Sir, - The contributions on the topic of ivy on trees from Fr Nolan (January 27th) and Dermot McCabe (February 7th) prompt me to offer some observations on safety considerations.Ivy can be harmful, especially to deciduous trees, in the following ways:when it prevents close scrutiny of old trees to assess their safety;when its massive envelope is of such a size and weight that it shifts the centre of gravity of the tree upwards, thus giving rise to massive levering forces in high winds tending to cause windthrow;when the extent of its coverage in effect turns a deciduous tree into a massive item of evergreenery. Without the ivy coverage storm winds whistle through the branches, whereas the evergreen ivy affords strong resistance to winter storm winds, and such ivy-enveloped trees are then more likely to be snapped off at the base, or be uprooted.A large proportion of winter storm-damaged trees are found to be heavy with ivy. Many such trees are healthy and could have weathered the storm, but for the massive envelopes of ivy. Landowners who allow trees overhanging public access to be covered with heavy ivy envelopes are putting lives at risk. - Yours, etc.,Karel Bacik,Meadowgrove,Blackrock,Cork.