Growth form and functional traits influence the shoot flammability of tropical rainforest species

• Published in: Forest ecology and management 2022-10, Vol.522, p.120485, Article 120485
• Main Authors: Potts, Ebony, Tng, David, Apgaua, Deborah, Curran, Timothy J., Engert, Jayden, G. W. Laurance, Susan
• Format: Article
• Language: English
• Subjects: Fire; Flammability; Functional Traits; Rainforest; Rainforest Restoration
• ISSN: 0378-1127; 1872-7042
• DOI: 10.1016/j.foreco.2022.120485

The image on the left-hand side shows a shoot sample burning on the flammability testing device. The right-hand side graph shows the post-hoc plot burnt biomass results for growth form (top) and family (bottom) with leaf dry matter content. The green squares represent low flammability groups and red squares represent high flammability groups. [Display omitted] •Rainforest trees are higher in flammability compared to shrubs and vines.•Plant families Sapindaceae, Proteaceae, Fabaceae, and Lauraceae are especially high in flammability while Moraceae is very low.•Plant functional trait leaf dry matter content is significantly positively associated with flammability.•Restoration plantings in the Wet Tropics of Australia include large proportions of highly flammable plant species. Canopy fires are increasing globally with anthropogenic climate and land-use changes, even in fire-sensitive rainforest ecosystems. Identifying the ecological drivers that may be aiding canopy fires, such as species or growth form flammability, is crucial to recognising and mitigating fire risks. To address this, we quantified the shoot-flammability of 124 rainforest plant species using an experimental approach. We compared three flammability measures (burnt biomass, total burn time and maximum temperature reached) with plant functional traits across seven different growth forms (i.e., canopy, pioneer, and understory trees; pioneer, understory and invasive shrubs, and vines) and nine common plant families and other higher-level clades, such as conifers, hereafter abbreviated to families. From burning > 600 sun-exposed shoots, we found trees were higher in flammability than shrubs and vines, and the plant families: Sapindaceae, Proteaceae, Fabaceae, and Lauraceae, had especially high flammability, whereas Moraceae was very low. Of the functional traits examined, leaf dry matter content was consistently and significantly positively associated with species flammability. Invasive shrubs as a group were not particularly flammable, although there were exceptions, e.g., wild tobacco (Solanum mauritianum) was highly flammable. This study has two important implications for the management of fire in rainforests. First, we have demonstrated that many tropical rainforest trees may readily burn under severe fire conditions if fire were to reach the rainforest canopy. Second, a large proportion of the > 1 million rainforest trees planted in the Wet Tropics under restoration planting schemes are from