[FRCGC top] [ECRP top] [ECRP researcher's web site]
Last update: 18 Dec 2006
The KOE region, consisting of the Kuroshio, Oyashio and Transition zone, shows the highly variable, complex environments, where dynamics of those currents greatly influence biological production. We report the decadal change in geographical distribution pattern of copepods in the Oyashio and Transition zone using the historical zooplankton collection (Odate Collection). Temporal variation of the copepod community was examined by the principal component analysis (PCA). PC1 time-series mirrored interannual variation of the abundance of “Oyashio assemblage.” The “jumps” of the PC1 value were detected in 1976 and 1988, both of which coincided the years of the major and minor climatic Regime Shifts in the North Pacific. On the other hand, PC2 time-series mirrored the variation of small-sized, warm-water species, defined as the “Transition zone assemblage” copepods, and a jump year was observed in 1982. The distribution of the Oyashio assemblage shifted southwestward after 1976, responding to the southern intrusion of the Oyashio. It further shifted west toward the Japanese coast after the 1988, presumably due to the northern intrusion of the Kuroshio. Although there was no clear change in the geographical distribution of the Transition zone assemblage before and after 1982, increase in its abundance was manifest. Considering that geostrophic transport of the Kuroshio increased in the early 1980s, several years after the southward shift of the Oyashio, it is suggested that distribution pattern of the copepod community was determined by the combined effects of lagged and un-lagged hydrographic variations, which are closely related to the Pacific Decadal Oscillation.
To examine the response and feedback of carbon cycle to climate change, we have conducted global warming experiments using an integrated earth system model. Our model has a positive climate-carbon cycle feedback and shows the further warming of 0.8oC. Most of the land shows a positive feedback and the feedback is mainly determined by soil carbon dynamics. Siberia is the primary area with intense and large-scale positive feedback. Amazon also shows a strong positive feedback though no Amazon dieback. However, some areas show negative feedback due to enhanced litter fall. Most of the ocean also shows a positive feedback and the feedback is due mainly to temperature effect on the carbonate system at the ocean surface. The positive feedback in the North Atlantic is particularly strong because CO2 transport by NADW is reduced following the weakening of its formation.
We developed a coupled climate-carbon cycle model composed of a process-based terrestrial carbon cycle model, Sim-CYCLE, and the CCSR/NIES/FRCGC atmospheric general circulation model. We used this model to examine the multi-temporal scale functions of terrestrial ecosystem carbon dynamics induced by human activities and natural processes and evaluated their contribution to fluctuations in the global carbon budget during the 20th century. Global annual net primary production (NPP) and heterotrophic respiration (HR) increased gradually by 6.7% and 4.7%, respectively, from the 1900s to the 1990s. A difference between NPP and HR was the net carbon uptake by natural ecosystems, which was 0.6 Pg C yr-1 in the 1980s, while the carbon emission induced by human land use changes was 0.5 Pg C yr-1, which had a significant effect of offsetting the natural terrestrial carbon sequestration. Our results indicate that monthly to interannual variation in atmospheric CO2 concentration anomalies showed 19- and 18-month time lags behind anomalies in temperature and the NiNO3 index, respectively. The simulated anomaly amplitude in monthly net carbon flux from terrestrial ecosystems to the atmosphere was much larger than in the prescribed air-to-sea carbon flux. Fluctuations in the global atmospheric CO2 growth rate were dominated by the activity of terrestrial vegetation, with a 1- to 2-year time lag behind climatic fluctuations such as El Nino/Southern Oscillation (ENSO) events. These results suggest that terrestrial ecosystems have acted as a net neutral reservoir for atmospheric CO2 concentrations during the 20th century on an interdecadal timescale, but have acted as the dominant driver for atmospheric CO2 fluctuations on a monthly to interannual timescale.
A three dimensional ocean circulation model (the ORCA2 configuration of OPA), which has a foodweb/biogeochemistry model (PISCES) embedded in it, and which has been forced with NCEP reanalysis fluxes, has been used to study variability in the supply of nutrients to the euphotic zone/upwelling regions of the eastern Equatorial Pacific. Our main finding is that the model exhibits a significant decrease in Fe, Chl, and NO3 concentrations after 1976 for the upwelling regions of the Eastern Equatorial Pacific.
For Fe and Chl, this shift in the mean state is shown to reflect a large change in the amplitude of the seasonal cycle, with seasonally maximum values having been larger for the earlier period. For NO3, there is more of a change in the mean state. These changes can be understood as being due to the interplay of two mechanisms. First, the s0=25.0 potential density surface corresponding to the core of the Equatorial Undercurrent (EUC) was deeper in the western Equatorial Pacific during the earlier period, resulting in an enhanced eastward transport of Fe. Second, as a result of stronger tradewinds, the upwelling was deeper and stronger during the upwelling-favorable season during the early period, increasing the vertical transport of Fe to the surface. The implications of this nonlinear response in ocean biogeochemistry for climate change are discussed.
Being able to forecast into future is one of the ultimate goals of science. If so, conversely, forecast capability may be used effectively to examine system dynamics. Based on out-of-sample forecast skill, we employ nonlinear time series techniques to investigate system dynamics. These methods are rooted in the theory of state-space reconstruction of the system attractor. These techniques have ability to distinguish low-dimensional nonlinear dynamics from high-dimensional linear noise in natural time series. This exercise is fundamental to understanding and modeling systems. For example, if it can be shown that a system is governed by a dominant low-dimensional nonlinear mode, then it should be possible in principle to construct a reasonable (low dimensional) mechanistic model that captures this behavior. By contrast, this will not be possible if it is found that the underlying system is predominantly high-dimensional or linear-stochastic (involving the additive action of many variables).
Using these nonlinear methods, we investigated potential catastrophes of ecosystems, diagnosed pathological infant heart rates, characterized neural feefback control of flying behavior of drosophila, forecasted episodic larval supply of reef fish, and determined the relative contributions of intrinsic and extrinsic processes to the regulation of biological populations.
The first part of the talk will be dedicated to the analysis of the phenological variations in taiga in 1920-2005. According to several studies, the onset of spring has tended to get earlier in the last few decades. However, most studies analyze the phenological variations either for a short time period (since 1982 with satellite observations), or for a restricted region using ground observations. Ground observations, satellite observations and modeling were analysed jointly to study phenological variations in boreal Eurasia in 1936-2005, and 1920-2005 in Central Siberia. The results show that the temporal trends in phenology have a marked spatial distribution. In West Siberia and European Russia, the trend to an earlier spring has existed since as early as 1940. In contrast, the central and eastern parts of Siberia display successive trends with opposite signs.
The second part of the talk will concern the modeling of phenology in tundra. According to different authors, the leaf out of shrubs in tundra may be caused either by the soil warming subsequent to snowmelt, or by the effect of air temperature on the bud development. Recent results show that the phenological model which was originally developed for taiga and and which is based on the air temperature hypothesis, reproduces spring phenology in the whole low arctic tundra, from Alaska to North Siberia.
A new theoretical model for simulating climate- and grazing-induced changes in plant community composition and vegetation distribution was developed. Initial simulations reveal the possibility of multiple, stable steady-states for a given amount of annual precipitation and this possibility increases with the grazing pressure. These results indicate that extreme climatological anomalies, such as sustained drought, may induce catastrophic vegetation change from which the original vegetation may not recover. This research provides the basis for improved reliability in accounting for the interaction between vegetation, grazing and the climate system. Further, I report the progress in quantification of the model. The vegetation in Northern Mongolia exhibits clear discontinuous pattern (i.e., Forest-Steppe) at the slope-scale, whose main determinant factor is not identified. The potential evaporation rate in summer (i.e., the water contdition) estimated from topological data could acounts for the direction of vegetation transition but not for the discontinuity. Permafrost and Grazing pressure (by sheeps and goats) might gives bistability to the system.
(1) Latest simulation results of SEIB-DGVM
I will present recent evaluation of SEIB-DGVM at global scale under current climatic condition. Predicted changes of ecosystem structures and functions for the next 200 years will be also presented.
(2) Demonstration of SEIB-Viewer
I will demonstrate a newly developed freeware SEIB-Viewer, which provides easy way to show and analyze simulation results of SEIB-DGVM (Station version). I will also talk its potential usages in future.
(3) Next working scheme
In tropical rain forest, tree canopy is composed of multiple layers, which differs in photosynthesis properties. Oikawa (1985) examined the fate of this stratification structure when atmospheric CO2 increased. In his simulation, LAI of upper crown layer increased with atmospheric CO2, reducing intensity of radiation passed to the lower layers, and decaying the stratification structure. He claimed that this mechanism may cause catastrophic destruction of tropical forest by inhibiting smooth turnovers of gaps. But, this possibility was not examined due to lack of models that can treat gap dynamics and stratification structure of canopy. I will present my next working scheme to examine this possibility using SEIB-DGVM.
More and more studies indicate continental margins to be an important part of the CO2 sequestration machinery in the ocean with an estimated strength of 0.1-1 Gt C/yr, representing 5-50% of the global ocean CO2 uptake. In spite of the rather large range of estimates, the current notion of a continental shelf pump is in sharp contrast to conventional wisdom that the continental margins are sources of CO2 to the atmosphere. It has been cautioned that simple linear extrapolation from limited observations is unwarranted because the biogeochemical conditions in continental margins are highly variable, both in space and in time. The joint JGOFS-LOICZ Continental Margin Task Team (CMTT) initiated an effort to involve many local experts to contribute to a global synthesis of carbon and nutrient fluxes in continental margins. More than 50 scientists have labored to provide regional syntheses of 38 margins in 7 types and to review 7 cross-cutting issues with a grand global synthesis. Some key findings are highlighted as follows: The CO2 fluxes vary drastically across the salinity gradient in the river-estuary-shelf system, where there is an anthropogenic signature in biogeochemical fluxes despite high variability and insufficient data coverage; The coastal upwelling in the eastern boundary current systems does not necessarily lead to outgassing of CO2; Temperature plays an important role in controlling the remineralization rate and pCO2, and, consequently, margins at low latitudes act most likely as a source of CO2; Dissolved organic carbon is potentially an important carbon exporter; Rich supply of sediments enhances continental shelf pump; Both nitrogen fixation and denitrification are very active in continental margins and may regulate carbon fluxes; Many Asian margins are phosphate limited. The synthesis is still in progress and expected to conclude by the end of 2006. The outcome will be published in the IGBP Book series of Global Change by Springer.
Earth observing data archive, integration and analysis system, which is a government(MEXT)-promoted project, has been initiated in this summer. This is the preliminary 5-year project in advance of the following primal phase of huge scientific movements on the earth observation and data related to GEOSS. There are three major tasks in this project: ecosystem management, climate change, and water & material cycle in river basin. The University of Tokyo, JAMSTEC, and JAXA are charged for these tasks, and ECRP would be recommended to take part in the category "ecosystem management" of the project. ECRP should be the sole group of researchers in Japan that has broad scientific perspectives from observation (satellite and surface-based) to model studies on both land and ocean ecosystems. Such feature of ECRP has a considerable potential to contribute to the project.
I present an idea of an ECRP's way for the project. In addition, a short-term research plan (until June 2008), "Study on linking system of land ecosystem over Asia" which must be intensively promoted by ECRP in these two years is introduced at the seminar.
(1) Yokohama National University
(2) Frontier Research Center for Global Change
Biodiversity is widely believed to be crucial for the maintenance of life on earth . But how exactly the diversity of species, in particular, contributes to ecosystem functioning and stability, and how it is affected by environmental change is only poorly understood [2-4]. Extremely little is known for ecological communities with more than one trophic level . Practical and moral limits forbid conducting experiments of an appropriate scale. This suggests, similar as for climate issues, the use of numerical models. However, as long as such models are unable to reproduce the known generic patterns of ecosystems structure, model predictions of the system dynamics and of responses to perturbations will remain implausible.
I will talk about two models: The first  describes only topology of food web (the network of who is eating whom), the second one  describes the food web and the population dynamics of high-diversity communities. Both models reproduce empirical community structure in unpreceded detail and accuracy.
 Millennium Ecosystem Assessment (2005) Ecosystems and Human Well-being: Biodiversity Synthesis. Washington, DC: Island Press.
 Loreau M, Naeem S, Inchausti P, Bengtsson J, Grime JP, et al. (2001) Biodiversity and ecosystem functioning: Current knowledge and future challenges. Science .
 Hooper DU, III FSC, Ewel JJ, Hector A, Inchausti P, et al. (2005) Effects of biodiversity on ecosystem functioning: a consensus of current knowledge. Ecol Monog 75:3?35.
 de Ruiter PC, Wolters V, Moore JC, Winemiller KO (2005) Food web ecology: Playing jenga and beyond. Science 309:68?71.
 Rossberg AG, Matsuda H, Amemiya T, Itoh K (2006) Food webs: Experts consuming families of experts. J Theor Biol Doi:10.1016/j.jtbi.2005.12.021. [external link]
 Rossberg AG, Ishii R, Amemiya T, Itoh K (2006) A unified allometric model reproduces complex multitrophic community structure. [external link]
To understand the global carbon cycle, we need to know the spatio-temporal variation of biomass as the carbon stock in vegetation. The Phased Array type L-band Synthetic Aperture Radar (PALSAR), an onboard sensor of a brand-new satellite Advanced Land Observing Satellite (ALOS), has a high potential to acquire the information on the biomass of forest vegetation over an extensive land area by using L-band microwave. To estimate the biomass, in situ information is necessary as a ground truth value for the remotely sensed value. Therefore, biomass surveys in many forests are needed, and regression formulas which express the relation between the ground-based and satellite-sensed measurements will be required. Forest surveys for biomass estimation which uses the relascope and laser range finder etc are now planned at Fujiyoshida and along the south-north transect in Alaska and Siberia.
Land use and Land cover changes are an important component of global environmental change research, and in understanding the interactions of the human activities with the environment. GEC issues are complex phenomenon not because of how natural processes interplay but also due to the ever changing uses of resources & new developments that result from human needs. Human decision making processes thus contribute to the current state and to changes in the environment. Also, it is affected by changes in both the immediate environment & the perceived changes that are not local. Thus, it is very important to understand and explain, to a manageable extent, the factors and process of decision making ｨC whether at the household level (of adapting/coping) or at levels of governance.
We would like to present here our experiences in developing GIS based spatially explicit, agent-based, land use model that integrates the biophysical conditions with the socio-economic characteristics to simulate land use changes. It is an integrated and dynamic spatio-temporal simulation model called the ｡ｮAnthropogenically Engineered Transformations of Land Use and Land Cover｡ｯ (AGENT-LUC) Model. The model builds up the changes in land use as an outcome of options available & the decision made at the level of analysis ｨC be it a grid or a village. The agents are defined based on their socio-economic characteristics & the ability to take decisions at the scale of simulation at each time step (seasonal or annual). Through the agents, the macro (economics, etc) and micro (soil, topography, etc) information are assimilated into the decision making process. The major outcomes are agricultural & urban land use, shifting cultivation and migration. The model has been applied to Thailand, Bangladesh and Laos to understand the processes of change.
In addition, the presentation would highlight some of our current research at linking these land use changes to resource utilization, contributions to carbon cycle, and socio-economic consequences.
(from a paper by Smith and Yamanaka, just submitted for review):
We present a new, optimization-based model for uptake kinetics of multiple nutrients, which has the same number of parameters (two for each nutrient) as the Michaelis-Menten model. We fit this model and an existing inhibition-based model to data from chemostat experiments at various flow rates (under extreme limitation by both N and P), and compared these models and the Michaelis-Menten model to an independent dataset for the same species in a chemostat at various N:P input ratios (at constant flow rate). Our model also fit the data well, with only slightly higher square error than the much more complex inhibition model. We also successfully applied our model to a dataset for a different species under various degrees of VitaminB12- and P- limitation. Our model agrees with measured cell quotas of non-limiting nutrients when supply ratios differ greatly from the optimal ratio for phytoplankton, whereas the Michaelis-Menten model greatly overestimates uptake of non-limiting nutrients at these extreme nutrient supply ratios. The key to our model's success is the optimization of uptake for the limiting nutrient, which results in distinct behavior for limiting versus non-limiting nutrients, without additional parameters; phytoplankton allocate their internal resources (nitrogen) to optimize uptake of the limiting nutrient, but not in response to changes in ambient nutrient ratios. This is consistent with evolution in an ocean with highly variable nutrient concentrations (in the euphotic zone) but constant stoichiometry of nutrients.
The ocean is considered to be a major sink of CO2 produced by industrial activity. Much progress has been made in recent years in understanding and quantifying this sink. However, many uncertainties remains as to the distribution of anthropogenic CO2 in the ocean, and its precise rate of uptake over the industrial era. To address this important issue in climate science, we have recently developed a new technique for inferring the distribution of anthropogenic CO2 in the ocean from measurements of transient tracers. Our method is based on the recognition that the transport of tracers in the ocean is described by a Green's function or ``transit-time distribution'' (TTD) which may be parameterically estimated from tracer data. The TTD technique allows us to account for both the ocean's complex transport, and the time-varying air-sea disequilbrium of CO2 over the industrial era.
In this talk, I will discuss the ideas underlying the TTD technique, and describe a preliminary application using global ocean measurements of CFC12.
To evaluate the net greenhouse effect of a forest ecosystem, we developed a process-based model simulating the net carbon dioxide (CO2) exchange, methane (CH4) oxidation, and nitrous oxide (N2O) emission. We considered two existing methane oxidation schemes, in which CH4 oxidation by soil was parameterized as a function of temperature and soil moisture, and two existing schemes of nitrous oxide emission, in which N2O emission from soil was parameterized as a function of soil inorganic nitrogen, soil pH, temperature, and soil moisture. We applied the model to a cool-temperate, deciduous broad- leaved forest at Takayama, an AsiaFlux site in central Japan. The model estimated that the temperate forest absorbed CO2 and CH4 at a net rate of 804.53 g CO2 m-2 yr-1 and 0.35 g CH4 m-2 yr-1, and released N2O at a net rate of 0.02 g N2O m-2 yr-1. The land- atmosphere exchange of greenhouse gases showed clear seasonal variations, and the model estimates showed fair agreement with flux tower and soil chamber data. From the 100-year global warming potential (GWP) of greenhouse gases, we estimated that the forest had a negative greenhouse effect of 821.64 g CO2 (equivalent) m-2 yr-1 on the atmosphere.
Atmosphere-ecosystem exchange is a key process to regulate the atmospheric CO2 concentration and then climatic change in the future. We developed a process-based carbon cycle model on the basis of a global-scale simple model, Sim-CYCLE. The new model was firstly applied to the representative AsiaFlux site in Takayama, central Japan, where a variety of ecological, micrometeorological, and biogeochemical data are obtained from cool-temperate deciduous broad-leaved forest. In this seminar, our recent results will demonstrate how our modeling study is effective to interpret and integrate the observational data.
I will summarize my reseach life in Ecology during 40 years because I will retire the University of Tsukuba at the end of this March. My work has been based on production ecology which was initiated by Prof. Masami Monsi, my superviser at the time of the graduate student in the University of Tokyo. Prof. Monsi and Prof. Saeki published a famous paper in 1953, where the significance of light energy for dynamics of plant communities was clarified by a newly devised stratified clipping technique and a production formula combining a light-photosynthesis relation of a single leaf and light-microclimate within a plant community.
I extended the Monsi-Saeki production theory from a population with random leaf distribution to one with square-planted plants by appling the Monte Carlo technique. In this work, the most up-to-date great computer HITAC 5020E in the University of Tokyo was employed (Oikawa, 1977).
A series of papers in my doctoral thesis showed that the plant productivity is determined by the major factor of light energy and the minor factor of CO2 diffusion driven by wind turbulence (Oikawa, 1978).
Based on these works, I extended my work to a simulation model dealing with carbon dynamics of a plant community ranging from a tropical rain forest to a grassland (Oikawa, 1985). Details will be presented in seminar.
Oikawa, T. (1977) Light regime in relation to plant population geometry. II. Light penetration in a square-planted population. Bot. Mag. Tokyo 90:11-22.
Oikawa, T. (1978) Canopy photosynthesis of the plant population simulated on the basis of light and CO2 conditions. JIBP Synthesis 19:167-183.
Oikawa, T. (1985) Simulation of forest carbon dynamics based on a dry-matter production model.I. Fundamental model structure of a tropical rain forest ecosystem. Bot. Mag. Tokyo 98; 225-238.
Recently flux observation and modeling studies have suggested that the increase in diffuse photosynthetically active radiation (PAR) enhances forest canopy photosynthesis. The mechanism of this effect can be explained that incident diffuse PAR is efficiently distributed throughout the whole canopy leaves and therefore many leaves can contribute to the canopy-scale photosynthesis. On the other hand, direct PAR is inefficiently concentrated on only a small portion of canopy leaves where light saturation can reduce the canopy-scale photosynthesis and light-use efficiency. Cohan et al.(2002) investigated this issue in various atmospheric aerosol optical thickness (AOT) and cloud optical thickness (COT) conditions. However they did not consider angular dependency of incident PAR distribution in their simulation. In the low or medium-level AOT cases, most of diffuse PAR is concentrated around the solar disc. In such conditions, the effect of photosynthesis enhancement may be less significant than the case of uniformly distributed diffuse PAR. In this seminar, we examine the PAR regime and canopy photosynthesis relationship using a three-dimensional forest light environmental simulator. Our simulation results demonstrated that spatial APAR distribution depends on the hemispherical distribution characteristics of atmospheric PAR regime even though the fraction of diffuse PAR does not vary. These results suggest the detailed knowledge of relationship between AOT/COT and APAR/canopy photosynthesis may be necessary for the reliable modeling of the forest canopy photosynthesis.
Increasing atmospheric carbon dioxide concentrations are reducing ocean pH and carbonate ion concentrations, and thus the level of calcium carbonate saturation. To investigate how seasonal and interannual variability affects surface CO2, results from a model are analysed. The model is forced with daily atmospheric data over 1948-2003 according to OCMIP-3 (Ocean Carbon-Cycle Model Intercomparison Project) protocol. Seasonal variability of surface oecan CO2 is significant in the high latitudes where surface waters become less saturated with regard to calcium carbonate during winter, although the amplitude is small when compared with the magnitude of the anthropogenic decline predicted in the twenty-first-century. Interannual variability is also small but it may affects the estimate where undersaturation will be first rearched.
Data on visible spectral radiometry (ocean colour) collected by satellites in space have many aplications in oceanography. Indexed as chlorophyll concentration, they are important for inititiation and validation of coupled circulation-ecosystem models; they can be used to quantify, at regional and basin scales, the carbon flux through phytoplankton (primary production), with many implications for ocean biogeochemistry and climate change; they allow us to quantify the influence of the ocean microbiota on the heat budget of the mixed layer; and they are important as an information base for sustainable management of the ocean, including fisheries. We can best interpret ocean-colour data if we have also an in situ research program on the optical properties of the region concerned. The BEAGLE cruise had a small bio-optical program on all legs. The results are valuable for optimal exploitation of ocean-colour data in the southern Hemisphere. Furhter they provide new insight into the factors contolling the basin-scale distribution of phytoplankton at the physiological and genetic levels.
In this seminar, I'd like to introduce a novel approach to estimate basin-scale distribution of partial pressure of carbon dioxide (pCO2) using satellite-derived sea surface temperature (SST) and chlorophyll-a concentrations (chl-a) and climatological sea surface salinity (SSS). In this approach, multiple regression equations were developed for mixed layer dissolved inorganic carbon (DIC) data with SST, SSS and chl-a, whereas mixed layer total alkalinity (TA) data were linearly regressed with SSS. Then the pCO2 is computed from the DIC and TA. Using the monthly mean SST and Chl-a derived from the Advanced Very High Resolution Radiometer (AVHRR) and SeaWiFS (Sea-viewing Wide Field of view Sensor), respectively, and climatological salinity, monthly basin-scale pCO2 fields in the North Pacific were computed. The derived pCO2 agreed well with the shipboard pCO2 observations within an error of 15-18 μatm.This study strongly suggests that satellite based techniques are promising tools for prediction of pCO2 fields on a basin scale.
Rates of photosynthesis and vegetation-atmosphere carbon-dioxide exchange, and their contribution to carbon cycling in terrestrial ecosystems, are controlled by the interaction of numerous biotic and abiotic factors: 1) vegetation factors (ecophysiology and structure), 2) soil factors (water and nutrient availability, temperature), and atmospheric factors (carbon dioxide concentration, humidity, wind, temperature, and solar radiation. Knowledge and understanding of the mechanisms of these controlling factors are essential for accurate and reliable modeling of the terrestrial carbon cycle. Among the most fundamental of these factors is solar radiation (specifically, photosynthetically active radiation, or PAR), which provides the fundamental energy source to support photosynthesis. Changes in atmospheric conditions associated with climate change (e.g. cloudiness) or human activities (e.g. aerosol emissions) can significantly alter the amount and quality of PAR available at the Earth's surface. However, questions remain about the magnitude and characteristics of such alternation to PAR regimes and their significance for terrestrial photosynthesis and carbon-dioxide source-sink dynamics. The problem is compounded by insufficient availability of ground-based and satellite-based PAR data for research and modeling. This presentation will review the major issues and challenges regarding radiation-vegetation-carbon cycle relations, and summarize research in the ECRP Ecosystem Spatial Observation and Modeling (ESOM) Group that is aimed at advancing our knowledge and capability to accurately model and monitor the dynamics of the terrestrial carbon cycle.