Tropical vegetation dynamics and ecosystem carbon (C) stocks typically vary with local topography and forest disturbance history. Yet, neither remote sensing nor vegetation modeling captures the underlying mechanistic processes determining ecosystem functioning and therefore the resulting estimates often do not match field observations of vegetation C stocks, especially so in hyperdiverse tropical forest ecosystems. This mismatch is further aggravated by the fact that multiple interacting factors, such as climatic drivers (i.e., temperature, precipitation, climate seasonality), edaphic factors (i.e., soil fertility, topographic diversity) and diversity-related parameters (i.e., species composition and associated plant functional traits) in concert determine ecosystem functioning and therefore affect tropical forest C sink-strength.

Here, we propose a novel framework designed for integrating in-situ observations of local plant species diversity with remotely sensed estimates of plant functional traits, with the goal to deduce parameters for a recently developed trait- and size-structured demographic vegetation model. Plant-FATE (Plant Functional Acclimation and Trait Evolution) captures the acclimation of plastic traits within individual plants in response to the local environment and simulates shifts in species composition through demographic changes between coexisting species, in association with differences in their life-history strategies.

Our framework may be used to project the functional response of tropical forest ecosystems under present and future climate change scenarios and thus should have crucial implications for assisted restoration and management of tropical plant species threatened by extinction.

How to cite: Hofhansl, F., Hietz, P., Huber, W., Weissenhofer, A., and Wanek, W.: Landscape-scale And Spatially Explicit Representation of vegetation dynamics and ecosystem carbon stocks in a hyperdiverse tropical forest ecosystem (LASER), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5862, https://doi.org/10.5194/egusphere-egu24-5862, 2024.

The impact of elevated atmospheric CO₂ concentrations on forest productivity depends on the capacity of plants to balance the additional CO₂ with the demand for additional nutrients. One hypothesis states that plants may allocate the extra carbon belowground in producing and maintaining fine roots to alleviate nutrient limitation. In the Amazon basin, where approximately 60% of the forest is on old and weathered soil, the litter layer is an important nutrient source. In some regions, root mats growing in the litter layer can be observed, where the roots intercept the newly mineralized nutrients before they reach the soil and may bind to the mineral matrix. To improve their nutrient uptake capacity, trees can either modify their root morphology to a ‘do-it-yourself” strategy, increasing root length and branching intensity or alternatively, they can outsource the same function by investing in symbioses with mycorrhizal fungi. Additionally, fine roots can stimulate microbial decomposition of recalcitrant substrates (e.g., wood debris) by exuding low molecular weight organic compounds (LMWO) and increasing P mobilization by phosphatase activity without changing decomposition. These strategies could also vary depending on the growing depth of roots due to the different physical conditions between the organic upper and mineral layers. However, little is known about the role of trait differences in roots under higher CO₂ concentrations.

To increase our understanding of belowground responses of understory plants to elevated CO₂ concentrations, we set up an Open-Top Chamber experiment in a lowland forest in the Central Amazon. We observed that under eCO_2, root productivity did not change in the litter layer but showed a decreased pattern in the soil layer. Moreover, plants intensified root foraging in the litter layer by increasing their specific root length more than threefold under elevated CO₂. In contrast, roots in the soil mineral layer followed an “outsourcing” strategy by increasing arbuscular mycorrhizal colonization by 117%. In addition, our results showed a decrease in the organic P in litter without a change in C decomposition under higher CO₂ concentrations, suggesting a direct P mobilization.

Our results suggest that plants may plastically adjust resource acquisition strategies to increase nutrient uptake efficiency and be able to directly affect P mobilization from the litter layer. We conclude that this ability of plants to adapt their P acquisition strategies in response to eCO₂ by tackling different sources within the litter-soil continuum and maximizing nutrient acquisition represents an important mechanism to support the CO₂ fertilization effect and might affect the resilience of the Amazonian rainforest to climate change, and thus global carbon balance.

How to cite: Martins, N. and the AmazonFACE team: Multiple plant root strategies improve phosphorus acquisition under elevated CO2 in the Amazon rainforest, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10719, https://doi.org/10.5194/egusphere-egu24-10719, 2024.

The Central Amazon comprises mosaics of forest ecosystems with different water dynamics and soil characteristics. The water dynamics from each ecosystem affect the evaporation signal seasonally expressed in the water isotopes (δ¹⁸O and δD). The recognition of the evaporative signal from different forest segments is essential for the development of hydrological and eco-hydrological studies in the complex Amazon biome. In this study, we used stable isotopes to evaluate how the water dynamics of different forest ecosystems affect seasonal water evaporative signals in each environment. We monitored water isotope signals from 2018-2020 in different compartments (precipitation, soil, stream, groundwater, river, lake, and flooded areas) of two non-flooded forests (clay soils - “plato” and sandy soils – “campinarana”) and three flooded forests (pristine igapó, disturbed igapó and várzea). We found that the soil water sampled by lysimeters in the upland forest seasonally expresses the isotope signal from the rainwater (Local Meteorical Water Line-LMWL) without a strong evaporative overprint. The water isotope signal from flooded forests is more variable. The isotopic composition of pristine rivers has an overlapping signal from the rain isotope signal (LMWL). However, water from the river downstream from the very large hydropower dam (Balbina) has a strong evaporative signal. During the flooded period, the water within the flooded forests has a more evaporated signal than the signal from the source (such as the river or lakes). During the non-flooded period, the water isotope signal from the soil inside the flooded forest corresponds to the rainwater signal. To the best of our knowledge, these represent the first description of the water isotope signals from the compartments in different Central Amazonian forest ecosystems. They illustrate and identify the high variation of the evaporative signal from the complex Amazon biome, knowledge that is essential to understanding how different forest ecosystems influence water recycling in the Amazon hydrological cycle.

How to cite: Durgante, F., Schöngart, J., Piedade, M. T. F., Trumbore, S., Jones, S. P., Gastmans, D., Komiya, S., Oliveira, R., Gleixner, G., Lavric, J., Moossen, H., Geilmann, H., Weiss, B., Macedo, M., Rincon, L. M., Sá, P. A. D., and Wittmann, F.: Seasonal variation of water isotopes in different forest ecosystems in the Central Amazon , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10823, https://doi.org/10.5194/egusphere-egu24-10823, 2024.

The Amazon rainforest is of vital importance for biodiversity, regional climate, as well as global water and carbon cycling. However, over the past decades, ecosystem functions of the Amazon rainforest have diminished through a combination of increasing anthropogenic pressure in form of land-use change and intensifying natural disturbances. Recent studies suggest that unabated deforestation and climate change could tip large parts of the Amazon towards a different, savanna-like vegetation state. Although such a scenario could lead to severe impacts on the climate system from regional to global scales, a holistic assessment of the risk of large-scale Amazon forest loss due to land-use change and climate change in the 21^st century is currently lacking. 

Here, we use data from multiple CMIP6 Earth System Models under two low climate mitigation scenarios to attribute Amazon forest loss until 2100 to land-use change and climate change, applying a novel ensemble member approach. We find that around 1 mio. km² of forest will diminish by 2100, corresponding to a loss of around one fifth of the pre-industrial forest area. Historically and over the first half of the 21^st century, land-use change is the main driver of forest loss, whereas forest loss due to climate change increases non-linearly beyond 2°C global warming and even exceeds forest loss caused by land-use change by the end of the century in some models. We further find a consistent increase in the probability of abrupt (rather than gradual) forest loss with progressing deforestation and climate change. 

Overall, our results highlight that under plausible low mitigation socio-economic pathways 1) the Amazon rainforest will substantially diminish due to anthropogenic climate and land-use change and 2) the risk of forest loss due to climate change increases significantly beyond 2°C global warming. This stresses the urgent need for increased efforts to reduce deforestation and forest degradation through forest protection, conservation and sustainable land-use practices and for climate mitigation efforts in line with the Paris Agreement.

How to cite: Bultan, S., Bathiany, S., Boers, N., Ganzenmueller, R., Gyuleva, G., Moustakis, Y., and Pongratz, J.: Attributing future Amazon forest loss to land-use change and climate change, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11932, https://doi.org/10.5194/egusphere-egu24-11932, 2024.

Land surface temperature (LST) is a dominant influence on the health and productivity of ecosystems. Deforestation in the Brazilian Amazon has led to extensive land-use transitions from forests to pastures and industrialized agriculture. This has resulted in elevated land surface temperatures, with impacts on the energy, water, and carbon cycles. Forest fragmentation increases the area of forest edges, where exposure to sunlight, wind, and bordering land-uses alters the forest microclimate. While the changes in forest edge temperature due to bordering land-use transitions is acknowledged, the magnitude of these changes between specific agricultural land management practices has yet to be determined. This case study uses a remote sensing approach to investigate forest edge temperatures in Mato Grosso, Brazil, with a primary goal of discerning how distinct agricultural practices, such as cover cropping or double cropping, can potentially mitigate adverse temperature impacts on forest edges. These findings will strengthen the understanding of forest edge temperatures, with a focus on the potential of sustainable land management, contributing to broader conservation efforts in the Amazon Rainforest. 

How to cite: Hellenkamp, S., Brando, P., and Starinchak, B.: Understanding the role of temperature in forest edges: a remote sensing approach in the Brazilian Amazon, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13403, https://doi.org/10.5194/egusphere-egu24-13403, 2024.

The Amazon Tall Tower Observatory is located in the central Amazon (S 02 08.9°, W 059 00.2°) inside the Uatumã Sustainable Development Reserve and has been monitoring continuously the atmospheric composition since 2013. The site is set up with two measurement towers of 80 meters and a tall tower of 325 meters for continuous monitoring of trace gases and aerosols. The surface influence (hereafter footprint) of the research station covers a large area to the east and northeast with the fetch extending for hundreds of kilometres, overlapping with the main branch of the Amazon River reaching the city of Belém (during the dry season) and large swaths of primary forest over the Amapá state (during the wet season).  We have analysed trends in fire counts (using MODIS thermal anomalies) and burned area (GFED4 and GFED5, Global Fire Emission Database 4th and 5th version) over the last two decades (2000-2023) inside the ATTO footprint and found that both show increasing and significant trends for the months of June (14,68 fire counts/year) July (42,23 fire counts/year), August (59,6 fire counts/year) and September (148,6 fire counts/year). Spatially, fires are located on easternmost part of the footprint and there is no evidence of a spatial trend approaching ATTO. Interestingly, in October the mean longitude of the fire counts over the period of interest shows a trend migrating from -56°W to -54°W, but with no significant trend in fire counts. We complement these results by analysing mole fractions of carbon monoxide (a proxy for biomass burning) at ATTO for an overlapping period (2013-2023). In addition, we provide links to the environmental drivers explaining these trends and spatial patterns. Observing biogenic greenhouse gases enhances our understanding of the Amazonian rainforest’s carbon budget, influenced by climatic conditions, land use alteration and other anthropogenic impacts.  

How to cite: Dajti, G., Urquiza, D., van Asperen, H., Jones, S., Komiya, S., Lavric, J., Hantson, S., and Botía, S.: Fire trends on ATTO footprint over the last two decades, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15363, https://doi.org/10.5194/egusphere-egu24-15363, 2024.

Nitrogen oxides (NOx = NO and NO₂) are chemical compounds that affect and control the abundance of ozone (O₃) and hydroxyl radicals (OHx = OH and HO₂), the main oxidizing agents in the atmosphere. In pristine environments, these oxidizers react with biogenic volatile organic compounds (BVOCs), such as isoprenes, to produce oxidized secondary organic products. Further reaction with NOx leads to the formation of nitrates. Nitrates deposit on surfaces and grow aerosol particles which eventually act as cloud condensation nuclei. This makes NOx an important atmospheric component, even in low concentrations. Therefore, NOx measurements are being made at the Amazon Tall Tower Observatory (ATTO) research site in the central Amazon forest basin, a pristine region.

Here we present the measurements of NO, O₃ and meteorological parameters collected at the Walk-up tower, at a height of approximately 40 m, just above the canopy.  

How to cite: Monteiro, C., Tsokankunku, A., Harder, H., and Wolff, S.: NO and O3 mixing ratios above the canopy in the rainforest, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16499, https://doi.org/10.5194/egusphere-egu24-16499, 2024.

Phosphorus (P) is a key driver of terrestrial productivity. However, the lack of spatial data on various P forms in soils hinders the large-scale application of process-based vegetation models. To address this, we used a model selection approach based on Random Forest regression models to predict different P forms (total, available, organic, inorganic, and occluded P) in the pan-Amazon region. Our models were trained and tested using data from 108 sites of the RAINFOR network, including soil group and textural properties, geolocation, nitrogen (N) and carbon (C) contents, terrain elevation and slope, soil pH, and mean annual precipitation and temperature. The models were then applied to several spatially explicit datasets to predict the target P forms. The resulting maps depict the distribution of total, available, organic, inorganic, and occluded P forms in the topsoil profile (0 - 30 cm) at a spatial resolution of 5 arcminutes. Our models achieved a good level of mean accuracy (77.37 %, 76,86 %, 75.14 %, 68.23 %, and 64.62% for the total, available, organic, inorganic, and occluded P forms, respectively). Our results reveal a clear gradient of soil development and nutrient content, with the mapped area generally exhibiting very low total P concentration status. Total N was the most important variable for predicting all target P forms. Despite some gaps in the training and testing data, most of the area could be mapped with a good level of accuracy. Our maps can aid in the parametrization and evaluation of process-based terrestrial ecosystem models and promote the testing of new hypotheses about P availability and soil-vegetation feedbacks in the pan-Amazon region.

How to cite: Darela-Filho, J. P., Rammig, A., Fleischer, K., Reichert, T., Lugli, L. F., Quesada, C. A., Hurtarte, L. C. C., de Paula, M. D., and Lapola, D. M.: Mapping Phosphorus Forms in the Pan-Amazon Region: A Machine Learning Approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18326, https://doi.org/10.5194/egusphere-egu24-18326, 2024.

The Congo basin is home to the second largest tropical forest in the world Therefore, it plays a crucial role in the global carbon cycle. Yet very few field based data on related processes exist. Gaining knowledge on a species level is also crucial for understanding these ecosystems. Leaf chamber measurements allow to measure photosynthetic capacity on a leaf level and by so, quantify the photosynthetic capacity of individual species. Moreover, they allow to quantify a plant´s reaction to environmental parameters such as light, atmospheric CO₂ concentration and temperature. Such data is crucial to improve the calibration and robustness of global vegetation models. These models are key tools to estimate the global carbon budget and ecosystem responses to climate change as a part of the Intergovernmental Panel on Climate Change exercises.

To date, no such data exists for the forests of the Congo Basin which prevents us to properly understand forest dynamics and resilience to global changes.In this research, we quantify leaf level carbon uptake and its response to light, CO₂ and Temperature for dominant tree species within the footprint of the CongoFlux tower in Yangambi (DR Congo).

As such, we deliver the first in-field leaf-level photosynthetic parameters dataset for a lowland tropical forest of the Congo Basin. Doing this, we explore the controls of interspecific variation in photosynthetic capacity including plant guild, species and vertical canopy position. Our study takes place at the research site of CongoFlux, Yangambi (DR Congo).

How to cite: Sibret, T., Peaucelle, M., Meunier, F., Bauters, M., Ellsworth, D., Crous, K., Boeckx, P., and Verbeeck, H.: Quantifying the photosynthetic capacity of dominant tree species in a humid lowland tropical forest of the Congo Basin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19990, https://doi.org/10.5194/egusphere-egu24-19990, 2024.

CO is an indirect greenhouse gas because it reacts with OH, therefore increasing the lifetime of methane: its possible indirect radiative forcing has been estimated as larger than that of N₂O. Previous studies have indicated that temperate and boreal forests act as a net sink for CO, but the role of tropical rain forest ecosystems has not been investigated. We present the first CO flux measurements from tropical forest and forest soils, and can show that tropical rain forests are a net source of CO to the atmosphere.

During two intensive field campaigns at tropical rain forest fieldsite ZF2 (Manaus, Brazil), soil CO fluxes were determined by use of flux chambers. In addition, nighttime vertical CO concentration profiles were measured and different micro-meteorological techniques were applied to estimate ecosystem CO fluxes. Furthermore, we performed nocturnal CO concentration measurements in a seasonally inundated valley, which was hypothesized as a potential hotspot for ecosystem CO emissions.

Soil CO fluxes ranged from -0.19 (net soil uptake) to 3.36 (net soil emission) nmol m^-2 s^-1, averaging ∼1 nmol CO m^-2 s^-1. Fluxes varied with season and topographic location, with highest fluxes measured in the dry season in a seasonally inundated valley. Nocturnal canopy air profiles show consistent decreases in CO mixing ratios with height, which requires positive surface fluxes between 0.3 and 2.0 nmol CO m^-2 s^-1. Similar fluxes are derived using a canopy layer budget method, which considered the nocturnal increase in CO over time (1.1 to 2.3 nmol CO m^-2 s^-1). Using wet season concentration profiles of CO, the estimated valley ecosystem CO production exceeded the measured soil valley CO fluxes, indicating a potential contribution of the valley stream to overall CO emissions.

Based on our field observations, we expect that tropical rain forest ecosystems are a net source of CO. Extrapolating our first observation-based tropical rain forest soil emission estimate of ∼1 nmol m^-2 s^-1, a global tropical rain forest soil emission of ∼16.0 Tg CO yr^-1 is suggested. Total ecosystem CO emissions might surpass this estimate, considering that valley streams and inundated areas could serve as local CO emission hotspots. To further improve tropical forest ecosystem CO emission estimates, more in-situ tropical forest soil and ecosystem CO flux measurements are essential.

How to cite: van Asperen, H., Warneke, T., Carioca de Araújo, A., Forsberg, B., José Filgueiras Ferreira, S., Röckmann, T., van der Veen, C., Bulthuis, S., Komiya, S., P Jones, S., Botía, S., Ramos de Oliveira, L., de Lima Xavier, T., da Mata, J., de Oliveira Sá, M., Ricardo Teixeira, P., Andrews de França e Silva, J., Notholt, J., and Trumbore, S.: Tropical forests: a source of CO!, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12352, https://doi.org/10.5194/egusphere-egu24-12352, 2024.

The response of plants to increasing atmospheric CO₂ concentration depends on several factors such as life history of specific species, availability of water, nutrients and light, and the ecological context that the plants are found. Although several experiments with elevated CO₂ (eCO₂) have been done worldwide, none was performed in the Amazon forest understory focusing in a community growing naturally. The understory of the central Amazon is limited by both light and phosphorus. Understanding how such ecosystem responds to eCO₂ is important to foresee how the forest will function in the future. Also, quantifying the response of this forest compartment helps to constrain Ecosystem Models that compute carbon and water fluxes.

For this study, we used the open-top chamber (OTC) approach, with a CO₂ enrichment of +250 ppm above the ambient concentration. Eight OTC were installed (4 with ambient CO₂ and another 4 with eCO₂) in the understory of a natural forest in the Central Amazon, approximately 70 km from Manaus city. The eCO2 experiment started in November 2019 and, after 120 days, we quantified the average community response of the following photosynthetic parameters: light saturated carbon assimilation rate (A_sat), stomatal conductance (g_s), transpiration rate (E), intrinsic water use efficiency (iWUE), apparent quantum yield (Φ), light compensation point (LCP), maximum carboxylation capacity (V_cmax), maximum electron transport rate (J_max). After 240 days of treatment, we quantified mean individual leaf production and accumulated leaf production, leaf area (Lf_area). After 300 days, we quantified the increment in base diameter (BD), height (H_t) and relative growth rate (RGR).

Under eCO₂, we observed increases in A_sat (67%), J_max (19%), Φ (56%), and iWUE (78%), in agreement with the hypothesis that plants near the light compensation point respond strongly to eCO₂. We also detected an increase in Lf_area (51%) and BD (65%), indicating that the extra primary productivity was not allocated to growth in height, but to supporting more light intercepting organs (leaf and conducting tissues). No detectable changes were observed for the other variables.

Apart from the expected increase in assimilation rates, understory plants in Central Amazon responded positively to eCO₂ by increasing their ability to capture and use light (leaf size, Φ, and J_max). The increment in leaf area while maintaining E rates signifies that this forest compartment will increase its contribution to the whole forest water fluxes to the atmosphere. That might be related to the prevailing acquisitive strategy necessary for competing for phosphorus brought by water flow through plants. As a possible consequence, this forest might be less resistant to extreme drought associated with El Niño years.

Funding: Coordination for the Improvement of Higher Education Personnel - CAPES (grants 312589/2022-0) and São Paulo Research Foundation-FAPESP processes numbers (2022/07735-5) and (2015/02537-7). 

How to cite: Domingues, T., Damasceno, A., Garcia, S., Aleixo, I., Menezes, J., Pereira, I., De Kauwe, M., Ferrer, V., Fleischer, K., Grams, T., Santana, F., Hartley, I., Kruijt, B., Lugli, L., Martins, N., Norby, R., Portela, B., Rammig, A., Quesada, C., and Lapola, D. and the AmazonFACE team: Amazonian understory response to elevated CO2, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18954, https://doi.org/10.5194/egusphere-egu24-18954, 2024.

Deforestation of the Amazon rainforest biome has been of considerable international concern, as extensive forest loss has negative impacts on global carbon storage, hydrological cycles and biodiversity. Ongoing climatic change is predicted to make these effects worse, as climatic models suggest that increasing temperatures will often be accompanied by decreasing precipitation. Such change would put the continued existence of the rainforest biome at risk, as moisture-demanding species would be replaced by more drought-resistant ones. Field observations already indicate that even those Amazonian forests that are not directly affected by deforestation have started to change, and that they grow faster, store less carbon and contain more lianas than before. However, field measurements can only be carried out in a limited number of sites, and these only cover a minute part of the entire Amazon biome. To get a more complete understanding of the changes within the remaining Amazonian forests, we are carrying out broad-scale analyses using Landsat imagery. We first did pixel-based compositing using all image acquisitions within a 10-year time window in order to obtain a clean cloud-free reflectance surface. Two such composites were produced for different time periods (2000-2009 and 2013-2022) in order to identify potential changes across the forested landscape. The results are expected to identify areas where significant but non-obvious changes in the structure and/or function of the forest could be happening, and thereby to facilitate in assessing the degree of threat to the ecosystem

How to cite: Gupta, R., Ruokolainen, K., and Tuomisto, H.: Using Landsat composites to document temporal change within Amazonian forest vegetation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7786, https://doi.org/10.5194/egusphere-egu24-7786, 2024.

A new carbon flux tower has been established in the tropical rainforest of Ghana to measure carbon fluxes as well as emissions of biogenic volatile organic compounds. African tropical forests constitute about 20% of Global Tropical Forest cover but have been understudied due to a lack of in-situ observations. The establishment of GhanaFLUX in the Bia-Tano forest reserve in western Ghana will help to fill this gap, allowing in-depth assessments of carbon sequestration and storage in African forests. Here, we present a snapshot of the facilities available at GhanaFLUX, and measurements taken in the first year of operation. We show time series analysis of carbon dioxide and meteorological datasets obtained from GhanaFLUX, highlighting the seasonal variations in these observations. We also share some of our experiences and challenges during the establishment and operation of the flux site to guide researchers who are planning to set up new sites in challenging environments like rainforests. 

How to cite: Otu-Larbi, F., Mensah, C., Agyemang Prempeh, N., Kumi, N., and Kyere-Boateng, R.: GhanaFLUX: Meauring carbon fluxes in an African Rainforest, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20858, https://doi.org/10.5194/egusphere-egu24-20858, 2024.