CO2 and O3 are accumulating in
the atmosphere and are potent modifiers of forest growth, causing changes that
could alter composition and functioning of forest ecosystems. We have examined the effects of elevated CO2
( +CO2; 560ppm), elevated O3 (+O3; 1.5X
ambient), and their combination (+CO2+O3),
on the growth and productivity of model aspen (Populus tremuloides Michx.) and aspen-birch (Betula papyrifera Marsh.) forest ecosystems growing in an open
free-air exposure (FACE) system in northern Wisconsin USA. After eight years of fumigation, +CO2
increased aspen tree and stand volume growth by 39 + 9% and 38 +
10%, respectively, whereas +O3 decreased them by 27 + 6% and
34 + 4%, respectively. +CO2+O3 resulted in a net
canceling of the effects of the single gases on aspen growth. Forest
growth responses to +CO2 and +O3 interacted strongly with
present-day interannual variability in climatic conditions. The amount and
timing of photosynthetically active radiation and temperature coinciding with
growth phenology explained 33-61% of the annual variation in growth responses
of aspen trees, and explained 20-63% of annual variation in growth responses of
aspen tree stands.
Author: M.E. Kubiske, V.S. Quinn, W.E. Heilman, et al (ndnelson at fs dot fed dot us)
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