Clay Trauernicht

We use the fire ecology and biogeographical patterns of Callitris intratropica, a fire‐sensitive conifer, and the Asian water buffalo (Bubalus bubalis), an introduced mega‐herbivore, to examine the hypothesis that the continuation of Aboriginal burning and cultural integration of buffalo contribute to greater savanna heterogeneity and diversity in central Arnhem Land (CAL) than Kakadu National Park (KNP). The ‘Stone Country’ of the Arnhem Plateau, extending from KNP to CAL, is a globally renowned social–ecological system, managed for millennia by Bininj‐Kunwok Aboriginal clans. Regional species declines have been attributed to the cessation of patchy burning by Aborigines. Whereas the KNP Stone Country is a modern wilderness, managed through prescribed burning and buffalo eradication, CAL remains a stronghold for Aboriginal management where buffalo have been culturally integrated. We surveyed the plant community and the presence of buffalo tracks among intact and fire‐damaged C. intratropica groves and the savanna matrix in KNP and CAL. Aerial surveys of C. intratropica grove condition were used to examine the composition of savanna vegetation across the Stone Country. The plant community in intact C. intratropica groves had higher stem counts of shrubs and small trees and higher proportions of fire‐sensitive plant species than degraded groves and the savanna matrix. A higher proportion of intact C. intratropica groves in CAL therefore indicated greater gamma diversity and habitat heterogeneity than the KNP Stone Country. Interactions among buffalo, fire, and C. intratropica suggested that buffalo also contributed to these patterns. Our results suggest linkages between ecological and cultural integrity at broad spatial scales across a complex landscape. Buffalo may provide a tool for mitigating destructive fires; however, their interactions require further study. Sustainability in the Stone Country depends upon adaptive management that rehabilitates the coupling of indigenous culture, disturbance, and natural resources.

Summary: 1. Callitris intratropica is a long‐lived, obligate‐seeding, fire‐sensitive overstorey conifer that typically occurs in small groves (C. intratropica groves of varying canopy cover to examine the role of feedbacks between fire and tree cover in the persistence of a fire‐sensitive tree species and the maintenance of habitat heterogeneity in a highly flammable savanna.2. We examined the population structure and floristic composition of C. intratropica groves and conducted controlled burns with Aboriginal landowners to test the prediction that groves of C. intratropica with closed canopies inhibit savanna fires by physically altering the fuel arrays below trees. We measured pre‐ and post‐burn fuel availability, the probability of burning and fire intensity along transects (55–75 m) spanning entire C. intratropica groves and extending into the surrounding savanna matrix.3. We found that closed‐canopy groves of C. intratropica had higher densities of seedlings and saplings than open‐canopy groves and supported a distinct plant community. Closed‐canopy groves also had a lower probability of burning and less severe fires due to a lower availability of fine fuels than the surrounding savanna.4. Synthesis. Our results suggest that the observed regeneration within closed‐canopy C. intratropica groves within frequently burnt savanna reflects a vegetation–fire feedback. A significant, negative relationship between canopy cover and the probability of burning provides strong evidence that closed‐canopy C. intratropica groves are capable of excluding low‐intensity savanna fires, thereby enabling the persistence of patches of fire‐sensitive forest or woodland amid open, highly flammable savanna vegetation. We present our findings as evidence that alternative stable state dynamics may play a role in determining savanna diversity and structure.