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

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. 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 nonsavanna 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 noneucalypt 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 Journal of Vegetation ScienceROWE et al.

Exploring palaeoecology in the Northern Territory: the Walanjiwurru rockshelter, vegetation dynamics and shifting social landscapes in Marra Country

“…Thirdly, to have been able to provide palaeoecological detail for the past 500-year time window is highly unique. For example, such resolution has not been captured in pollen records from the three nearest Holocene study sites, despite their 'traditional' lake site types (central Gulf lowlands and offshore islands: Shulmeister 1992; Prebble et al 2005;Rehn et al 2021b;Rowe et al 2022). This period of the very late Holocene has also been largely overlooked in early archaeological investigations in favour of searching for longer chronologies, however with recent studies in Arnhem Land shifting this focus to the recent past (Shine et al 2013(Shine et al , 2015(Shine et al , 2016Wesley et al 2018a, b).…”

“…The terrain's remoteness of access, together with the age and geological stability of the landscape and contrasting seasonal climate have created poor conditions for organic preservation, which have inhibited widespread development and investigation of sites suitable for time-depth investigations. What is evident therefore in current efforts to build the discipline, is the use of less traditional site types, namely caves/ rockshelters (Clarkson and Wallis 2003;Rowe et al 2020) and sinkholes (Rowe et al 2019(Rowe et al , 2022Rehn et al 2021b), both protected environments allowing soft sediments (and potentially, preserved pollen and microcharcoal) to accumulate in good chronostratigraphic order. Caves/rockshelters and sinkholes are both found in physiographically different environments from lakes and swamps, providing valuable palaeoecological potential (Rowe et al 2020).…”

“…Jones 1985;Clarkson et al 2017;David et al 2019). Camacho et al (2000) and Rowe et al (2020Rowe et al ( , 2022 provide discussion on the interpretation of micro-botanical proxy assemblages from rockshelters and sinkholes, and outline the considerations required in how varied proxy types reach and are incorporated into such sites, including the balance required in researching cultural introductions, as well as differential particle preservation verses destruction properties.…”