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Pacific Northwest Research Station
Mapped Atmosphere-Plant-Soil System Study

Corvallis Forestry Sciences Laboratory
3200 SW Jefferson Way
Corvallis, Oregon 97331

United States Forest Service.

MAPSS Home > About Us > Dynamic Vegetation Models > BIOMAP

About Us: Dynamic Vegetation model—BIOMAP

BIOMAP is a dynamic global vegetation model (DGVM) that is a hybrid between the MAPSS biogeography model and the BIOME-BGC biogeochemical cycling model, as well as a process-based fire model. DGVMs operate by combining the dynamic capability of vegetation distribution change with that of nutrient cycling, productivity, and disturbance. The processes of vegetation change require the capability for the replacement of one or more vegetation life forms with others via the processes of disturbance, competition, and succession. Even static vegetation distribution modeling requires the capability to simulate competition among life forms in order to accurately simulate the distribution and boundaries between different vegetation types, such as forests, savannas, and grasslands. The "savanna" structure is considered to be the general structure of ecosystems, as forests are essentially savannas without grass and grasslands are savannas without trees. MAPSS creates the savanna structure by competing woody and grass life forms over multiple soil layers with differential rooting depths. BIOME-BGC, on the other hand, simulates a single life form over a single soil layer. Thus, in hybridizing the two models, BIOME-BGC was generalized to the MAPSS-based savanna structure. BIOMAP is being used as a prototype for development of the vegetation life-form competition algorithms for use in the IRC Terrestrial Carbon Model. Thus, BIOMAP incorporates all the fundamental physiological canopy algorithms and soil biogeochemistry of BIOME-BGC, but simulates overstory-understory competition among life forms for light, water, and nutrients. The soil biogeochemistry was originally adapted from the CENTURY model. BIOMAP is being developed to handle multiple life forms within each of multiple canopy layers over multiple soil layers. The user can specify the level of "multiple" in each case. Because the model is fundamentally a physiologically based model, it is possible to parameterize it at a species level over landscape to regional domains, or at the functional group or life-form level over larger spatial extents. Thus, scaling of model behavior from landscapes to regional and continental is enhanced by the model structure.

Light competition follows the Beer's law reduction in radiation as a function of leaf area index. In addition a "clumping" algorithm has been added to allow fine-scale spatial heterogeneity in situations where the overstory is sufficiently thin to allow direct sunlight to "patches" in the understory, but still allow root competition for water and nutrients. Water competition follows the MAPSS approach, where each life form withdraws water from different soil layers in direct proportion to both canopy demand for water and the vertical distribution of roots. The canopy demand for water for each vegetation life form is a function of leaf area and stomatal conductance, which is sensitive to both vapor pressure deficit and the soil water potential as pro-rated by the vertical root distribution. That is the canopy "sees" the soil water potential that is only directly available to the roots in proportion to the root density through the profile. Nutrient competition and uptake are similarly handled. However, nutrient uptake is also directly coupled to soil water content. That is, nitrogen cannot be extracted from a dry soil layer, even if it is abundant. However, the capacity for luxury uptake of nitrogen, when the soils are wet, has also been included in the nutrient uptake algorithms.

Preliminary simulations in the ponderosa pine savannas of eastern Oregon suggest that the model is capable of complex dynamics, switching over hundreds of years between grass- and tree-dominant phases, dependent on long-wave soil nitrogen dynamics and periodic fires, within the context of a semi-arid climate.

US Forest Service - Pacific Northwest Research Station, Mapped Atmosphere-Plant-Soil System Study
Last Modified: Monday, 16 December 2013 at 14:18:44 CST

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