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Source: Environment Canterbury Regional Council

The unique ecosystems of the Upper Ōhau River area – including braided riverbeds, wetlands and native beech forest – are now better protected thanks to the completion of a major weed control project.  

We collaborated with local landowners Glen Lyon Station, Toitū Te Whenua LINZ (Jobs for Nature fund), the Upper Waitaki Water Zone Committee and Project River Recovery of the Department of Conservation (DOC), on the three-year project to target a range of introduced pest species – including crack willow and Russell lupins. These weeds can dominate existing native vegetation and landscapes, as well as modify river channels, which are important habitat for threatened species such as the upland longjaw galaxais fish, and braided river birds including the kakī/black stilt, tarapirohe/black-fronted tern and ngutu pare/wrybill. 

Upper Waitaki zone lead, Peter Burt, said the joint project is a fantastic example of undertaking proactive weed control work to ensure a better ecological future for a special area.  

“This is a stunning and remote landscape and luckily the horse hadn’t bolted yet in terms of these invasive species, so we were able to take advantage of a window to take action and protect the area. Once the seedlings for these invasives spread, it’s very difficult to get rid of them.  

“Working collaboratively was the key to being able to complete this project over a three-year period and we are really pleased to have got these weeds under control over such a vast area.”

Contributions from agencies and landowners provided a combined budget between $70,000 and $100,000 per year. This investment has been successful in removing crack willows and lupins from 1,800 hectares of braided river and wetland habitat, and controlling outlying populations of cotoneaster, elderberry and old man’s beard that threaten beech forest and native shrublands in the upper valleys.  

DOC senior ranger for project river recovery, Dean Nelson, said that recent surveys had indicated the Dobson was an important site for the threatened upland longjaw galaxies. 

“This work to maintain the dynamics of the braided river channels is critical to ensuring that this population continues to thrive.” 

A key challenge for the team was the scale and variety of the different types of weeds. 

Senior biodiversity officer Kennedy Lange said they used different approaches across the area. 

“We needed to control outlier populations as a priority while chipping away at core populations to limit seed input. Control techniques included ground spraying and cutting, and aerial boom and spot spraying – and the follow up assessments have shown excellent results so far.”

With large parts of the project area now only needing minor maintenance control, the project partners are now setting their sights on extending the work to include the Lake Ōhau shoreline and surrounds to ensure these landscapes and habitats are protected into the future.  

“This is still largely a natural ecosystem compared to other places in New Zealand” Kennedy added, “so it’s great that we’ve been able to nip some of these weed issues in the bud.”