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

Abstract

Possible effects of kiore (Rattus exulans) on selected indigenous tree species in coastal forests ot northern New Zealand are surveyed from recent field sampling and a literature review Recruitment rates are compared on islands 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 geographically separated islands with and without kiore In addition kiore‐proof exclosurcs enabled some comparisons to be made of seed germination and survival in the presence and absence of kiore There is evidence that kiore have substantially reduced recruitment of Pittosporum crassifohum, Poutena costata Streblus banksu, and Nestegis apetala by eating the seed Seed consumption and/or depressed recruitment is demonstrated for Rhopalostyhs sapida, Vitex lucens and Pisoma brunoniana, but the extent ot recruitment reduction is not yet clear No depressive effect by kiore on the recruitment ot some species, including Dysoxylum spectabde Beilchmiedia tawa B twain Corvnocarpus laevigatus, Melicytus ramiflorus Pseudopanax arboreus P lessonu and Coprosma macrocarpa, has yet been demonstrated, juveniles remain abundant in the presence of kiore Some tree species most affected by kiore are now rare in coastal forest of the northern islands and mainland Evidence from recruitment reduction in these species suggests that the composition of northern coastal forest before kiore arrived was significantly different from that of the present It also suggests that if rats are present, current successional pathways following burning or other disturbance of coastal forest will not restore the forest to its pre‐human composition