While some eucalypts are hard to kill, climate change may test the ability of others to survive

While some eucalypts are hard to kill, climate change may test the ability of others to survive Swati Mestri Scientific Editor Andrew Zinin Chief Editor There's no tree like the humble eucalypt. Eucalypts play a pivotal role in forests, cycling nutrients, storing carbon and providing hollows and shelter for animals, including the elusive yellow-bellied glider (Petaurus australis) and aptly named glossy black cockatoo (Calyptorhynchus lathami). In particular, large, old eucalypts are critically important for thriving ecosystems. Eucalypt forests across the country have been ravaged by fire in recent years. In early 2019, fires in Tasmania killed many of Australia's largest known eucalypts. A short time later, the Black Summer wildfires of 2019–20 burned roughly 7 million hectares (17.3 million acres) of eucalypt forests across eastern Australia. Our latest research examined eucalypt forests burned by the 2019–20 wildfires. Our findings suggest large, old trees growing in wet forests were most affected. Our other research shows species growing at the dry edge of their natural range are most at risk of being wiped out by future severe fires. From the ashes More than 800 known species of eucalypts are found across Australia, from the arid deserts of Central Australia to Victoria's high country. There are few environments to which they haven't adapted. Following fire, many species can resprout by growing new leaves. A tree's "resprouting response" depends on several factors, including stem size, bark type, prior fire damage and fire severity. However, existing resprouting classifications for eucalypts don't account for these factors. This means some populations or individuals of "resprouting" species might not recover in the expected way. For example, they may have greater rates of tree mortality than expected and rely on new seedlings for the forest to recover. What's more, scientists don't fully understand how eucalypts cope with fire if they are at the limit of their "climatic range." Consider a tree growing at the extreme low-rainfall edge of its distribution. Could it struggle to resprout? Might it fail to produce seedlings? The 2019–20 Black Summer fires ignited following three devastatingly dry years, known as the "Tinderbox drought." Our current climate change trajectory suggests the conditions necessary for fires to spread through the landscape may become increasingly common. In the wake of the Black Summer, scientists studied the amount of forest affected by fire, including the amount that was severely burned. Our latest research examined how this "one-two punch"—record-breaking drought followed by severe wildfires—transformed eucalypt forests across eastern Australia. What we studied We measured several variables that signal change in eucalypt forests. These included: - Seedling recruitment, or the process in which seeds successfully germinate and grow into new trees. - Tree mortality, meaning the complete death of trees in a forest. - "Topkill," where a tree's trunk and branches are killed and the tree survives only by resprouting new leaves from its base. We surveyed multiple forest types, ranging from dry eucalypt forests on poor soils to wet eucalypt forests on more fertile soils. We also took measurements across the climatic range of several different species, with field sites stretching from far northern New South Wales to Victoria's East Gippsland region. Dry forests growing on poorer soils proved surprisingly tough. Fewer large trees died and more young trees survived, compared with forests growing on wetter, more fertile soils. Wet forests lost many of their biggest trees, which were either topkilled or wiped out completely. Two species, Eucalyptus dalrympleana and Eucalyptus radiata, suffered higher mortality and topkill at the dry end of their range. But a third species, Eucalyptus dives, held firm across its range, experiencing average levels of damage irrespective of the climate it grew in. Recruitment of new seedlings was generally lower in drier areas, though results varied across species. Big trees most at risk Some forests are at risk of losing their big trees and more trees in general. We may want to pay more attention to these forests, particularly when it comes to managing fire in the landscape. Eucalypt forests may take decades to regain their structure and complexity or be at risk of more permanent changes if severe fires become more common. Our research suggests large trees with fire scar injuries are particularly vulnerable to severe fires. Fire scars can damage the structural and conductive tissues that help trees survive. They also allow fire, fungi and insects to enter the tree, creating cavities and increasing the tree's risk of collapse. Some eucalypt species suffered higher rates of topkill among large trees. While these trees did not die, they will likely need a long time to recover. Other species generally resprouted from their trunks and branches, suggesting they may be capable of coping with the worst nature throws at them. More work ahead Our findings suggest forests adapted to drier, challenging conditions may be more able to withstand severe disturbance, at least structurally. Forests adapted to more fertile, moist conditions appear less able to cope with the double whammy of severe drought plus fire, losing more large trees. Importantly, if we identify species that respond poorly to fire at the edge of their climatic range, we can factor this knowledge into forest management. For example, we could aim for longer fire intervals and lower fire severity where appropriate to minimize impacts on sensitive tree populations. We must also rethink how we classify resprouting behavior to account for tree size, climate and the severity of fire or other disturbances. There's still much we don't know about how eucalypts recover from fire. But every bit of research will help us protect them from future blazes. Publication details Eli R. Bendall et al., Demographic change and loss of big trees in resprouting eucalypt forests exposed to megadisturbance, Global Ecology and Biogeography (2024). DOI: 10.1111/geb.13842 Eli R. Bendall et al., Tree Species Vulnerability to Fire Increases at Dry Range Edge, Global Change Biology Communications (2026). DOI: 10.1002/gcb4.70053 Journal information: Global Ecology and Biogeography Key concepts effects of climate changedroughtsecosystem resiliencefire damageforest ecosystemsWildfiresProvided by The Conversation This article is republished from The Conversation under a Creative Commons license. Read the original article.