Review. Reproductive ecology of riparian elms

Abstract

This paper review our current knowledge of the reproductive ecology in the genus Ulmus, for which few investigations has been conducted and relatively little information is available. In the genus Ulmus, as in other riparian or sub-riparian genera, trees reproduce either vegetatively (by sprouting) or sexually. These mechanisms work differently. Sprouting permits colonization of open areas close to the trees, being especially frequent from large trees following death of their stem. Sprouting from the surviving roots of trees affected with Dutch Elm Disease is abundant in Spanish Ulmus minor. Sexual reproduction is infrequent, and requires some special conditions to be successful. It probably occurs coincidently with massive river floods that remove riparian vegetation and deposit a fertile muddy bed suitable for seed germination. Many Ulmus minor genotypes do not produce seed owing to seed abortion and other mechanisms. As a result, two gender-classes, male and cosexual, are presumably present in Spain, although this requires confirmation. A hypothesis trying to explain female sterility as the result of a trade-off between sexual and vegetative reproduction has been recently proposed, but it requires to be confirmed. Further research is also necessary for a better knowledge of flooding effect on elm regeneration and for evaluating other aspects of its reproductive ecology.