New study shows invasive aliens exacerbate wildfires

A recent study by Dunja McAllister at the University of Cape Town has highlighted the perilous role exotic plants play in amplifying wildfire risks within urban settings, particularly in the fire-susceptible Western Cape. Conducted following the destructive Table Mountain blaze of April 2021, the study, soon to appear in the South African Journal of Botany, demonstrates that certain non-native species, prized for their ornamental appeal, exhibit traits that markedly enhance their flammability, thus heightening both the probability and ferocity of wildfires.

The research scrutinised 42 plant species, split between 22 native and 20 exotic varieties, assessing leaf attributes such as thickness, specific leaf area, and total leaf surface area. The findings are unequivocal: exotic species ignite more readily and burn with greater intensity than their native counterparts. Species such as stone pine and date palm emerged as notably hazardous, owing to their expansive leaf surfaces and thin foliage.

Native plants, by contrast, while slower to ignite, sustain less intense burns, underscoring a critical disparity in fire risk. This distinction carries profound implications for urban policy and planning, especially in regions where wildfires loom large. Climate change, with its attendant hotter, drier conditions, is poised to exacerbate these dangers. The study’s lead author, Dunja MacAlister, notes that the Western Cape’s Mediterranean climate, characterised by wet winters and arid summers, is growing more volatile, with increased evapotranspiration rendering vegetation ever more combustible.

Exotic plants, rich in oils and biomass, become potent fuel sources under such conditions, a vulnerability laid bare by the 2021 fire, which razed over 650 hectares and left infrastructure in ruins. That conflagration, fanned by wind-borne embers and fuelled by debris from exotic trees, defied containment efforts, crossing highways and firebreaks with ease.

This echoes the 2017 Knysna wildfires, where exotic vegetation and extreme weather conspired to devastating effect, claiming lives and vast swathes of land. In response, the researchers propose a “fire smart” paradigm for urban greening. This entails eschewing high-flammability exotics in favour of native species with lower combustibility, while embedding fire behaviour insights into municipal planning. Such a shift, they argue, could bolster urban resilience, curbing the economic and ecological toll of wildfires. MacAlister stresses the urgency of this adaptation, warning that global wildfire risks are mounting, particularly in Mediterranean ecosystems like the Western Cape, where climate trends amplify the threat.

For policymakers, the message is that proactive vegetation management is no longer optional. Prioritising native, low-risk species and maintaining rigorous fuel-load controls could shield cities from escalating fire hazards. Cape Town’s experience serves as a cautionary tale. With wildfire seasons intensifying, the cost of inaction may prove far steeper than the price of prudent reform.