This paper discusses the general processes by which trees cause damage to rock slopes. It discusses the actions of root elongation, which can cause root jacking, and trunk expansion. It discusses research aimed at establishing a relationship between root diameter and the forces applied by roots. The results of this research are inconclusive and at this stage provide little useful information for local geotechnical design purposes. It is concluded that, in general, trees should be removed from bare rock slopes adjacent to public infrastructure where there is greater than a moderate risk associated with rockfalls unless other measures are taken to reduce the risk (e.g. rockfall fence or mesh).