Motivations for planting the dunes Planting and stabilising dunes, has been done for such a long time, that we collectively think of it as a good thing. It is taught at school; volunteer groups spend their free time planting dunes; governments have departments planting dunes and they allocate copious funds for doing so. The botanist Dr Leonard Cockayne understood the beach/dune process when he wrote in his book New Zealand plants and their story (first print in 1906):

The problems obviously started when people began interfering with the natural dune system. Runaway wandering dunes needed to be pinned down, usually with pine plantations and grass. From the back dunes, moving towards the sea, farmers managed to tame the dunes by planting shelter belts, seeding grass and by fertilising.

Cities grew where small beach settlements arose. The dunes were flattened and paved over as humans moved ever closer to the water line. Wherever humans moved in, the moving sand was stabilised. In the end hardly any dune system remained that functions today as it would naturally. The short-term gains were such that nobody could envisage anything wrong, but as we will see, the cost proved high in the long term.

Planting the dunes close to the sea was often done, believing that nature would have done so anyway but is that true?
 

A lesser known fact of roots in dunes is that they form steep scarps after large storms have eroded away the base of the scarp. By preventing the dune from collapsing, these roots hinder the formation of a gradual wind profile, necessary for the beach to repair its damage. As a result, the eroded sand remains in the sea, laying the beach flat. Successive storms keep eroding the steep bank further.

At Hatfield's Beach, near Orewa, New Zealand, the sea is eating into the shore where Pohutukawa trees have been planted. Although their root systems slow down beach erosion, they cannot stop it. Notice that the beach behind the tree has been eroding faster.

North of Ahipara along Ninetymile Beach, Pohutukawa trees have recently been planted right behind the foredune which is tall and has a steep scarp at the other end. The water's edge is only 20m away.

At Ocean Beach, near Whangarei, New Zealand, many Pohutukawa trees have been planted in an effort to control erosion and drifting sand. If such trees stand well back from the beach, while not lifting the sea wind, they can be tolerated. But the wilderness is no more. Do people really want parks everywhere, rather than pristine wilderness?

At Long Bay, just north of Auckland, New Zealand, trees and shrubs have been planted in an effort to control erosion. But the biggest problem stems from pollution, preventing the sand from drying. Shelter belts lift the sea wind and beach erosion becomes permanent. These plantings cannot stop that.

Before the steep bank above, dune grass has been planted, trapping the sand successfully. Because of the steep scarp along the entire beach, sand moves along the beach, around this corner. It is hoped that a foredune will form. However, this sand remains within reach of the water at spring high tide.

The myth of succession Anyone visiting the dunes, can observe that there exists a kind of habitat zoning running parallel with the waterline. When going landward from the beach, one first traverses a stretch of bare sand, followed by a zone with advancing dune grasses, behind which comes a zone with low plants. At the very back of the dune, the shrubs growing taller and there may be a forest. It is clear that there exists a kind of 'succession', but how is it brought about? What is 'natural' ?

1) The common thought is that the zones are succeeding one another while they march up towards the beach. First come the brave and hardy pioneering grasses with their running roots. They bind the soil, nutrients and moisture for the next wave of plants, hardy dune weeds and small shrubs. These pave the way for the forest. So eventually the forest will arrive at the water's edge. Dune plantings, it is thought, just help this natural process. But there's something wrong with this idea because if it were true, all our dunes would have been covered in lush native forest many thousands of years ago.

2) Another explanation is that each habitat zone is suitable only for the type of vegetation which is able to germinate and live there, even during times of adversity. Natural dunes have sparse vegetation that has evolved in time to exist, yet without adversely affecting the dynamics of the dune/beach system. In other words, the dunes were able to keep moving, while uprooting or burying vegetation in the process. When humans interfere by planting or fertilising, the balance swings in favour of vegetation and against the dune's dynamics.

3) From an evolutionary viewpoint, a different story emerges. The recent ice age some 10,000 years ago lowered the sea by some 100m, moving the shoreline many kilometres, almost to the edge of the continental shelf. The land between our present shoreline and the shore line back then, became covered in lush native vegetation. Dunes and beaches must have formed as usual at the edge. As the climate warmed, the sea level rose, and the shoreline with its beaches moved up. One would thus have expected the beaches to be bordered by lush native forest, but this is not so. As the water rose and beaches moved landward, they also destroyed the forests ahead of them by a zone of sand. One would thus expect to find remnants of  forest underneath the dunes, but this is not so either (but true in some places). It follows that beaches oscillated inland in a series of destructive and constructive phases. During the destructive phase, sand is blown into the forest, and a tall dune forms, obstructing its own maintenance, and inviting the sea to move in and take it all out: sand, soil and vegetation. Then a constructive phase follows with dune formation as we know it, followed by a long period of stability.
This destructive capacity also allowed the 'living' beach/dune system to influence the natural selection of those plant species that could live in harmony with it, some native dune grass species, but only in densities allowing the sand to move freely. The natural state of a dune system is thus one of sparse vegetation, growing sparser towards the water's edge.
What we are doing by planting the dunes, either too densely or with inappropriate species, is to start its natural destructive cycle, resulting in permanent erosion until all the dunes and all our work has been annihilated. The situation is made more acute by centuries of excessive human-induced erosion, during which too much sand and mud was deposited in the coastal environment. The effect of this will be discussed in a separate chapter.

Let's begin by examining how dynamic dunes move naturally and how dune plantings interfere with it.

Rolling dunes The sand of which dunes and beaches are made must possess four conflicting properties: It must move easily in the water It must stay put in the water It must move easily in the wind It must stay put in the wind Only a small range of grain sizes satisfies these criteria. Contrary to popular belief, sand is not blown in clouds like dust would. Such fine particles would not stay put and blow all the way inland. The grains that make the dunes, move by jumping (saltating). Seen from a distance it appears as if a sheet of sand moves some distance off the ground (5-10cm). Thus sand grains cannot jump from one dune top to the next. The way sand moves in the dunes is rather different.

The saltating sand comes to rest immediately in the lee of any object. So it drops out of the air immediately behind the foredune (top drawing), giving it a steeper slope to lee-ward. It makes the foredune roll landward in a peristaltic movement, eventually joining the second dune, which is also rolling inland to join the third dune and so on (second drawing). In order to stay healthy, dunes must be able to move (roll) inland. They can do so only when sparsely vegetated, which is the natural situation. If humans replant dunes in order to stabilise them, the dunes can no longer roll, which has serious long term consequences.

Effects of dune planting The first drawing shows a healthy situation with a steep wet beach, an area of dry beach, low fore dunes and rolling dunes further inland. The dune vegetation is sparse. Sand moves. Once dunes have been planted for stabilisation, the dense vegetation starts to trap the sand. Once trapped, the sand can no longer move. The dunes grow and become a single large dune (second drawing). The plan appears to work. But once the dune has grown sufficiently tall, it lifts the sea wind from the beach, impairing its self repair mechanism. The sea starts to eat into the tall dune, carving a steep bank (scarp). Sand can no longer saltate up this bank and the dune stops growing.

The Dutch have been fighting the sea for thousands of years but it is a fight that is never won. Holland's entire easterly flank, its border with the sea, consists of dunes and beaches. The photo on left shows an aerial view of a typical Dutch dune system near Haamstede. Houses are well set back. There are no high-rise buildings. The dunes have been planted densely and they have become very tall. The beach has flattened. Sand banks appear where they never were before. The beach needs regular infusions of sand to combat erosion. The cost is high. The photos below were taken in the top left corner of this aerial view.

All the sand shown in this picture has been pumped from the sea with fossil fuel: wet beach, dry beach and fore dunes (planted immediately afterwards). Although polluted, the sand dries reasonably well but in the weakened sea wind, it can no longer move sufficiently fast to keep ahead of natural erosion.

Because their self repair mechanism has weakened considerably, the dunes need help and workers create wind breaks from willow twigs, planted in rows. Such wind breaks slow the sea wind, inviting the sand to settle behind them, hopefully creating a new foredune before the next storm arrives.

At Port Waikato (NZ) where the Waikato River enters the sea (in the far distance), the dunes have been stabilised by densely planted native spinifex. As a result, the dunes have grown too tall. Notice the flat beach and the sand banks extending far into the sea. There is too much sand in the sea.

The black sand consists of black iron sand and transparent quartz. When wet, it looks very black. In the mid-day sun, the sand becomes too hot to walk on but it dries fast. Unfortunately this beach sand forms crusts that prevent the sand from blowing.

The sea has carved a steep bank out of the dunes, which further blocks the transport of excess sand from the sea to the land. Conservation groups, assisted by scientists and the regional council are hard at work to make the situation worse.

A dune blowout is the dune system's natural response to heal itself. The tall dune puts pressure on the wind and eventually the weakest point gives way. The dune blowout now provides the sea with a conveyor belt to move sand inland. But humans view it as a disaster that needs fixing.

Until....
Until a small beach care group near Wollongong, Eastern Australia, achieved just that, with overwhelming results in a very short time.
They understood the  chapters you are reading here on the Seafriends' website, and they succeeded by political means, to convince the local council to try it out.
It is not my intention to steal their thunder, so here is in their own words: