Managing coastal sand drift in the Anthropocene: A case study of the Manawatū-Whanganui Dune Field, New Zealand, 1800s-2020s

In the Anthropocene, predicted sea-level rise is expected to continue, threating human life and activities along the coast. Dunes play a vital role in providing protection from this threat, aside from the ‘ecosystem’ services that they supply. This article uses scientific, popular and unpublished sources from the nineteenth century and twentieth to examine New Zealand’s largest coastal dune system: the Manawatū-Whanganui dune field. Extending south from Pātea to Paekakariki, it comprises approximately 900 square kilometres. Here, destabilized dunes drifting inland caused social, economic and political problems over the last 150 years. In the nineteenth century, human activities were responsible for setting the dunes in motion. Debates about the matter and attempts to prevent and stop it were then occurring in many parts of the world. Since dunes were a common concern, knowledge and practices were shared and travelled between countries though experts and migrants. The consequences of the solutions implemented and new environmental conditions explain that dunes are still a major issue in the Manawatū-Whanganui region. This article presents a comparative analysis of historical and present-day human responses to dune management to better understand long-term dune drift, its mechanisms and responses. Despite looking at a local case, this study can be extrapolated to dunes worldwide. It shows that holistic management of coastal ecosystems must take into account interdisciplinary analyses of long-term relations between dunes and society. Otherwise, the full picture about the present situation of dunes cannot be apprehended, compromising the implementation of future adaptation measures.


INTRODUCTION
Coastal dunes form and evolve in response to fluvial and marine sediment supply and transportation processes. These, in turn, respond to tides, waves, and wind, as well as soil moisture content, geomorphology of the nearshore and the beach, and the extent and type of vegetation cover. Coastal dunes fulfil many different functions: they provide habitat for animals and plants adapted to extreme conditions; contribute to the shore sediment budget, thus playing a dual role as a sediment sink or source to maintain the long-term stability of a coastal system; and they protect the hinterland from flooding caused by sealevel rise and storm surges. 1 Dune destabilization generated by natural processes or human activities can lead to persistent inland sand movement, which has the potential to inundate settlements and overwhelm infrastructure and fields, while the infilling of sand into rivers and estuaries can inhibit navigation by silting and creating marshlands. 2 Faced with disturbance, their deterioration has serious socio-economic and environmental impacts. 3 Sand drift has by Beattie, whose book is the first transnational study of sand drift in Australia, New Zealand and South Asia. 14 His work uses the framework of environmental history and ends in the early twentieth century. So, there is clearly room for an approach to coastal sand dunes drift and management in a historical perspective, taking a local example to throw a light on this matter as a broader global issue, like Worster and Bailey did for the dust bowl.
Using a case study of sand drift in the Manawatū-Whanganui region, this paper seeks to combine historical and scientific analysis of sand dune spread to examine the long-term social, economic and ecological outcomes of environmental disturbance and management dating from the nineteenth-to the twenty-first century. It examines the various solutions adopted for coping with these environments. In the nineteenth century and early twentieth, this included notably the gradual adaptation of European ideas of dune reclamation to local circumstances, based both on introduced plants and the use of native New Zealand ones. The drifting sands, seen by European settlers as waste lands and evil hazards, were planted with vegetation and trees to fix and turn into forest areas. Later, the set of values and the economic driver changed and new environmental global and local issues arose. Ecological thinking and more sophisticated geomorphological knowledge came to inform understandings of dunes formation and processes. These are now the object of ecological restoration projects to rehabilitate their natural functioning. Yet, the purpose is not consensual. The measures taken to convert dunes into indigenous fauna and flora habitats may not be compatible with the ones necessary to assure they work as coastal defences against sea erosion and inundation. This paper combines detailed 14 Beattie, Empire and environmental anxiety, pp. 177-213. This is a pre-copy-editing, author-produced version of an article accepted in June 29, 2021 following peer review for publication in Environment & History [forthcoming] © The White Horse Press 7 archival research over 150 years and contemporary scientific analysis, and is the product of collaboration between a scientist and two environmental historians. Such long-term, interdisciplinary research presents a unique opportunity for a study of a nationally and internationally significant dune region as well as addressing coastal management issues that are common to many other areas in the world.

REGIONAL SETTING OF THE STUDY AREA
The Manawatū-Whanganui dune field is New Zealand's largest. Extending south from Pātea to Paekakariki, it comprises approximately 900 square kilometres of the southwestern coast of the North Island. 15 In New Zealand, sandy coasts comprise less than onethird of the total coastline; the rest are rocky cliffs. 16 The Manawatū coastal strip between Paekakariki and Whanganui consists of 24km of settlements, 50km of forest plantation, with the rest mostly farmland. 17 Geomorphologically, the region has incised-valleys, estuaries, and a prograding coastline with transgressive dune fields that have now largely evolved into a parabolic system (Figure 1). 18 The coastline progrades because of an travellers started to describe the region, Māori had burned and cleared large areas of the coastal strip, leaving a mosaic of scrub-and fern-land stretching some 5-6km inland.
Newcomers, primarily from Britain, arrived in increasing numbers from the 1840s, after New Zealand formerly became a colony in 1840. They brought new ways of looking at the environment and of transforming the territory. From the late 1850s onwards, the European population increased significantly by reason of the implementation of a series of assisted migration schemes, the arrival of soldiers for wars and the discovery of gold. 34 Like Māori before them, Europeans concentrated their settlements on low-lying coastal areas. They intensified activities already initiated by Māori, like forest clearing for agriculture, and started others, such as timber milling and cattle breeding. Notably they introduced stock into an environment that had not previously known hoofed animals.
Settlers were also responsible for introducing other exotic species as food sources and for sport, like rabbits and sambar deers, which ran freely in the sand hills. 35 Consequently, the removal, by humans and animals, of native sand-binding plants, such as spinifex and pingao, contributed to dune destabilization. 36    Kaitaia, all in the upper North Islandwas to offer work to the unemployed, prevent sand encroachment to farmlands and create productive forests. According to Whitehead, the Forest Service was also involved in those operations, which were limited to essential maintenance level during the war years. 74 In the 1950s, the Forest Service again took control of sand fixation, but a major issue In 1964, P.S. Whitehead, 78 a senior Forest Ranger, explained the three-step method of dune stabilization (Figure 4). A primary stabilizer developed 'establishing' foredunes with the help of catching fences and the close planting of marram. As primary stabilizers did not achieve complete fixing of the dune sands without further aid, secondary cover involved plantings of shrubs such as mānuka, Olearia, Cassinia and Pimelea. As their growth was usually slow and sparse, other quicker-growing species, such as tree-lupin and Acacia sophorae, were required for the success of reclamation work. Against Cockayne's recommendations, post-war foresters sowed tree-lupin after the marram had This is a pre-copy-editing, author-produced version of an article accepted in June 29, 2021 following peer review for publication in to increased rates of urbanisation. 93 Parabolic dunes form with ruptures to the foredune, due to high levels of unstable sand accumulation, or to disturbance by storm episodes or human action. 94 The strength of blowouts and the degree of lee-side stabilization with vegetation, also determines the dune roll-over by giving it a parabolic shape. 95

Dune management in Manawatū-Whanganui
Under the Resource Management Act, 108 a Regional Policy Statement is mandatory. In the Manawatū-Whanganui region, natural resources management and response to natural disasters are coordinated by the Horizons Regional Council, the name of the regional authority for Manawatū-Whanganui. This entity prepared, in 2014, an integrated plan, identified as "One Plan" that promotes a holistic approach for managing the present environment with a vision for preserving and enhancing it for generations to come. 109 Three key issues identified in the One Plan have implications for dune management: found that the first settler management approaches in the nineteenth century and early twentieth adapted techniques and models from France to New Zealand environments. The strategy for dune stabilization in a later period comprised a three-tier approach: 1) a primary stabilizer using fences to create foredunes to protect the grow of exotic plants, such as marram grass; 2) a secondary stabilizer based on the planting or sowing of treelupin, two years after; and 3) a tertiary stabilizer, making use of pines. This methodology, even if the early-stage implementation was not successful, was continuously improved with local scientific studies and trial and error attempts, until it become quite efficient.
Sand-drift stabilisation altered natural processes and feedbacks associated with dunes and caused a significant reduction in native biodiversity. The contrast in dune management, between historic practices of the nineteenth-and twentieth-centuries and the practices of the present, is that in the earlier period the approach was to fix the dunes, preventing them from moving. The later approach was to restore stabilized dunes to activate their natural processes by removing exotic plants. These approaches reveal two different perceptions about these ecosystems. First, it shows that settlers viewed sand as dangerous wastelands, a threat to agriculture, which justified interventions to stabilize and turn them into This is a pre-copy-editing, author-produced version of an article accepted in June 29, 2021 following peer review for publication in Environment & History