Rainfall and its possible hysteresis effect on the proportional cover of tropical tidal wetland mangroves and saltmarsh-saltpans

Duke, Norman C., Field, Colin, Mackenzie, Jock R., Meynecke, Jan-Olaf, and Wood, Apanie L. (2019) Rainfall and its possible hysteresis effect on the proportional cover of tropical tidal wetland mangroves and saltmarsh-saltpans. Marine and Freshwater Research. (In Press)

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View at Publisher Website: https://doi.org/10.1071/MF18321
 
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Abstract

Mangroves and tidal wetlands are highly dynamic ecosystems, responding and adapting to climate and physical conditions that vary at all spatial and temporal scales. In these times of rapidly changing climatic conditions, identification of previously unrecognised large-scale ecosystem processes influenced by climate variables are highly relevant. This applies in particular, to a more enlightened understanding of the corresponding influences on respective beneficial ecosystem services. In deference to the many factors thought to influence tidal wetland ecosystems, we confirm that average annual rainfall (AAR) (250-5000 mm, 20-30 year average) has had a dominant influence on the vegetative cover and relative abundances as well as the composition and biomass of tidal wetlands. And, that the different condition states were predictable. Based on 205 unmodified, tropical and subtropical estuaries of predominately northern Australia, a sigmoidal relationship was derived between rainfall and the relative amounts of high-biomass mangroves and low-biomass saltmarsh-saltpan vegetation. The presence and probability of the observed combinations of these plant types were usefully quantified using the Wetland Cover Index (WCI), being the ratio of total mangrove area compared to the mangrove area plus the area of upper intertidal saltmarsh and saltpans. For tidal wetland sites well-within the latitudinal range of mangroves, 1368 mm average annual rainfall marked a centroid inflection point in the probability of the transition between the alternate dominance of respective vegetation types of high and low biomass states. In the range of 1066 mm AAR and 1651 AAR the rate of change of the probability of mangrove dominance per 100 mm AAR was greater than 5%. These findings were consistent with rainfall having a significant effect on relative abundances of key vegetation types within tidal wetlands. Furthermore, periodic fluctuations are likely manifest as either encroachment or dieback of mangroves occurring along the ecotone separating mangroves from upper tidal saltmarsh-saltpans. To explore this concept further, a new conceptual framework and model was developed to display these ecosystem-scale processes taking place in tropical and subtropical tidal wetlands.

Item ID: 48884
Item Type: Article (Research - C1)
ISSN: 1448-6059
Keywords: climate change, ecosystem state change, ecotone shift, tidal saltmarsh, wetland cover index
Copyright Information: Copyright © CSIRO 2019.
Date Deposited: 05 Feb 2019 21:46
FoR Codes: 05 ENVIRONMENTAL SCIENCES > 0501 Ecological Applications > 050101 Ecological Impacts of Climate Change @ 40%
05 ENVIRONMENTAL SCIENCES > 0501 Ecological Applications > 050104 Landscape Ecology @ 30%
06 BIOLOGICAL SCIENCES > 0602 Ecology > 060205 Marine and Estuarine Ecology (incl Marine Ichthyology) @ 30%
SEO Codes: 96 ENVIRONMENT > 9603 Climate and Climate Change > 960305 Ecosystem Adaptation to Climate Change @ 40%
96 ENVIRONMENT > 9605 Ecosystem Assessment and Management > 960503 Ecosystem Assessment and Management of Coastal and Estuarine Environments @ 40%
96 ENVIRONMENT > 9607 Environmental Policy, Legislation and Standards > 960701 Coastal and Marine Management Policy @ 20%
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