At the Request of ‘Friends of Okura Bush’ I conducted a field inspection of the current track in March 2016 to assess issues and required improvements to ensure adequate protection of forest canopy trees.
The inspection took place with Geoffrey and Lezette Reid and with a copy of currently proposed treatments supplied to them by the Department of Conservation.
I have 36 years’ experience in native forest management, monitoring and providing advice on track and road construction to protect or restore root environments of native canopy trees, including kauri. Successful innovative construction techniques I have prescribed have included award winning kauri root bridges on State Highway 12, perforated concrete pad road over porous scoria layer, pine bark over wheki log bush tracks, and a temporary highway traffic (including logging trucks) bridge over sensitive kauri roots constructed of timber over polystyrene over wheki log.
- Healthy survival of trees receiving protective works treatment = 100%
- Number of healthy mature kauri trees that subsequently died (1985-2016) when government agencies refused to implement track construction recommendations at Trounson Park and Waipoua Forest (recs made in 1978, 1990, 1996,) = 26.
- Number of PTA positive trees in remission from disease symptoms since prescribed track rehabilitation implemented = 1 of 1.
The current departmental recommendations appear to have only taken kauri protection into account. This is inadequate given the high public use, dedicated community interest and the presence of a number of kahikatea and matai trees on the route, which are highly vulnerable to internal rot and premature death resulting from arterial and feeder root damage from track impacts.
My inspection takes into account the needs of the forest rather than simply a single species response to phytophthora agathidicida threats to meet a confined programme objective.
The reserve is an integral part of a coastal forest – estuarine environment which is both rare and extremely high in ecological value. The natural continuum between coastal forest and estuary adds significant ecological value to the reserve and adjoining clear felled plantations earmarked for restoration provide for expansion, consolidation and a stronger sense of hope for long term ecological viability and biodiversity capacity of the reserve.
The coastal forest includes outstanding mature taraire- puriri- kohekohe forest with scattered large kowhai (sophora chathamica). Of special interest among the native emergent or regenerating conifers is the large mature matai, a species which is now rare on the North Shore.
A superb large kauri specimen is present away from the track system.
The ancient puriri trees speak clearly of a pre European era and have a very high advocacy value.
Recent past mistakes
Arterial roots of canopy trees have been cut or compromised through gravel track construction. In particular this includes a number of strongly leaning mature or pre European taraire, some of which have already died or collapsed causing premature canopy opening and a reduction in reserve quality and visitor experience. These trees need to be respected and protected. In context, they are more rare than young kauri. Such work falls well below the normal standard of professional conservation and undermines the value of the public asset. It reflects a departure from well established best practice that has been known since the 1980s and seriously compromises this small vulnerable jewel. Such coastal forest is irreplaceable and extremely rare on the mainland.
Proposed boardwalk sections
Boardwalk or floating timber ramp (equally effective) are apparently recommended for most kauri root zones, but the designated lengths in many instances are not long enough to ensure root protection. As a guide, the minimum coverage should be drip line plus 50%, especially in such situations where young trees are still expanding crowns and root systems.
At the leaning kauri site it appeared that the proposed boardwalk is destined to lie downslope of the trunk. This tree has a high advocacy value and I recommend placing the boardwalk upslope in the existing alignment to preserve the special visitor experience and to show off the tree to advantage. This will avoid creating new impacts on an undisturbed root sector.
Boardwalks/ramps should be used over all kahikatea and matai root systems and in other specific areas to protect valued canopy trees. It requires a more detailed site inspection.
Proposed geocell cover
Geocell is NOT generally recommended, especially on kauri root zones for the following reasons:
- Although providing short term reprieve on level ground, the solution is not permanent and risks creating a very problematic situation in future.
- Over time, kauri roots will grow up into the geocells creating two problems: firstly, kauri roots will ultimately be under direct stress again from track use, increasing their vulnerability to infection or development of disease symptoms from infection; and
- secondly, removing damaged geocells or removal to upgrade the truck in future will result in further direct disturbance to kauri roots.
- It is difficult to see how the surface of the geocells will be successfully maintained on slopes, when direct scuffing and/or erosion of fill occurs.
- The appearance of exposed plastic geocell will become very unsightly and out of character with a forest environment.
Note: The use of pine bark tracks at Waipoua Forest provided a superb walking experience and rooting medium for kauri roots, but have are not viable in the long term (20 yrs +) because the root filled medium is now exposed to direct stress. Bark/gravel mix is also a good rooting medium for kauri roots in a forest environment (even geocell protected gravel is likely to be penetrated by kauri roots). Any path structure over kauri and kahikatea roots must be above ground with an air layer separating the root system from the a renewable walking surface.
Routing the track to preserve the visitor experience and advocacy value of giant puriri trees, matai and coastline
- At one point the track steps walk up under a grand old puriri. The experience is quite fantastic and rather magical. The currently proposal to re route the track to avoid this tree (and steps and coastal erosion) should be discarded in favour of the status quo to preserve the currently high advocacy value of the puriri. Options exist to follow an earlier track alignment to reduce the distance of steps and remove the steeply stepped section.
- The coastal erosion could be readily addressed by installing a rock spawl or concrete tile crib wall at the slip toe to protect the face against coastal erosion. The existing track could be infilled by cutting away the bank above. This, or some comparable solution would preserve the old puriri route and the estuarine experience, which is a key advocacy element of the coastal reserve.
Superb large examples of kowhai are a feature of the reserve, both in terms of ecological heritage and scenic beauty. The size of some examples are outstanding. Often such trees are a legacy of earlier forest disturbance time kowhai tend to diminish in quantity in small reserves. Kowhai have a limited life of usually less than 100 or so years and so are becoming less common as each decade rolls on.
Carefully planned track construction and maintenance could provide for active disturbance (exposed fresh soil/clay etc) and with a little direct seeding by the Friends of Okura Bush, soon a new generation of kowhai will ensure generations to come will enjoy the same experience.
Effective footwear cleaning for PTA (phytophthora agathidicida)
- Landcare Research trials conducted for the Kauri Dieback Programme clearly show that Trigene is INEFFECTIVE against oospores of PTA. While very effective at killing zoospores, the chemical is clearly inadequate overall and offers virtually zero benefit in dry weather when viable zoospores are not present.
- An alternative system that offers genuine protection needs to be provided and/or to encourage people to do a chlorine wash at home before they come.
- There is space for an chlorine based system to be installed (chlorins has shown to kill zoospores and a majority of oospores, but not all).
- The world best practice is 70% ethanol (70% meths) spray. There is a need to acquire or design a safe containerised automatic spray system for footwear using this chemical. This is what is used by New Zealand scientists working in the field with PTA samples. Why should the public also not be offered something that works. In the UK, quaternary ammonium compounds similar to Trigene are also used for public phytophthora biosecurity stations. However it is acknowledged as a compromise for public convenience and as being less than fully effective.
In New Zealand, Kiwis are more pragmatic and expect to be given something that works and genuinely benefits the forest, rather than something that merely creates an appearance of working.
Attention to this issue is overdue and essential if public confidence and participation in cleaning stations is not to be undermined.
Substantial native plantings were noted on adjoining development land at the northern end of the reserve. Some native species chosen here are not native to the district, and the provenance of kowhai highly questionable. These present a liability to the integrity and ecological value of the reserve and need to be replaced with locally ecosourced species to ensure the reserve is not compromised. In particular: coprosma repens, pittosporum crassifolium and outsourced variety or species of kowhai.