Depression of tree recruitment by the Pacific rat (Rattus exulans Peale) on New Zealandʹs northern offshore islands Original Research Article

Recruitment of tree populations on islands with and without Rattus exulans Peale, and recruitment changes on islands before and after rat eradication are compared using size-class analyses. Seedling establishment in rat-proof exclosures was compared with adjacent control areas. R. exulans depress recruitment of 11 species of coastal trees among 17 species studied: Coprosma macrocarpa, Coprosma repens, Dysoxylum spectabile, Melicytus novae-zelandiae, Nestegis apetala, Pisonia brunoniana, Pittosporum crassifolium, Pouteria costata, Pseudopanax lessonii, Rhopalostylis sapida and Streblus banksii; some to the point of local extinction. Where R. exulans has reached small islands supporting dense colonies of petrels (Procellariidae, Pelecanoididae), the numbers of some plant and animal species have been greatly reduced. Successional pathways in vegetation recovering on larger islands formerly occupied by Maori, have also been altered by this rat. Similar effects by R. exulans on the plant life of Pacific islands are probable considering the length of time R. exulans has been present.