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The effects of inter-annual climate variability and increased CO2 on the growth of a temperate pine forest.

Ballantyne, Ashley *,1, Baker, Paul1, Clark, Jim1, Jackson, Robert1, Oren, Ram1, 1 Nicholas School of the Environment, Durham, NC, USA

ABSTRACT- Conservative model scenarios project a doubling of CO2 by the year 2100. Such an outcome will have serious implications for Earth's atmosphere and biosphere. The most recent ensembles of general circulation models, subjected to a doubling of CO2, predict a median global warming of 3.4°C; however, there is less of a concensus among model predictions in the spatial variability of precipitation. Very few studies have investigated the interactions of increased CO2 and important climatic variables (e.g. temperature and precipitation), especially at the ecosystem scale. Here we present findings from a long term CO2 enrichment study in a pine forest of the southeastern, U.S. Our results suggest increased temperature and decreased soil moisture during the growth season may reduce growth and thus carbon storage. We also found that inter-annual climate variability was strongly modulated by the El Niño Southern Oscilation; although only one strong and prolonged El niño event (1997-1998) occurred during the experiment. Time integrated measurements of carbon isotopes in the cellulose of trees suggested a 40% increase in relative water use efficiency and a significant decline in the partial pressure gradient of CO2 at the leaf-atmosphere interface. Similar long-term studies of carbon dynamics are necessary at the ecosystem scale to better constrain predictions of the biosphere to future climate scenarios.

Key words: global change, CO2 enrichment, bigeochemical cycles

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