Progress in modeling the global carbon cycle is inhibited by the lack of a high-quality data set based upon field observations of net primary productivity (NPP) with which to calibrate, parameterize, and evaluate terrestrial biosphere models. Under the auspices of the Global Primary Production Data Initiative (GPPDI), an activity endorsed by the International Geosphere–Biosphere Program’s Data and Information System, a small international workshop was held in Cincinnati, Ohio, USA, in December 1996 to address the problem of extrapolating sparse field observations of NPP to produce a consistent database representative of major biomes. We report the conclusions of this workshop and the goals of GPPDI—to further expand the existing data compilation, to agree upon consistent standards for cross-site comparisons and allometric relationships for various biome types, and to document methodologies for spatial extrapolation from point measurements to grid cells. The resulting NPP database will also have intrinsic ...

Terrestrial npp: toward a consistent data set forglobal model evaluation

Seed bank densities respond to factors across local to landscape scales, and therefore, knowledge of these responses may be necessary in forecasting the effects of climate change on the regeneration of species. This study relates the seed bank densities of species of Taxodium distichum swamps to local water regime and regional climate factors at five latitudes across the Mississippi River Alluvial Valley from southern Illinois to Louisiana. In an outdoor nursery setting, the seed banks of twenty-five swamps were exposed to non-flooded (freely drained) or flooded treatments, and the number and species of seeds germinating were recorded from each swamp during one growing season. Based on ANOVA analysis, the majority of dominant species had a higher rate of germination in non-flooded versus flooded treatments. Similarly, an NMS comparison, which considered the local water regime and regional climate of the swamps, found that the species of seeds germinating, almost completely shifted under non-flooded versus flooded treatments. For example, in wetter northern swamps, seeds of Taxodium distichum germinated in non-flooded conditions, but did not germinate from the same seed banks in flooded conditions. In wetter southern swamps, seeds of Eleocharis cellulosa germinated in flooded conditions, but did not germinate in non-flooded conditions. The strong relationship of seed germination and density relationships with local water regime and regional climate variables suggests that the forecasting of climate change effects on swamps and other wetlands needs to consider a variety of interrelated variables to make adequate projections of the regeneration responses of species to climate change. Because regeneration is an important aspect of species maintenance and restoration, climate drying could influence the species distribution of these swamps in the future.

Regeneration potential of Taxodium distichum swamps and climate change

[EN] Water is the foundation for all biological life on Earth and one of the basic links between the biosphere and atmosphere. It is equally fundamental for humans and nature (Tolba, 1982). In an environment of growing scarcity and competition for water, increasing the understanding of all fluxes of the water cycle lies at the heart of the scientific community's goals. Traditionally, water and vegetation have been considered as different systems. However, it is necessary to take a holistic approach which considers the question of the water cycle in an integrated manner by taking into account both: blue water and green water (Birot et al., 2011). Around this idea, the new discipline Ecohydrology emerged in the early 20th century and, from then; it has grown steadily as shown by the increasing number of research lines and scientific papers related to this new field.
However, most of the current hydrological models includes the vegetation as static parameter and not as state variable. There are some exceptions taking explicitly the vegetation as state variable but in those cases, the models' complexity and parametrical requirements increase substantially. In practice, we have to deal against the 'data scarcity - high parametrical requirements' issue really often.
To reduce that issue, two strategies can be applied: (1) simplification of the models' conceptual scheme and (2) increase of data availability by incorporating new sources of information. In this thesis, we explored the use of a distributed parsimonious ecohydrological modelling (with low parametrical requirements) calibrated and validated exclusively with remote sensing data.
First, we used the parsimonious ecohydrological model proposed by Pasquato et al. (2015) in an experimental plot located in a semi-arid Mediterranean forest. The results in this previous stage suggested that the model was able to adequately reproduce the dynamics of vegetation as well as the soil moisture variations. In other words, it has been shown that a parsimonious model with simple equations can achieve good results in general terms. But, as long as we applied the model at plot scale, the challenging task to reproduce the spatial variation of the vegetation and water cycle remained.
To explore the spatio-temporal variation of the vegetation and the water cycle, the distributed version of the parsimonious ecohydrological model used previously was applied in a basin located in Kenya, concretely in the Upper Ewaso Ngiro River basin. In order to explore the potential applicability of the satellite data, we calibrated the model using exclusively the NDVI provided by NASA. First of all, we had to deal with the fact that we were not calibrating the model with only one temporal series such as historical streamflow as usual. In fact, satellite data is composed by one temporal series per pixel. We had to identify how to use spatio-temporal (and not only temporal) data during models' calibration and validation. In that sense, unfortunately, there is still a deep lack in literature.
A…

/pdf/on-the-use-of-satellite-data-to-calibrate-a-parsimonious-57pfor3the.pdf

On the use of satellite data to calibrate a parsimonious ecohydrological model in ungauged basins

Climate research today is ultimately driven by the need for a better understanding of the impacts of human activities on ecological, hydrological and socioeconomic systems. Theory and model development and testing are required in order to understand climate itself, and its impacts. The impacts disciplines however must progress rapidly if they are to meet the challenge. Ecosystem impacts models in particular need to be global in scope, in order to be physically consistent in their modelling of different regions, and if they are to predict feedbacks. Mounting evidence attests to the importance of feedbacks from ecosystems to climate, through biogeophysical interactions like surface albedo and conductance changes, and changes in biogeochemical cycles mediated by fluxes of CO2 and other trace gases between ecosystems and the atmosphere. A major shift of focus in ecology from the micro- to the macro-scale is underway, spurred by the need for improved understanding of these linkages. Powerful tools are already at hand, including the routine use of numerical models at various levels of complexity, and the recognition of “fuzzy laws” that serve as globally applicable, robust elements of ecosystem models. Models are also moving rapidly towards integration across subsystems with different space and time scales. For example, biogeographic modelling has progressed from static formulations in terms of ecophysiological constraints to more explicitly mechanistic formulations including energy and water exchanges, nutrient cycling, resource competition, adaptive acclimation and allocation strategies, and vegetation dynamics. Increasingly complex models require ingenuity and rigour in testing. Again powerful tools exist, ranging from isotopic measurements on individual leaves, through CO2 flux measurements on ecosystems, to remote atmospheric measurements of seasonal cycles, interannual variations and long-term trends in O2, CO2 and isotopic indicators of biospheric activity. Further challenges and possibilities for model validation are provided by palaeodata, if properly interpreted and analysed. Attempts to simulate equilibrium climate and biome distributions for past times, constrained by data that record shifting regional patterns in vegetation and hydrology, have produced surprising results that firmly establish the need to include feedbacks from climate-induced vegetation changes in simulations of future climates. The dynamics of the Earth system, including atmospheric trace gas composition, ocean circulation and ice-sheet dynamics during the past 150 000 years, present still greater challenges: we eventually must model the coupled Earth system, including non-linear interactions that may well generate complex transient behaviour in the future just as they have in the past.

Ecology and the Earth System

Professor Colin Prentice said that biosphere modelling was easy. I think this is typical British understatement. I say that good biosphere modelling is difficult. In my summary I should like to comment on the general remarks of Professor Prentice with respect to biosphere modelling, on the global Biome Model by Prentice et al. [7], generally referred to as Biome1, and on the results from the Biome2 model, which is not yet published, so I have a little difficulty to review it. As an introduction to my comments I should like, however, to relate to the general boundary conditions for modelling the biosphere and the global carbon cycle.

Commentary on “Ecology and the Earth System”

Carbon exchange fluxes of terrestrial ecosystems are expected to depend on the internal dynamics of C stocks in vegetation and soils, on nutrient availability, and on the local climatic conditions / weather. The model structure which we present focuses on the internal dynamics in the living vegetation. The mathematical description is derived from two basic hypotheses: 1) vegetation tends to maximize photosynthesizing tissue, and 2) the relative amounts of C in pools with relatively short and long turnover times are given by allometric relations. The model can be calibrated for any vegetation type in a typical climate under the condition to meet mean ecological estimates of e.g. biomass and NPP. For C cycle modeling the FBM yields the net CO 2 flux between the grid elements and the atmosphere in a daily resolution. It is demonstrated that simulations with a l~ ~ spatial resolution reproduce the response of the time course of C fluxes to local climates.

The frankfurt biosphere model (fbm)

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The frankfurt biosphere model (fbm)