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Mapped Atmosphere-Plant-Soil System Study

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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 Department of Agriculture Forest Service.

MAPSS Home > Publications > Abstract: Daly et al 2000



Daly, C.; Bachelet, D.; Lenihan, J.; Neilson, R.; Parton, W.; Ojima, D. 2000. Dynamic simulation of tree-grass interactions for global change studies. Ecological Applications. 10(2): 449-469.

The objective of this study was to dynamically simulate the response of a complex landscape, containing forests, savannas, and grasslands to potential climate change. It was thus essential to accurately simulate the competition for light and water between trees and grasses. To accurately represent water competition requires simulating the appropriate vertical root distribution and soil water content. The importance of differential rooting depths in structuring savannas has long been debated. In simulating this complex landscape we examined alternative hypotheses of tree and grass vertical root distribution and their impacts on savanna dynamics under historical and changing climates. MC1, a new dynamic vegetation model, was used to estimate the distribution of vegetation and associated carbon and nutrient fluxes for Wind Cave National Park, South Dakota.

The MC1 model consists of three linked modules simulating biogeography, biogeochemistry, and fire disturbance. This new tool allows us to document how changes in rooting patterns may affect production, fire frequency, and trace gas emissions, and if current vegetation types and life-form mixtures can be sustained at the same location or replaced by others. Since climate change may intensify resource deficiencies, it will likely affect allocation of resources to roots and their distribution through the soil profile.

By manipulating the rooting depth of two life forms—trees and grasses—that are competing for water, and running MC1 for historical climate (1895-1994) and a GCM-simulated future scenario (1995-2094), we document its impact on ecosystem processes and vegetation distribution. Deeply rooting trees cause higher tree productivity, lower grass productivity, and longer fire-return intervals. When trees, are shallowly rooted, grass productivity exceeds that of trees, even if total grass biomass only represents a third to a fourth that of trees. Deeply rooted grasses develop extensive root systems that increase nitrogen uptake and the input of litter into soil organic matter pools. Shallowly rooted grasses produce smaller soil carbon pools.

Under the climate change scenario, net primary production and live biomass increase for grasses and decrease for trees, and total soil organic matter decreases. However, differences between alternative rooting patterns remain similar. Deeply rooted grasses grow larger than shallowly rooted ones and deeply rooted trees outcompete grasses for resources. Consistent changes in fire frequency and intensity are simulated; more fires occur during the climate change scenario, because temperatures are higher, which results in decreased fuel moisture. Fire also increases in the deeply rooted grass configurations, because grass biomass, which serves as a fine-fuel source, is relatively high.

USDA 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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