This session is about process understanding of scalable ecophysiology and ecosystem function relevant to carbon and water cycles, above- and below-ground. We facilitate dialogue across scales and techniques, from mesocosm experiments to field experiments, remote sensing and modelling.
The climate crisis is pushing forests to a limit. Modern forest management aims to help forests maintain viability and ecosystem functions and services. However, making appropriate management decisions is difficult since our understanding of the connections between climate variations and detailed tree physiological and phenotypic responses is not well interlinked or well represented in current models. We need to open the black box of physiological and metabolic processes that provide the missing link between environmental and phenotypically observable changes. Once achieved, we can refine and test hypotheses about which processes must be better represented and incorporated into models.
New high-resolution bioanalytical mass spectrometers offer high-throughput metabolite identification and compound- and intramolecular position-specific isotope analysis in the natural isotope abundance range. Changes in the commitment of substrates to metabolic pathways and the activation or deactivation of others alter enzyme-specific isotope effects. This leads to differences in reaction products’ intra-molecular and compound-specific isotope compositions. Substantial intramolecular position-specific isotope information of intermediates of metabolic pathways is integrated into the tree ring chemical compounds, allowing to inversely model metabolic fluxes and pathway commitments. By combining disciplines, such as metabolomics, stable isotope ecology and tree ring research, we can use this “multidimensional isotopic fingerprint” in the tree ring archive to unveil the mechanisms of metabolism-environment interaction on scales ranging from cellular regulation to whole plant resource allocation. This will allow retrospective testing of whether processes such as sink control and stomatal growth optimisation respond to selected environmental drivers and affect tree functioning and whether they are correctly incorporated into models. Hence, deciphering past processes will allow us to reveal insights into the future trajectories of forests.
How to cite: Gessler, A.: What if we could reconstruct tree metabolism and explore how environmental factors influence it through tree rings?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2529, https://doi.org/10.5194/egusphere-egu25-2529, 2025.
Dynamic global vegetation models (DGVMs) are used to attribute historical and forecast future atmosphere-land carbon (C) exchange. While mean long-term behaviour across DGVMs is compatible with observational constraints on the global C cycle over recent decades, differences between models are high both in annual fluxes and attribution of the long-term net carbon uptake to drivers such as atmospheric CO2, indicating significant uncertainty regarding process understanding. These models are largely C source-driven, with behaviour primarily determined by the environmental responses of photosynthesis. However, real plants are integrated wholes, with feedbacks between sources (e.g. photosynthesis) and sinks (e.g. growth) resulting in homeostatic concentrations of metabolites such as sugars. An approach to implementing such behaviour in a plant growth model is presented and its implications for responses to environmental factors assessed. The approach uses Hill functions to represent inhibition of C sources (net photosynthesis) and activation of sinks (structural growth) based on sugar concentrations. The model is parameterised for a mature tropical rainforest site and its qualitative behaviour is found to be consistent with experimental observations. Key findings are that sinks and sources strongly regulate each other. For example, doubling potential net photosynthesis (i.e. the rate that would occur without feedback) results in growth increasing by only 1/3 at equilibrium, with increased sugar concentration causing feedback-inhibition of photosynthesis. A C source-only driven response, as in current DGVMs, would result in close to a doubling of growth. Hence, in this approach, environmental factors that affect potential net photosynthesis, such as atmospheric CO2, have greatly reduced effects on growth and net C uptake when homeostatic behaviour of sugars is considered. Implications for understanding and modelling the global carbon cycle are discussed.
How to cite: Friend, A., Chen, Y., Eckes-Shephard, A., Fonti, P., Hellmann, E., Rademacher, T., Richardson, A., and Thomas, P.: Implications of plant metabolic source-sink feedbacks for modelling the terrestrial carbon balance, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20116, https://doi.org/10.5194/egusphere-egu25-20116, 2025.
Climatic warming influences ecosystem-scale carbon fluxes directly via effects on photosynthesis and respiration, and indirectly via effects on the plant community. Here, we report on a 10-year factorial warming and dominant plant species removal experiment established in both a high- and in a low-elevation montane meadow to explore how dominant plants modify the effect of warming on the carbon cycle across space and over time. At low-elevation, warming increased peak-season net carbon uptake in most years, driven by higher primary productivity, but only in plots where the dominant was left intact. Here, net carbon uptake tended to be positive, but was more likely to be negative when the dominant plant was removed, and in dry years. Surprisingly, the high-elevation site was unaffected by the warming and plant removal treatments, suggesting these sites are resistant to these disturbances. Taken together, these results demonstrate that dominant plant species can modify the impacts of warming on carbon fluxes, but show how this influence can vary spatially and temporally. These findings provide insight into when and how abiotic and biotic factors influence ecosystem carbon source/sink dynamics.
How to cite: Brinkhoff, R., Sanders, N., Henning, J., Newman, G., Read, Q., Sundqvist, M., Hovenden, M., Prager, C., Rewcastle, K., Souza, L., Vought, O., and Classen, A.: The impact of warming on peak-season ecosystem carbon uptake is influenced by dominant species in warmer sites, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-245, https://doi.org/10.5194/egusphere-egu25-245, 2025.
Greening and browning of vegetation of terrestrial ecosystems in response to climate change and its variability, global change, as well as ground anthropogenic drivers, has been widespread across the globe. India is the most populous country with two global biodiversity hotspots, complex monsoonal and other climate systems interacting with diverse biomes. It is undergoing high rates of land-use change due to development pressures. It also offers a diversity of social-ecological systems with potentially variable responses to climate dynamics and global warming. We investigate the role of climate dynamics in the greening and browning of vegetation, as well as other local and regional drivers. Such interplay between complex local and regional factors on vegetation has implications for both semi-wild and agro-biodiversity, and human well-being linked to ecosystem services. Here, we evaluate how global and local drivers influence the greening and browning trends over the past four decades for the Indian region using GIMMS (1982-2022) and MODIS (2000-2023) data. We used a multi-dimensional vegetation index measured as the mahalanobis distance which captures complex vegetation dynamics and is a better measure of vegetation greening/browning. We find widespread greening (51.3%, 1.65 million sq.km) across India, predominantly in arid and semi-arid regions driven by increase in monsoonal rainfall and change in winter temperatures. Browning of vegetation (13.5%, 0.43 million sq.km) was restricted to some regions, especially Gangetic plains. Interestingly, Gangetic plains showed reversal of trends in vegetation from browning to greening over the past two decades. Rest of the regions (nearly 1.12 million sq.km) showed no major change in vegetation responses despite changes in climate and other factors. Protected areas showed differential rates of greening and browning compared to nearby areas across various biogeozones. An analyses of hotspots of greening revealed the role of factors such as spread of invasive species, woody encroachment in floodplain grasslands, tree plantations and changes in cropping patterns. Importantly, we find that urban areas showed greening within the city centre possibly subsidised by increase in water supply, but outskirts and peri-urban areas showed drastic browning trends due to replacement of vegetated areas by built up land-use. Although greening trends in vegetation provide positive contribution to climate change mitigation, they can have trade-offs with other ecosystem services. Overall, a holistic understanding of such greening and browning trends and its drivers, is vital for climate adaptation, biodiversity conservation, carbon sequestration and sustenance of ecosystem services.
How to cite: Naidu, D. and Krishnaswamy, J.: A Greening and Browning Atlas of India: Role of diverse global and local drivers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-611, https://doi.org/10.5194/egusphere-egu25-611, 2025.
Analysing root traits to identify below ground acquisition mechanisms and relating them to above ground traits, such as leaf phenology, can improve the understanding and design of resource use efficiency in drought resilient agroforestry systems. Shade trees play a key role in regulating above and below ground resource use dynamics in agroforestry systems. Specific shade tree functional traits such as leaf phenological development, crown architecture and leaf traits such as specific leaf area and nitrogen content have been related to shade tree impact on productivity, ecosystems service provision and drought resilience of agroforestry systems. Understanding the influence of many different shade tree species on resource use and the productivity outcome resulting from their interaction with cocoa plants have, so far, mainly focused on aboveground traits. Yet, there is an urgent need to put adequate emphasis to the equally important belowground processes, root systems, and root-rhizosphere interactions. Root trait research is significantly limited in tropical communities, constraining understanding of belowground processes and interactions within complex systems such as agroforestry. There is lack of understanding of strategies in belowground resource acquisition among functional groups of shade tree species. In this study, two key roots traits, i.e. fine root length density and fine root diameter of 13 common shade trees species belonging to 6 functional (leaf phenology) groups and cocoa were evaluated under farmer field conditions. Fine root samples were acquired for 4 replicates of each shade tree species through extensive root coring up to 60 cm depth and at three horizontal shade tree impact zones (inner, mid and outer). Scanned sorted shade tree and cocoa plant root images were analysed with WINRHIZO. All cocoa plants irrespective of their associated shade tree functional group exhibited resource acquisitive (non-conservative) fine root traits, i.e. with higher root length density and smaller diameter. Similarly, shade trees in the ‘brevi deciduous during dry season’ functional group exhibited the notable paradox of leaf flushing during dry season characterized by higher, leaf area-related, water uptake in the dry season exhibited non-conservative root traits. Evergreen and complete deciduous functional groups showed a conservative root trait showing lower fine root length density and larger diameter. Shade trees with conservative root traits are therefore considered complementary to the cocoa plant acquisitive traits, thereby enhancing belowground resource use efficiency and drought resilience in cocoa agroforestry systems.
How to cite: Abdulai, I., Hoffmann, M., Kahiluoto, H., Ahmed, M. A., Dippold, M. A., Asare, R., and Rötter, R. P.: Shade tree root traits in cocoa agroforestry systems are associated with their functional leaf phenology groups, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17041, https://doi.org/10.5194/egusphere-egu25-17041, 2025.
Biodiversity affects ecosystem functioning by regulating the biogeochemical exchange of carbon, water, energy, and nutrients within and between ecosystems. While this has been proven experimentally, ecosystem-level investigations of the effects of biodiversity on measured biogeochemical processes are understudied.
We leveraged fine-scale remote sensing data from Sentinel-2 to estimate plant diversity at 148 flux network sites across the globe. At these sites, measured eddy covariance fluxes of carbon, water, and energy can be used to compute ecosystem functions and metrics of multifunctionality, i.e. the simultaneous provision of multiple ecosystem functions. We estimated remotely-sensed biodiversity through the entropy-based metric known as Rao Q. To assess the effect of biodiversity on the biogeochemical functioning of ecosystems, we then related Rao Q to the derived ecosystem functions and ecosystem multifunctionality metrics.
Rao Q computed from near-infrared reflectance of vegetation (NIRv) was a major predictor of single ecosystem functions and multifunctionality metrics, highlighting the mostly positive effects of biodiversity on the functioning of ecosystems. Rao Q was generally more important than meteorology and comparable to vegetation structural components in predicting ecosystem functions and multifunctionality. In addition, Rao Q was more important than traditional biodiversity indices of taxonomic diversity measured at a subset of sites in North America where systematic plant species surveys were available. This reinforces the idea that structural and functional diversity, rather than species diversity per se, are key aspects in the worldwide functioning of natural ecosystems.
We provide strong evidence for significant positive effects of a biodiversity-proxy derived from satellite remote sensing measurements on single ecosystem functions and ecosystem multifunctionality. The positive biodiversity effects are robust to the inclusion of most major meteorological and structural parameters that might drive ecosystem functioning or confound the biodiversity-ecosystem functioning relationship. Considering recent and future advances in remote sensing of both diversity and ecosystem functions, our study paves the way to continuous spatiotemporal assessments of the biodiversity-ecosystem functioning relationship at the landscape, regional, and global scales.
How to cite: Gomarasca, U., Duveiller, G., Pacheco-Labrador, J., Cescatti, A., Wirth, C., Reichstein, M., and Migliavacca, M.: Ecosystem multifunctionality is positively affected by remotely-sensed biodiversity at global eddy covariance sites, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8558, https://doi.org/10.5194/egusphere-egu25-8558, 2025.
The increasing frequency and intensity of extreme climate events threaten the continued provision of forest ecosystem services. Large-scale mortality events and changes in growth and Water Use Efficiency (WUE) in European forest ecosystems have already been observed in response to stressors such as droughts and climate-related outbreaks in tree pests and diseases. Long-term changes in mean temperature and precipitation are also expected to drive forest growth, mortality and WUE in the coming decades. The need for European forest ecosystems to adapt to climate change comes at a time when these ecosystems are still recovering from the impacts of elevated sulphur and nitrogen deposition, with many still exposed to the latter. Sulphur and nitrogen deposition were observed as key drivers of forest growth and mortality in Central Europe in the 1980s, with the impacts on soil chemistry still evident today.
As part of the WG2 activities in the COST Action CA21138 CLEANFOREST - Joint effects of CLimate Extremes and Atmospheric depositioN on European FORESTs- we are conducting a systematic review on trends in European forest growth, mortality and water use efficiency (WUE). The direction of trends in forest growth, mortality and WUE as observed between 1990-2023 by a range of methods, from dendrochronology, ecosystem fluxes, to remote sensing, were extracted from published literature alongside a wealth of information on forest type and characteristics, covering >1100 observations from >500 papers.
The produced database provides the opportunity to evaluate agreement between spatial scales and identify needs for integration to understand mechanisms underpinning forest responses to changes in atmospheric deposition and extreme climatic events. We will broadly discuss opportunities to connect existing long-term monitoring networks with new approaches to fill knowledge gaps.
How to cite: Lewis, C., Creek, D., Fyllas, N., Lévesque, M., Pugh, T., Menucuccini, M., Loustau, D., Černý, J., Ziemblinska, K., Koren, G., Dalmonech, D., Puchi, P. F., Fotelli, M., Markos, N., Petrík, P., Romeralo, C., La Porta, N., Klisz, M., and Guerrieri, R.: Assessing the knowledge base on long-term trends in forest growth, mortality and Water Use Efficiency in Europe using a multi-scale approach, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13569, https://doi.org/10.5194/egusphere-egu25-13569, 2025.
Multiple facets of global change affect the Earth System interactively with complex consequences for ecosystem functioning and stability. Simultaneous climate and biodiversity change are of particular concern, because biodiversity may contribute to ecosystem resistance and resilience and may mitigate climate change impacts. Yet, the extent and generality of how climate and biodiversity change interact, remain insufficiently understood, especially for the decomposition of organic matter, a major determinant of the biosphere – atmosphere carbon feedbacks. Decomposition depends on the characteristics and diversity of plant-produced organic matter as the primary energy source, and is further regulated by an astounding diversity of soil organisms ranging from prokaryotes to macro-invertebrates that are organized in highly complex food webs. With an inter-biome experiment, we tested here how biodiversity in the multi-trophic decomposer system drives decomposition in forest ecosystems under drier conditions. Our results show at a relevant spatial scale covering distinct climate zones that forest floor biodiversity across trophic levels has a strong potential to mitigate drought effects on C and N dynamics during decomposition. Preserving biodiversity at multiple trophic levels contributes to ecosystem resistance and appears critical to maintain ecosystem processes under ongoing climate change.
How to cite: Luan, J., Li, S., Wang, Y., and Liu, S.: Biodiversity mitigates drought effects in the decomposer system across biomes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4706, https://doi.org/10.5194/egusphere-egu25-4706, 2025.
Soil moisture droughts are defined by the prolonged, abnormally dry conditions in the soil. These extreme dry events directly impact terrestrial ecosystem activities like photosynthesis, biomass production, rehydration, and carbon uptake, which can be monitored at regular intervals using satellite-retrieved different vegetation descriptors such as solar-induced fluorescence, leaf-area index, vegetation optical depth, and gross primary productivity, respectively. While previous studies have primarily focused on the vegetation anomalies during drought and its recovery time, very little attention was put on how the ecosystem resistance can vary in terms of different vegetation descriptors. The resistance is defined as the ratio between the maximum perturbance in vegetation and the time taken to reach it. It can infer which ecosystem activity is more vulnerable to drought events or can persist through such abnormal dry conditions.
Previous investigations have demonstrated that soil moisture droughts are frequently initiated by meteorological droughts at the sub-seasonal-to-seasonal scale. Therefore, the onset of a soil moisture drought event coincides with or succeeds by a meteorological drought. Alongside, a soil moisture drought can also arise due to a , primarily overserved over dryland regions, which depends on the evapotranspiration constraint imposed by the regional soil moisture deficiency. The state of land (dry-down rate) and atmosphere (specific humidity and vapour pressure deficit) differ across these conditions under which the soil moisture drought occurs. Due to this, the expected response of the terrestrial ecosystem under the three scenarios of soil moisture drought would also be different. The current work examines the effects in different vegetation descriptors due to soil moisture droughts occurring under three situations: 1) soil moisture and meteorological droughts co-occurring, 2) delayed onset of soil moisture drought from the onset of meteorological drought, and 3) self-propagating soil moisture droughts. While the concurrence of meteorological and soil moisture drought would be severely devastating for agricultural practices, self-propagated and meteorological drought-driven soil moisture drought could pose a continuous threat to the natural ecosystems. We hypothesise that the anomalies in land-atmosphere conditions during a drought govern the ecosystem resistance. Since the initiation of soil moisture drought could vary, as mentioned earlier, the subsequent resistance by an ecosystem would also differ. In addition, we checked how these associations vary for different vegetation descriptors for different plant-functional types (croplands, grasslands, shrublands, and evergreen, deciduous and mixed forests). Our study encompasses the soil moisture drought events that occurred at a seasonal scale during the period of 2003-2020, which were identified using the GLEAM data. The vegetation descriptors are acquired from multi-satellite sources.
This study will help to infer how land and atmosphere anomalies jointly attribute to the ecosystem state in subsequent times and how much these impacts vary in terms of different vegetation descriptors. A region-specific global-level analysis would also highlight the most vulnerable regions, where a seasonal early-warning system can be designed using the inferences drawn from the current study looking into the land and atmospheric anomalies during a drought event.
How to cite: Gupta, A. and Lanka, K.: Ecosystem resistance to concurrent and propagated soil moisture droughts, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19430, https://doi.org/10.5194/egusphere-egu25-19430, 2025.
In a future climate, drought events are expected to become more frequent and severe, with largely unknown consequences for ecosystem functioning. Based on a number of experiments in temperate mountain grasslands we show that drought recurrence, simulated for more than 16 subsequent years, altered the responses of ecosystem productivity and of carbon and water fluxes to subsequent drought. Under future conditions of recurrent drought combined with warming and elevated atmospheric CO2 concentrations, drought severity and its impacts on grassland carbon and water fluxes were further enhanced. Moreover, under such future conditions the movement and storage of water in soil upon post-drought rewetting was substantially altered, with implications for plant water access and use. We conclude that increasing drought recurrence and severity alter their legacies on grassland carbon and water fluxes through changes in species composition as well as changes in soil structure, with cascading consequences for grassland functioning in a future world.
How to cite: Bahn, M., Radolinski, J., García Favre, J., Hwang, B., Schärer, M.-L., and Tissink, M.: Increasing drought recurrence and severity alter legacies on grassland carbon and water fluxes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20559, https://doi.org/10.5194/egusphere-egu25-20559, 2025.
Due to climate change there have been major shifts in weather events, with a predicted increase in extreme drought events in Western Norway. These events in combination with land-use change, are putting the red-listed ecosystem coastal heathlands under high pressure. In Norway, there has been a loss of 90% of coastal heathland cover over the last decades, with the remaining 10% being dominated by the mature successional stage.
In recent years, there has been research highlighting how the mature heathlands are vulnerable to drought. This includes a higher input of litter into the system and also less seeds seeds, which are of lower quality when exposed to drought. These results indicate an effect on the leaf and flower phenology of the dominant species in coastal heathlands.
To expand our knowledge, this project has investigated the responses to drought through leaf and flower phenology for the dominating dwarf-shrub species in coastal heathlands; Calluna vulgaris, Empetrum nigrum, Vaccinium myrtillus and Vaccinium vitis-idaea. The project was conducted from April 2023 until May 2024 using the DroughtNet rainout shelters established at Lygra in 2017. This experiment is one of few long term drought experiments in coastal heathlands. Within the site there are 3 successional stages (young, intermediate, mature), with 3 drought treatments (control, 60% and 90% roof coverage), which is replicated by 3, resulting in 27 plots. Within each plot a replica of 5 for each species were subjected to phenology measurements: plant height, branch length and thickness, flowering time, number of flowers, and number, length, and colouration of leaves.
Our results show an earlier flowering in the mature stage, with less flowers with increasing drought. The number of leaves seems to be less affected by drought, except in the mature stage, where the leaf count is overall lower, especially in the extreme drought treatment (90% roof coverage). Our results build upon previous research and confirms that the older mature successional stage is more sensitive to drought.
How to cite: Birkeli, K., Vandvik, V., and Althuizen, I.: Drought and successional stage affects leaf and flower phenology, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-987, https://doi.org/10.5194/egusphere-egu25-987, 2025.
The severity and frequency of extreme droughts have increased dramatically due to global change, often causing devastating consequences because of their high intensity. Grasslands, which cover approximately 40% of Earth's surface and provide essential resources and services to humanity, are particularly sensitive to changes in precipitation. With models predicting a rising probability of drought events in many regions worldwide, it is increasingly crucial to understand their impacts on grassland ecosystems to accurately assess ecosystem resistance to climate change and predict future ecosystem functionality. While previous studies have shown that extreme droughts often lead to significant declines in grassland productivity, key questions remain unanswered: What are the overarching patterns at larger spatial scales? How do these responses evolve over time? And how do grasslands recover after extreme drought events? To address these questions, we conducted a coordinated, distributed experiment to explore the relationship between productivity sensitivity to drought and mean annual precipitation, the multi-year effects of extreme drought on grassland productivity, and the resilience of productivity in the aftermath of extreme drought.
How to cite: Yu, Q.: The Impacts of Extreme Drought on Grassland Primary Productivity, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1231, https://doi.org/10.5194/egusphere-egu25-1231, 2025.
Flash droughts have received widespread attention due to their abrupt onset or swift intensification, which makes it challenging to forecast and prepare for them, hence posing serious impacts on ecosystems, socioeconomic development, and agriculture. Most of the studies deal with conventional drought and lack knowledge of flash drought. To date, how the terrestrial ecosystem responds to flash over India has not been examined. As we know India is an agricultural-based economy, where a large fraction of the population relies on agriculture. In the present study, we have developed a novel method to quantitatively establish the definition of FD using the Aridity Index (AI). The spatiotemporal characteristics, including trends, and the causes of FDs in 25 significant river basins across India between 1981 and 2021 were then examined using this novel methodology. The hydrometeorological conditions were assessed extensively during the study at various flash drought stages. Also, we investigated flash drought's impact on the terrestrial ecosystem. The results show that FDs with rapid intensification are more common in humid areas compared to semi-arid and sub-humid areas. Furthermore, the study shows that in a substantial area of the research area, temperature and precipitation are both important major FD triggers. The differential effects of precipitation and soil moisture serve as FD triggers in some areas, such as the Western Ghats and northeast India. Furthermore, atmospheric aridity can create conditions that are favorable for the occurrence of FDs. It may accelerate the rapid onset of these flash droughts when combined with decreased soil moisture. The terrestrial ecosystem has been found to be extremely vulnerable to flash drought episodes, with the Ganga basin and Southern India exhibiting the most severe responses. Further, a serious decrease in Water Use Efficiency (WUE) and underlying WUE is also observed over some parts of Southern India and Ganga river basin, which indicates the non-resilient nature of the ecosystem towards flash drought conditions. The findings will provide policymakers with helpful information for developing appropriate effective regulations to reduce the effects of FDs on crop production, water scarcity, and allow them to develop proper water resource utilization methods in India.
Keywords: Aridity; Drivers, Flash drought; Drought intensification; Vapor pressure deficit.
How to cite: Poonia, V.: An Innovative Approach to Characterize Intensified Flash Drought Detection and its Impact on Terrestrial Ecosystem across Indian River Bains , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-625, https://doi.org/10.5194/egusphere-egu25-625, 2025.
Land-atmosphere carbon exchanges and feedbacks constitute one of the largest uncertainties in future climate projections. A large increase in the seasonal cycle amplitude (SCA) of CO2 has occurred since the 1950s, especially in northern high latitudes, reflecting enhanced vegetation activity. However, global land-surface and dynamic vegetation models have produced a very wide range of magnitudes for the SCA, and have generally (sometimes drastically) underestimated its increase. We explored the controls of the SCA using a parameter-sparse eco-evolutionary optimality (EEO) model for gross primary production, the ‘P model’, combined with simple, generic representations of plant and decomposer respiration, to simulate seasonal cycles and decadal trends of net ecosystem exchange (NEE). Simulated NEE fields were used to generate near-surface CO2 concentrations with the help of the atmospheric chemistry-transport model TM5. Modelled CO2 SCA and SCA trends were similar to those observed at CO2 monitoring stations in northern high latitudes, outperforming state-of-the-art Earth System Models. Rising CO2 was shown to be the primary driver of increasing SCA. Climate showed a mixed but overall positive impact; however, the influence of climate shifted from positive to negative in the late 1990s, resulting in a slight reduction in SCA amplitude over the satellite era.
How to cite: Cai, W., Prentice, I. C., and Hooghiem, J.: Increasing CO2 seasonal cycle amplitude in the north: analysis with an eco-evolutionary optimality model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2147, https://doi.org/10.5194/egusphere-egu25-2147, 2025.
More frequent and intense episodes of drought are expected to affect terrestrial nitrogen (N) cycling by altering N transformation rates, the functioning of soil microorganisms, and plant N uptake. However, there is limited empirical evidence of how progressive water loss affects N cycling processes at the plant-soil interface. In this study, we addressed this challenge by employing 15N tracing techniques, and metagenomic analyses of microbial genes involved in N cycling. Our goal was to assess how different levels of soil water availability influence the fate of N derived from decomposing needle litter within a Scots pine saplings and forest soil mesocosm platform. We observed that with increasing water limitation, the release of N from the decomposing needle litter into the soil declined rapidly. However, moderate levels of water limitation barely affected the microbial metagenome associated with N cycling processes and the uptake of N by the saplings. Comparatively, severe levels of water limitation clearly impaired plant N uptake, and increased the prevalence of microbial N cycling genes potentially involved in mechanisms that protect against water stress, as opposed to genes associated with the uptake and release of N during mineralization and nitrification processes. An increased allocation of N to fine roots was further observed under reduced levels of soil moisture, to support the physiology of the saplings and potentially enhance drought resilience. Our study overall indicates that when soil water becomes largely unavailable, the cycling of N at the plant-soil interface is slowed down, and microbial and plant tolerance mechanisms may prevail over N uptake and microbial decomposition processes.
How to cite: Solly, E. F., Jaeger, A. C. H., Barthel, M., Humbert, L., Six, J., Mueller, R. C., and Hartmann, M.: Drought intensity alters nitrogen cycling at the tree and soil interface in Scots pine mesocosms , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8346, https://doi.org/10.5194/egusphere-egu25-8346, 2025.
Climate change is profoundly affecting ecosystems globally, increasing the frequency and severity of droughts. The eastern Mediterranean, characterized by high climatic variability and water scarcity, faces critical challenges to biodiversity and ecosystem functionality. This study leverages over two decades of rainfall manipulation experiments at the Matta LTER site in Israel to investigate how Mediterranean ecosystems respond to chronic and extreme drought conditions and altered rainfall patterns.
Experimental treatments included 30% and 66% reductions in annual precipitation, coupled with variations in rainfall distribution, simulated through rainout shelters. Results revealed that the ecosystem demonstrated resistant to moderate drought, with minimal changes in biomass and species diversity under a 30% rainfall reduction. However, extreme drought conditions (66% reduction) significantly impacted aboveground biomass and altered species composition, suggesting the presence of ecological thresholds. The study highlights the importance of soil moisture dynamics, drought-resistant plant traits, and seed bank contributions in maintaining ecosystem functionality under stress.
The findings underline the critical need for long-term monitoring and advanced methodologies, including AI-driven modeling, to identify tipping points and predict ecosystem responses under future climate scenarios. These insights provide valuable guidance for adaptive management strategies to enhance the resilience and sustainability of Mediterranean ecosystems amid accelerating climate change.
How to cite: Sternberg, M., Cohen, O., and Kigel, J.: Simulating Climate Future: Long-Term Drought Impacts on Mediterranean Ecosystem Structure and Function, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11463, https://doi.org/10.5194/egusphere-egu25-11463, 2025.
In Central Europe extreme summer droughts are becoming more intense while extremely long periods with intermittent drought stress are likely getting extended as sequential precipitation deficits follow one another at shorter intervals with climate warming. Since the effects of long and mild ‘press’ vs. short and intense ‘pulse’ droughts have rarely been directly compared at the same site so far, the interplay between drought duration and intensity is largely unknown. Using precipitation-reduction and precipitation-exclusion shelters consecutively in a Swiss semi-natural grassland we investigated the impacts of a mild but extremely long (4 years) press drought and an extremely intense but short (5 months) pulse drought on species composition and biomass from 2015-2021.
The press drought showed a consistently lower intensity than the pulse drought based on meteorological and soil moisture metrics: treatments resulted in a tenfold smaller average daily water deficit between gains from precipitation and losses from evapotranspiration and a tenfold smaller average daily difference compared to controls in topsoil water potential for the press than for the pulse drought. Contrary, tenfold longer reduction than exclusion of precipitation resulted in higher drought severity based on meteorological, but lower drought severity based on soil moisture metrics: treatments showed a threefold larger cumulative reduction in precipitation, but an eightfold shorter duration of limiting conditions for plant growth (topsoil moisture <−100 kPa) for the press drought than for the pulse drought.
Plant responses to both extreme droughts were not related to precipitation-based, but mirrored soil moisture-based drought severity metrics. Productivity and composition showed higher resistance but lower resilience to the press drought than to the pulse drought. Secondly, the interactions between press and the pulse drought were only faint and overshadowed by additive main effects expressed by species groups that differ in maximal rooting depth. Specifically, press drought had a strong persistent impact on forb coverage and persistently changed the coverage of species that maximally root at medium (50-100 cm) depth, while pulse drought had a strong persistent impact on graminoid coverage and the coverage of species without deep roots.
Thus, the impact of intermittent and intense stress induced by sequential very extreme precipitation-reduction and precipitation-exclusion treatments in a temperate-humid climate was moderated by different plant functional groups supporting the idea that extreme droughts of various intensity and duration contribute to the coexistence of functional groups in semi-natural grassland.
How to cite: Zeiter, M. and Stampfli, A.: Extreme press and pulse droughts diversify rooting depth in a semi-natural grassland, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17956, https://doi.org/10.5194/egusphere-egu25-17956, 2025.
Climate change is expected to increase the frequency, intensity, and duration of droughts in most regions around the world. The ecohydrological response will not occur immediately because it involves changes ranging from rapid physiological change to slower evolutionary and community composition change. Acclimation is the speed by which these phenomena occur while reaching a new state in equilibrium with novel climate conditions. Data show that average aboveground net primary production is relatively more sensitive to changes in average precipitation than when observing the same changes of precipitation in one site. The spatial model relating average production and precipitation represents full acclimation and the temporal model minimum acclimation. Estimating acclimation is critical for predicting the impacts of future climate change and requires an in-depth understanding of its ecohydrological mechanisms. Our long-term experimental drought in the Chihuahuan Desert in the SW provides evidence of the direct and indirect mechanisms driving acclimation. Experimental drought, when lasting less than 4 years, caused immediate reduction in primary production driven by changes in plant ecophysiology and relative species abundance. On the contrary, sustained drought caused changes in species composition that offset the direct effects and reduced the speed of acclimation. Finally, the mechanisms and the rate of acclimation show thresholds highlighting acclimation rate not just as a linear time process but a more complex phenomenon involving multiple scales and discontinuities. Thresholds result from cumulative ecological phenomena, such as reductions in grass tiller density, acting in combination with broad-scale climatic patterns, such as El Niño and the Pacific Decadal Oscillation.
How to cite: Sala, O. and Maurer, G.: Unexpected indirect effects of field simulated drought offset direct climate-change impacts, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7444, https://doi.org/10.5194/egusphere-egu25-7444, 2025.
Vegetation plays a crucial role in regulating the water cycle through transpiration, which is influenced by the root zone storage capacity (SR). SR is dynamically influenced by climate, land use, and vegetation, with ecosystems adapting to environmental changes by modulating SR. Human interventions, such as deforestation, agriculture, and irrigation, significantly alter SR by changing vegetation cover and water availability. This study aims to quantify human-induced modifications to SR at global scale. Through a lens of human domination, we highlight the repurposing of SR and its implications for ecosystem resilience.
A random forest model was developed to estimate SR based on climate, land and vegetation related variables, trained on available present-day estimates of SR derived from process-based methods. By substituting actual vegetation with potential natural vegetation (PNV) and altering climate variables to reflect preindustrial, present, and future conditions, we assess the impact of land use change and climate change on SR.
Under current land use, average SR is approximately 7.5 mm lower than in the PNV scenario, assuming the same climate conditions. In future extreme warming scenarios (RCP8.5), SR requirements are projected to increase from about 136 mm to 243 mm, which is deemed unrealistic, suggesting potential transgression of limits to root zone adaptation in ecosystems.
These findings underscore the significant and widespread anthropogenic modification of root zone storage capacity, and point at risks for ecosystem resilience loss in regions where climate change outpaces adaptive capacity. We call for more systematic and observation-based studies to understand these dynamics better.
How to cite: Lasantha, V., Wang-Erlandsson, L., Rocha, J., van der Ent, R., and Hrachowitz, M.: Characterizing Anthropogenic Modification of Root Zone Storage Capacity, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18391, https://doi.org/10.5194/egusphere-egu25-18391, 2025.
The atmosphere–land interaction is crucial to the climate and earth system through the exchange of energy, water, momentum and carbon among vegetation and atmosphere. In recent times, a great deal of variability in anthropogenic land use along with climate variability has greatly altered the terrestrial biosphere all around the globe. The global vegetation dynamics has garnered substantial attention due to its potential impact on food security, water cycle and terrestrial carbon sinks. The non-climatic factors have a very straightforward and regional impact on vegetation. However, there remains uncertainty regarding the response of the terrestrial ecosystems to climate change as vegetation-climate interactions is very intricate and intriguing. In the recent times, higher temperature (T) and evapotranspiration (ET) accompanied by insufficient precipitation (P) has depleted soil moisture (SM). We find temperature (T) is the dominant driver of global photosynthesis. Across biomes and land cover types, moisture availability (P and SM) is the key climatic control in tropical and arid but T in temperate and cold biomes. For croplands and forests, T is the predominant driver, but P is the key driver for grasses suggests Machine Learning (ML) based Random Forest (RF) model. However, there is decline in the control of temperature on photosynthesis due to saturation of boreal warming-induced greening and increasing dryness stress. The influence of water availability and energy has substantially grown on global photosynthesis. Interestingly, in regions where both increase in energy and decrease in water availability is present, the photosynthetic activity is largely moisture controlled. Therefore, the global photosynthesis is largely driven by moisture ahead of warmth and energy in the drying world.
How to cite: Kashyap, R. and Kuttippurath, J.: Changing Global Vegetation-Climate interaction during recent decades , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1022, https://doi.org/10.5194/egusphere-egu25-1022, 2025.
Mediterranean grasslands of southwest Spain and Portugal are a crucial part of the largest agroforestry ecosystem in Europe, known as dehesa in Spain. This multi-use system is recognized to be a balanced combination of environmental and economic values. Grasslands contribute to both aspects, with a high diversity of plant species, providing essential feeding resources for extensive livestock, the primary economic activity in many of these areas. Water availability is the main limiting factor for plant growth in the region, and the production of the grasslands is closely linked to its continental Mediterranean climate, resulting in significant differences in biomass production throughout the seasons and between years. Optimizing grassland management and adapting it to the increase in droughts and extreme events described by climate projections is vital for preserving a healthy and productive ecosystem. Accurate and timely information on grassland productivity is needed at appropriate spatial and temporal scales to meet management requirements.
Light use efficiency (LUE) models link plant growth to incident solar radiation to estimate gross primary production (GPP) or aboveground biomass. The advancements and availability of remote sensing technology have led to a renewed interest in this approach, resulting in extensive research and numerous applications across various land uses, particularly at global or large scales. This study aims to improve the monitoring of grassland productivity by developing a model specifically designed to estimate GPP for this water-controlled and highly variable grassland ecosystem.
Several methods for modeling water stress in LUE models have been compared using a series of CO2 exchange measurements from eddy covariance systems at three sites in southern Spain over eight years. The opportunities and limitations of the different methods are evaluated, and a proposal is presented that effectively balances operativity and accuracy for monitoring grasslands at a high spatial and temporal resolution.
How to cite: González-Dugo, M. P., Muñoz-Gómez, M. J., Calbet, A., Garcia-Moreno, A., and Andreu, A.: Evaluation of water stress modeling methods for estimating gross primary production in Mediterranean grasslands, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15519, https://doi.org/10.5194/egusphere-egu25-15519, 2025.
Nutrient resorption from senescing leaves is a critical process of plant nutrient cycling that can significantly affect plant nutrient status and growth, making it essential for land surface models (LSMs) in order to predict long-term primary productivity. Most models assume leaf resorption to be a fixed value of 50% for nitrogen (N) partially because we lack the knowledge of what drives this process, making it unclear what its implications are when simulating nutrient cycling. Based on our own analysis of global patterns of nutrient resorption from trait data (Sophia et al., 2024), we developed a dynamic scheme of N resorption driven by leaf structure and environmental limitation and implemented it in the QUINCY model. This scheme assumes that all metabolic N is fully mobilizable and available for resorption, representing the maximum resorption capacity for each plant functional type based on the leaf construction costs. Environmental limitations then downregulate the remaining mobilizable nutrients considering soil N availability relative to plant demand, adjusting their internal recycling in face of N stress and leaf C:N ratio. The model performance was validated by comparing the model's predicted values of N resorption against observational data analyzed in Sophia et al., 2024, using spatial-scale measurements of resorption efficiency across diverse plant types and climate zones, as well as gross primary productivity (GPP) observational data from plumber sites (Ukkola, et al., 2022) used for model application. We present the implications of this novel scheme for ecosystem functioning and show that we can improve the plant internal N available to growth with cascading implications for ecosystem nutrient pools and fluxes, better predicting plant and soil nutrient dynamics at steady state and crucially, under elevated CO2 conditions. For the first time, we show the importance of an ecologically realistic representation of nutrient resorption in an LSM and its implication for predicting the future of the terrestrial biosphere.
How to cite: Sophia, G., Caldararu, S., Stocker, B., and Zaehle, S.: Dynamic nitrogen resorption improves predictions of nutrient cycling responses to global change in a next generation ecosystem model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19396, https://doi.org/10.5194/egusphere-egu25-19396, 2025.
The relationship between precipitation (PPT) and aboveground net primary productivity (ANPP) has intrigued ecologists for decades because of its fundamental importance to the global carbon cycle. Across gradients from grassland to forest, the PPT-ANPP relationship is statistically well-defined and non-linear. Temporal patterns within a site over time, however, are generally weaker than spatial patterns and nearly always linear despite statistical attempts to bend the line. Linear relationships are inconsistent with positive asymmetry occurring when the increase in ANPP in a wet year is greater than the decline in ANPP in a comparably dry year. This led to the double asymmetry model which predicts that non-linear, concave down responses will occur when extreme wet and dry PPT years occur in a time series. Using long-term ANPP data from ambient plots, along with rainfall addition and reduction experiments in a Chihuahuan Desert grassland we tested the hypothesis that extending the range of precipitation would lead to a non-linear relationship between PPT and ANPP as predicted by the double asymmetry model. Based on a historical precipitation calculator for the past 2000 years, our experimental rain addition treatments matched the wettest years in the record, whereas our extreme drought experiments reduced precipitation ~43mm below historic lows. By extending the precipitation gradient to extremes through drought, water and nitrogen addition treatments we found support for the double asymmetry model with one important exception. The response was concave up under high precipitation under nitrogen fertilization. Without N addition, the response under high precipitation was linear. By experimentally extending the range of monsoon precipitation we were able to bend the rules and generate a non-linear PPT-ANPP relationship in this desert grassland, but only when nutrient limitation was alleviated. Because of strong water limitation, dryland ANPP is highly sensitive to year-to-year variability in precipitation. Water limitation under drought and nutrient limitation in wet years govern non-linear responses of ANPP to precipitation variability in this dryland ecosystem.
How to cite: Collins, S., Patton, M., and Brown, R.: Trying to bend the rules: precipitation-productivity relationship in desert grassland, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-135, https://doi.org/10.5194/egusphere-egu25-135, 2025.
We quantified the impacts of four years of nominal (within the historic range of variability) and extreme (1-in-100-year recurrence frequency) droughts on aboveground productivity with the International Drought Experiment (IDE), a coordinated, distributed network of 74 grassland and shrubland sites located on six continents across the globe. We expected that aboveground productivity, a key measure of terrestrial ecosystem functioning, would be impacted progressively (i.e., decline over time) as duration and severity of droughts increased. An alternative prediction is that acclimation may occur, whereby – productivity is either maintained or may even recover when drought is prolonged over multiple years. On average across all IDE sites and irrespective of whether drought was nominal or extreme, aboveground productivity declined significantly in the first of year drought, but the magnitude of loss in productivity did not change in years 2 to 4. Thus, we found evidence overall for acclimation to prolonged drought, and a similar acclimation response was observed with prolonged, nominal drought. Yet, when drought was extreme, progressive losses in ecosystem productivity was observed, with the largest losses observed with increasing drought severity in the third and fourth years of drought. Furthermore, the largest losses in productivity (>70%) were observed when drought was extreme for more than two consecutive years. Our results provide evidence for a strong interaction between drought severity and duration. When drought is within the historic range of variability, grassland and shrubland ecosystems have the potential to acclimate, but when extreme, ecosystems that historically were resistant may experience profound losses in functioning over time. This finding has important implications for terrestrial ecosystem functioning in the future, given forecasts for more severe and longer duration droughts with climate change - ecosystems may shift from being resistant to prolonged drought to experiencing catastrophic losses in ecosystem functioning.
How to cite: Smith, M., Ohlert, T., Collins, S., and Knapp, A. and the The International Drought Experiment Network: Drought severity interacts with duration to erode resistance of terrestrial ecosystem productivity, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6970, https://doi.org/10.5194/egusphere-egu25-6970, 2025.
Forest ecosystems in Europe are under a growing threat from recurring drought and heat extremes. Resource acquisition and allocation strategies determine the ability of species to cope with such stresses, so better understanding their variation with the environment is key to forecasting species and forest resilience. Resilience to weather and climate extremes also varies with the efficiency of a plant’s hydraulic transport system, yet limited information is available on how hydraulics influence investments into root, stem, branch, and leaf growth. This calls for an exploration of how plant hydraulic function interacts with carbon allocation over time. Here, we propose a new experimental design for the paired monitoring of above- and belowground carbon allocation and water fluxes in two European oak species (Quercus robur and Quercus cerris) with different drought tolerance levels. The growth and functional status of 52 4-year-old saplings of each species, transplanted in two different soils, are to be recorded between March 2025 and December 2025, including during a 4-month-drought treatment (i.e., stepwise decreased watering until significant canopy damage is achieved). Both root and canopy dynamics (e.g., growth, desiccation/wilting) will be recorded on sub-daily timescales using automated robotic minirhizotrons and measurements of canopy transmittance; dendrometers will monitor stem growth. Diurnal canopy gas exchange and photosynthetic response curves will be measured monthly. Above-ground hydraulic variables and traits (water potential, hydraulic conductance, P50) and non-structural carbohydrates in different organs will be measured periodically, as will synchronous leaf and woody anatomical traits. Taken together, the data gathered in our experiment will form a comprehensive picture of inter-species differences in whole-tree carbon allocation patterns and their hydraulic control under drought.
How to cite: Tang, Z., Sabot, M., El-Madany, T.-S., Hildebrandt, A., Huang, J., Nair, R., Weber, E., and Zaehle, S.: Getting to the root of allocation change: identifying allocation trade-offs under drought, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12015, https://doi.org/10.5194/egusphere-egu25-12015, 2025.
In the context of global climate warming, the rising temperatures have triggered a surge in both the frequency and severity of drought in subtropical regions. Consequently, extensive vegetation mortality has emerged, posing a substantial threat to vegetation ecosystems. Accurate quantification and understanding of vegetation drought are imperative for regulating vegetation mortality rates of drought events. However, controversy persists surrounding the precise quantification of vegetation drought. Therefore, the development of timely and effective methods for the accurate monitoring of widespread vegetation drought is of utmost importance. Despite the studies revealing vegetation drought at different temporal and spatial scales, the precise quantification of drought variations among various vegetation covers, as well as within the same vegetation cover, remains unexplored.
In this study, for the precise quantification of "same vegetation cover with different drought degrees" and "same drought degree with different vegetation covers", a vegetation drought response (VDR) module is developed. This module accurately characterizes the spatiotemporal response of vegetation to soil moisture over time, based on spatio-temporal features constructed using the multispectral-based modified vegetation index and land surface temperature. To scientifically define drought boundaries, the study leverages knowledge involving "decreasing soil moisture leading to withering vegetation" and "increasing soil moisture resulting in flourishing vegetation" to identify the time intervals during the vegetation drought process (VDP). Within the VDP intervals, the sensitivity of vegetation response to soil moisture determines the characteristics of VDR in the beginning of drought, which is then utilized to establish the vegetation drought threshold (VDT). By applying the VDT to VDR, the study constructs a process-cognizant vegetation drought model (PCVDM) to achieve a quantitative inversion of vegetation drought. Using the Hunan-Jiangxi region in the central subtropical zone of China as a case study, this research employs remote sensing techniques to quantitatively retrieve the spatiotemporal changes in vegetation drought from 2000 to 2023. Furthermore, it conducts a spatiotemporal differentiation analysis and causation discrimination by integrating altitude and lithology conditions.
The findings of this study highlight the valuable insights on the spatiotemporal dynamics of vegetation drought supported with the PCVDM. The PCVDM can be utilized for remote sensing monitoring of vegetation drought in subtropical regions, enabling the identification of spatial differentiation in vegetation drought in the Hunan-Jiangxi region based on altitude and geological lithology. This study reveals the overall trends in vegetation changes in the Hunan-Jiangxi region since the beginning of this century: areas at higher altitudes (>800m) exhibit increased greenness due to rising temperatures, while lower altitude areas (<200m) experience intensified vegetation drought due to increased evapotranspiration. Meanwhile, moderate altitude areas (~400m) are influenced by the spatial differences in geological lithology, where increased greenness coexists with vegetation drought phenomena.
How to cite: Zhang, Z., Jiao, Z., and Wu, L.: A Process-Cognizant Remote Sensing Model for Subtropical Vegetation Drought in the Hunan-Jiangxi Region, China, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6305, https://doi.org/10.5194/egusphere-egu25-6305, 2025.
Large-scale fire in the desert Southwest was historically rare but is
becoming more common owing to human activity. In June 2020, a large wildfire burned the
eastern half of the Sycamore Creek, AZ watershed, leaving the mainstem and western half
unburned. During storms, which occurred twice during the year of the fire and not again until a
year later, large quantities of ash were transported to the stream and deposited on stream banks
as well as along upland flowpaths. Because up to 70% of this fire-associated carbon transported
during floods was consumed over 21 d, we investigated the properties of the ash, including
amounts of carbon and nutrients leached from the ash, utilization (measured as loss of carbon
across 3- and 21-d incubations), and carbon quality of the DOC leached from the ash and of that
remaining after incubations.
We found that heavy but episodic subsidies of DOC to desert stream ecosystems occur following
fire. Spatial and temporal patterns of rainfall that produced runoff determined the amount of
these subsidies. Ash collected from upland and riparian depositional areas contained measurable
quantities of carbon that were consumed during laboratory incubations with an inoculum of
microbial communities from stream sediments. Leached ash also released inorganic and organic
nitrogen and other materials. These data suggest that catastrophic release of materials during fire,
when transported to desert streams, can support microbial metabolism by enhancing nutrient-
limited primary production or supplying a novel source of organic matter to heterotrophic microbes.
How to cite: Grimm, N., Barendrick, J., Gaines-Sewell, L., Grabow, J., and Harms, T. K.: Quantity and quality of carbon from ash deposits associated with desert fire, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21934, https://doi.org/10.5194/egusphere-egu25-21934, 2025.
Climate change has intensified the severity and duration of droughts in grasslands globally, increasing the risk of extreme multiyear droughts. While most grasslands are considered to be resilient to short-term drought, extreme multiyear droughts can have longer-lasting consequences. For instance, full recovery of ecosystem structure after the 1930s central US Dust Bowl drought required 20 years. Due to the rarity of such multiyear droughts, we know little about the influence of drought duration on ecosystem recovery post-drought or the mechanisms influencing recovery. Here, we evaluated the recovery dynamics of carbon uptake (estimated via aboveground net primary productivity, ANPP) in a semi-arid shortgrass steppe ecosystem after 4 vs. 5-years of experimental drought (66% precipitation reduction). We also assessed the influence of post-drought precipitation amounts on recovery by implementing treatments equivalent to 150% of long-term average (LTA) for this site after the drought ended. Non-droughted plots experienced similar treatments. We observed dramatic differences in recovery in the 150% LTA treatments after four vs. five years of drought, and thus identified a clear threshold in drought duration impacts in this grassland. After four years of drought, C4 grass productivity increased substantially in the first year and fully recovered by the second. In contrast, there has been little to no recovery of C4 grasses after five years of drought. Plant communities in the 5-year drought treatment shifted to dominance by annual (weedy) forbs, with 3-4 times greater ANPP compared to non-droughted plots. This increase in ANPP was likely due to a 20-fold increase in available soil nitrogen in the recovery period. Our results demonstrate the existence of an abrupt threshold in response to drought duration in this grassland. Once this drought duration threshold is crossed, catastrophic changes in vegetation structure, carbon dynamics, and ecosystem recovery ensue.
How to cite: Knapp, A., Tooley, G., and Smith, M.: Evidence for a threshold in ecosystem functioning during an extreme drought in a semi-arid grassland, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1956, https://doi.org/10.5194/egusphere-egu25-1956, 2025.
Posters virtual: Wed, 30 Apr, 14:00–15:45 | vPoster spot A
EGU25-2383 | Posters virtual | VPS4
Hydrological responses to vegetation-climate interactions at two subtropical forested watersheds of TaiwanWed, 30 Apr, 14:00–15:45 (CEST) | vPA.12
Forested upstream watersheds support clean freshwater and maintaining stable hydrological conditions of ecosystem services. The associations between vegetation growth and climatic variations play a vital role on hydrological regimes that are region-dependent, but the associations of climate-phenology-hydrology have rarely been investigated in tropical/subtropical regions particularly. In this analysis, the hydroclimate records (1991-2020) at two long-term studied forest watersheds, Fushan (FS) and Leinhuachi (LHC) experimental forest, Taiwan were used, and showed that the incidences of meteorological and hydrological droughts are becoming prominent after 2001. We further investigated the effects of monthly climate variables (temperature and precipitation) on vegetation growth using monthly PV (photosynthetic vegetation fraction) of a watershed derived from MODIS (Moderate Resolution Imaging Spectroradiometer), and examined the effects of spring and summer rainfall on the variations of vegetation phenological patterns and subsequent watershed streamflow during 2001–2020. The PV and temperature showed a linear relationship without time-lag effect (R2 = 0.51-0.57, p < 0.001), whereas PV and precipitation exhibited no time-lag in FS but a log-linear relationship with 2-month lag (R2 = 0.15-0.59, p < 0.001) existed in LHC, indicating the accumulation of rainfall during relatively dry season (winter-spring) was critical for vegetation growth. Structural equation modeling (SEM) revealed that earlier start of growing season (SOS) caused by relatively high spring rainfall (February-March) led to longer growing season (LOS) and higher P-Q deficit (precipitation minus runoff) during the growing season in LHC. Nevertheless, the large amount of precipitation during growing season has no effect on the end of growing season (EOS), LOS and P-Q deficit. Neither EOS has influence on LOS and P-Q deficit. However, these patterns were not found in FS. Understanding the vegetation responses to climatic variations is required for future hydrologic regime projections, especially under changing climate.
How to cite: Chang, C.-T., Lee, J.-Y., Chiang, J.-M., Wang, H.-C., Huang, C., and Huang, J.-C.: Hydrological responses to vegetation-climate interactions at two subtropical forested watersheds of Taiwan, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2383, https://doi.org/10.5194/egusphere-egu25-2383, 2025.
