What's been happening?
Fuchsia excorticata
Since 1994, the Department of Conservation has been controlling possum numbers in more than 60,000 hectares of Tararua Forest Park. Every year about 9000 hectares are treated by the aerial application of cereal baits containing the pesticide 1080. There are seven management areas that receive possum control on a rotational basis.
Why has this occurred?
Possums eat tree fuchsia (Fuchsia excorticata) berries and leaves. Fuchsia flowers and berries are also an important food source for tui, bellbirds, and kereru. Stands of young fuchsia colonise slips and forest gaps. They stabilise the soil and help produce conditions that allow the establishment of canopy trees.
Surveys of mountain forests in 1975 and 1985 in the Tararua ranges suggested fuchsia trees declined by 25 percent due to possum impacts. The goal of possum control was to prevent a similar decline in fuchsia between 1994 and 2004.
How was the goal assessed?
More than 1000 fuchsia trees were monitored at different times over the last 10 years. Fuchsia trees were tagged and their health tracked by assessing the condition of their canopy. This was done in four management areas, and also in an area of Tararua Forest Park where possum control is not undertaken.
What did we find?
Significantly fewer fuchsia trees died where we controlled possums. Only 3 percent
of the 739 stems monitored died where we completed possum control. This compares to 30 percent of the 272 stems dying in the area that has not received possum control.
Possum browsing on fivefinger
The basal area (trunk size) of surviving trees in the possum controlled areas increased by 3 percent, indicating that surviving fuchsia trees increased in growth, and maintained their importance in the forest. However, a 15 percent basal area loss in the area without possum control, pointed to a significant change occurring in these forests from possums killing trees.The accelerated loss of fuchsia negatively affects long-term forest processes such as the stabilisation of landslide areas, and reduces the amount of food available for native birds.
Did we achieve our goal?
The department is confident that it has achieved its conservation goal of protecting the fuchsia from possums in the seven treatment areas. A number of other plant species, such as northern rata, tawa and kamahi, probably also benefited from the possum control.
Where to from here?
The Department of Conservation is looking to extend protection in the Tararua ranges to at risk forest birds and lowland plants.
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