Photo caption: Damage to Port Hills from fires in 2024 and 2017 provides researchers with important insights into regeneration.
New research from Te Whare Wānanga o Waitaha | University of Canterbury (UC) examining the aftermath of the February 2024 Port Hills wildfire found some young native trees and shrubs were able to resprout after being badly damaged by fire.
But researchers say the bigger lesson lies in what was growing around them.
Highly flammable non-native grass had grown densely through the restoration site at Mt Ada before the fire and quickly re-established afterwards, creating conditions that could repeatedly expose regenerating native vegetation to fire before it matures.
UC School of Biological Sciences researcher Professor Emerita Paula Jameson says this can create what ecologists call a "fire trap", where repeated fires continually reset native regeneration.
"You can plant native trees and shrubs, but if highly flammable grasses and weeds remain around them, fire can keep setting that regeneration back before it has the chance to develop into mature forest."
The research, published in Forests, followed native woody plants for 17 months after fire swept through the Mt Ada site on 14 February 2024. The area was previously burnt during the major Port Hills wildfire in 2017 and was subsequently replanted. It was these plants that burnt in 2024.
The response varied considerably between species. Broad-leaved Coprosma showed the strongest recovery, with 16 of 17 monitored plants resprouting.
Co-author Dr John Clemens, also from UC, says the results show which native plants are more likely to survive wildfire.
"Age and size matter, as do fire intensity and the conditions around each plant. This research gives us another piece of the puzzle about how we might design restoration plantings and protect naturally regenerating areas with wildfire in mind."
Flammability also matters. Scientists at Lincoln University and Manaaki Whenua Landcare Research have been studying the flammability and fire ecology of native species. One approach Dr Clemens and Professor Jameson believe warrants greater consideration is the use of green firebreaks. These are strategically planted areas of lower-flammability plants to help protect regenerating native bush. Coupled with plants shown to resprout after fire, native bush recovery should be faster in the event of a wildfire.
They say active management also needs to include controlling highly flammable weeds and grasses and planting native species in ways that encourage faster canopy closure.
