Last winter’s cold weather has hit trees such as the New Zealand cabbage tree
and is known as the cabbage tree, or Cordyline australis. Despite its tropical, somewhat truffula tree-like appearance, it’s generally considered hardy in Ireland, except in very cold, inland parts of the country where it can sometimes struggle. Although it can happily tolerate temperatures as low as minus 7C, last winter’s sustained, exceptionally cold weather meant that even mature plants growing in coastal Irish gardens suffered.
I’m guessing this is the cause of your cordyline trees’ unhappy appearance. To help them recover, I’d suggest cutting back all of their dead or badly damaged swordlike leaves. Then use a sharp secateurs to prune back any dead or damaged sections of the trunks. In some cases, this might mean cutting them right back to the base but they should soon reshoot.
Occasionally cabbage trees that have been badly affected by extreme winter cold will also develop a condition known as cordyline slime flux, where both the frost-damaged crown of the plant as well as its frost-damaged leaves subsequently become infected with bacteria. When this happens, the affected parts of the plant have an unpleasant smell and an orange or white liquid might ooze from them.