Reducing fire risk and dune planting in the Abel Tasman

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The objectives of Project Janszoon’s planting projects on the foreshore in Abel Tasman National Park are to reduce the fire risk to the national park and to help build resilience in native foreshore ecosystems.    Some area of foreshore can be stable for long periods of time, but it is a dynamic ecosystem and will always be subject to damage in extreme weather events.  Sandspits will always be subject to fluctuations where there is an estuary subject to high water flows.   The recent cyclone events gives us a lot of information that we can build on as to where we should plant and where we should leave nature to do the work.

The priority for Project Janszoon is to reduce the risk of a fire starting from camping stoves or illegal fires on the beaches and spreading to nearby vegetation.   Fire is the greatest risk to the investment that Project Janszoon are making in the national park.   The focus therefore is to remove flammable non-native vegetation, mostly gorse, from around campgrounds and to replace it where possible with less flammable native species.    We are also taking the opportunity to try and establish populations of native species which have been lost and a secondary benefit of this is to improve the look of the dunes at places of high public use.

Answers to common questions

Q. Why are we planting on the foreshore?

A. To reduce the fires risk, to help build resilience in native ecosystems and to improve the visual look of the dunes.

Q. Why plant, if high tides during storms are going to impact the dunes?

A. When gorse is removed it needs to be replaced by ground cover of some kind in order to reduce the germination of gorse seeds.  We have replanted with sand binding plants such as spinifex and pingao which stabilise the sand with their rhizomes. Plantings have mostly only been done above the current high tide mark but recent storms have brought the waves further up than previously, therefore causing some damage to these.   However in some places it has also removed the woody species that we are trying to eliminate so has assisted this process.

Some plantings below the extreme high tide mark were done for visual purposes only (eg Medlands Beach) but these are recognised to be temporary, something along the lines of annual amenity plantings in council reserves which are often replaced every year.  These are now unlikely to be replaced because of lack of space.

Q.  Did any of the plantings survive the recent cyclones?

A.  Native spinifex survived at most dune planting sites but in some cases it was buried beneath sand deposits.  Spinifex can withstand storms, winds and king tides because it’s adapted to the changeable environment of the dunes. It has a very deep root system which helps stabilise the dunes and will re-establish.

North facing beaches like Medlands and Anchorage were worst hit and some of the plantings at these sites were washed away.

Q.  In the past, trees like pines have been planted on dune areas – will they survive?

A.  It has been shown during recent storms that no vegetation can withstand the wave action and prevent erosion.  On north facing beaches, large mature trees which have been present for many years were torn out of the bank by the waves.  In more sheltered bays most trees and other woody species within the inundation zone although still standing are now dying from the effects of salt on their roots.

Q.  Can retaining walls prevent erosion?

A.  Most retaining walls that were previously erected around camping sites have been washed away in recent years.    Erosion is a natural event.   The only reason to try and prevent it is to attempt to protect infrastructure.   Building retaining walls in front of infrastructure has a negative effect on the natural erosion and rebuilding process and it can cause sand to be lost from beaches, which is undesirable in a national park.   It can protect infrastructure for a time but it is very costly and when the sea level rises it will not be able to withstand the wave action and so should only be regarded as temporary

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