Rowe, Cassandra, Rehn, Emma, Brand, Michael, Hutley, Lindsay B.B., Comley, Rainy, Levchenko, Vladimir, Zwart, Costijn, Wurster, Christopher M.M., and Bird, Michael I. (2022) Holocene climate-fire-vegetation feedbacks in tropical savannas: Insights from the Marura sinkhole, East Arnhem Land, northern Australia. Journal of Vegetation Science, 33 (6).

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Abstract

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. LocationNorthern 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.

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