the common rhododendron is perhaps the greatest threat to the ecology of the park. it is an evergreen shrub with a natural distribution in the mediterranean and black sea areas. rhododendrons died out in ireland because of climate change thousands of years ago. it was introduced to the killarney area during the 19th century, and rapidly took hold. it has spread through its large numbers of very small easily dispersed seeds. it shades the ground flora and so prevents the regeneration of native woody species. more than of the park are now completely infested. they have had a devastating effect in certain parts of the park. as light cannot penetrate the dense thickets of rhododendrons, very few plants can live beneath it. the park's oak woods are in long-term danger because they cannot regenerate. there is a policy of control and eradication of rhododendrons in the park.