Publication: Seedling recovery after eradication of Pacific rats

[Dave Houston]

Seedling recovery on Hauturu/Little Barrier Island, after eradication of Pacific rats Rattus exulans
By D.J. Campbell
DOC Research & Development Series 325. 53 p.

What's it about?
Pacific rats (Rattus exulans, kiore) eat seeds and seedlings of native plants. Seedlings of selected woody plants on Hauturu/Little Barrier Island were counted in 18 linear plots twice before rat eradication in 2004, and again 4 years after. All seedlings ≤ 30 cm tall were measured and grouped into 5-cm classes. The same species were counted at the same time on rat-inhabited Taranga Island and Great Barrier Island (Aotea Island), and the ratios of post-eradication to pre-eradication seedling numbers on the control islands were used to predict likely post-eradication seedling numbers on Hauturu. Post-eradication numbers of 14 species increased more on Hauturu following rat eradication than on the control islands, listed here in descending order of increased abundance: Pisonia brunoniana, Coprosma macrocarpa, Ixerba brexoides, Knightia excelsa, Rhopalostylis sapida, Phyllocladus trichomanoides, Nestegis lanceolata, Dacrycarpus dacrydioides, Ripogonum scandens, Hedycarya arborea, Dysoxylum spectabile, Pittosporum umbellatum, Macropiper excelsum and Corynocarpus laevigatus. Five species had fewer seedlings: Agathis australis, Beilschmiedia tawa, Beilschmiedia tarairi, Vitex lucens and Prumnopitys ferruginea. Small seedlings of 11 other species, not systematically counted previously, were searched for in 2008 and 2009. Seedlings of Coprosma arborea, which was not monitored, were very abundant in 2009. Several less-common, rat-affected species have not yet responded. Early changes in seedling abundance indicate that rats have influenced the vegetation composition of the modified part of the island. No evidence was found for any suppression of the spread of kauri (Agathis australis) into känuka (Kunzea ericoides) forest, but Pacific rats had inhibited the spread of some bird-dispersed species into känuka forest.

The above new publication is now in press and can be downloaded from:
http://www.doc.govt.nz/upload/documents/science-and-technical/drds325entire.pdf (1527 KB)

[Steptoe]

Im not suprised ... ever since we have had a maintaince program in our backyard for rodents  etc, there has been a very noticable increase in  coprosa, kakakawa, pururi, totatra, five finger...and plum, cherry tree and privit, the latter 3 considered weeds
Also mercury bay (dicondra?)  puha (not sure if native or introduced species, appears to me 2 species thu

How much is bird spread and how much is just old seed dorment in the ground I dont know...both ?
Now many of the plants have grown a bit and started to self seed, the seedliungs are thick  like grass
The blackbirds and thrush dsig around but dont seem to desturb the seedlings...I sudpect the bird digging tends to ptomote any dorment seeds .