Holocene climate–fire–vegetation feedbacks in tropical savannas: Insights from the Marura sinkhole, East Arnhem Land, northern Australia

Aims: Informed management of savanna systems depends on understanding determinates of composition, structure and function, particularly in relation to woody-plant components. This understanding needs to be regionally based, both past and present. In this study, Holocene plant patterns are explored at a site within the eucalypt savannas of northern Australia. Australian savannas are the least developed globally and uniquely placed to track ecological change. Location: Northern Territory, Australia. 

Methods: Palynological analyses were undertaken on a 5-m sediment core, spanning the last 10,700 calendar years. Pollen was categorised to capture vegetation type, classified further according to plant function and/or environmental response. Detrended Correspondence Analysis was used to quantify ecological dissimilarities through time. 

Results: At the Pleistocene transition, grasses were abundant then declined and remained low relative to increased woody cover from the mid-late Holocene. Savanna composition gradually transitioned from Corymbia to Eucalyptus dominance until significantly disturbed by a phase of repeated, extreme climate events. Highest non-savanna variability in terrestrial and wetland plant types formed mixed vegetation communities through the mid-Holocene.

Conclusions: Savannas are not homogeneous but the product of plant changes in multiple dimensions. In the Northern Territory, dynamic though restricted non-eucalypt shifts are embedded within larger, slower eucalypt change processes. Primary climate–vegetation relationships determine the long-term fire regime. The role of large but infrequent disturbance events in maintaining savanna diversity are significant, in degrees of impact on tree–grass turnover, its form and the extent of vegetation recovery. People's landscape interactions were found to be interwoven within this feedback hierarchy.