Dung beetles have joined the fight to clean up New Zealand’s waterways and Lake Wairarapa is a key target.
In November the first region-wide release of non-native dung beetles in New Zealand began at an open day at Featherston’s Kaiwaiwai Dairies, in a paddock beside the farm’s wetland.
The 0.75-hectare Kaiwaiwai wetland is part of the wider Wairarapa Moana wetland project, which includes Wairio. Both wetlands won Morgan Foundation Awards in 2015.
Greater Wellington-subsidised packages of four species of dung beetles have contributed to about 200 dung beetle colonies, primarily in Wairarapa.
Contamination of pasture by dung reduces the amount of forage available for grazing, and has other economic, environmental, ecological and social effects, such as pollution of waterways.
Introducing dung beetles to deal with pastoral dung provides an opportunity to help mitigate risks to freshwater quality.
Greater Wellington’s offer of discounted beetle packages is focused on properties along the eastern shore of Lake Wairarapa, where the lake contains high levels of nitrates and other pollutants, some of which leach into the water from dung.
“We will introduce measures that will show whether the beetles are spreading, whether we’re witnessing a reduction in dung, and whether other benefits are being realised.
“We’ll work with Lake Wairarapa farmers to plan a monitoring regime covering the next few years,” says Greater Wellington land management advisor Kolja Schaller.
It is planned to have most of the dung beetles released in an area along the eastern lake shore of Lake Wairarapa in partnership with catchment farmers, though a small number may be released outside of this area.
The Wario Wetland has come in for some close scrutiny by Victoria University Student Bridget Johnson who is this year studying towards an MSc in Ecological Restoration. The overall title of her thesis is “Ecological restoration of the Wairio Wetlands, Lake Wairarapa: vegetation dynamics and succession”.
A Summer Scholarship meant she was able to do 10 weeks of research in her chosen field at Wario with the title for that part of her research being “Temporal & Spatial Patterns of Wetland Vegetation during the Summer Desiccation Period at Wairio Wetlands, Wairarapa”. In addition to the summer scholarship, Bridget has started preparing a second site at Wairio for a large scale experimental project where around 2400 trees have been planted.
The summer study programme provided an introduction to the Wairio Wetland for Bridget where she continues the research for her thesis on factors contributing to wetland restoration. Flight, with help from Jim Law, has been able to follow Bridget’s research so far.
A poster she produced she said was just a snap shot of some of that research. “Due to the limiting size of the poster, I only talked about rare species vulnerability.” All the summer scholars got to show their posters at a poster evening. Her poster included the following information plus a number of illustrations.
Small in size, New Zealand’s native wetlands plant species are repeatedly outcompeted by more aggressive weeds. The surrounding vegetation invades when wetland plants are most vulnerable, during the desiccation (dry) period. A number of threatened low-lying plants (Pratia and Glosso) inhabit the Wairio Wetlands. To conserve these native plants a greater understanding is required of their optimal conditions and their spatial and temporal dynamics. “My aim was to investigate the temporal scale of the native species, and which abiotic factors affect their spatial distribution.”
Vegetation composition was sampled in 20 quadrants over a 10 week summer period. The quadrants were set five metres apart along two 50 metre perpendicular transects. The first transect followed a moisture gradient, whilst the other ran parallel. Additional abiotic variables were measured, such as soil moisture, soil pH, percentage open ground, sunshine hours and rainfall. Water Plantain was chosen as a comparative species as it is a common invader and an indicator of high soil moisture.
The rare species are restricted to a small band of high moisture sites. A smaller number of invasive species can grow in these moist soils, so there are fewer competitors for the natives. In drier soils, the invasive species can spread easily, giving the vulnerable natives little chance of survival. This means the natives have truly specialised ecological requirements, as their time frame of existence and habitat preference is small. This is a contributing factor to what makes them vulnerable. Further research can be expanded from this study, for example: Should water plantain (and other invasive high moisture soil species) be managed to decrease the competition on the native species? Illustrations on the poster included Glasso, Pratia and Water plantain. Glosso and Pratia grow in soil with high moisture content and Water plantain grows more abundantly in high moisture soil but is adaptable to a greater variance of soil moisture. Bridget said the native species emerge later in the summer season, whereas water plantain is a consistent species. When the natives start emerging they have a higher percentage cover than the invasive water plantain.
“I would like to thank Dr Stephen Hartley, Tony Silbery (Department of Conservation Wairarapa), Jim Law (Ducks Unlimited) and Don Bell (Greater Wellington Regional Council) for their technical support,” said Bridget.
References: New Zealand Plant Conservation. 2010.