IBIS-2 is the version 2 of the land-surface model Integrated Biosphere Simulator (IBIS), which includes several major improvements and additions to the prototype model developed by Foley et al. 996 IBIS was designed to explicitly link land surface and hydrological processes, terrestrial

biogeochemical cycle A biogeochemical cycle (or more generally a cycle of matter) is the pathway by which a chemical substance cycles (is turned over or moves through) the biotic and the abiotic compartments of Earth. The biotic compartment is the biosphere and ...

s, and

vegetation Vegetation is an assemblage of plant species and the ground cover they provide. It is a general term, without specific reference to particular taxa, life forms, structure, spatial extent, or any other specific botanical or geographic charact ...

dynamics within a single physically consistent framework

IBIS Functionality

The model considers transient changes in vegetation composition and structure in response to environmental change and is, therefore, classified as a

Dynamic Global Vegetation Model A Dynamic Global Vegetation Model (DGVM) is a computer program that simulates shifts in potential vegetation and its associated biogeochemical and hydrological cycles as a response to shifts in climate. DGVMs use time series of climate data and, ...

( DGVM) This new version of IBIS has improved representations of land surface physics, plant

physiology Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemic ...

, canopy

phenology Phenology is the study of periodic events in biological life cycles and how these are influenced by seasonal and interannual variations in climate, as well as habitat factors (such as elevation). Examples include the date of emergence of leav ...

, plant functional type (PFT) differences, and

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon makes ...

allocation. Furthermore, IBIS-2 includes a new belowground biogeochemistry submodel, which is coupled to detritus production (litterfall and fine root turnover). All process are organized in a hierarchical framework and operate at different time steps, ranging from 60 min to 1 year. Such an approach allows for explicit coupling among ecological, biophysical, and physiological processes occurring on different timescales.

IBIS Structure

The land surface module is based on the land surface transfer model (LSX) package of Thompson and Pollard, and simulates the energy, water, carbon, and momentum balance of the soil-vegetation-atmosphere system. The model represents two vegetation canopies (e.g., trees versus shrubs and grasses), eight soil layers, and three layers of snow (when required). The solar radiative transfer scheme of IBIS-2 has been simplified in comparison with LSX and IBIS-1; sunlit and shaded fractions of the canopies are no longer treated separately. The model now follows the approach of Sellers et al. 986and Bonan 995 Infrared radiation is simulated as if each vegetation layer is a semitransparent plane; canopy emissivity depends on foliage density. Another difference between IBIS-2 and IBIS-1 and LSX, is that IBIS-2 uses an empirical linear function of wind speed to estimate turbulent transfer between the soil surface and the lower vegetation canopy, and IBIS-1 and LSX use a logarithmic wind profile. The total

evapotranspiration Evapotranspiration (ET) is the combined processes by which water moves from the earth’s surface into the atmosphere. It covers both water evaporation (movement of water to the air directly from soil, canopies, and water bodies) and transpir ...

from the land surface is treated as the sum of three water vapor fluxes: evaporation from the soil surface, evaporation of water intercepted by vegetation canopies, and canopy transpiration. IBIS simulates the variations of heat and moisture in the soil. The eight layers are described in terms of soil temperature, volumetric water content and ice content. All the process occurring in the soil are influenced by the soil texture and amount of organic matter within the soil. One difference from the physiological processes in previous version of the model is that IBIS-1 calculates the maximum

Rubisco Ribulose-1,5-bisphosphate carboxylase-oxygenase, commonly known by the abbreviations RuBisCo, rubisco, RuBPCase, or RuBPco, is an enzyme () involved in the first major step of carbon fixation, a process by which atmospheric carbon dioxide is co ...

carboxylation capacity (Vm) by optimizing the net assimilation of carbon by the leaf. IBIS-2 prescribes constant values of Vm for the plant functional typed (PFT). To scale

photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...

and transpiration from the leaf level to canopy level, IBIS-2 assumes that the net photosynthesis within the canopy is proportional to the APAR within it.

Soil Biogeochemistry

In the original version of IBIS there was no explicit below ground biogeochemistry model to complete flow of carbon between the vegetation, detritus, and

soil organic matter Soil organic matter (SOM) is the organic matter component of soil, consisting of plant and animal detritus at various stages of decomposition, cells and tissues of soil microbes, and substances that soil microbes synthesize. SOM provides numerous ...

pools. IBIS-2 includes a new soil biogeochemistry module. ucharik et al., submitted manuscript, 1999/ref>

References

{{Reflist Biological models Systems ecology

IBIS Functionality

IBIS Structure

Soil Biogeochemistry

Further reading

References