The Big Idea: Restoring an Island Ecosystem
It takes a large amount of work to put a forest back together! After years of industry, clearance and stock pressure, only a hand full of trees remained on the island. The island was also overun with mice and rats, the odd cat, and possums eating the remaining trees. Two of the primary goals of FOMLI therefore were to re-establish the coastal forest that would have once dominated the island, and eradicate the mammalian pests.
From humble beginnings in 1989, a huge number of trees have now been planted on Matakohe-Limestone Island. At least 150,000 have been planted to date and the planting continues. This includes over 100 different species of native trees and plants, with seeds sourced locally. In the year 2000, to celebrate the millenium, over 23,000 were planted in one season, including 14,000 planted in a single day by over 400 volunteers!
The planting approach adopted on the island is to plant the fast growing pioneer species, such as kanuka and manuka, that rapidly form canopy cover, essential to shade out the dense buffalo grass that thrives on the island. These pioneer species then act as a nursery crop for other native trees.
The planting plan also recognises the unique character of the island and its important cultural features. The historic cement factory ruins and surrounds and the Matakohe pa site and site of the kumara gardens and storage pits are being left in open grassland to preserve these features. These grassland areas also provide habitat for different bird, insect and lizard species, as well as preserving the amazing views from the high points on the island.
Dealing to the pesky pests
Before the island could become a safe habitat for native species like kiwi and forest gecko, the pests had to be removed. This process started in 1989 when the possums were targeted. Initial attempts used night shooting but when more possums kept surfacing, FOMLI switched to laying toxic baits which successfully eradicated possums from the island. In total nearly 300 possums were removed from the island - a huge number considering how few trees remained!
Rats, a small infestation of weasels and two feral cats were the next to be targeted. The cats and weasels were succesfully eradicated in 1991, however rats proved more tricky. Toxic baits had been hand laid in baitstations by volunteers, but despite limited bait take, rats persisted in low numbers on the island. In June 1996 a more intensive aproach was adopted; an aerial drop of Talon toxic bait was undertaken on the Matakohe-Limestone and two of the adjacent islands. This seemed to be successful, but in 1999 signs of rats and stoats began to appear again. It was established that they were swimming from the mainland and so a permanent trapping network was set up.
Mice also continue to prove a challenge for the island. A second bait drop in 2001 targetting mice failed to eradicate them completely and so a grid of 800 stations at 25m x 25m intervals was set up across the entire island. This grid continues to maintain the island as effectively mouse-free with extremely low population densities.
Ongoing Predator Control
Being so close to the mainland is great for visitor access but not great for pests - stoats and rats are suprisingly good swimmers and sometimes make the swim across to the island or hitch a ride with unwary visitors. Because of this, the ranger maintains a permanent network of DOC 200 stoat traps, Victor rat traps and perimeter bait stations on the island, which are checked every week. The ranger also undertakes trapping and baiting in the 'buffer zone' - the islands and mainland headlands that surround Matakohe-Limestone - to reduce the chances of a stoat or rat using these as stepping stones to reach the island.
The island also has a network of nearly 800 bait stations on a 25m grid designed to target mice. These stations are baited every few months to ensure the island remains effectively mouse free. Each station contains a small amount of bromadiolone bait to kill rodents.
This trapping and baiting is essential to mantain the island as predator free and protect the vulnerable species that live here. The traps can break fingers and the baitstations contain a toxin, so please do not disturb them and be particularly mindful of children when visiting.
Every three months the Ranger sets out 48 tracking tunnels around the island to check for predators that could have made it to the island. These consist of a cardboard strip with an inked area in the middle, placed inside a tunnel. These are baited with peanut butter (crunchy!). When something walks through the tunnel, it leaves footprints on the paper. Detecting the footprints of any mustelids and rodents is the primary target, but the tunnels also show insect tracks, lizard tracks, frog tracks and the occasional kiwi chick footprints!