Heavy rotation: Florian Kirschbaum saves the forest from his helicopter

Smoothly, the pilot puts down the huge spreader while keeping the helicopter steadily hovering above. A wheeled loader fills the container and then the chopper gets back to spreading. It's all done in a matter of seconds. Marc waits a short while until the dust falls a little further down. Then he takes his foot of the brake and drives directly towards the loading area. "That was Flo," he says, pointing to the sky with his finger. The air outside tastes chalky. Your mouth feels as dry as dust.

The Hetralog team for which Marc and Florian Kirschbaum work is responsible for liming an 1800-hectare area in the forests of the eastern Erz mountains. They let 5400 tonnes of lime flutter down onto the treetops, from where it slowly makes its way down to the forest floor. As part of this operation, Florian takes to the air for several weeks in his helicopter. On average, around 300 tonnes of the product are released on a daily basis.

The pilot has now landed the aircraft – time to refuel. "We use the lime to counteract the acidic ground," he explains, opening the clasp on his yellow helmet at the same time. Over the decades, industrial facilities have left their mark on the region. Rain with greater levels of sulphur and thus higher acidity has put enormous strain on the forest. "The purpose of the lime is to improve the pH value of the ground and thus create beneficial conditions for the roots of trees and plants. It's our way of helping stabilise the ecosystem in the forest," says the 38-year-old.

To obtain fresh supplies of lime, Marc and his colleague Rigo Knobelsdorf drive with their Arocs and Actros respectively between the forest and the quarry two hours away. 26 tonnes of lime are on-board each vehicle. "We clock up a right amount of mileage on the motorways. But then it gets balanced out by driving through the forest each day. If the loading areas are on tough routes, we need the engine's full power and torque. That gives the Hydraulic Auxiliary Drive the chance to show us what it's made of," says the Dortmund-born trucker.

Flo removes the fuel pump from the nozzle of the helicopter and brings it back to the refuelling vehicle. He has to land at Hetralog's makeshift refuelling pad every 50 minutes. The maximum take-off mass of the helicopter is 2800 kilogrammes. 1200 kilogrammes of which already have to be removed due to the lime spreader and its load, then there are the 200 kilogrammes of kerosene, the 90 kilogrammes of the pilot and his affairs, not to mention the unladen weight of the helicopter at 1250 kilogrammes. That means Flo is literally flying at the limit. Here, every single kilogramme counts. The cockpit is emptied to contain only the absolute bare minimum. A seat for a co-pilot or passenger? No. "The aircraft is constantly working at the performance limits, otherwise the project wouldn't be economically viable," he says, locking up the refuelling vehicle which is parked next to the helicopter.

Flo wants to get back in the air. But first, he has to carry out a check of the aircraft's exterior – the pre-departure checklist. "This is something for which you have to make time," he says, inspecting the helicopter in a concentrated manner. Every surface is checked meticulously for any suspicious traces of oil, and he also checks whether the play around the bearings is in order. Then he checks the displays in the cockpit: are the oil pressure and oil temperature correct? Are there any warning lights which are lit? If everything is OK, he can depart. The storm which the rotors kick up shakes the surrounding trees.

Good organisation is everything – both at work and at home.

He's already on his way back to the loading area. Flo's shift time must not exceed ten hours. 8.5 hours of which he spends flying.

"If there are strong, gusting winds, extremely bad weather or repairs which prevent me from taking off, we can't change anything," says Wilhelms. "That's why our team always keeps a close eye on everything else over which we do have control." Smooth collaboration and perfectly timed processes are extremely important to guarantee safety, but also for completion of the order.

Bernd Hell drives the wheeled loader during operations and is constantly in radio contact with Flo and Klaus-Peter Wilhelms. The pilot has to know which loading areas still have sufficient lime available and also informs the team of those areas which need refilling. There's no space for long detours or waiting times.

During the week, the Hetralog team is away from home. "But my family is used to it," says Marc. Tomorrow, I'll be heading back to my wife, daughter and son in the Ruhr area. Flo, too, currently only sees his wife and two sons at the weekend when he's back home in Düsseldorf. "We're well-organised. Otherwise, it would be tough for us all," he says. Marc: "We certainly don't get board, not even at night. That's when we talk through the plan of action for the next day and chat about absolutely anything that comes to mind." Forestry liming is all about team work. Flo and Marc's team will be in action until winter time in the forests. Until then, everything has to be complete so that the lime has time to do its job until the next growth period.