Lantana camara is an invasive species that is listed as one of the world’s 100 worst weeds. It has invaded ecosystems around the world including many in Australia, and is successful in disturbed areas such as those damaged by fire. Many studies have shown how fire encourages the invasion of L. camara and even suggested that the presence of L. camara encourages fire. However, few have examined how L. camara promotes fire. Extensive L. camara invasion of dry rainforest in Forty Mile Scrub National Park, North Queensland, Australia, has been implicated with increased fire frequency in this ecosystem. We tested two models by which L. camara could cause this: 1) by increasing ecosystem flammability through L. camara being more flammable than native species, and 2) by altering the amount and continuity of potential fuels, facilitating fire spread. The former was tested by measuring functional traits correlated with flammability (Leaf Dry Matter Content-LDMC, Twig Dry Matter Content-TDMC) and flammability tests in the laboratory (time to combustion onset, combustion duration, flame height) while the latter was measured through field fuel bed measurements (fuel bed depth, leaf litter depth, percent cover of fuel).   

Results/Conclusions

Trait measurements found L. camara to have the lowest LDMC and TDMC values (significantly less than the majority of native species studied), suggesting lower flammability. Leaf burning trials showed L. camara had the shortest combustion duration (significantly less than six of seven native species). Lantana camara also registered the second shortest flame height, again suggesting low flammability. However, plots infested with L. camara had significantly higher fuel bed depths, leaf litter depths, and percent of quadrats covered with potential fuels than plots without L. camara. Hence, L. camara may increase fire susceptibility by providing taller fuel beds, thicker leaf litter layers, and greater fuel coverage of the forest floor rather than by being more flammable than native species. Dry rainforest is susceptible to fire damage and seems especially prone to degeneration as a result. Lantana camara will cause greater fire damage to dry rainforest through increased fuel loads and then invade disturbed areas. If this cycle persists, increased fire frequency will likely result in L. camara dominance of the ecosystem. To mitigate these threats future management plans need to focus on breaking up fuel loads and providing fire barriers from surrounding fire-prone savanna ecosystems.