits in communities, and associated biotic processes, informing a biodiversity-LSM. We apply the framework to a megadiverse tropical mountain forest. We use a plot design along an elevation and a land-use gradient to collect data on abiotic drivers, functional traits, and biotic processes. We integrate these data to build the biodiversity-LSM and illustrate how to test the model. REF results show that aboveground biomass production is not directly related to changing climatic conditions, but indirectly through associated changes in functional traits. Herbivory is directly related to changing abiotic conditions. The biodiversity-LSM informed by local functional trait and soil data improved the simulation of biomass production substantially. We conclude that local data, also derived from previous projects (platform Ecuador), are key elements of the research framework. We specify essential datasets to apply this framework to other mountain ecosystems.}, language = {en} } @misc{LimbergerHomeierFarwigetal., author = {Limberger, Oliver and Homeier, J{\"u}rgen and Farwig, Nina and Pucha-Cofrep, Franz and Fries, Andreas and Leuschner, Christoph and Trachte, Katja and Bendix, J{\"o}rg}, title = {Classification of Tree Functional Types in a Megadiverse Tropical Mountain Forest from Leaf Optical Metrics and Functional Traits for Two Related Ecosystem Functions}, series = {Forests}, volume = {12}, journal = {Forests}, number = {5}, issn = {1999-4907}, doi = {10.3390/f12050649}, abstract = {Few plant functional types (PFTs) with fixed average traits are used in land surface models (LSMs) to consider feedback between vegetation and the changing atmosphere. It is uncertain if highly diverse vegetation requires more local PFTs. Here, we analyzed how 52 tree species of a megadiverse mountain rain forest separate into local tree functional types (TFTs) for two functions: biomass production and solar radiation partitioning. We derived optical trait indicators (OTIs) by relating leaf optical metrics and functional traits through factor analysis. We distinguished four OTIs explaining 38\%, 21\%, 15\%, and 12\% of the variance, of which two were considered important for biomass production and four for solar radiation partitioning. The clustering of species-specific OTI values resulted in seven and eight TFTs for the two functions, respectively. The first TFT ensemble (P-TFTs) represented a transition from low to high productive types. The P-TFT were separated with a fair average silhouette width of 0.41 and differed markedly in their main trait related to productivity, Specific Leaf Area (SLA), in a range between 43.6 to 128.2 (cm2/g). The second delineates low and high reflective types (E-TFTs), were subdivided by different levels of visible (VIS) and near-infrared (NIR) albedo. The E-TFTs were separated with an average silhouette width of 0.28 and primarily defined by their VIS/NIR albedo. The eight TFT revealed an especially pronounced range in NIR reflectance of 5.9\% (VIS 2.8\%), which is important for ecosystem radiation partitioning. Both TFT sets were grouped along elevation, modified by local edaphic gradients and species-specific traits. The VIS and NIR albedo were related to altitude and structural leaf traits (SLA), with NIR albedo showing more complex associations with biochemical traits and leaf water. The TFTs will support LSM simulations used to analyze the functioning of mountain rainforests under climate change.}, language = {en} } @misc{KnerrTrachteEglietal., author = {Knerr, Isabel and Trachte, Katja and Egli, Sebastian and Barth, Johannes A. C. and Br{\"a}uning, Achim and Garel, Emilie and H{\"a}usser, Martin and Huneau, Fr{\´e}d{\´e}ric and Juhlke, Tobias R. and Santoni, S{\´e}bastien and Szymczak, Sonja and Geldern, Robert van and Bendix, J{\"o}rg}, title = {Fog - low stratus (FLS) regimes on Corsica with wind and PBLH as key drivers}, series = {Atmospheric Research}, volume = {261}, journal = {Atmospheric Research}, issn = {0169-8095}, doi = {10.1016/j.atmosres.2021.105731}, abstract = {The French Mediterranean island of Corsica is already today confronted with a clear tendency towards water shortage, leading not only to socio-economical, but also to ecological problems. A potential, but not very widespread source of water is the presence of near-ground clouds, mostly fog. In this study, we investigate fog-low stratus (FLS) frequencies in Corsica, derived from a data set of Meteosat Second Generation SEVIRI, whereby a distinction between fog and low stratus is hardly feasible using remote sensing data. The FLS frequency was studied with respect to its interaction with distinct locally-generated wind and its dependence on the planetary boundary layer height (PBLH) obtained by ERA5 reanalysis (the fifth generation of the European Centre for Medium-Range Weather Forecasts, ECMWF). Results show that radiation FLS is formed in coastal areas at sunrise, with low PBLH. On the other hand, in the interior of the island at sunset, a maximum of advection FLS is formed, fostered by locally-generated and related transport of moisture. On the east side of the island, FLS frequency is lower throughout the year due to frequent lee situations. This situation is reinforced by reduced synoptic moisture transport by westerly winds, so that westerly exposed slopes benefit from moisture input by FLS formation.}, language = {en} } @misc{HaeusserAryalBarthetal., author = {H{\"a}usser, Martin and Aryal, Sugam and Barth, Johannes A. C. and Bendix, J{\"o}rg and Garel, Emilie and Geldern, Robert van and Huneau, Fr{\´e}d{\´e}ric and Juhlke, Tobias R. and Knerr, Isabel and Santoni, S{\´e}bastien and Szymczak, Sonja and Trachte, Katja and Br{\"a}uning, Achim}, title = {Xylem formation patterns from Mediterranean to subalpine climate conditions reveal high growth plasticity of pine species on Corsica}, series = {Trees}, volume = {37}, journal = {Trees}, number = {4}, publisher = {Springer Berlin Heidelberg}, issn = {0931-1890}, doi = {10.1007/s00468-023-02402-8}, pages = {1027 -- 1039}, abstract = {Investigating seasonal wood formation is crucial to understand tree growth responses to climate impact. The present study quantifies the variability of xylogenesis along an elevation gradient on the Mediterranean island of Corsica, where two native pine species (Pinus nigra Arnold ssp. laricio Maire and Pinus pinaster Aiton) grow from the upper tree line to sea level, partly in sympatry. We extracted microcores from 35 trees at 5 sites along an East-West transect from the coasts (10 m asl) to the island's central mountain ridge (1600 m asl) during bi-weekly sampling campaigns between 2017 and 2019. We applied generalised additive models to detect radial growth differences in elevation and species along with minimum temperatures for growth initiation. We found that trees in low elevations experienced over 2 months longer growth periods with higher maximum growth rates than in high elevations. The results show a 1-month delay for the beginning of tracheid formation between the low, mid and high-elevation belts but comparable timing for its termination. At the sites where both species co-occur, P. nigra accumulates more radial cells in a shorter time than P. pinaster. Trees at the two contrasting coastal sites have similar growth period lengths, but exhibit a time shift of over a month. Minimum temperatures around growth initiation vary between 3.1 °C for P. nigra and 9.9 °C for P. pinaster. These findings emphasise the high plasticity in the growth behaviour of one of the most widespread tree genera in Mediterranean and temperate zones.}, language = {en} } @misc{MurkuteSayeedPuchaCofrepetal., author = {Murkute, Charuta and Sayeed, Mostafa and Pucha-Cofrep, Franz and Carrillo-Rojas, Galo and Homeier, J{\"u}rgen and Limberger, Oliver and Fries, Andreas and Bendix, J{\"o}rg and Trachte, Katja}, title = {Turbulent energy and carbon fluxes in an Andean Montane Forest—energy balance and heat storage}, series = {Forests}, volume = {15}, journal = {Forests}, number = {10}, publisher = {MDPI}, issn = {1999-4907}, doi = {10.3390/f15101828}, abstract = {High mountain rainforests are vital in the global energy and carbon cycle. Understanding the exchange of energy and carbon plays an important role in reflecting responses to climate change. In this study, an eddy covariance (EC) measurement system installed in the high Andean Mountains of southern Ecuador was used. As EC measurements are affected by heterogeneous topography and the vegetation height, the main objective was to estimate the effect of the sloped terrain and the forest on the turbulent energy and carbon fluxes considering the energy balance closure (EBC) and the heat storage. The results showed that the performance of the EBC was generally good and estimated it to be 79.5\%. This could be improved when the heat storage effect was considered. Based on the variability of the residuals in the diel, modifications in the imbalances were highlighted. Particularly, during daytime, the residuals were largest (56.9 W/m 2 on average), with a clear overestimation. At nighttime, mean imbalances were rather weak (6.5 W/m 2 ) and mostly positive while strongest underestimations developed in the transition period to morning hours (down to -100 W/m 2 ). With respect to the Monin-Obukhov stability parameter ((z - d)/L) and the friction velocity (u*), it was revealed that the largest overestimations evolved in weak unstable and very stable conditions associated with large u* values. In contrast, underestimation was related to very unstable conditions. The estimated carbon fluxes were independently modelled with a non-linear regression using a light-response relationship and reached a good performance value (R 2 = 0.51). All fluxes were additionally examined in the annual course to estimate whether both the energy and carbon fluxes resembled the microclimatological conditions of the study site. This unique study demonstrated that EC measurements provide valuable insights into land-surface-atmosphere interactions and contribute to our understanding of energy and carbon exchanges. Moreover, the flux data provide an important basis to validate coupled atmosphere ecosystem models.}, language = {en} } @misc{GrigusovaLimbergerMurkuteetal., author = {Grigusova, Paulina and Limberger, Oliver and Murkute, Charuta and Pucha-Cofrep, Franz and Gonzalez-Jaramillo, Victor Hugo and Fries, Andreas and Windhorst, David and Breuer, Lutz and Dantas de Paula, Mateus and Hickler, Thomas and Trachte, Katja and Bendix, J{\"o}rg}, title = {Radiation partitioning in a cloud-rich tropical mountain rain forest of the S-Ecuadorian Andes for use in plot-based land surface modelling}, series = {Dynamics of atmospheres and oceans : planetary fluid, climatic and biogeochemical systems}, volume = {110}, journal = {Dynamics of atmospheres and oceans : planetary fluid, climatic and biogeochemical systems}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0377-0265}, doi = {10.1016/j.dynatmoce.2025.101553}, pages = {1 -- 16}, abstract = {Understanding the partitioning of downward shortwave radiation into direct and diffuse components is essential for modeling ecosystem energy fluxes. Accurate partitioning functions are critical for land surface models (LSMs) coupled with climate models, yet these functions often depend on regional cloud and aerosol conditions. While data for developing semi-empirical partitioning functions are abundant in mid-latitudes, their performance in tropical regions, particularly in the high Andes, remains poorly understood due to scarce ground-based measurements. This study analyzed a unique dataset of shortwave radiation components from a tropical mountain rainforest (MRF) in southern Ecuador, developing and testing a locally adapted partitioning function using Random Forest Regression. The model achieved high accuracy in predicting the percentage of diffuse radiation (\%Dif; R²=0.95, RMSE = 5.33, MAE = 3.74) and absolute diffuse radiation (R²=0.99, RMSE = 5.30, MAE = 14). When applied to simulate upward shortwave radiation, the model outperformed commonly used partitioning functions achieving the lowest RMSE (8.62) and MAE (5.82) while matching the highest R² (0.97). These results underscore the importance of regionally adapted radiation partitioning functions for improving LSM performance, particularly in complex tropical environments. The adapted LSM will be further utilized for studies on heat fluxes and carbon sequestration.}, language = {en} } @misc{BendixLimburgerBreueretal., author = {Bendix, J{\"o}rg and Limburger, Oliver and Breuer, Lutz and Dantas de Paula, Mateus and Fries, Andreas and Gonzalez-Jaramillo, Victor Hugo and Grigusova, Paulina and Hickler, Thomas and Murkute, Charuta and Pucha-Cofrep, Franz and Trachte, Katja and Windhorst, David}, title = {Simulation of latent heat flux over a high altitude pasture in the tropical Andes with a coupled land surface framework}, series = {The science of the total environment}, volume = {981}, journal = {The science of the total environment}, publisher = {Elsevier}, address = {Amsterdam}, issn = {1879-1026}, doi = {10.1016/j.scitotenv.2025.179510}, pages = {1 -- 21}, abstract = {Latent heat flux is a central element of land-atmosphere interactions under climate change. Knowledge is particularly poor in the biodiversity hotspot of the Andes, where heat flux measurements using eddy covariance stations are scarce and land surface models (LSMs) often oversimplify the complexity of the ecosystems. The main objective of this study is to perform latent heat flux simulations for the tropical South Eastern (SE) Ecuadorian Andes using a coupled LSM framework, and to test the performance with heat flux and soil moisture data collected from a tropical high-altitude pasture. Prior to testing, we applied multi-criteria model calibration of sensitive model parameters, focusing on improving simulated soil water conditions and radiation fluxes as a prerequisite for proper heat flux simulations. The most sensitive parameters to improve soil moisture and radiation flux simulations were soil porosity, saturated hydraulic conductivity, leaf area index, soil colour and NIR (Near Infrared) leaf optical properties. The best calibrated model run showed a very good performance for half-hourly latent heat flux simulations with an R² of 0.8 and an RMSE of 34.0 W m⁻², outperforming simulations with uncalibrated and uncoupled LSM simulations in comparable areas. The slight overall overestimation in the simulated latent heat flux can be related to (i) simulation uncertainties in the canopy heat budget, (ii) an imbalance in the observed flux data and (iii) slight overestimations in the simulated soil moisture. Although our study focuses on latent heat fluxes and their relation to simulated radiation fluxes and soil moisture, model outputs of sensible heat fluxes were also discussed. The systematic overestimation of sensible heat flux in the model seems to be mainly a result of overestimated canopy temperatures. The improved simulation for latent heat flux has a high translational potential to support land use strategies in the tropical Andes under climate change.}, language = {en} } @misc{LimbergerHomeierGonzalezJaramilloetal., author = {Limberger, Oliver and Homeier, J{\"u}rgen and Gonzalez-Jaramillo, Victor and Fries, Andreas and Murkute, Charuta and Trachte, Katja and Bendix, J{\"o}rg}, title = {Foliar trait retrieval models based on hyperspectral satellite imagery perform well in a biodiversity hotspot of the SE Ecuadorian Andes}, series = {International journal of remote sensing}, journal = {International journal of remote sensing}, publisher = {Taylor \& Francis}, address = {London}, issn = {1366-5901}, doi = {10.1080/01431161.2025.2511211}, pages = {1 -- 19}, abstract = {The determination of the spatial distribution of canopy traits is crucial for understanding the spatio-temporal dynamics of ecosystem functions, such as carbon sequestration, water and energy fluxes in tropical montane forests. Especially in remote areas such as the Andes of south-east Ecuador, remote sensing using satellites has been proven to provide valuable information on canopy traits. However, the performance of the multispectral models to date is limited. Here, we analyse the potential of DESIS (DLR Earth Sensing Imaging Spectrometer) hyperspectral surface reflectance data for the prediction of specific leaf area (SLA), foliar toughness, nitrogen (N) and phosphorus (P) content by calibrating a PLSR model for each foliar trait. Model validation showed a high explanation of variance (R2 : 0.78-0.92) and a low model error (mean-normalized RMSE: 8-13\%) for all traits, showing an improved performance compared to models based on multispectral imagery and ancillary data within the same forest type. Hyperspectral models predicting foliar traits from individual tree crowns showed a lower performance for most traits, probably related to the difference in spatial resolution compared to this study. Given the high species richness of the Andean biodiversity hotspot and the complex topography, the high quality of the DESIS models is remarkable, considering that the multispectral models from the region require topographic predictors in addition to reflectances to achieve a good performance. The spatial trait maps generated by our models based on the reflectances only show clear relationships with terrain elevation. Thus, the hyperspectral trait maps from satellite orbit are capable of supporting large-scale ecological analyses between features, diversity and ecosystem functions.}, language = {en} }