The team found that the Hope Valley in South Westland still supports a large and healthy population of the rare New Zealand scarlet mistletoe (Peraxilla colensoi), while in the nearby Stafford Valley, the mistletoe have all but disappeared.
Why this contrast?
It is a success story for repeated aerial control of possums in the Hope Valley. This started in 2005, when possums had only just arrived in the valley and mistletoe were still numerous and healthy. Regular control, keeping possums continuously at low levels, has kept our mistletoe relatively safe. The number of mistletoe the team counted on their monitoring plots increased from 58 to 74 between 2006 and 2011. In 2016, there were 70, slightly less, but still more than in 2006. This means the Hope Valley is one of very few places where you can still experience mistletoe the way they were before possums arrived, adding a glorious spray of red flowers to the forest every festive season.
The possum problem
The Stafford Valley was not so lucky. Possums also arrived late, but were not regularly controlled. Numbers increased to high levels. In their latest assessment, the monitoring team found only one small mistletoe in one of the monitoring plots. All others had gone. The scary thing is that the rapid decline from a healthy population to near extinction happened within 30 years of possums arriving in the area. The monitoring results highlight how important it is to respond quickly and regularly, maintaining possum numbers at low levels, to protect the most sensitive elements of our biodiversity.
Monitoring and management
The monitoring results also highlight how management and monitoring go hand-in-hand. By monitoring the contrast between the Hope and Stafford Valleys we are gaining an understanding of what happens without management, and in turn, we can demonstrate the difference made by our management.
The monitoring is also giving us the hard data we need to assess the long-term effectiveness of our management. Are we actually successful in protecting mistletoe in the Hope Valley into the future? So far, it is looking good, but the slight decline in numbers noted in 2016 and an observed increase in possum damage prompted management to give possum control in the Hope Valley a higher priority. The next aerial control operation is now planned for next year.
The observed decline in mistletoe numbers may mean that currently, pest control in the Hope Valley does not keep possum numbers low enough to sustain the mistletoe population long-term.
Further monitoring, hand-in-hand with more intensive management, will tell us what we need to do to achieve effective mistletoe protection, so you can continue to enjoy your mistletoe for Christmas.