Growth responses of different tree species to elevated CO2
vary enormously, even when grown under the same basic experimental conditions
(such as nutrient supply and light conditions). A test of the hypothesis
that this variation is associated with the species’ shade-tolerance is
presented. A meta-analysis of 74 logarithm-transformed response ratios
RR (total biomass in ~700 micromol mol-1 CO2 / biomass
in current ambient CO2), grouped according to the
species’ relative tolerance to shade, revealed that RR differed widely
and significantly between seedlings or saplings of woody species of different
shade-tolerance. Only comparative studies were included in the meta-analysis,
and interference from differences in basic experimental conditions between
experiments was minimised. The mean RR of species with very high shade-tolerance
was 1.51. This was significantly greater than the value of 1.18 for species
intolerant of shade. Smaller differences in mean RR were found between
groups of species that differed less widely in shade-tolerance. When responses
were categorised according to two aspects of light environment in the experiments,
daily integrated or peak photosynthetically active photon flux density
(PFD), the differences in RR between different shade-tolerance classes
disappeared at daily integrated PFD below ~20 mol m-2 d-1 or peak PFD below
~250 micromol m-2 s-1. Growth stimulation in juvenile trees is likely to
cause increased survivorship in subsequent years. Even if the observed
differences in RR were restricted to sites experiencing no or only moderate
shading, it appears likely that they will affect species composition of
naturally regenerating forests in the long term. © 2001 Éditions
scientifiques et médicales Elsevier SAS
Kerstiens, G., 2001. Acta Oecologica 22, 61-69.