Mount Nelson prescribed burn

The Mount Nelson area of Tasmania carries a considerable bushfire risk: steep, hilly terrain and high, uninterrupted fuel loads running directly up against an urban edge. Inside the project area sit high-value community assets — Hobart College among them — and the surrounding Mount Nelson residential community.

A prescribed burn was scheduled for 2025 in an area FiSci Mitigate estimates carries very high fuel loads, its boundaries defined by a trail to the north and previous fire boundaries to the west and south. We took that planned burn and modelled it before it happened.

What the landscape looked like going in

Fuel load map showing large contiguous areas above 20 tonnes per hectare adjacent to the Mount Nelson urban edge. — Fuel loads in excess of 20 t/ha, uninterrupted across much of the project area.

The initial analysis confirmed the exposure:

The main vegetation communities are Eucalyptus variations, with fuel loads exceeding 20 t/ha in high-risk areas.
Under extreme weather, the average uncontrolled fire across the project area runs to roughly 130 hectares in eight hours.
The uninterrupted fuel load significantly increases the capacity for a large, uncontrollable fire.

Historical hazard reduction exists to the south and west, and near the Mount Nelson Theatre, but those burns were carried out between 2016 and 2021 — long enough ago that the fuel has substantially recovered.

The burn, before and after

Fuel load after the modelled prescribed burn, with the treated block substantially reduced. — Modelled fuel load either side of the planned 2025 prescribed burn.

Fuel load across the Mount Nelson project area before the prescribed burn, with heavy contiguous loads. — Modelled fuel load either side of the planned 2025 prescribed burn.

Following the treatment, simulations under the same extreme weather estimate a 40 per cent reduction in average fire size across the project area — a material increase in protection for property and urban areas from fires approaching from the north-west and the south-east.

Scenario one — north-north-westerly

The same north-north-westerly scenario after treatment, with reduced spread toward the community. — Extreme fire day, wind from the NNW. Before treatment, high fuel in the north and west means any ignition can develop into a large, uncontrollable fire.

Simulated fire spread on an extreme day with north-north-westerly wind, before treatment. — Extreme fire day, wind from the NNW. Before treatment, high fuel in the north and west means any ignition can develop into a large, uncontrollable fire.

Post-treatment, the reduced fuel load substantially lowers the risk to Hobart College and the community to the east.

Scenario two — south-easterly

The same south-easterly scenario after treatment. — Extreme fire day, wind from the SE — the common summer pattern. Ignitions in the south and east drive large fires toward the college.

Simulated fire spread on an extreme day with south-easterly wind, before treatment. — Extreme fire day, wind from the SE — the common summer pattern. Ignitions in the south and east drive large fires toward the college.

A south-easterly, common in summer, poses less risk to Hobart College and the community to the east once the fuel load to the south has been lowered.

Inspecting a single asset

The same inspection view after treatment, with smaller and slower fires reaching the college. — The inspection tool, focused on Hobart College. Before treatment: high exposure to large, fast fires from the south, with minimal response time.

Asset inspection view showing Hobart College highly exposed to large, fast-spreading fires from the south. — The inspection tool, focused on Hobart College. Before treatment: high exposure to large, fast fires from the south, with minimal response time.

After treatment, the same analysis shows the risk significantly reduced — fires are smaller, they spread more slowly, and they leave a much larger and safer window for reaction.

What we would do next

Based on the post-treatment projections, FiSci recommends an additional treatment to the west in 2026, establishing a low-fuel-load barrier between the heavy fuels to the south and the college.

Eight-hour fire spread model after the recommended follow-up treatment, showing the largest fires deflected around Hobart College. — With the follow-up treatment in place, the largest fires are deflected around the college, and the reduced fuel along the southern campus edge slows spread — buying time for evacuation and defence.

The outcome the strategy is built around is simple to state: protect Hobart College from a fire starting in the south of the project area. The model lets us say how much each block of work contributes to that, before anyone lights a match.