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Introduction: A Kiwi Innovation in Land Clearing
In the rugged hill country of New Zealand, traditional dozing methods often fall short. The terrain is too steep, the scrub too dense, and the risk of rollover too high. Out of necessity, a unique method of land clearing emerged in the 1970s and 1980s—known locally as “gravity scrub rolling.” This technique combined modified bulldozers, logging winches, and massive rolling drums to crush vegetation on slopes that would otherwise be inaccessible. It was a blend of engineering creativity and brute force, and it transformed forestry operations across the region.
The Machine: A Terex Transformed
One of the most iconic machines used in gravity scrub rolling was a heavily modified Terex 82-30. These tractors were chosen for their robust undercarriage and adaptability. The modifications included:
Terminology Explained
Field Anecdote: Merv’s D6D and the Razorback Ridge
One veteran operator, known as Merv, recalled working on the Coromandel Peninsula with a Caterpillar D6D. Though he didn’t use the dual-drum setup himself, he often blade-crushed scrub on less steep terrain. He described watching modified Terex and Allis Chalmers HD16DP machines in action—massive rollers swinging out over cliffs, shredding vegetation with surgical precision. “Absolutely awesome to watch,” he said, “they could clear a hillside in a day.”
Suggested Parameters and Setup Tips
While Terex tractors were popular, other machines were adapted for scrub rolling:
Historical Context: Forestry and Fire Management
Gravity scrub rolling wasn’t just about clearing land—it was a strategic tool in forestry development and fire prevention. In the 1970s and 1980s, New Zealand saw a boom in radiata pine plantations. Steep, scrub-covered land was a barrier to expansion, and traditional bulldozing methods were too risky. Gravity rolling allowed foresters to open up new areas while minimizing erosion and fire hazards.
In Australia, similar techniques were used in Queensland’s hill country, where dense lantana and wattle made conventional clearing nearly impossible. Modified dozers with winch-controlled rollers became essential tools in both land development and wildfire mitigation.
Case Study: Reclamation in Whangarei
In Whangarei, New Zealand, a contractor used a modified Terex to reclaim over 200 hectares of steep scrubland. The operation took six months and involved coordinated burning, replanting, and erosion control. The success of the project led to increased adoption of gravity rolling across the region, with local councils funding equipment upgrades and training programs.
Conclusion: Ingenuity on the Edge
Gravity scrub rolling is a testament to the ingenuity of operators working in extreme conditions. By repurposing and modifying existing equipment, they created a method that was safe, efficient, and uniquely suited to the challenges of steep terrain. Though the boom years have passed, the legacy of these machines lives on—in the forests they helped plant and the stories shared by those who ran them.
In the rugged hill country of New Zealand, traditional dozing methods often fall short. The terrain is too steep, the scrub too dense, and the risk of rollover too high. Out of necessity, a unique method of land clearing emerged in the 1970s and 1980s—known locally as “gravity scrub rolling.” This technique combined modified bulldozers, logging winches, and massive rolling drums to crush vegetation on slopes that would otherwise be inaccessible. It was a blend of engineering creativity and brute force, and it transformed forestry operations across the region.
The Machine: A Terex Transformed
One of the most iconic machines used in gravity scrub rolling was a heavily modified Terex 82-30. These tractors were chosen for their robust undercarriage and adaptability. The modifications included:
- Two independent winch drums mounted on either side of the tractor
- Separate clutches and brakes for each drum, allowing directional control of the roller
- A forward-mounted operator station on the nose cone for better visibility
- Fairleads mounted on the blade to guide winch ropes
- Reinforced blade used as a brake to anchor the machine on steep ridges
Terminology Explained
- Fairlead: A device that guides a rope or cable to prevent chafing and ensure smooth operation.
- Logging Winch: A heavy-duty winch used in forestry to pull logs or equipment, often mounted on dozers.
- Scrub Roller: A large cylindrical drum fitted with chopper blades, used to flatten and shred vegetation.
- Razorback Ridge: A narrow, steep ridge with sharp drop-offs on either side.
- The dozer is positioned on a narrow ridge, facing downhill.
- The roller is winched out at an angle using the side-mounted drums.
- As the roller descends, it crushes scrub in a wide path.
- The operator uses the independent winches to steer the roller.
- Once the swath is complete, the roller is winched back uphill.
- The dozer moves forward and the process is repeated.
Field Anecdote: Merv’s D6D and the Razorback Ridge
One veteran operator, known as Merv, recalled working on the Coromandel Peninsula with a Caterpillar D6D. Though he didn’t use the dual-drum setup himself, he often blade-crushed scrub on less steep terrain. He described watching modified Terex and Allis Chalmers HD16DP machines in action—massive rollers swinging out over cliffs, shredding vegetation with surgical precision. “Absolutely awesome to watch,” he said, “they could clear a hillside in a day.”
Suggested Parameters and Setup Tips
- Roller Diameter: 1.5–2 meters for optimal crushing force
- Blade Angle: Slightly tilted to act as a brake and guide for winch ropes
- Winch Drum Torque: Minimum 1,200 Nm per drum for reliable control
- Operator Visibility: Elevated nose cone position with reinforced canopy
- Rope Type: 5/8" steel cable with anti-kink properties
- Safety Gear: Harnesses, remote kill switches, and slope monitoring sensors
While Terex tractors were popular, other machines were adapted for scrub rolling:
- Allis Chalmers HD16DP: Known for its torque and stability
- Caterpillar D7F: Used with standard logging winch setups
- Fiat and Eimco dozers: Occasionally modified for lighter scrub work
Historical Context: Forestry and Fire Management
Gravity scrub rolling wasn’t just about clearing land—it was a strategic tool in forestry development and fire prevention. In the 1970s and 1980s, New Zealand saw a boom in radiata pine plantations. Steep, scrub-covered land was a barrier to expansion, and traditional bulldozing methods were too risky. Gravity rolling allowed foresters to open up new areas while minimizing erosion and fire hazards.
In Australia, similar techniques were used in Queensland’s hill country, where dense lantana and wattle made conventional clearing nearly impossible. Modified dozers with winch-controlled rollers became essential tools in both land development and wildfire mitigation.
Case Study: Reclamation in Whangarei
In Whangarei, New Zealand, a contractor used a modified Terex to reclaim over 200 hectares of steep scrubland. The operation took six months and involved coordinated burning, replanting, and erosion control. The success of the project led to increased adoption of gravity rolling across the region, with local councils funding equipment upgrades and training programs.
Conclusion: Ingenuity on the Edge
Gravity scrub rolling is a testament to the ingenuity of operators working in extreme conditions. By repurposing and modifying existing equipment, they created a method that was safe, efficient, and uniquely suited to the challenges of steep terrain. Though the boom years have passed, the legacy of these machines lives on—in the forests they helped plant and the stories shared by those who ran them.
