Event Title

Facing Changes in Atmospheric Transparency: Mediterranean and Sub-Arid Trees Growth Responses for the Last 150 Years

Event Website

http://www.nafew2009.org/

Start Date

23-6-2009 10:30 AM

End Date

23-6-2009 10:50 AM

Description

Short term variations in atmospheric transparency, such as volcanic eruptions, are known to affect forest productivity. But few ecological studies are available for long term impacts of regional changes in atmospheric transparency (also called global dimming). It has been shown that ecosystem carbon fluxes are affected by current changes in the atmospheric composition. However, the impact of these changes on the productivity of trees are unknown. By selecting data with strict criteria we present results for tree ring width sites across the globe representing Mediterranean and sub-arid ecosystem. These data were within a 50 km and 150 km range of aerosol optical depth (AOD) stations. We investigated the interactions of the AOD and changes in the solar constant which were estimated from solar cycles on tree growth from tree ring chronologies. Results show interactions between AOD and solar irradiance on growth. A decrease in atmospheric air quality increased the negative impact of solar irradiance on growth during most of last century. The slope of this relationship changed slowly until in turned positive in the 60's-70's. We argue that decreases in atmospheric transparency result in less radiation for photosynthesis, but lead to higher fraction of diffuse irradiance. Overall, plant photosynthesis in complex, multilayerized canopies, such as those of trees, will benefit from this increased diffuse irradiance. We propose that this amelioration of growth observed is due to a decreased in sun leaf overheating and more generally in water stress during summer drought whereas shade leaf will benefit from more diffuse light. These findings have important implications for modeling of forest response to anthropogenic changes of the atmosphere and questioned some management policies in ecosystems with very dry seasons. Showing that trees responses are highly complex.

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Jun 23rd, 10:30 AM Jun 23rd, 10:50 AM

Facing Changes in Atmospheric Transparency: Mediterranean and Sub-Arid Trees Growth Responses for the Last 150 Years

Short term variations in atmospheric transparency, such as volcanic eruptions, are known to affect forest productivity. But few ecological studies are available for long term impacts of regional changes in atmospheric transparency (also called global dimming). It has been shown that ecosystem carbon fluxes are affected by current changes in the atmospheric composition. However, the impact of these changes on the productivity of trees are unknown. By selecting data with strict criteria we present results for tree ring width sites across the globe representing Mediterranean and sub-arid ecosystem. These data were within a 50 km and 150 km range of aerosol optical depth (AOD) stations. We investigated the interactions of the AOD and changes in the solar constant which were estimated from solar cycles on tree growth from tree ring chronologies. Results show interactions between AOD and solar irradiance on growth. A decrease in atmospheric air quality increased the negative impact of solar irradiance on growth during most of last century. The slope of this relationship changed slowly until in turned positive in the 60's-70's. We argue that decreases in atmospheric transparency result in less radiation for photosynthesis, but lead to higher fraction of diffuse irradiance. Overall, plant photosynthesis in complex, multilayerized canopies, such as those of trees, will benefit from this increased diffuse irradiance. We propose that this amelioration of growth observed is due to a decreased in sun leaf overheating and more generally in water stress during summer drought whereas shade leaf will benefit from more diffuse light. These findings have important implications for modeling of forest response to anthropogenic changes of the atmosphere and questioned some management policies in ecosystems with very dry seasons. Showing that trees responses are highly complex.

http://digitalcommons.usu.edu/nafecology/sessions/processes/3