Growth of<i>Quercus robur</i>seedlings after experimental grazing and cotyledon removal

Abstract

Grazing of leaves and stem or removal of the cotyledons, partly or completely, are two possible dangers for seedlings of Quercus robur that could influence their growth and survival. Acorns rely to a great extent on caching by animals for their dispersal. It has been suggested that the large nutrient reserve in the acorn is used to recover from grazing, or to grow longer to reach the light from a cache in the soil. We designed two experiments in which we studied (i) the effects on the seedlings of artificial grazing and removal of cotyledons and (ii) the effects of grazing after reduction of the cotyledons with acorns sown at different depth. Manipulated seedlings in both experiments produced a new leaf-set. The necessary resources are taken from the development of the shoot and the root system, except after severe defoliation when some resources were taken from the cotyledons. Defoliation and grazing caused the shoot and root system to become smaller and probably more vulnerable to, e.g. grazing, trampling or drought. Caching depth only affected emergence day. These results suggest that the cotyledons are not of vital importance for regrowth of the seedlings, but they may be of primary importance for dispersal of acorns.