Effects of kiore (Rattus exulans Peale) on recruitment of indigenous coastal trees on northern offshore islands of New Zealand

Possible effects of kiore (Rattus exulans) on selected indigenous tree spec ies in coastal forests of northern New Zealand are surveyed from recent fie ld sampling and a literature review. Recruitment rates are compared on isla nds with and without kiore: (i) on the same island before or at the time of rat eradication compared with recruitment some years later, and (ii) on ge ographically separated islands with and without kiore. In addition, kiore-p roof exclosures enabled some comparisons to be made of seed germination and survival in the presence and absence of kiore. There is evidence that kior e have substantially reduced recruitment of Pittosporum crassifolium, Poute ria costata, Streblus banksii, and Nestegis apetala, by eating the seed. Se ed consumption and/or depressed recruitment is demonstrated for Rhopalostyl is sapida, Vitex lucens and Pisonia brunoniana, but the extent of recruitme nt reduction is not yet clear. No depressive effect by kiore on the recruit ment of some species, including Dysoxylum spectabile, Beilschmiedia tawa, B . terairi, Corynocarpus laevigatus, Melicytus ramiflorus, Pseudopanax arbor eus, P.lessonii, and Coprosma macrocarpa, has yet been demonstrated: juveni les remain abundant in the presence of kiore. Some tree species most affect ed by kiore are now rare in coastal forest of the northern islands and main land. Evidence from recruitment reduction in these species suggests that th e composition of northern coastal forest before kiore arrived was significa ntly different from that of the present. It also suggests that, if rats are present, current successional pathways following burning or other disturba nce of coastal forest will not restore the forest to its pre-human composit ion.