Terrestrial Ecosystem Analyses 
Dennis S. Ojima 
Natural Resource Ecology Laboratory 
Colorado State University 
USA 
Global analysis of terrestrial ecosystem response to environmental changes, such as global warming, 
acid rain, tropospheric ozone increases, or land use changes, need to be able to link process studies to 
a range of environmental factors. Global data on environmental factors important to ecosystem 
dynamics, such as climate, soils, land use, need to be developed in a geographically explicit manner 
in order to assess the impact of these changes to terrestrial ecosystems. The dynamic nature of the 
analysis of ecosystem responses to global change adds to the analytical complexity of the problem. 
Development of data bases and analytical techniques to assess spatial and temporal changes in 
climate, soils, hydrology, land use, and vegetation structure need to take place in concert with 
development of modeling and other analysis techniques for global change assessment. These 
analytical structures will allow us to assess the global and regional impact of global environmental 
changes on soil carbon storage and other ecosystem feedbacks to the atmospheric system (e.g., H,O, 
CH,, and N,0). 
An integrated approach to global change analyses provides a mechanism to quantify the level of biotic 
and abiotic controls on terrestrial ecosystem-climate interactions. Regional data bases of climate, soil, 
and land use characteristics have been applied to represent the spatial distribution of land surface 
properties across a region using ecosystem models (Parton et al 1987, Burke et al 1990, Schimel et al 
1990, Pielke, et al, 1991, Ojima et al. 1993 ). These can be linked to remote sensing observations 
which are used to cross-verify the spatial variation and temporal dynamics of land surface processes 
that control ecosystem C flux, including plant productivity and canopy nutrient content (Aber et al. 
1990, Sellers et al. 1990). 
Plant functional attributes, such as C allocation, nutrient content, photosynthetic pathway, and 
turnover of different plant components, also play an important role in modeling ecosystem dynamics. 
Changes in species composition from C3 to C4 vegetation (Ojima et al 1991, Tieszen et al, in press) 
or structural changes resulting from shifts between grasslands and savannas affect nutrient dynamics, 
water utilization, biomass allocation, and other characteristics which modify the biosphere- 
atmosphere linkage (Eagleson 1986, VEMAP et al, accepted). Modifications of resource use 
efficiency among various vegetation communities are important to projecting how an ecosystem will 
respond to increased atmospheric CO,, change in climate, or increases in atmospheric deposition of 
N. Our ability to model the interactions between these characteristics in a systematic fashion allows us 
to make better estimates of how the terrestrial biosphere responds to environmental change and to 
project how this feedback may be enhanced or dampened with modifications to plant attributes. 
Development of models that link photosynthesis with other ecosystem properties, such as canopy 
structure, plant N concentrations, and allocation patterns, would provide a framework to study the 
rapid abiotic responses and the slower biotic controls of plant structure and nutrient cycling (Schimel 
et al 1991, Coughenour and Parton, in press). 
Development of multi-year dynamics of changes in the land surface is needed for global and regional 
modeling of terrestrial ecosystem responses of biogeochemical dynamics that couple atmosphere- 
biosphere studies. The CENTURY model (Parton et al. 1987) simulates the spatial and temporal 
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