From
Transient to Steady State Response of Ecosystems to
CO2-Enrichment and Global Warming
April 28 - May 1, 2002, Durham,
NH
This workshop will evaluate temporal scaling issues in understanding and predicting the response of terrestrial ecosystems and ecosystem components to elevated CO2 and global climate change In particular, differences between transient vs longer-term responses will be explored. These issues represent one of our biggest challenges in accurately predicting long-term changes in ecosystems and associated feedbacks to the climate system. The focus of the workshop will be on C and nutrient cycling interactions, and linkages between experiments and models will be emphasized.
Specific issues that were addressed include:
* Time scale of response – CO2 fertilization and warming will affect essentially all ecosystem processes, but at different time scales of response. For example, leaf-level photosynthesis may respond to CO2 enrichment or elevated temperature on times scales of seconds or hours whereas changes in the storage and turnover of soil N stocks may take years or decades.
* Direct vs Indirect Effects – Direct effects of CO2 fertilization and warming on ecosystem processes are relatively well understood. Indirect effects, which may occur at different time scales then direct effects, are more complex and will require considerably more effort to accurately predict and model.
* Acclimation – Evidence is accumulating that many ecosystem processes acclimate to elevated CO2 and warming at the physiological level, thereby reducing their sensitivity to these perturbations, and invalidating our prediction of future responses. Considerable effort must be made to understand the mechanisms underlying physiological acclimation at the organism level and to incorporate acclimation into existing models.
* Sustainability of the Magnitude and Direction of Response – Closely related to acclimation are questions on the sustainability of the magnitude and direction of response, which may be largely dependent on availability of resources and ecosystem stoichiometry. For example, ecosystems with large stocks of relatively labile C may show a larger and more sustained increase in soil respiration in response to warming then an ecosystem with low initial C stocks.
* Biodiversity - Change in species composition can have a profound impact on nutrient cycling dynamics. The time scale of response varies directly with the life span of the biota, with changes occurring on the scale of months for soil microbes, to years for annual plants, to decades and even centuries for longer-lived perennials and woody species. In order to accurately predict ecosystem response to a warmer, CO2 rich world, we clearly need to consider expected changes in species assemblages.
The workshop was organized around five central Themes:
THEME 1: THEORETICAL CONSIDERATIONS - What do we expect will occur given current knowledge?
THEME 2: EXPERIMENTAL RESULTS - What are the results from longer-term experiments and are they consistent with theory?
THEME 3: GRADIENT STUDIES AND LONG-TERM OBSERVATIONS OF UNDISTURBED SYSTEMS– What can we learn from natural gradients which represent long-term adjustment to various climatic regimes? How do experimental results, or short-term responses, compare to natural gradients?
THEME 4: MODELLING - How are these transient and longer-term responses represented in various ecosystem, landscape, and global scale models? Do model assumptions fit with experimental and observational data?
THEME 5: FUTURE DIRECTIONS - What kind of experiments or analyses of existing data will best address these issues? How do we better integrate experiments and models?
Meeting Publication
Rustad, Lindsey E. 2006. From transient to steady-state response of ecosystems to atmospheric enrichment and global climate change: conceptual challenges and need for an integrated approach. Plant Ecology DOI 10.1007/s11258-005-9030-2.
For more information contact Lindsey Rustad at rustad@maine.edu
This
material is based upon work supported by the National Science
This web page hosted by the University of Maine