A global ‘greening’ of coastal dunes: An integrated consequence of climate change?

Derek W.T Jackson,Susana Costas,Rita González-Villanueva,Andrew Cooper

doi:10.1016/j.gloplacha.2019.103026

Abstract

In the context of global climate change and sea-level rise, coastal dunes are often important elements in the coastal response to storm wave and storm surge impacts on coastal lowlands. Vegetation cover, in turn, has profound impacts on coastal dune morphology and storm-buffering function; it binds existing sediment, promotes fresh sediment accumulation and thereby increases dune volume and dune crest elevation where a sediment-plant interaction plays out with vegetation growth attempting to out-pace the vertical sediment accumulation. A global analysis shows that vegetation cover has increased substantially on multiple, geographically dispersed, coastal dune fields on all continents in the period 1984–2017. The observed ‘greening’ points to enhanced dune stability and storm buffering effects at a time when, paradoxically, coasts are being subjected to increased flood and erosion risk from rising sea levels and changing patterns of storminess. Causal attribution of biological trends to climate change is complicated, but we contend that the global scale ‘greening’ of coastal dunes is driven by a combination of changes to climate and atmospheric composition and reflects the cumulative effects of changes in temperature, precipitation, nutrient concentration and reduced windiness (global stilling). Global-scale increases in temperature, nutrients and precipitation (all of which are vegetation growth stimulants) and widespread reduction in windiness (“stilling”) (which reduces sediment activity, promoting the spread of vegetation) coincide in time with the observed changes in vegetation cover. The observed changes in coastal dunefields enhance contemporary and near-future coastal resilience to climate change and may represent a previously unrecognised morphological feedback mediated by climate change. • Widespread coastal dune vegetation growth at many latitudes in the last three decades • Increased dune vegetation cover may afford better erosion resistance along dune-fringed coastlines • Coastal dunefields may be moving toward a phase of static dynamics • Global scale ‘greening’ of coastal dunes may be driven by a combination of changes to climate and atmospheric composition

Highlights

Global climate change and sea-level rise are producing a general landward migration and loss of sedimentary coastlines (Parmesan and Yohe, 2003; FitzGerald et al, 2008; Ranasinghe and Stive, 2009; Mentaschi et al, 2018)
Dune crest elevation is a key determinant of overwash vulnerability (Houser et al, 2008), while increased dune volume leads to greater inertia and slows the rate of retreat of barrier shorelines
We cannot realistically isolate the relative importance of the changing climate parameters, but regardless of driver specifics, their change is coincident with a significant proliferation in coastal dune vegetation cover globally

Summary

Introduction

Global climate change and sea-level rise are producing a general landward migration and loss of sedimentary coastlines (Parmesan and Yohe, 2003; FitzGerald et al, 2008; Ranasinghe and Stive, 2009; Mentaschi et al, 2018). Coastal dunes exhibit various forms and behaviour in response to changing environmental variables These are often recorded by changes from stable, vegetated conditions to periods when active sand-blow causes dunes to breakdown and migrate. Several other coastal dunes in Europe, less impacted by human activities such as from agricultural practices and landscape modification, show a clear stabilisation trend in recent decades that has been linked to changing climatic variables (Jackson and Cooper, 2011; Provoost et al, 2011). Jackson and Cooper's (2011) work, focussing on Ireland's remote coastal dunes on its western seaboard, showed remarkable changes in just a single decade of observations with significant revegetation patterns clearly evident Prompted by these examples, we investigate whether this is a global pattern and if so, might it be driven by changing environmental conditions that favour vegetation growth at a global scale. (NDVI) derived from the Landsat scenes to enable quantification of vegetation cover at biannual intervals (1984–2017)

Methods

Results and discussion

Conclusions