GYMNOSPERMAE

As for many other cultivated trees and shrubs regeneration of formerly planted conifers is poorly documented in Belgium. In recent years sexual reproduction has been detected in numerous species but some processes probably already started long ago (for instance Pseudotsuga menziesii). Several additional ornamental species doubtlessly self-sow in Belgium but additional research is required. Many conifers are reputed environmental weeds worldwide (see for instance Richardson & Rejmánek 2004).