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Carbon dioxide sequestration by forests: The importance of cation and phosphorous limitation and its relationship to landscape evolution

This interdisciplinary research will investigate how landscape processes may influence chemical weathering, which may have important impacts on the input of nutrients to forest ecosystems. This project will develop coupled numerical models of landscape evolution and chemical weathering, and test and calibrate these models in the ecosystems in Hawaii and tectonically active areas along the Pacific Rim. In so doing, researchers intend to build predictive models that will be able to identify forests that have the greatest long-term ability to sequester CO2.

One of the most significant carbon dioxide reservoirs on Earth is its forests. As anthropogenic inputs increase atmospheric CO2 levels, there is potential that an increase in total plant biomass the greening of the earths forests might serve as a long-term sink for human-produced carbon dioxide. Such a sink will only be sustainable if the other requisite nutrients for plant growth are readily available and do not limit photosynthesis.

In terrestrial ecosystems, the nutrient flux (Mg, Ca, K, and PO4 3- , Ca, K, and Mg) into the system is controlled to a large extent by the chemical weathering of the primary minerals that make up underlying bedrock. In the temperate zone, these nutrient fluxes have been severely disturbed by anthropogenic activity, such as acid rain, resulting in forest ecosystems that may be cation-limited and thus not have the ability to serve as long-term sinks of anthropogenic CO2 (Federer et al., 1989; Bailey et al., 1996; Fitcher et al., 1998; Lawrence et al., 1999; Yanai et al., 1999; DeWalle et al., 1999; Huntington et al., 1999). In many tropical forests, these nutrient fluxes are thought to be minimal, because the soils often appear highly weathered and are so deep as to preclude biotic access to unweathered bedrock.

Most of the work in temperate forests has been done in the northeastern United States and western Europe, while much of the tropical work on nutrient limitation has been done in Central and South America, and Hawaii. Many of these studies may paint an unrepresentative picture of nutrient input rates, because they are on the low end of the spectrum of tectonic activity and uplift.

Preliminary investigations have demonstrated that the dominant control of chemical weathering rates is the exposure of fresh rock to the weathering zone, through such processes as rock uplift in tectonically active areas and/or hill slope stability in mountainous terrain (Waldbauer and Chamberlain, in press). These models show that chemical weathering rates may be several orders of magnitude higher in tectonically active areas such as the Pacific Rim than in relatively stable areas such as the east coast of North America or Amazon (both areas that have received considerable attention with regard to their ability to store CO2 in forests).

This EVP will couple numerical models of landscape evolution (Hilley) with numerical models of chemical weathering (Chamberlain), and test and refine these models with data from terrestrial ecosystems (Porder and Vitousek). The overall goal of this research will be to build predictive models that will be able to identify forests that have the greatest long-term ability to sequester CO2. We will systematically and quantitatively determine the link between chemical weathering and landscape evolution and test these models through a series of field investigations.

By quantifying rates of nutrient inputs to forests, and by understanding landscape evolution and its relationship to chemical weathering, it should be possible to identify forests that will have the ability to serve as sinks for CO2. If successful, this will aid policymakers and NGOs in select the most important CO2 sinks for management and preservation.

Funding Year: 
2005
Region(s): 
Asia
North America
South America
Research Areas: 
Natural Capital