Burning giants in the tropics

The need to maintain a mosaic of rainforest and eucalypt forest in the Australian Wet Tropics World Heritage Area poses a perplexing conundrum for land managers. Rose Gum (Eucalyptus grandis) dominated giant eucalypt forests at the margins of World Heritage tropical rainforests are habitats for threatened marsupials like the Yellow-Bellied Glider. Rainforest developing in the understoreys of these forests is believed to threaten the dominant overstorey eucalypts and associated fauna. Land managers prescribe frequent low-intensity fires to try to stop rainforest species from establishing in Rose Gum forests understory. However, these practices are not consistent with the ecology of Rose Gum forest: 1. Rose Gums are obligate seeders and need rare, large, high-intensity landscape fires for successful regeneratation. Low-intensity fires do not stimulate Rose Gum regeneration because they do not release seeds stored in the canopy or create conditions suitable for initial growth. Repeated fires may kill young Rose Gum trees that do not have fully developed bark and these fires can reduce the protective capacity of the bark of mature trees. 2. Under current climatic conditions, rainforest expansion averages 0.6m/decade, and is occuring across all landscape conditions likely due to a global driver like increased atmospheric CO2. Using low-intensity fire to control this process is difficult because rainforest will only burn under exceptional conditions. Also, many rainforest species recover from a single fire. Natural and rare high-intensity fires will likely enable Rose Gum regeneration throughout the landscape. The landscape ecology and plant functional biology of Rose Gum forest suggest that they are ecologically like secondary rainforest. Abstaining from prescribed burning and letting Rose Gum forests regenerate naturally from rare large fire events best approximates their regeneration ecology.