Severe fires cause declines in plants

Research on trees in North America paints a gloomy picture for the recovery of native plants in Aotearoa New Zealand following severe fires. Dr Nicola Day co-authored a recent study about plant re-establishment after forest fires.

forest fire with flames and trees
A recent study in the Proceedings of the National Academy of Sciences USA, co-authored by Dr Nicola Day from Te Herenga Waka—Victoria University of Wellington shows even the quickly regenerating black spruce can have difficulty re-establishing itself after the severest fires and dry weather.

Dr Day says black spruce has evolved to recover from fire, but New Zealand’s native plants evolved under very low fire activity so may find it even harder to regenerate after fires.

“Given we are expected to experience increased warming and drought in many parts of New Zealand under climate change, our native plants may be particularly vulnerable to threats from fire.

“The fact that the fire-adapted black spruce is suffering under increased fire activity in the northern hemisphere does not bode well for our non-fire-adapted native plants.”

If we lose native plants to fire, this will affect other native species which rely on plants for food and habitat, like birds and lizards, she says.

In previous work Dr Day has shown that soil fungi—which help plants grow—also decline with fire.

Dr Day, a Lecturer in plant biology and recent Rutherford Postdoctoral Fellow in Te Kura Mātauranga Koiora—School of Biological Sciences, says fire activity is increasing in New Zealand.

“Some of the largest fires in recent history have occurred over the past few years, such as the fire at Lake Ōhau last year, when 5000 hectares burned, and the Pigeon Valley fire in 2019, when 2400 ha burned.

“My current work is trying to understand what regenerates after these fires. Much of what burned at Lake Ōhau was native grassland and shrubland and some of our preliminary work shows that exotic plants instead are doing very well in those areas now.”

The PNAS study was a collaborative effort involving authors from across 22 institutions to investigate more than 1500 sites after fires within the vast boreal forest across the northern regions of North America.

The idea to bring together data from all these sites grew from a workshop funded by the NASA-ABoVE programme and co-led by Dr Day, lead author Associate Professor Jennifer Baltzer of Wilfrid Laurier University, Canada, and Professor Jill Johnstone of Yukon University and the University of Alaska Fairbanks.

Dr Day says black spruce is a dominant tree and has evolved to recover from fires over many thousands of years.

“In most cases, this tree regenerates very quickly after fires. However, our team’s study shows that spruce trees can have trouble regenerating when fires are very severe or when weather is very dry in the years after fires.

“These forests are incredibly important for the health of the planet. They hold almost one third of Earth’s land carbon, so declines in black spruce forests have implications for our global climate.”

In order to protect our native plants from fire, we need to mitigate impacts of climate change in New Zealand, Dr Day says.

“Planting fire-resistant species can take us so far, but ultimately we need to reduce our carbon emissions to prevent the warm and dry conditions that will cause fire.”

For more information, contact lecturer in Plant Biology Dr Nicola Day on Nicola.day@vuw.ac.nz,  twitter: @n_j_day