Simulating canopy dynamics, productivity and water balance of annual crops from field to regional scales

2016 Summer.Includes bibliographical references.To provide better understanding of natural processes and predictions for decision support, dynamic models have been used to assess impact of climate, soils and management on crop production, water use, and other responses from field to regional scales. It is important to continue to improve the prediction accuracy and increase the reliability. In this work, we first improved the DayCent ecosystem model by developing a new empirical method for simulating green leaf area index (GLAI) of annual crops. Its performance has been validated using experimental observations from different experimental field locations as well as more aggregate NASS yield data spanning the country. Additionally, sensitivity and uncertainty of important parts of the crop growth model have been quantified. Our results showed the new model provided reliable predictions on crop GLAI, biomass, grain yield, evapotranspiration (ET), and soil water content (SWC) at field scale at various locations. At national scale, the predictions of grain yields were generally accurate with the model capable of representing the geographically-distributed differences in crop yields due to climate, soil, and management. The results indicated that the model is capable of providing insightful predictions for use in management and policy decision making. Although there are challenges to be addressed, our results indicate that the DayCent model can be a valuable tool to assess crop yield changes and other agroecosystem processes under scenarios of climate change in the future

Bayesian inference of hydraulic properties in and around a white fir using a process-based ecohydrologic model

We present a parameter estimation study of the Soil-Tree-Atmosphere Continuum (STAC) model, a process-based model that simulates water flow through an individual tree and its surrounding root zone. Parameters are estimated to optimize the model fit to observations of sap flux, stem water potential, and soil water storage made for a white fir (Abies concolor) in the Sierra Nevada, California. Bayesian inference is applied with a likelihood function that considers temporal correlation of the model errors. Key vegetation properties are estimated, such as the tree\u27s root distribution, tolerance to drought, and hydraulic conductivity and retention functions. We find the model parameters are relatively non-identifiable when considering just soil water storage. Overall, by utilizing multiple processes (e.g. sap flow, stem water potential, and soil water storage) during the parameter estimation, we find the simulations of the soil and tree water properties to be more accurate when compared to observed data

Response of hydrological processes to input data in high alpine catchment : an assessment of the Yarkant River basin in China

Most studies of input data used in hydrological models have focused on flow; however, point discharge data negligibly reflect deviations in spatial input data. To study the effects of different input data sources on hydrological processes at the catchment scale, eight MIKE SHE models driven by station-based data (SBD) and remote sensing data (RSD) were implemented. The significant influences of input variables on water components were examined using an analysis of the variance model (ANOVA) with the hydrologic catchment response quantified based on different water components. The results suggest that compared with SBD, RSD precipitation resulted in greater differences in snow storage in the different elevation bands and RSD temperatures led to more snowpack areas with thinner depths. These changes in snowpack provided an appropriate interpretation of precipitation and temperature distinctions between RSD and SBD. For potential evapotranspiration (PET), the larger RSD value caused less plant transpiration because parameters were adjusted to satisfy the outflow. At the catchment scale, the spatiotemporal distributions of sensitive water components, which can be defined by the ANOVA model, indicate that this approach is rational for assessing the impacts of input data on hydrological processes

Hydrology-oriented forest management trade-offs. A modeling framework coupling field data, simulation results and Bayesian Networks

[EN] Hydrology-oriented forest management sets water as key factor of the forest management for adaptation due to water is the most limiting factor in the Mediterranean forest ecosystems. The aim of this study was to apply Bayesian Network modeling to assess potential indirect effects and trade-offs when hydrology-oriented forest management is applied to a real Mediterranean forest ecosystem. Water, carbon and nitrogen cycles, and forest fire risk were included in the modeling framework. Field data from experimental plots were employed to calibrate and validate the mechanistic Biome-BGCMuSo model that simulates the storage and flux of water, carbon, and nitrogen between the ecosystem and the atmosphere. Many other 50-year long scenarios with different conditions to the ones measured in the field experiment were simulated and the outcomes employed to build the Bayesian Network in a linked chain of models. Hydrology-oriented forest management was very positive insofar as more water was made available to the stand because of an interception reduction. This resource was made available to the stand, which increased the evapotranspiration and its components, the soil water content and a slightly increase of deep percolation. Conversely, Stemflow was drastically reduced. No effect was observed on Runof due to the thinning treatment. The soil organic carbon content was also increased which in turn caused a greater respiration. The long-term effect of the thinning treatment on the LAI was very positive. This was undoubtedly due to the increased vigor generated by the greater availability of water and nutrients for the stand and the reduction of competence between trees. This greater activity resulted in an increase in GPP and vegetation carbon, and therefore, we would expect a higher carbon sequestration. It is worth emphasizing that this extra amount of water and nutrients was taken up by the stand and did not entail any loss of nutrients.This study is a component of research projects: HYDROSIL (CGL2011-28776-C02-02), SILWAMED (CGL2014-58127-C3-2) and CEHYRFO-MED (CGL2017-86839-C3-2-R) funded by the Spanish Ministry of Science and Innovation and FEDER funds. The authors are grateful to the Valencia Regional Government (CMAAUV, Generalitat Valenciana), ACCIONA for their support in allowing the use of the experimental forest and for their assistance in carrying out the fieldwork.Garcia-Prats, A.; González Sanchis, MDC.; Campo García, ADD.; Lull, C. (2018). Hydrology-oriented forest management trade-offs. A modeling framework coupling field data, simulation results and Bayesian Networks. The Science of The Total Environment. 639:725-741. https://doi.org/10.1016/j.scitotenv.2018.05.134S72574163

Leveraging 35 years of Pinus taeda research in the southeastern US to constrain forest carbon cycle predictions: regional data assimilation using ecosystem experiments

abstract: Predicting how forest carbon cycling will change in response to climate change and management depends on the collective knowledge from measurements across environmental gradients, ecosystem manipulations of global change factors, and mathematical models. Formally integrating these sources of knowledge through data assimilation, or model–data fusion, allows the use of past observations to constrain model parameters and estimate prediction uncertainty. Data assimilation (DA) focused on the regional scale has the opportunity to integrate data from both environmental gradients and experimental studies to constrain model parameters. Here, we introduce a hierarchical Bayesian DA approach (Data Assimilation to Predict Productivity for Ecosystems and Regions, DAPPER) that uses observations of carbon stocks, carbon fluxes, water fluxes, and vegetation dynamics from loblolly pine plantation ecosystems across the southeastern US to constrain parameters in a modified version of the Physiological Principles Predicting Growth (3-PG) forest growth model. The observations included major experiments that manipulated atmospheric carbon dioxide (CO[subscript 2]) concentration, water, and nutrients, along with nonexperimental surveys that spanned environmental gradients across an 8.6  ×  10[superscript 5] km[superscript 2] region. We optimized regionally representative posterior distributions for model parameters, which dependably predicted data from plots withheld from the data assimilation. While the mean bias in predictions of nutrient fertilization experiments, irrigation experiments, and CO[subscript 2] enrichment experiments was low, future work needs to focus modifications to model structures that decrease the bias in predictions of drought experiments. Predictions of how growth responded to elevated CO[subscript 2] strongly depended on whether ecosystem experiments were assimilated and whether the assimilated field plots in the CO[subscript 2] study were allowed to have different mortality parameters than the other field plots in the region. We present predictions of stem biomass productivity under elevated CO[subscript 2], decreased precipitation, and increased nutrient availability that include estimates of uncertainty for the southeastern US. Overall, we (1) demonstrated how three decades of research in southeastern US planted pine forests can be used to develop DA techniques that use multiple locations, multiple data streams, and multiple ecosystem experiment types to optimize parameters and (2) developed a tool for the development of future predictions of forest productivity for natural resource managers that leverage a rich dataset of integrated ecosystem observations across a region.This article and any associated published material is distributed under the Creative Commons Attribution 3.0 License. View the article as published at: https://www.biogeosciences.net/14/3525/2017

First assessment of the plant phenology index (PPI) for estimating gross primary productivity in African semi-arid ecosystems

The importance of semi-arid ecosystems in the global carbon cycle as sinks for CO2 emissions has recently been highlighted. Africa is a carbon sink and nearly half its area comprises arid and semi-arid ecosystems. However, there are uncertainties regarding CO2 fluxes for semi-arid ecosystems in Africa, particularly savannas and dry tropical woodlands. In order to improve on existing remote-sensing based methods for estimating carbon uptake across semi-arid Africa we applied and tested the recently developed plant phenology index (PPI). We developed a PPI-based model estimating gross primary productivity (GPP) that accounts for canopy water stress, and compared it against three other Earth observation-based GPP models: the temperature and greenness model, the greenness and radiation model and a light use efficiency model. The models were evaluated against in situ data from four semi-arid sites in Africa with varying tree canopy cover (3 to 65 percent). Evaluation results from the four GPP models showed reasonable agreement with in situ GPP measured from eddy covariance flux towers (EC GPP) based on coefficient of variation, root-mean-square error, and Bayesian information criterion. The PPI-based GPP model was able to capture the magnitude of EC GPP better than the other tested models. The results of this study show that a PPI-based GPP model is a promising tool for the estimation of GPP in the semi-arid ecosystems of Africa.Comment: Accepted manuscript; 12 pages, 4 tables, 9 figure

Evaluation of Environmental Impacts of Short Rotation Coppice with Regard to the Amount and Quality of Groundwater Recharge

Während über die positiven Umweltauswirkungen von Kurzumtriebsplantagen (KUP) weitgehend Einigkeit herrscht, sind potentiell negative Auswirkungen auf die Grundwasserneubildungsmenge aufgrund eines potentiell hohen Wasserverbrauchs ein großes Thema. Der Wasserverbrauch von KUP übersteigt in der Regel den Wasserverbrauch von Ackerkulturen, kann aber auch den Wasserverbrauch von Laubwälder bei weitem übersteigen. Dadurch kommt es zu einer Abnahme der Grundwasserneubildung, über deren Ausmaß jedoch große Unsicherheit und auch Uneinigkeit besteht. Um die Wissensgrundlagen zum Wasserverbauch von KUP auf Standortebene zu erweitern, und um Faktoren zu identifizieren, die den Wasserverbrauch von KUPs beeinflussen, wurden mehrere Feldstudien zu Verdunstung, Grundwasserneubildung und Nitratauswaschung in mehreren KUPs durchgeführt, die sich in ihren standörtlichen Vorraussetzungen, dem Kronenschlussgrad, dem Blattenflächenindex und dem Bestandesalter zum Teil stark unterschieden. Die erste Feldstudie wurde im Trinkwassergewinnungsgebiet Fuhrberger Feld durchgeführt, um die Auswirkungen des Anbaus von KUP hinsichtlich Menge und Qualität der Grundwasserneubildung zu bewerten. Zu diesem Zweck wurde der Wasserhaushalt einer Weiden-KUP und einer stillgelegten Ackerfläche mit Hilfe eines prozessbasierten Simulationsmodells bestimmt, welches mit Beobachtungen zu Bodenwasserspannung und Bestandesniederschlag validiert wurde. Zusätzlich wurden Nitratkonzentrationen im Sickerwasser dieser Versuchsflächen und weiterer KUPs unterschiedlichen Alters erhoben. Eine zweite Studie wurde durchgeführt, um die Verdunstung und die Wassernutzungstrategie (isohydrisch oder anisohydrisch) zweier Pappel-KUPs mit unterschiedlichem Kronenschlussgrad und unterschiedlicher Blattfläche zu charakterisieren. Hieraus sollten Faktoren abgeleitet werden, die den Wasserverbrauch von KUPs beeinflussen können, und gleichzeitig durch Managemententscheidungen beeinflussbar sind. Eine dritte Studie lieferte zusätzliche Informationen zu Wasserverbrauch und Grundwasserneubildung einer Pappel-KUP mit nahezu optimaler Wasserversorgung. Insgesamt variierte der Wasserverbauch der untersuchten KUPs aufgrund der unterschiedlichen standörtlichen Gegebenheiten hinsichtlich Wasserversorgung und Verdunstungsbedarf sehr stark, überstieg jedoch in keinem Fall die Evapotranspiration von Laubwäldern. Die Ergebnisse der dritten Studie zeigten jedoch, dass der Wasserbedarf von KUPs sehr hoch sein kann, und dass bei ausreichender Wasserversorgung mit Transpirationsraten von mehr als 500 mm a-1 durchaus gerechnet werden muss. Der hohe Wasserbedarf von KUPs kann daher eine erhebliche Abnahme der Grundwasserneubildung im Vergleich zu annuellen Ackerkulturen mit sich bringen, von der insbesondere Standorte mit einer hohen pflanzenverfügbaren Wasserspeicherungskapazität betroffen sind. Für Regionen mit geringerer Wasserverfügbarkeit deuten die Ergebnisse der Weiden-KUP im Fuhrberger Feld, mit vergleichweise geringen Transpirationsraten (< 300 mm a 1) darauf hin, dass der hohe Wasserbedarf von KUPs für eine Vielzahl potentieller KUP-Standorte (i.e. Ackerböden geringen Ertragsniveaus) nicht gedeckt wird. Dadurch werden einserseits geringere Biomasseerträgen erzielt, andererseits wird aber auch die Abnahme der Grundwasserneubildung begrenzt. Speziell für das Fuhrberger Feld kann unter Hinzunahme der Erkenntnisse zur Nitratbelastung des Sickerwassers der untersuchten KUPs geschlussfolgert werden, dass der Anbau von KUP gut mit den Anforderungen des Grundwasserschutzes hinsichtlich Menge und Qualität vereinbar ist. Die Ergebnisse der zweiten Studie, die das Verdunstungsverhalten zweier Pappelplantagen untersucht, deuteten darauf hin, dass ein gewisses Potenzial zur Manipulation der Verdunstung von KUPs durch geschicktes Management besteht. Die Unterschiede im Gesamtwasserverbrauch zwischen den beiden KUPs waren zwar gering, und Strategien zur Begrenzung der Blattfläche oder des Kronenschlussgrads erschienen daher für die Gesamtverdunstung von KUP von untergeordneter Bedeutung. Eine vielversprechende Option zur tatsächlichen Beeinflussung der Verdunstung durch Managemententscheidungen scheint jedoch die Wassernutzungsstrategie des Pflanzmaterials zu sein. Während isohydrische Pappelhybriden die Transpiration mit steigendem Verdunstungsanspruch der Atmosphäre effizient abregeln, bleiben die Spaltöffnungen bei anisohydrischen Pappelhybriden weiter geöffnet, was zu sehr großen Unterschieden in der Transpirationleistung von Pappelklonen unterschiedlicher Herkunft führen kann. Da die Wassernutzungsstrategie auch den Biomassertrag und die Standortseignung beeinflusst, könnte mithilfe von Informationen zum Verdunstungsverhalten kommerziell vermarkteter Pappelhybriden eine sachkundige Auswahl von Klonmaterial erfolgen, welches optimal auf die ökologischen und ökonomischen Ansprüche eines Produktionsstandortes abgestimmt ist. Hierfür sollte vor dem Hintergrund eines möglicherweise steigenden Flächenbedarfs zur Erzeugung holziger Biomasse, aber auch hinsichtlich der Auswirkungen des Klimawandels eine Datenbasis geschaffen werden.While there is broad agreement on the positive environmental impacts of short rotation plantations (SRC), possible negative impacts on groundwater recharge due to potentially high water consumption of trees on arabale land are a major issue. The water use of SRCs usually exceeds the water use of arable crops, but can also far exceed the water use of deciduous forests. This leads to a decrease in groundwater recharge, the extent of which is, however, subject to considerable uncertainty and disagreement. In order to expand the knowledge base on SRC water use at the field scale for developing adaptive, sustainable management strategies for woody biomass production systems, field studies on evapotranspiration, groundwater recharge and nitrate leaching were carried out in several SRCs, which differed greatly in their pedo-climatic site conditions, canopy closure, leaf area index and stand age. The first field study was carried out in the drinking water abstraction area Fuhrberger Feld in order to assess the effects of SRC cultivation on the amount and quality of groundwater recharge. For this purpose, the water balance of a willow SRC and a set-aside arable land was determined with the help of a process-based simulation model, which was validated against observations of soil water tension and stand precipitation. In addition, nitrate concentrations were measured in the seepage water of these field plots and other SRCs of different ages. A second study was carried out to characterise the transpiration and water use strategy (isohydric or anisohydric) of two poplar SRC of contrasting canopy closure and leaf area, in order to evaluate factors potentially influencing SRC water use that can be controlled by management. A third study provided additional information on water use and groundwater recharge of a poplar SRC at near optimum water supply, derived from an inverse modelling approach using the newly developed process-based simulation model LWFBrook90R, which was trained on observations of bulk soil water storage. Overall, the water consumption of the investigated SRCs varied greatly due to the different site conditions with regard to water supply and evaporation requirements, but in no case exceeded the evapotranspiration of deciduous forests. Nevertheless, the results from the third study showed that the water demand of SRCs can be very high, and transpiration rates greater 500 mm y 1 can be observed when water supply is ample. The high water demand of SRCs can therefore lead to a considerable decrease in groundwater recharge compared to conventional arable crops, which particularly affects sites with a high plant available soil water storage capacity. For regions with lower soil water availability, the results from the willow SRC in the Fuhrberger Feld (transpiration < 300 mm y-1) indicate that the high water demand of SRCs is not covered for the majority of sites potentially available for SRC cultivation (i.e., marginal arable land). On the one hand a low soil water availability leads to lower biomass yields, but on the other hand also limits a potential reduction in groundwater recharge. Considering also nitrate concentrations in seepage water of SRCs in the Fuhrbeger Feld, it can be concluded that the environmental impacts of SRC cultivation do not conflict with the protection requirements respecting the amount and quality of groundwater recharge in the Fuhrberger Feld water abstraction area. The results of the second study, which investigates the water use patterns of two poplar plantations, indicated that there is a certain potential for manipulating SRC water use through informed management. The differences in total evapotranspiration between the two SRCs of contrasting canopy closure and leaf area index were small, and strategies to limit leaf area or canopy closure appeared to be of secondary importance for the total evapotranspiration of SRC. However, a promising option for actually influencing transpiration through management decisions seems to be the water use strategy of the plant material. While isohydric poplar hybrids efficiently control transpiration with increasing evaporative demand, anisohydric poplar hybrids maintain high stomatal conductance even when evaporative demand is high, and soil water availability is low. This can lead to very large differences in the transpiration rate of poplar clones of different provenence. Since the water use strategy also influences biomass yields and site suitability of individual poplar hybrids, information on the water use behaviour of individual poplar clones could be used to make an informed selection of plant material that is optimally adapted to the ecological and economic requirements of a production site. For this purpose, a data base should be created, with regard to increasing land requirements for the production of woody biomass, but also with regard to the effects of climate change

Decomposing sources of uncertainty in climate change projections of boreal forest primary production

We are bound to large uncertainties when considering impacts of climate change on forest productivity. Studies formally acknowledging and determining the relative importance of different sources of this uncertainty are still scarce, although the choice of the climate scenario, and e.g. the assumption of the CO2 effects on tree water use can easily result in contradicting conclusions of future forest productivity. In a large scale, forest productivity is primarily driven by two large fluxes, gross primary production (GPP), which is the source for all carbon in forest ecosystems, and heterotrophic respiration. Here we show how uncertainty of GPP projections of Finnish boreal forests divides between input, mechanistic and parametric uncertainty. We used the simple semi-empirical stand GPP and water balance model PRELES with an ensemble of downscaled global circulation model (GCM) projections for the 21st century under different emissions and forcing scenarios (both RCP and SRES). We also evaluated the sensitivity of assumptions of the relationships between atmospheric CO2 concentration (C-a), photosynthesis and water use of trees. Even mean changes in climate projections of different meteorological variables for Finland were so high that it is likely that the primary productivity of forests will increase by the end of the century. The scale of productivity change largely depends on the long-term C-a fertilization effect on GPP and transpiration. However, GCM variability was the major source of uncertainty until 2060, after which emission scenario/pathway became the dominant factor. Large uncertainties with a wide range of projections can make it more difficult to draw ecologically meaningful conclusions especially on the local to regional scales, yet a thorough assessment of uncertainties is important for drawing robust conclusions.We are bound to large uncertainties when considering impacts of climate change on forest productivity. Studies formally acknowledging and determining the relative importance of different sources of this uncertainty are still scarce, although the choice of the climate scenario, and e.g. the assumption of the CO2 effects on tree water use can easily result in contradicting conclusions of future forest productivity. In a large scale, forest productivity is primarily driven by two large fluxes, gross primary production (GPP), which is the source for all carbon in forest ecosystems, and heterotrophic respiration. Here we show how uncertainty of GPP projections of Finnish boreal forests divides between input, mechanistic and parametric uncertainty. We used the simple semi-empirical stand GPP and water balance model PRELES with an ensemble of downscaled global circulation model (GCM) projections for the 21st century under different emissions and forcing scenarios (both RCP and SRES). We also evaluated the sensitivity of assumptions of the relationships between atmospheric CO2 concentration (C-a), photosynthesis and water use of trees. Even mean changes in climate projections of different meteorological variables for Finland were so high that it is likely that the primary productivity of forests will increase by the end of the century. The scale of productivity change largely depends on the long-term C-a fertilization effect on GPP and transpiration. However, GCM variability was the major source of uncertainty until 2060, after which emission scenario/pathway became the dominant factor. Large uncertainties with a wide range of projections can make it more difficult to draw ecologically meaningful conclusions especially on the local to regional scales, yet a thorough assessment of uncertainties is important for drawing robust conclusions.Peer reviewe

Integrating Tracers and Soft Data Into Multi-Criteria Calibration : Implications From Distributed Modeling in a Riparian Wetland

Funding Information: Songjun Wu is funded by the Chinese Scholarship Council (CSC). This research has been supported by the BMBF (funding code 033W034A), which supported the IGB stable isotope Laboratory. Contributions from Soulsby are supported by the Leverhulme Trust through the ISO‐LAND project (Grant RPG 2018 375). Tetzlaff's contribution was partly funded through the Einstein Research Unit “Climate and Water under Change” from the Einstein Foundation Berlin and Berlin University Alliance. We deeply thank Jonas Freymüller and David Dubbert for the help on field work and laboratory analysis of the water isotopes. Hauke Dämpfling is acknowledged for conducting monthly UAV flights. We also thank Ke Chen for discussion on the paper. The valuable comments from associate editor and three anonymous reviewers are highly appreciated. Publisher Copyright: © 2023. The Authors.Peer reviewedPublisher PD

Parameter interactions and sensitivity analysis for modelling carbon heat and water fluxes in a natural peatland, using CoupModel v5

In contrast to previous peatland carbon dioxide (CO2) model sensitivity analyses, which usually focussed on only one or a few processes, this study investigates interactions between various biotic and abiotic processes and their parameters by comparing CoupModel v5 results with multiple observation variables. Many interactions were found not only within but also between various process categories simulating plant growth, decomposition, radiation interception, soil temperature, aerodynamic resistance, transpiration, soil hydrology and snow. Each measurement variable was sensitive to up to 10 (out of 54) parameters, from up to 7 different process categories. The constrained parameter ranges varied, depending on the variable and performance index chosen as criteria, and on other calibrated parameters (equifinalities). Therefore, transferring parameter ranges between models needs to be done with caution, especially if such ranges were achieved by only considering a few processes. The identified interactions and constrained parameters will be of great interest to use for comparisons with model results and data from similar ecosystems. All of the available measurement variables (net ecosystem exchange, leaf area index, sensible and latent heat fluxes, net radiation, soil temperatures, water table depth and snow depth) improved the model constraint. If hydraulic properties or water content were measured, further parameters could be constrained, resolving several equifinalities and reducing model uncertainty. The presented results highlight the importance of considering biotic and abiotic processes together and can help modellers and experimentalists to design and calibrate models as well as to direct experimental set-ups in peatland ecosystems towards modelling needs