Browsing by Author "Comley, R"

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    Holocene climate–fire–vegetation feedbacks in tropical savannas: insights from the Marura sinkhole, East Arnhem Land, northern Australia
    (Wiley, 2022-11) Rowe, C; Rehn, E; Brand, M; Hutley, LB; Comley, R; Levchenko, VA; Zwart, C; Wurster, CM; Bird, MI
    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. © 1999-2024 John Wiley & Sons, Inc or related companies. All rights reserved.
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    Holocene savanna hydroclimate record from Kinrara Lake, north-east Queensland, Australia
    (Elsevier, 2024-03) James, J; Comley, R; Wurster, CM; Levchenko, VA; Gadd, PS; Bird, MI
    We present a record of hydroclimatic change over the Holocene from Kinrara Lake, in a seasonally dry savanna location in north-eastern Australia. The record is derived from the oxygen (δ18O) and carbon stable isotope (δ13C) composition of endogenic and biogenic (gastropod) carbonate. The stable isotope proxy records are complemented by elemental geochemical (Itrax) and sedimentological proxy data providing a record of hydrologic and climate change, spanning 10.5 ka to the present day. Two main forms of endogenic carbonate occur in the lake sediments; (i) carbonate associated with biofilms during the early-Holocene, under drier-than-modern conditions, (ii) photosynthetic and evaporatively-enriched precipitates in the late-Holocene, associated with enhanced climate variability inducing drought periods. Strong relationships between negative δ18O values and increased Ti, Rb, Fe/Mn, inc/coh, are linked with strengthened monsoon conditions, while enhanced periods of dryness are inferred from more positive δ18O values, increased Ca/∑Fe, Ti, Al, and subsequent intensifications in lake productivity (higher Si/Ti, S/Ti, Mn/Ti). Three distinct phases can be identified in palaeohydrological history of the lake; (i) a relatively stable drier-than-modern phase during the early-Holocene (10.5 to 8.2 ka), (2) a significantly wetter-than-modern, monsoon-dominated phase through the mid-Holocene into the late-Holocene (8.2–2.8 cal yr BP), and (3) after 2.8 ka, increased intensity of ENSO-related rainfall variability during the late-Holocene, continuing into the present. © 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).