IN THE MATTER OF Of the Resource Management Act 1991 (the Act) and the Local Government ( Transitional Provisions) Act 2010

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IN THE MATTER OF The Proposed Auckland Unitary Plan Topic 033 and 034 – RPS General Coastal Marine Zone and Activities AND Other Coastal Zones Removal

SUBMITTER Gibbs Foundation (submission 5472)

PRIMARY EVIDENCE OF DR GRANT SPENCER DUMBELL (ECOLOGY) ON BEHALF OF GIBBS FOUNDATION

2 MARCH 2015

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QUALIFICATIONS AND EXPERIENCE

1. My name is Grant Spencer Dumbell. I am a self-employed ecologist based in Auckland and have been in private practice since 1988.

2. I hold a Ph.D. degree in Zoology from The University of Auckland from where I graduated in 1987. I also hold first class B.Sc. (Hons) and B.Sc. degrees from Victoria University of Wellington, both majoring in Zoology.

3. Over the past 36 years I have worked as a conservation and restoration ecologist in many parts of New Zealand with the former New Zealand Wildlife Service, the former Department of Scientific and Industrial Research, private conservation charities, the Department of Conservation and a wide range of public and private clients.

4. Since 2010 I have been intimately involved with the planning, consenting and project management of what I believe to be the largest single site mangrove removal project in the country, which has been carried out in the Kaipara Harbour. This project has to date removed just over 40 hectares of dense recently colonised mangrove forest and associated Spartina cordgrass meadows.

5. Prior to this I have worked in mangrove as a result of my research on the ecology of the New Zealand brown teal, pateke, (Anas chlorotis) in both Northland and on Great Barrier Island and although this research did not focus on it was partially undertaken in mangrove and salt-marsh habitats.

6. As a result of the planning for the Kaipara mangrove removal I have become familiar with a selection of other mangrove removal sites including a sub- of the Tauranga Harbour and the Pahurehure Inlet and Auckland Airport removal sites on the .

7. For the Kaipara Harbour mangrove removal I undertook benthic and avifaunal surveys at the project site, produced a model for the estimation of mulch volumes that would be produced by the mechanical mangrove removal and reviewed tidal and wind drift data collected by coastal engineers to model the off-site dispersal of the mangrove mulch to understand potential impacts on adjacent shorelines.

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8. This project was also intertwined with a concomitant project to eradicate Spartina cord-grass from the project site. This introduced aquatic weed is recognised as being one of the most invasive saltwater weeds in the world and was planted on the project site, probably during the 1970’s in an attempt to reclaim areas of the intertidal foreshore.

9. The Spartina eradication is being undertaken in conjunction with biosecurity staff from under the auspices of the Auckland Regional Pest Management Strategy. This recognises the project site as probably the largest infestation of this weed in the and project planning has needed to remain cognisant of the interactions between the Spartina and the mangroves. It involved extensive spray trials to satisfy the conditions of the two relevant resource consents, one to aerially spray Spartina and the other to mechanically remove mangroves.

10. I have been engaged by the Gibbs Foundation to provide expert advice on mangrove distribution and colonisation in the Kaipara Harbour, especially along the eastern shore of the harbour, to review the Foundation’s Proposed Auckland Unitary Plan (PAUP) submission on the plan’s proposed policies and rules regarding mangrove removal, to represent the Foundation at the PAUP mangrove mediation held on January 14 and to prepare this brief of evidence.

11. To prepare this evidence I have relied upon the data and information collected during the compilation of the resource consent application for the Gibbs Foundation to mechanically remove recently colonised mangroves from the intertidal foreshore south of the mouth of the Araparera River. This included avifaunal, vegetation and benthic fauna surveys across the project site, the interpretation of historic aerial photographs and general site observations of operative natural processes.

12. The relevant section of the Gibbs Foundation’s PAUP submission to which this evidence is addressed is Section 3.3.3 and the Foundation’s proposed amendment to Activity Table 4 for the General Coastal Marine Zone, particularly the first line of the Activity Table where the Foundation sought amendment to permitted activity mangrove removal (other than seedlings) from it applying at the arbitrary date of 1996 to it applying to specific spatial areas identified on planning maps.

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13. It is noteworthy that Council have not objected to this type of approach being applied in the Whangateau Harbour and have facilitated the drafting of a spatial zone within the confines of this harbour within which permitted activity mangrove removal may proceed using justifications other than the proposed 1996 threshold date.

CODE OF CONDUCT

14. I have read and agree to comply with the Environment Court’s Code of Conduct for expert witnesses outlined in the Environment Court’s Consolidated Practice Note 2011. I have complied with this practice note in preparing this statement of evidence. I also confirm that my evidence is within my area of expertise except where I state that I am relying on what I am being advised by another person or the evidence of another expert. I also confirm that I have not omitted to consider material facts known to me that might alter or detract from my expressed opinions.

SCOPE OF SUBMISSION

15. The Gibbs Foundation owns a large tract of land which fronts onto the Kaipara Harbour, generally between the mouth of the Araparera River in the north and Kakanui Point in the south. This extent of the coastal marine area (CMA) is the Foundation’s area of interest with respect to their PAUP submission. Their legal boundary extends into the CMA along much of the harbour frontage and extends inland as far as State Highway 16. 16. On this land the Foundation has developed and is continuing to expand an internationally significant collection of large sculptures that is unique in New Zealand and which rivals its international peers. The Foundation has also undertaken large-scale ecological restoration projects with the creation of several freshwater lakes and associated wetlands, extensive native revegetation and the construction of a very large coastal lagoon and marsh system, along with continuing mammalian predator control across the property.

17. The unique planning challenges that this land use activity presents means that, under the PAUP, the site will be subject to the rules of a specific planning precinct. The Foundation’s submission seeks to give effect to an extension of

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this philosophical approach into the CMA so as to preserve the inherent connectivity between the land and intertidal marine zone in the same way that the existing limited consent does with respect to mangroves.

18. The consented removal of invasive Spartina cordgrass and recently colonised mangroves is an extension of the Foundation’s land management ethos beyond their legal boundary into the public commons to restore the ecology of the foreshore and to unwind a site-specific history of regrettable human ecological modifications.

19. The Foundation have made their PAUP submission to seek amendments to the proposed provisions for mangrove management to provide the opportunity to continue implementing their land management ethos beyond the spatial and temporal limits of the non-notified consent they currently hold for mangrove removal without the need to repeat the expensive and time consuming process of applying for further resource consents to continue a management approach that has already received and passed Council scrutiny.

NATURE AND CHARACTERISTICS OF MANGROVES

20. The grey mangrove is the only species of mangrove present in New Zealand. It is a native woody tree that shows considerable variation in size across its range. At the southern extent of its range in the Ohiwa Harbour at Ohope it is less than one metre tall and cannot grow sufficiently dense to form a closed canopy. Further north in the Tauranga Harbour, mangroves grow to approximately two metres tall and form a dense shrubby canopy. In Auckland, mangroves grow up to five metres tall and in a dense stand they have a columnar growth form as adjacent trees compete aggressively for light. In the Hokianga Harbour in Northland, mangroves can grow as high as 10 metres.

21. Mangroves grow on soft sediment shorelines and are generally limited to the upper half of the tidal range as their roots must be above water for approximately six hours on each tidal cycle. They are supremely well adapted to this as they possess specialist aerial roots called pnematophores that protrude vertically above the substrate so their roots can respire in the waterlogged sediment. They also have specialist adaptations to be able to handle the concentration of salt in the water they transpire and they have a

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specialised reproductive mechanism whereby viable seeds germinate on the parent plant before dispersing as a propagule by floating on the . Once these become stranded on suitable substrate the rootlet can gain a toehold between subsequent high to prevent the propagule being washed away.

22. These characteristics of the species are important as they allow generalised conclusions to be made about past and future patterns of mangrove colonisation.

THE KAIPARA HARBOUR

23. Historic aerial photography for the southern Kaipara Harbour extends back to 1941.1 These records prove conclusively that the historic distribution of mangroves was severely restricted compared to their current distribution. Mangroves did occur within the area of interest but were not present on the open coast, instead being restricted to narrow, limited patches on the inside of riverbends along the tidal extent of the Araparera River.

24. The photos also confirm the presence of shellbanks along the coast, including on the high tide line north of Kakanui Point. These are important roosting and nesting habitats for endemic species such as New Zealand dotterel.

25. Prior to European settlement, the eastern shore of the Kaipara Harbour was characterised by massive estuarine salt marshes, some of which were likely only periodically flooded on spring tides. These shallow tidal flats have been extensively enclosed by coastal dykes, drained and converted to agricultural pasture. Approximately 25 ha of the Foundation’s land historically was intertidal flats that were enclosed, probably during the 1960’s.

26. However, during the 1970’s and possibly as late as the early 1980’s a previous landowner continued the drive to reclaim land from the harbour by undertaking extensive plantings of Spartina cordgrass beyond the enclosed area further out onto the intertidal flats. Historic aerial photos also show that these areas were

1 Attachment 1 shows the coastline between Kakanui Point in the south and the Araparera River in the north. Note bright white shell beaches north of Kakanui Point, the broad intertidal sand flats south of the Araparera River and the open meander loop of the Araparera River with dark mangroves on the inside of the river bend. Note the absence of mangroves from the general coastline.

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free of mangroves when these plantings were made.2 These photos also show that elsewhere mangroves were already beginning to expand onto areas previously free of vegetation.

27. By area, the Kaipara Harbour is one of the largest estuarine harbours in the world and experiences massive tidal movements on each incoming and outgoing tide as water streams into and out of the harbour and pushes almost 30km southwards from the harbour entrance to . Adjacent to the Foundation’s property, intertidal sandflats up to 4km wide are flooded and drained on each tidal cycle. As a result, while the tidal cycle does ebb and flow onto the shore, the most significant water movements are along the shoreline, southwards on the incoming tide and northwards on the outgoing tide.

28. Accordingly, the Kaipara Harbour has an asymmetric tide which means that tidal flows run harder and faster on the outgoing tide compared with the incoming tide. Therefore, material which becomes entrained in this tidal flow has the potential to be transported very long distances on each tide and to leave the harbour and be swept into the open ocean beyond the harbour mouth. It is noteworthy that the Foundation’s coastline is conspicuously free of a high tide wrack present on many coasts as floating material travels along the coast rather than onshore.

29. The construction of coastal bunds has had the effect of pushing these longshore tidal flows offshore. On the Gibbs Foundation coast, tidewater would traditionally have flowed northwards around Kakanui Point then swept the wide, open bay to the Araparera River. The construction of the coastal bund would have had a minor effect on these flows as it was sufficiently inshore to only affect only approximately the first hour the outgoing tide, a time when tidal flows would not have been fully developed. It is unlikely that a bund built only from uncompacted in-situ sediment would have been able to survive if it did extend further seaward as the tidal flows would likely have quickly eroded it.

2 Attachment 2. Note the enclosed and drained area of sandflats south of the river that were open to the tide in Attachment 1. Note also the extent of the Spartina cordgrass plantings west (left) of the coastal bund, the beginning of mangrove colonisation (shown as dark patches amongst the Spartina) and the occlusion of the Araparera River meander loop with mangroves.

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30. However, the plantings of Spartina cordgrass seaward of the bund intersected these mid tide flows and extended offshore as far as 3.5 hours after high tide, when tidal flows are at their peak. Furthermore, the plantings were perpendicular to the tidal flows so as they developed their vegetative mass they protected the inshore areas from being flushed by the tide and dampened the energy to which these areas were subjected.

31. Predictably, these plantings promoted the deposition of fine sediments and the nature of the substrate changed from sand to mud. They also acted as an entrapment matrix to capture floating mangrove propagules and from the late 1980’s mangroves colonised the area and completely vegetated every open space of intertidal flats not already occupied by Spartina cordgrass.3

32. At the same time, mangrove expansion was rapidly progressing on other parts of the coast as well. The small vestigial Kakanui estuary south of Kakanui Point became completely colonised by mangroves and an entire meander loop of the lower Araparera River became so clogged with mangroves that the river opened a new course to cutoff the loop as an oxbow.

33. In addition to the persistent development and increased density of the mangrove / Spartina cordgrass complex, and the general expansion of mangroves on the shoreline and in river channels, other changes have also occurred as a result of the altered tidal flows.

34. The dislocation of the tidal flows further offshore has meant that shellbanks north of Kakanui Point have become buried by mud over the same period of approximately 70 years that other shellbanks to the north and south have persisted, as recorded by sequential aerial photos. The shadow effect of such a large block of vegetation has meant that a very large dome of sediment has gradually built up to the north of, and in the lee of, the mangrove forest with the result that the course of the Araparera River intertidal channels have also been pushed further northwards.4

3 Attachment 3. Aerial photo from 2010 showing the Spartina plantings completely colonised by mangroves. This process took approximately 30 years from 1980 to 2010. 4 Attachment 4. Aerial photo from 1999 showing the same section of coastline as Attachment 1. Note the infilling of the Spartina plantings with colonising mangroves, and the complete loss of shell beaches north of Kakanui Point while shell beaches south of Kakanui Point and north of the Araparera River have persisted. Note also the mangrove colonisation of the Kakanui Point channel, the establishment of mangroves along the high tide line north of Kakanui Point and the realignment of the intertidal Araparera River channel compared to Attachment 1 as a result the accretion of sand north of the

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35. At the time of the lodgement of the resource consent application I concluded there was no evidence that the encroachment of mangroves onto the intertidal shore above the mid tide line had halted, or that any barriers existed that would halt it.

36. Two mechanisms of mangrove colonisation were identified, the first being the stranding of propagules on a high tide line and the development of solitary trees which form small groups and eventually coalesce, and the second being an advancing front of colonisation, generally observed on a lee edge of established mangroves where propagules are protected from being washed away.

37. It is widely held that mangrove expansion in Auckland’s harbours and is a result of increased sedimentation that has led to the deposition of mud onto which mangroves have naturally spread. The conclusion that flows from this is that mangrove expansion cannot be arrested until sediment runoff from surrounding catchments is significantly curtailed, therefore mangrove expansion is a function of terrestrial land use changes.

38. In any estuarine system, the sediment characteristics are a function of the parent geology and the energy of the tidal flows which sort and shift the sediment. When sediment inflows exceed the capacity of tidal flows to mobilise and transport the sediment the excess is deposited. When the reverse occurs shoreline erosion is the result as the tidal flows carry away previously deposited sediment. These processes can build and destroy massive structures such as dunes, spits, deltas and bars, therefore an estuary maintains a dynamic equilibrium between its sediment budget and sediment transport capacity.

39. With historic land clearances in New Zealand, terrestrial sediment flows would have massively increased with the removal of the catchment forest cover. It will also episodically increase with storm events such as floods. Over time it can be expected that as sediment runoff stabilises to its new equilibrium that tidal processes may be able to ‘catch up’ and remobilise and remove the excess sediment that has been deposited.

mangrove forest. Note also the extensive expansion of mangroves at the mouth of the Araparera River and associated coastline.

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40. Mangroves are a native species that are increasingly generating polarised debate, especially around their management. In general mangroves are portrayed as being passive responders to exogenic landscape processes and come with benefits such as increased habitat diversity, coastal protection and the amelioration of climate change through carbon sequestration.

41. In my view mangroves should not be seen as a passive response to fine sediment deposition, they should be seen as aggressive ecological colonists with the capacity to significantly shift the ecological trajectory of upper shore intertidal areas away from diverse open sandflats and saltmarsh to tall woody closed canopy monocultural forest.

42. The effect of the colonisation and expansion of mangroves is twofold. If mangroves colonise deposited muddy sediments they act to bind these in place and prevent their remobilisation by dampening tidal processes. Secondly, this dampening actually contributes to the deposition of muddy sediment, which in turn promotes more aggressive mangrove expansion.

43. It is also my opinion that insufficient weight is given to the adverse effects of mangrove colonisation as a result of the habitats they replace. Intertidal sand flats support dense beds of benthic shellfish in addition to saltmarsh and vegetation, which do not coexist with mangroves.

44. The Kaipara Harbour is an internationally recognised migratory wader habitat and large numbers of birds feed and roost in the Foundation’s area of interest. When the tide is out these areas are feeding grounds for a highly diverse assemblage of bird species, the effects of which extend as far northwards as Siberia and Alaska by virtue of New Zealand being at the southern extent of the East Asian flyway along which tens of thousands of migratory waders travel annually to overwinter during our southern summer before returning north to breed in the northern summer. They are replaced in wintertime by flocks of domestic migrants of South Island Pied Oystercatchers who over winter in northern harbours.

45. In contrast my ecological assessments of recently colonised mangrove forests show these habitats support a depauperate avifaunal species diversity with very low abundance. While birds do use mangrove forests, these do not provide primary habitat for any native species. Mangrove forest benthic

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epifauna is dominated by mud crabs and mud whelk molluscs, with the complete absence of benthic infauna. These habitats can be described as simplistic both structurally and functionally compared to what they have replaced.

46. Some commentators have pointed out that data suggests that banded that inhabit saltmarsh vegetation adjacent to mangroves spend more time foraging and extend their foraging further away from the saltmarsh when mangroves are present compared to when they are not. On the face of it this might suggest a significant benefit for the presence of mangroves, however, an alternative hypothesis is that the feeding habitat quality of mangroves is poor compared to open intertidal flats with the result that the birds are forced to spend much more time and have to travel greater distances to satisfy their feeding requirements. I am not aware that beyond direct observation there are any studies that have falsified this alternative interpretation.

47. In any , ecology is about understanding the interactions of plants and animals both between themselves and their abiotic environment. It is more than just identifying and enumerating plants and animals, it requires an understanding of biological and physical processes as it is these that shape the attributes of each ecosystem.

48. The Society for Ecological Restoration defines ecological restoration as:

An intentional activity that initiates or accelerates the recovery of an ecosystem with respect to its health, integrity and sustainability…. Restoration attempts to return an ecosystem to its historic trajectory

49. Disallowing the Gibbs Foundation’s submission relating to the permitted activity removal of mangroves other than seedlings present within mapped areas prior to 1996 will significantly hamper options to continue with the ecological restoration of the coastline adjacent to an acknowledged terrestrial precinct for which special planning provisions have already been made.

50. Historical evidence confirms that significant mangrove expansion that lies outside the currently consented mangrove removal area had already occurred prior to 1996 and without the acceptance of the Foundation’s

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submission these mangroves will receive de-facto protection when in fact it is only a historic accident that they had established prior to the artificial, arbitrary and ecologically meaningless date of 1996.

51. Furthermore, once the Foundation’s mangrove removal consent expires the Foundation will be forced into the onerous position of having to maintain the area free of mangrove by annually removing seedlings, before they progress beyond the conservative definition of a seedling as implemented by the PAUP. This will require significant annual investment of resources and may place at risk the gains that have already been made to restore this section of coastline to its original ecological trajectory.

52. Adoption of the Foundation’s spatial mapping provisions for permitted activity mangrove removal will provide a more flexible management regime for the currently cleared area by allowing less frequent maintenance clearance of mangroves, even if they have become small shrubs and moved beyond the definition of a seedling.

53. While the PAUP proposes that permitted activity mangrove removal can be undertaken to reinstate the situation as at 1996, subject to rules and methodologies, in the case of the Gibbs Foundation area of interest there is abundant historic evidence and an understanding of operative ecological processes to demonstrate that mangrove colonisation would not have proceeded as it has without significant human modification of the ecosystem.

54. Implementation of an arbitrary date of 1996 will, in this case, likely have the exact opposite of the intended effect of allowing reasonable, justifiable and defensible mangrove removals by preventing the very actions to which the plan provisions are designed to give effect simply because the ecological response of mangroves to human induced modifications occurred before the arbitrary date.

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CONCLUSION

55. It is my opinion that the implementation of the Gibbs Foundation submission for spatially based as opposed to temporally based provisions for permitted activity mangrove removal within their area of interest will provide better ecological outcomes for this small section of the Kaipara Harbour not only for intrinsic reasons but so that the large number of local and international visitors that annually visit the property can see and understand a section of ecologically restored coastline which mimics as closely as possible its original natural character and functioning.

56. There are no practical or technical reasons why this approach could not be implemented within the area of interest as the process of applying for and receiving consent, coupled with the project implementation and subsequent consent compliance regime has shown that sufficient knowledge, understanding and experience now exists to allow further mangrove removals to be able to be undertaken with the confidence that to do so will not result in any adverse environmental effects.

Dr Grant Spencer Dumbell 2 March 2015

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