Changes in the vegetation cover of transgressive dune fields: A case study in Cape Woolamai, Victoria

Abstract

Changes in vegetation cover and dune mobility of Woolamai dune fields on the southeast coast of Australia were quantified based on a time series of aerial imagery (1939 to 2020). Results showed that the dune fields have shifted from nearly all bare sand (with <5% vegetation cover) to a new quasi-equilibrium state, being almost fully stabilized by vegetation (>80%) from 1939 to 2020. Three temporal stages of vegetation change were identified, namely: (I) early expansion over 1939–1975; (II) rapid growth from 1976 to 2010; and (III) recent ‘quasi-equilibrium’ state in 2010–2020. In stage I, complex impacts of climate and human activities co-existed with uncertainty of the dominant factor. In this early stage, vegetation growth was constrained to the low and sheltered areas, indicating the influence of topography. Rapid vegetation growth took place in 1976–2010 (stage II), during which a re-vegetation programme combined with favourable climate conditions promoted vegetation growth. In the last decade (stage III), vegetation might have reached a new quasi-equilibrium when the vegetation almost reached a maximum. The slight loss of vegetation could be attributed to weed control and an unfavourable climate for growth (drier and windier) in Woolamai dune fields. This study showed that variations in vegetation cover and dune mobility through time are not simply linked to a single factor but depend on the occurrence of multiple factors (e.g. topography, climate and human activities) that promote stability, or alternatively, mobility of the dune system. This research contributes to expanding our understanding of the complexity of the bio-geomorphologic dynamics in dune fields. It also provides detailed observational evidence for the historical trajectory of vegetation expansion from the bare dune fields to a fully stabilized state, which can be used to verify and refine models for other similar dune sites.