2002 ARCSS All-Hands Workshop

The Role of Plant Functional Types in Land Surface Exchange in High Latitude Ecosystems: Measurements and Models

Catharine D. Copass¹, F. S. Chapin III², A. David McGuire³, Jason Beringer⁴, Donald A. Walker⁵, Amanda Lynch⁶, Gordan B. Bonan^7
1Department of Biology and Wildlife, University of Alaska Fairbanks, 211 Irving I, Fairbanks, AK, 99775, USA, Phone 907.474.9108, Fax 907.474.6716, ftcdc@uaf.edu
²Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK, USA
³Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK, USA
⁴School of Geography and Environmental Science, Monash University, Australia
⁵Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK, USA
⁶Cooperative Institute for Research in Environmental Science , University of Colorado, Boulder, CO, USA
⁷National Center for Atmospheric Research, Boulder, CO, USA

Climate change has the potential to influence vegetation dynamics in high latitude ecosystems, which may in turn feedback to the climate system through alterations in carbon storage and surface energy balance. Our component of the Arctic Transitions in the Land Atmosphere System (ATLAS) project focuses on improving our understanding of the role of species, or groupings of species (plant functional types, PFTs) in the land surface exchange of arctic ecosystems in response to warming. We hypothesize that changes in the distribution of plant functional types will exert control on land surface exchange in the arctic system, through changes in surface parameters such as albedo, roughness length and canopy resistance. We address our hypothesis through a combination of fieldwork and modeling experiments.

Fieldwork for this project occurred at ATLAS sites in Alaska (Ivotuk and Council), and in Russia (Cherskii). In conjunction with tower-based measurements of CO₂, water and energy exchange, we measured vegetation characteristics including biomass and leaf area index. The vegetation types at the study sites span a gradient from tundra through tall shrub tundra to forest. At Council, differences in albedo among vegetation types controlled summer season net radiation. These differences were attributed to increased canopy complexity and variation in the distribution of plant functional types along the sequence from tundra to forest. Canopy complexity, as indicated by measurements of leaf area index, ranged from 0.52 in the tundra to 2.70 in the forest. The significantly different distribution of functional types with the development of a complex canopy was reflected in an 8 fold difference in total biomass along the sequence from tundra to forest.

Extrapolation of the field measurements to broader spatial scales is a major component of the synthetic activities of our project. We have developed a dynamic version of the Terrestrial Ecosystem Model (TEM-DVM) that tracks carbon and nitrogen pools and fluxes through plant functional types, and are in the process of testing and validating that model. We have used the field data from the ATLAS sites to update parameterizations for the arctic and subarctic plant functional types in the Land Surface Model (LSM). In an asynchronous model coupling experiment, TEM-DVM will be used with LSM-CCM3 to evaluate the influence of vegetation dynamics in the arctic and subarctic north of 50° N on surface energy balance and boundary layer structure.

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