Different responses to shade of evergreen and deciduous oak seedlings and the effect of acorn size

An evergreen oak species, Cyclobalanopsis multinervis, and a deciduous oak species, Quercus aliena var. acuteserrata were grown from acorns under two light levels (full sunlight and shade at about 18 % of full sunlight, simul ating the light intensities in forest clearings and gaps, respectively) for one growing season. Three hypotheses were tested: (i) the deciduous specie s grows faster than the evergreen species in forest gaps and clearings; (ii ) the deciduous species responds more strongly in terms of growth and morph ology to variation in light climate than the evergreen species; and (iii) s eedling size is positively correlated to acorn size. The results showed: (i ) at both light levels, the deciduous seedlings gained significantly more g rowth in biomass and height than the evergreen seedlings; (ii) both species produced significantly more biomass in full sunlight than in shade, withou t showing any significant difference in height between treatments. Increase in light intensity improved the growth of the deciduous seedlings more str ongly; (iii) at a similar age, the deciduous seedlings showed a greater res ponse in leaf morphology and biomass allocation to variation in light level s, but when compared at a similar size, biomass allocation patterns did not differ significantly between species; (iv) bigger acorns tended to produce larger seedlings, larger leaf sizes and more leaf area, between and within species. These differences demonstrate that the deciduous species is gap-d ependent and has the advantage over the evergreen species in forest gaps an d clearings. (C) 1999 Editions scientifiques et medicales Elsevier SAS.