When a Fulton Hogan team in Hamilton removed more than 100 trees to allow for construction of the Wairere Drive extension project they were faced with a local bat challenge. .
The majority of trees (75 percent) had been identified as high-risk potential habitats for the urban long-tailed bats, so Department of Conservation (DoC) requirements meant the team had to undertake night monitoring of their movements, prior to felling any trees.
Bats are sensitive to weather conditions, so monitoring had to be started at least an hour before sunset, and finish an hour after sunrise.
The temperature was not able to drop any lower than 10 degrees four hours after sunset, or have no more than 2.5mm of rain for the first two hours after sunset. There were wind limitations throughout the night. Any of these factors would prevent bat movement, affecting reliable monitoring results.
Bats don’t fly one day either side of a full moon, and because they hibernate over winter, the DoC permit prohibits any tree felling from April 30 to October 1.
All these factors meant there were only two potential weekends – March 30/31 and April 6/7 – to complete all the felling. If the work was unable to be carried out over those two weekends, the project would have faced significant delays.
In order to meet Work Safe requirements of having a two tree length clear zone when felling a tree, the team closed Cobham Drive (State Highway One) during the work, from 7am to 7pm. Weekends were identified as having lower traffic usage than weekdays, so it was agreed as the preferred time.
Fulton Hogan asked some residents to vacate their homes for a short space of time, as a number of the trees being felled were in close proximity to dwellings, and in one case, a tree was growing through a property boundary fence.
Several planning meetings with all parties, including the NZ Transport Agency and Hamilton City Council, identified several alternative routes around the city, to try and reduce the volumes of traffic on the diversion route around the site.
Fulton Hogan communicated these routes to the public and heavy vehicle companies via radio advertising, along with letter box drops in the wider affected area, and held a public information evening.
Leading up to the weekend, bat monitoring of the trees away from the road “fall zone” saw a clear period with no bat activity during key times, allowing for project ecologists Tonkin and Taylor to approve the removal of these trees.
However, the days leading up to the operation saw bat activity recommence in the area. As the ecologists couldn’t be sure there were no bats roosting overnight, all trees being felled needed to be climbed and checked, using an endoscope in the cavities, to ensure no bats were roosting.
Along with climbing the trees to check prior to felling, all trees identified as potential bat roost trees had to be examined by the ecologists immediately after felling, to ensure there were no injured bats.
All this was factored into the planning of the weekend, and although the team was optimistic it could get done in one day, the likelihood was that it would take two.
Saturday March 30 dawned clear and warm, with a karakia performed by members of the working group prior to work starting. Three arborist companies – BAX, Franklin Trees and Treescape – worked closely together, with six crews of climbers used initially to look for bats, then remove the trees.
As well as the climbers, the work involved four ecologists from Tonkin and Taylor, excavator operators to hold, guide and move the trees, chainsaw operators, site safety crews and the project team onsite – an operation of 27, plus the traffic management staff.
By early afternoon, significant progress had been made. The arborists, working closely with the ecologists around the “bat” trees, were climbing and checking trees for bats, before clearance was given to fell. Some trees couldn’t be climbed, so a bucket lift was used instead.
Once felled, excavators moved trees to a central location to keep the site safe, with a stump grinder following up behind.
By the time 7pm rolled around, the team had felled all bar three tall poplars on the northbound side of Cobham Drive, and had the road reopened to traffic. The three poplars on the northbound side had seen bat activity on the Thursday night, and as they could not be climbed for safety reasons, or checked by bucket lift, the team waited until they had two consecutively clear nights (over a minimum of three nights monitoring) of no bat activity.
Fulton Hogan advised NZTA and Hamilton City Council that the road wouldn’t be closed on the Sunday, and the three poplars would be felled as soon as there were two consecutive nights with no bat movements. Fortunately, Saturday night and Sunday morning’s data showed no bat activity on these trees, and they were removed under a temporary stop/go system Sunday afternoon.
Fulton Hogan Project manager Dan Parkes says the operation wouldn’t have been successful without the collaborative approach taken by all parties in organising both the road closure and detours, and the safe felling of trees without impacting bats.
“The day was not only a success because we got all the trees removed, it was also a success because it was done in a collaborative and efficient way.
“The site was managed well, there were no health and safety incidents, and everyone went home well at the end of a long and busy day. I’d like to thank all parties involved for their hard work and dedication in making this a successful operation.”